Thesis--University of Wisconsin.

Η φωτοσύνθεση των καρπών έχει μελετηθεί σε έναν αριθμό ειδών κατά το παρελθόν. Σε αυτές τις εργασίες έγινε, κατά βάση, χρήση των παραδοσιακών μεθόδων εκτίμησης της φωτοσυνθετικής ικανότητας και από αυτές κατέστη σαφές ότι οι ρυθμοί αφομοίωσης του διοξειδίου του άνθρακα είναι εξαιρετικά χαμηλοί στο χλωρέγχυμα των καρπών εν συγκρίσει με αυτούς των αντιστοίχων φύλλων. Κατά τα τελευταία έτη έχουν καταβληθεί λιγοστές προσπάθειες προσέγγισης του ζητήματος με τη βοήθεια νέων τεχνικών φθορισμού της χλωροφύλλης και φαίνεται ότι η γραμμική ροή ηλεκτρονίων είναι περιορισμένη στους χλωροπλάστες των καρπών. Ωστόσο, δεν διαπιστώθηκαν σημαντικές διαφορές σε ότι αφορά τη μέγιστη φωτοχημική ικανότητα του φωτοσυστήματος ΙΙ. Για το λόγο αυτό προτάθηκε ότι η φωτοσύνθεση των ιστών αυτών εξυπηρετεί στην επανάκτηση του από την αναπνοή προερχομένου διοξειδίου του άνθρακα. Εντούτοις, βιβλιογραφικές αναφορές που να επιβεβαιώνουν μία τέτοια υπόθεση είναι εξαιρετικά σπάνιες. Στα πλαίσια της παρούσας διατριβής μελετήθηκε η φωτοσύνθεση των καρπών τεσσάρων φυτών που αναπτύσσονται στα μεσογειακά οικοσυστήματα. Συγκεκριμένα δε των φυτών Acacia cyanophylla, Ailanthus altissima, Nerium oleander και Quercus coccifera. Χρησιμοποιήθηκαν νέες και καινοτόμες τεχνικές του φθορισμού της χλωροφύλλης σε συνδυασμό με παραδοσιακές μεθόδους με σκοπό να προσδιορισθούν τα βήματα εκείνα στα οποία η φωτοσύνθεση των καρπών συναντά περιορισμούς. Κάτι τέτοιο καθίσταται δυνατό με την ανάλυση της κινητικής της επαγωγής του φθορισμού της χλωροφύλλης, το λεγόμενο JIP-test, το οποίο για πρώτη φορά εφαρμόσθηκε σε αυτούς τους ιστούς. Παράλληλα, μελετήθηκε, η μορφολογία του φωτοσυνθετικού ιστού των καρπών αυτών, αφού αυτή διαδραματίζει σημαντικό ρόλο στη διαμόρφωση των χαρακτηριστικών της φωτοσύνθεσης. Ελήφθησαν επίσης σοβαρά υπ’ όψιν οι ιδιάζουσες συνθήκες που επικρατούν στο εσωτερικό των ιστών και συγκεκριμένα, οι διαφορετικές συγκεντρώσεις των αερίων που εμπλέκονται άμεσα ή έμμεσα στη φωτοσύνθεση και οι χαμηλότερες εντάσεις φωτός. Τα περικάρπια των τριών φυτών παραμένουν πράσινα μέχρι και πριν την ωρίμανση του καρπού. Οι καρποί της A. cyanophylla και του N. oleander διαρρηγνύονται απελευθερώνοντας τα σπέρματα ενώ στη περίπτωση του Q. coccifera ολόκληρη η βάλανος απελευθερώνεται από το κυάθιο. Το A. altissima αποτελεί εξαίρεση καθώς οι καρποί παραμένουν στο μητρικό φυτό για μεγάλο χρονικό διάστημα. Σημαντικό είναι να τονισθεί ότι στη περίπτωση της A. cyanophylla και του N. oleander πράσινα παραμένουν και τα σπέρματα, γεγονός το οποίο επέτρεψε τη μελέτης φωτοσύνθεσης και αυτών των ιστών. Ο αριθμός των στομάτων στα περικάρπια των A. cyanophylla, N. oleander και A. altissima είναι κατά πολύ μικρότερος του αντιστοίχου των φύλλων ενώ στο Q. coccifera δεν υπάρχουν καθόλου στόματα. Το γεγονός αυτό σε συνδυασμό με τη παρουσία ελάχιστων μεσοκυττάριων χώρων στο εσωτερικό του καρπού αλλά και τους έντονους μεταβολικούς ρυθμούς του ιστού οδηγεί σε ένα ιδιαίτερο μικροπεριβάλλον αερίων που δεν συναντάται ποτέ στα φύλλα. Αυτό ακριβώς το μικροπεριβάλλον έχει διαδραματίσει καταλυτικό ρόλο στη διαμόρφωση των χαρακτηριστικών της φωτοσύνθεσης του καρπού. Στους ιστούς του καρπού των A. cyanophylla, A. altissima και N. oleander η συγκέντρωση των φωτοσυνθετικών χρωστικών είναι μικρότερη από των φύλλων. Επίσης διαπιστώθηκε ότι η γραμμική ροή ηλεκτρονίων συναντά εμπόδια στην αναγωγική αλλά και την οξειδωτική πλευρά του φωτοσυστήματος ΙΙ. Αυτά τα προσκόμματα έχουν ως αποτέλεσμα μία εξαιρετικά χαμηλή γραμμική ροή ηλεκτρονίων. Παράλληλα, η μη φωτοχημική απόσβεση του φθορισμού είναι υψηλότερη στους εν λόγω ιστούς πράγμα το οποίο ενδεχομένως να συνδέεται με τον επίσης υψηλότερο λόγο συνολικών καροτενοειδών προς συνολικές χλωροφύλλες. Συνεπώς, η υπόθεση ότι η φωτοσύνθεση των καρπών επανακτά το πλεονάζον CO2 δεν επιβεβαιώνεται για τα τρία αυτά φυτά. Η χαμηλή γραμμική ροή ηλεκτρονίων ωστόσο δεν συνοδεύεται από αντίστοιχα χαμηλή κυκλική ροή. Μάλιστα, το μικρότερο μέγεθος των τελικών υποδοχέων ηλεκτρονίων του φωτοσυστήματος Ι και ο λιγοστός χρόνος που απαιτείται για την κατά το ήμισυ αναγωγή τους καταδεικνύουν ότι η κυκλική ροή ηλεκτρονίων μάλλον ευνοείται. Υπενθυμίζουμε εδώ ότι στο εσωτερικό καρπών επικρατούν ιδιάζουσες συνθήκες. Συγκεκριμένα, η συγκέντρωση του CO2 τείνει να αυξηθεί ενώ ταυτόχρονα αυτή του O2 είναι εξαιρετικά χαμηλή εξ αιτίας των υψηλών ρυθμών αναπνοής των σπερμάτων. Οι καρποί είναι συνεπώς ιστοί εξόχως επιρρεπείς στην υποξία. Η χαμηλή γραμμική ροή ηλεκτρονίων σε συνδυασμό με μία ενισχυμένη κυκλική ροή έχουν ως αποτέλεσμα την αύξηση του λόγου ATP/NADPH ο οποίος σε περιπτώσεις υποξίας εμφανίζεται μειωμένος. Ως εκ τούτου, προτείνεται από τον γράφοντα ότι οι χλωροπλάστες των καρπών των τριών αυτών φυτών λειτουργούν ως ρυθμιστές του λόγου ATP/NADPH και αποτρέπουν τις συνέπειες της υποξίας στους ευαίσθητους αυτούς ιστούς. Η περίπτωση του Q. coccifera διαφέρει από των υπολοίπων τριών φυτών. Οι συνολικές φωτοσυνθετικές χρωστικές είναι περισσότερες ανά μονάδα επιφάνειας στο χλωρέγχυμα της βαλάνου από ότι στα αντίστοιχα φύλλα. Η δε τιμή της ταχύτητας της γραμμικής ροής ηλεκτρονίων αλλά και η ικανότητα αφομοίωσης του CO2 δεν παρουσιάζουν διαφορές μεταξύ των φύλλων και των περικαρπίων. Τα γεγονότα αυτά σε συνδυασμό με την υψηλή πιθανότητα τα φύλλα του φυτού να φωτοαναστέλλονται την περίοδο της ανάπτυξης του καρπού υποστηρίζουν την άποψη που έχει ήδη διατυπωθεί για τη φωτοσύνθεση των καρπών, ότι δηλαδή συμβάλλει στο συνολικό ισοζύγιο άνθρακα του φυτού σε μία δυσμενή γι αυτό περίοδο. / Fruit photosynthesis has been studied in the past in a number of species. Traditional methods of estimating photosynthetic capacity have been used and CO2 uptake rate of fruit chlorenchyma has been found to be significantly lower when compared to the one of respective leaves. During the recent years, attempts to clarify the phenomenon have been made using chlorophyll fluorescence methods and it appears that electron transport rate (ETR) is inhibited in fruit chloroplasts. Hence, maximum photosynthetic capacity of PSII was found to be similar to that of the leaves. Therefore, it was proposed that fruit photosynthesis may contribute to the refixation of respiratory carbon dioxide. Nevertheless, scarce reports regarding the phenomenon can be found in the literature. In the present work fruit photosynthesis of four species of the Mediterranean basin was studied. Namely, of Acacia cyanophylla, Ailanthus altissima, Nerium oleander and Quercus coccifera. New and innovative chlorophyll fluorescence techniques were used along with traditional methods in order to locate possible limiting steps in photosystem function in exposed, non-stressed green fruits, while corresponding leaves served as controls. This was possible due to the analysis of polyphasic (O-K-J-I-P) fast chlorophyll fluorescence transient, which was for the first time used in these tissues. The anatomy of the fruit parenchyma was also studied, given that it plays a significant role in the shaping of photosynthetic characteristics. The specific aerial microenvorment as well as the different levels of penetrating light into the fruit chlorenchyma have also been taken into account. The pericarps of three out of four studied species remain green until just before fruit maturation. A. cyanophylla and N. oleander fruits dehiscent and the seeds are then dispersed, while the cork of Q. coccifera fruit is detached from the cap-shaped bracts. A. altissima appears to be an exception to this rule as fruits remain on the maternal plant long after fruit maturation. It is notable that in the case of A. cyanophylla and N. oleander the seeds are as well green during fruit development which allowed the study of photosynthesis in these remote tissues. The number of stomata in the pericarps of A. cyanophylla, A. altissima and N. oleander is much lower than the one of corresponding leaves, while no stomata occur in Q. coccifera pericarps. This fact when combined with the presence of limited intercellular spaces in the fruits chlorenchyma as well as the high metabolic rates of the tissue, results to a specific aerial microenvironment never encountered by leaves. It is proposed that such a microenvironment has affected fruit photosynthesis characteristics. Fruits of A. cyanophylla, A. altissima and N. oleander contain less chlorophyll than leaves. Electron flow was also found to be limited both at the donor and the acceptor side of PSII. Such a limitation results in considerable reduction of the electron transport rate (ETR) values. At the same time, non – photochemical quenching (NPQ) is higher in fruit tissues, which is probably related to the high Car/Chl ratio found in those tissues. Low linear electron flow does not necessarily predispose a low cyclic electron flow. As a matter of fact, the size of PSI electron end acceptors pool and the time needed for its half reduction indicate that cyclic electron flow is facilitated in these tissues. It is here important to remind the specific conditions of the fruits inside. CO2 concentration is always higher and O2 concentration is always lower than in the outer atmosphere because of high respiration rates. Therefore, fruit tissues may suffer from hypoxia. A low linear electron flow combined with a higher cyclic electron flow elevates the ATP/NADPH ratio, which is regularly lower in hypoxic tissues. So, a function for fruit chloroplasts of these three species as valves for the adjustment of ATP/NADPH ratios is proposed. The case of Q. coccifera differs from the other species studied. The pericarps of the plant contain more chlorophylls than the respective leaves. Moreover, electron transport rates and CO2 assimilation rates were found to be similar with these of the leaves. These findings along with potential photoinhibition of the plant leaves during fruit development support the hypothesis already stated for fruit photosynthesis, namely that it may contribute to the overall carbon equilibrium of the plant.

Thesis (MScAgric)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Fruit size can be a problem in 'Clementine' mandarin and 'Valencia' orange in the Western Cape region of South Africa. Small fruit is not only unacceptable to the consumer but is also more difficult and expensive to harvest. Means of alleviating this problem is to manage the crop load. Hand thinning trials were conducted to evaluate the effect of timing and severity thereof in enhancing fruit size. The benefits of enhancing large fruit size was obtained by a heavy-thinning (60% fruitlet removed) treatment, but the actual benefits were offset by a reduction of total yield. Yield was reduced up to 30% when heavy thinning treatments were applied. No effect on early or late treatments were obtained since the trial was conducted rather late (4 to 6 weeks after the physiological fruit drop period) to obtain the desirable results. However, better packouts are expected with thinning treatments since blemished fruit are also removed. The effect of multiple 2,4-dichlorophenoxy propionic acid (dichlorprop) sprays were also evaluated on 'Nules Clemetine' mandarin. Comparing multiple sprays with a single spray, it was observed that more than one spray was no better in improving fruit size. The use of multiple dichlorprop sprays resulted in no additional yield reduction, while internal fruit quality was also not affected. The best results were obtained with dichlorprop at 50 mg. L-1 • The use of dichlorprop with different surfactants was evaluated in both 'Clementine' mandarin and 'Valencia' orange. The fruit size was increased from 50 mg. L-1 up to 100 mg. L-1 • Yield was usually not affected but, where reductions were experienced, yield of large fruit (>55 mm) was not significantly affected. In the 'Valencia' orange trials, during the first year, dichlorprop was sprayed relatively late (fruit diameter: 19 mm). No fruit size, yield and internal fruit quality effects were observed. The following year, when early and late sprays (fruit diameter at spray time = 8 and 12 mm, respectively) were evaluated, it was observed that late sprays had no effect on fruit size, whereas fruit size (48 fruit per carton) was significantly increased by early sprays. This implies that the dichlorprop effect on fruit size is during the early stages of fruit development, just after or during the late stage of the physiological fruit drop period. Yield was drastically reduced by up to 35%, which affected the actual kilograms of large fruit adversely in some treatments. Juice percentage was inconsistent and tended to be reduced by dichlorprop application. Dichlorprop tended to increase TSS slightly in year one and significantly so in year two, but did not affect the TSS:TA ratio. The use of Orchex mineral oils as surfactant at 150 mL. 100 L-1 was effective and seemingly allowed lower rates of dichlorprop to be used. Therefore, surfactants seemed to show potential in enhancing dichlorprop efficiency to reduce the application cost. The dichlorprop-sprayed fruit was used to measure carotenoid content of the rind during the later stage of fruit development. Observations indicate that dichlorprop-sprayed fruit at 50 mg. L-1 obtained better carotenoid content in both 'Clementines' mandarin and 'Valencia' orange. Also, fruit exposed to light had higher carotenoid levels as compared to fruit shaded with brown paper bags. However, dichlorprop-sprayed fruit at 100 mg. L-1 , even though exposed to light did not show significant differences with unsprayed in both shaded and exposed conditions. Therefore, no consistent effect of dichlorprop was established on total carotenoid content of the rind. / AFRIKAANSE OPSOMMING: Vruggrootte van 'Clementine' mandaryn en 'Valencia' lemoene kan 'n probleem wees in die Wes Kaap area van Suid Afrika. Klein vrugte is nie net onaanvaarbaar vir die verbruiker nie, maar is ook moeilik om te oes. Vrugdrag manipulasie is een manier om hierdie probleem te beheer. Hand uitdunningsproewe is uitgevoer om die effek van tyd en graad van uitdunning op vruggrootte te bepaal. Strawwe vruguitdunning (60% van vruggies verwyder) het groter vrugte tot gevolg gehad maar het gelei tot 'n verlaagde opbrengs. Opbrengs is tot soveel as 30% verlaag met die strawwe vruguitdunning. Vroeë en laat behandelings het egter geen effek gehad nie, aangesien die proewe te laat uitgevoer is (4 tot 6 weke na die fisiologiese vrugvalperiode) om die gewenste effek te verkry. Beter uitpak word verwag na uitdunning, aangesien vrugte met letsels ook verwyder word. Die effek van veelvuldige 2,4-dichlorofenoksie-propioonsuur (dichlorprop) spuite IS ook geëvalueer op 'Nules Clementine' mandaryn. Daar is geen verskil gevind tussen enkel en veelvuldige spuite in terme van vruggrootteverbetering nie. Die gebruik van veelvuldige dichlorprop spuite het nie tot 'n verlaging in opbrengs gelei nie, en interne vrugkwaliteit is ook nie beïnvloed me. Die beste resultate is verkry met die 50 mg. L-1 dichlorprop behandeling. Die gebruik van dichlorprop saam met verskillende benatters is op beide 'Clementine' mandaryn en 'Valencia' lemoene geëvalueer. Vruggrootte het toegeneem vanaf 50 mg. L-1 tot 100 mg. L-1 • Opbrengs was net in sekere gevalle verlaag en dan sonder 'n betekenisvolle verskil in groot-vrug produksie (>55 mm: Clementines). Tydens die eerste jaar van die 'Valencia' lemoen proef is die dichlorprop relatief laat gespuit (vrug deursneë: 19 mm). Daar was geen effek op vruggrootte, opbrengs en interne vrugkwaliteit nie. Tydens evaluasie van vroeë en laat bespuitings die volgende jaar is waargeneem dat laat bespuitings geen effek op vruggrootte gehad het nie, terwyl vruggrootte (48 vrugte per karton) betekenisvol verhoog is deur die vroeë bespuitings (Vruggrootte voor bespuiting = 8 en 12 mm, onderskeidelik). Dit impliseer dat dichlorprop se effek op vruggrootte gedurende die vroeë stadiums van vrugontwikkeling is, net na of gedurende die laat stadiums van die fisiologiese vrugvalperiode. Opbrengs is drasties verlaag deur dichlorprop, tot soveel as 35% wat die kilogram groot vrugte negatief beïnvloed het in sommige behandelings. Sappersentasie was nie konsekwent affekteer nie, maar is verlaag deur die dichlorprop bespuitings. Dichlorprop het die TSS effens verhoog in beide jare, maar het geen effek gehad op die TSS:TA verhouding nie. Die gebruik van Orchex minerale olie as benatter was effektief by 150 mL. 100 L-1 , en laat klaarblyklik die gebruik van dichlorprop by laer konsentrasies toe. Dus, kom dit voor dat benatters die potensiaal het om die effektiwiteit van dichlorprop te verbeter wat lei tot 'n verlaging in toedieningskoste. Die dichlorprop gespuite vrugte is gebruik om karotenoïed-inhoud van die skil te meet tydens die laat stadiums van vrugontwikkeling. Vrugte gespuit met dichlorprop teen 'n konsentrasie van 50 mg. L-1 het 'n beter karotenoïed-inhoud in beide 'Clementine' mandaryn en 'Valencia' lemoene tot gevolg gehad. Vrugte blootgestel aan lig het ook 'n hoër karatenoïedkonsentrasie gehad as vrugte wat met bruin papiersakke bedek was. Dichlorprop bespuite vrugte teen 100 mg. L-I, alhoewel blootgestel aan lig, het geen betekenisvolle verskil gehad in vergelyking met onbespuite vrugte nie. Dus is daar geen konsekwente effek van dichlorprop op karotenoïde inhoud van die skiI waargeneem nie.

Objective: To evaluate if fruits and vegetables consumption is associated with overweight and obesity in Peruvian adults and as to describe the sociodemographic profi le of the people with overweight and obesity. Subjects and methods: Populationbased study that used data from the National Demographic and Health Survey (DHSENDES) performed in the 25 regions of Perú. The outcomes were overweight and obesity assessed using the Body Mass Index, whereas the exposure variable was the fruit and vegetable consumption evaluated by self-report during the last seven days. Poisson regression models adjusted by potential confounders were used to evaluate associated factors with overweight and obesity, as well as the association of interest, reporting prevalence ratios (PR) and 95% confi dence intervals (95%CI). Results: Data from 4,641 participants, mean age 37.1 years (SD: 11.8) and 53.6% women, were analyzed. Only 220 (4.8%; 95%CI 4.1%-5.4%) individuals reported a fruit and vegetable consumption of ≥5 portions per day, whereas 1,818 (39.2%; 95% CI 37.8%-40.6%) had overweight and 865 (18.6%; IC95% 17.5%-19.8%) presented obesity. Factors associated with overweight and obesity included gender, age, education level, socioeconomic level, marital status, and hypertension diagnosis. No association was found between a greater fruit and vegetable consumption and overweight (p=0.98) or obesity (p=0.99). Conclusions: No evidence of association between overweight and obesity with fruit and vegetable consumption was found. Only 1 out of 20 individuals reported consuming the recommended amount of fruit and vegetables per day, whereas 60% had overweight and obesity. / Revisión por pares

The biosynthetic origin of the plant growth regulator abscisic acid remains equivocal and almost nothing is known about the enzymes involved in this process. The present research programme describes the development of a cell-free system, capable of synthesizing abscisic acid and attempts to provide further information about the biochemistry and enzymology of this important biosynthetic pathway. Cell-free extracts were prepared either directly from the flavedo (crude) or from an acetone powder derived from flavedo, of mature coloured fruits of Citrus sinensis L. cv. Midknight and incubated with mevalonic acid, isopentenyl pyrophosphate, famesylpyrophosphate, geranylgeranyl pyrophosphate, ß-carotene and 1',4'-trans-abscisic acid diol. The neutral and acidic products formed were purified by thin-layer chromatography and high performance liquid chromatography, and quantified by high performance liquid chromatography, gas chromatography-electron capture and unequivocally identified by combined gas chromatography-mass spectrometry. Abscisic acid, 1',4'-trans-abscisic acid diol and phaseic acid were unequivocally identified as the major acidic products formed in this cell-free system. The acid fraction also contained xanthoxin acid. Labelled and unlabelled ß-carotene was converted into the neutral compounds xanthoxin and xanthoxin alcohol. In addition. high performance liquid chromatography-photodiode array analYSis of the oxy-carotenoid fraction revealed the complete spectrum of ß, ß-carotenoids induding zeaxanthin, antheraxanthin and violaxanthin with accumulation of an oxygenated carotenoid tentatively identified as 9- cis-violaxanthin. Identification of putative C₁₅ intermediates was achieved by either UV spectrophotometry and combined capillary gas chromatography-mass spectrometry or microchemical analYSis and co-chromatography. Refeeding studies using (±)-[2-¹⁴C]_ abscisic acid diol as substrate revealed that abscisic acid was not metabolized to abscisic acid diol, suggesting that it was/is produced as an intermediate rather than as a catabolite of ABA in this system. Stigmasterol, and to a lesser extent cholesterol reduced conversion of ß-carotene to abscisic acid but did not influence transformation of 1',4'-trans-abscisic acid diol to abscisic acid. AM01618 stimulated fonnation of abscisic acid and appeared to exert its effect at the level of conversion of 1' ,4'-trans-abscisic acid diol. Zeatin and the cytokinin analogue, ancymidol inhibited the biosynthesis of abscisic acid whereas dithiothreitol increased incorporation of label from ß-carotene into abscisic acid suggesting involvement of a cytochrome P450-type mixed function oxidase in this reaction sequence. Sodium dodecylsulphate polyacrylamide gel electrophoresis of the enzyme extract derived from Citrus flavedo revealed the presence of a 53 kD protein with peroxidase activity characteristic of a cytochrome P-450. Abscisic acid biosynthesizing activity was always greater in extracts from acetone powder and abscisic acid biosynthesis was enhanced in the presence of AMO 1618, NAD+, NADH, NADPH, MgCI₂ and Molybdate but was inhibited by FAD. Activity was further enhanced by the addition of (R,S)-abscisic acid as a cold-pool trap and by induding 0.1% w/v of either Tween 20 or Triton X 100 in the extraction buffer. When cis-ß-carotene was used as substrate, no abscisic acid was produced. Conversely when either all-trans-ß-carotene or a mixture of the two isomers was used, incorporation into abscisic acid occurred. Upoxygenase activity in cell-free extracts of Citrus flavedo increased with increasing protein concentration. As the ability of lipoxygenase to make xanthoxin from violaxanthin, had been reported, increased activity in the cell-free system implied that carotenoid deavage was being brought about by a non-haem oxygenase with lipoxygenase-like properties. Reports had implicated phoshorylation in the activation of many catalytic enzymes (Hanks et aI., 1985). Phosphorylation of the enzymes in this cell-free system proved unsuccessful. Further, it had been reported that in vitro phosphorylation of several membrane polypeptides and soluble polypeptides from com, had been promoted by the addition of Ca²₊ In this cell-free system Ca + did not have a stimulatory effect on protein phosphorylation. Dioxygenases generally occur as soluble enzymes, where they catalyse many oxygenation reactions in metabolic pathways. The addition of 2-oxo-glutarate, a requirement of most soluble oxidases, did not affect the activity of the cell-free system.

No description available.

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Yield and fruit quality of Citrus species relative to foliar sprays of macronutrients Marginal fruit colour and poor internal quality have been primary problems in the production of early-maturing mandarins in the Western Cape region (34 Os t 9°E). This leads to a reduction in the percentage of exportable fruit, a delay in the picking and consequent reduction in internal quality due to over-maturity. Therefore, a well-developed rind colour and internal quality of citrus are quality parameters of major importance in the fruit market. The effect of soil-applied limestone ammonium nitrate (LAN) and foliar low-biuret on fruit colour, yield and internal fruit quality of 'Mihowase' Satsuma on 'Troyer' citrange rootstock were evaluated. A significant reduction in leaf N levels was recorded where soil N has been reduced from 168 kg N/ha per annum to 126 kg Nlha per annum. Nitrogen applications influenced internal quality, although differences between treatments were too small to be of commercial importance. Despite tree appearance being more yellow in some years where N was predominantly applied as foliar spray, no consistent reduction in fruit size or yield was found. There were no clear significant differences in fruit colour, probably due to the fact that leaf N-Ievels were still within or below the norms suggested for Satsuma. The effect of Seniphosf , a mineral mixture of 31Og/L P20S, 56g/L CaO and 30g/L total N, and mono-potassium phosphate (MKP) [52% P20Sand 34% K20] on fruit colour, yield and internal fruit quality of mandarins, viz., 'Mihowase' Satsuma and 'Nules' Clementine on 'Troyer' citrange rootstock were evaluated. Seniphos'" and MKP applied during autumn colour break also did not influence fruit colour, yield and internal fruit quality, viz., juice content (%), total soluble solids (TSS), titratable acid (TA) and TSS:TA ratio of 'Nules' Clementine and 'Mihowase' Satsuma. In the Citrusdal region of South Africa (Western Cape Province), rind roughness is a general problem which often limits the percentage of exportable fruits. The effect of foliar mono-potassium phosphate (MKP) applied at 3% or 5% and urea ammonium phosphate (UAP) at 2% at 4 or 6 weeks, respectively, after full bloom (AFB) on yield, internal and external fruit quality (rind texture) of Citrus spp on rough lemon rootstock were evaluated. MKP and UAP had no consistent effect on yield, juice content (%), TSS, TA and TSS:TA ratio of 'Nouvelle' tangor, 'Valencia' orange, 'Shamouti' midseason and 'Oroval' Clementine. MKP and UAP sprays significantly, but inconsistently improved rind texture of 'Nouvelle' tangor, 'Shamouti' midseason and 'Valencia' orange. However, no positive effect was found on rind texture of 'Oroval' Clementine and 'Eureka' lemon. Inconsistent effects ofMKP and UAP sprays were also found on % leafN, P and K. / AFRIKAANSE OPSOMMING: Opbrengs en vrugkwaliteit van sitrus spesies relatief tat blaar toedienings van makroelemente Marginale vrugkleur en swak interne kwaliteit is die prim ere produksieprobleme in vroee seisoen mandaryne in die Wes-Kaap (34 Os 19°E). Die gevolg is 'n lae persentasie uitvoerbare vrugte omdat die oesdatum uitgestel word wat 'n afname in interne kwaliteit veroorsaak weens oorrypheid. Goed ontwikkelde skilkleur en interne kwaliteit is dus van groot belang vir bemarking van die vrugte. Grond-toegediende kalksteen-ammonium-nitraat (KAN) en lae biuret ureum se effek op vrugkleur, oesgrootte en interne vrugkwaliteit van 'Mihowase' Satsuma op 'Troyer citrange' onderstamme is ge-evalueer. 'n Betekenisvolle afname van die N viakke in die blare is gevind nadat grondtoediening van N vanaf 168 kg N/ha/jaar na 126 kg N/ha/jaar venninder is. N toedienings het interne kwaliteit beinvloed, maar die verskille tussen die behandelings was nie van kornmersiele waarde nie. Al was die boomvoorkoms geler in sommige jare waarin N hoofsaaklik as blaarvoedings toegedien is, was daar nie konstante afnames in vrug-of oesgrootte nie. Daar was geen betekenisvolle verskille in vrugkieur nie, waarskynlik omdat die blaarvlakke van N steeds binne die nonne daarvoor in Satsumas was. Die effek van Seniphos ('n minerale mengsel van 310g/L P20S, 56g/L CaO en 30g/L totaal N en monokaliumfosfaat (MKP) [52% P20S en 34% K20] op vrugkleur, oesgrootte en interne vrugkwaliteit van 'Mihowase' Satsumas en 'Nules' Clementine op Troyer citrange onderstarnme is geevalueer. Seniphos en MKP, toegedien tydens kleurbreek in die herfs, het ook nie skilkleur of interne vrugkwaliteit (sappersentasie, totale oplosbare vaste stowwe (TOV), suurheid (TS) en TOV:TS) betekenisvol bemvloed nie. In die Citrusdal-omgewing in die Wes-Kaap Provinsie (Suid-Afrika) is skilgrofheid 'n algemene probleem wat die hoeveelheid uitvoerbare vrugte beperk. Die effek van blaartoegediende MKP teen 3 en 5% en ureum-amrnoniurn-fosfaat (UAP) teen 2%, op onderskeidelik 4 of 6 weke na volblom, is geevalueer ten opsigte van oesgrootte, interne en ekstenne (skil grofheid) vrug kwaliteit in Citrus spp op growweskilsuurlemoen onderstam. Nie MKP of UAP het konsekwente verskille getoon t.o.v. oesgrootte, sappersentasie, TOV, TS, of TOV:TS in 'Nouvelle' tangor, 'Valencia' orange, 'Shamouti' midseison of 'Oroval' Clementine nie. Skiltekstuur is egter betekenisvol, hoewel inkonsekwent, verbeter in laasgenoemde drie. Skiltekstuur van 'Oroval' Clementine en 'Eureka' suurlemoen is nie bemvloed nie. Blaarpersentasies van N, P en K is ook inkonsekwent deur MKP en UAP beinvloed.

Citrus is among the most important fruit crops worlstwide, and therefore the preservation and improvement of citrus germplasm is of the essence. Citrus breeders are often faced with the difficulty of distinguishing between new and existing cultivars because of the ambiguous nature of morphological traits due to environmental influences and error in human judgement. The protection of new varieties is very important to the breeder. New varieties cannot be patented in South Africa, but it can be protected by Plant Breeders' Rights, only if it is genetically distinguishable and significantly different economically from existing varieties. Cultivars in four genera (c. sinensis, C. paradisi, C. grandis and C. reticulata) included in the Citrus Improvement Programme (CIP) or cultivars awaiting recognition of Plant Breeders' Rights by the International Union for the Protection of New Plant Varieties (UPOV) were analyzed with Isoenzymes, Restriction Fragment Length Polymorphism (RFLP) and Random Amplified Polymorphic DNA (RAPD). Five enzyme systems (PGM, PGI, MDH, GOT and IDH) were analyzed and founded to be suitable for grouping together cultivars belonging to the same genera. It was not suited for routine discrimination of cultivars in a particular genus. RFLP studies were conducted on five grapefruit cultivars, using cDNA clones from a genomic library of Rough Lemon. RFLP studies were valuable for the discrimination of closely related cultivars which probably originated from a common ancestor by bud mutations. This technique was, however, abandoned due to its biohazardous nature and replaced by the PeR-based Random Amplified Polymorphic DNA. RAPDs are easy to perform and gave promisin& results which were exploited to reveal polymorphisms between cultivars within the various groups. Although the interpretation of data produced by this method is often suspicious, it is the best method currently available for cultivar identification. It can playa complementary role in the protection of new varieties when classical morphological interpretation of differences is not capable of determining sufficient distinctness for the awarding of Plant Breeders' Rights.

Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Rind colour is one of the most important external quality characteristics of citrus fruit and plays an important role in purchasing decisions by consumers. Consumers perceive brightlycoloured fruit to be sweet and mature, whereas citrus with a green rind is perceived to be sour and immature. However, there is a poor correlation between rind colour and internal quality, contradicting what is generally assumed by the fruit-buying public. In general, a bright orange rind colour improves consumer acceptance. Thus, it is important to ensure that the rind of citrus fruit is well-coloured on arrival at the market. Various pre-harvest cultural practices and postharvest techniques can be applied to improve rind colour. Degreening with ethylene gas is the most commonly used postharvest technology to improve rind colour, but has various negative side-effects. Degreened fruit are more prone to decay, have rinds which appear dull and flaccid, have been reported to develop off-flavours and have a shorter shelf-life period. Therefore, it is necessary to find alternatives to ethylene degreening and to extend shelf-life of citrus fruit. Under normal orchard conditions, rind colour development is associated with low night temperatures, usually experienced during autumn or following the passing of a cold front. To simulate cold front conditions, a hydrocooler and cold room were used to rapidly drop fruit temperature to 4 ºC for 6 hours, and then fruit were incubated at 20 to 22 ºC for 72 hours. This “cold shock” treatment of ‘Nules Clementine’ mandarin improved rind colour to a level similar to that of degreened fruit in the 2002 season due to a decrease in chlorophyll content and increase in carotenoid content. However, this result could not be repeated. Storage temperature is one of the most important postharvest factors affecting rind colour. Citrus fruit shipped to export markets requiring low temperatures (-0.6 ºC) for pest disinfestations purposes have been reported to arrive with poor rind colour. Shipping under low temperatures results in poor rind colour of fruit on arrival in the market. To comply with the USA’s phytosanitary requirement for imported citrus, fruit is held at -0.6 ºC for a minimum of 22 days. The effect of shipping at various temperatures (-0.6 ºC or 4.5 ºC), durations and the influence of initial rind colour, “orange” or “yellow”, on fruit colour upon arrival in the market was evaluated. Fruit shipped at a higher temperature (4.5 ºC) had a marginally better rind colour than fruit shipped at -0.6 ºC. The perceived loss of rind colour following shipping at sub-zero temperatures is probably due to carotenoid degradation. Therefore, initial rind colour plays a critical role in final product quality. Depending on market destination and shipping temperature, pale-coloured fruit should not be packed for markets sensitive to rind colour. Holding temperature after shipping can be effectively used to improve the rind colour of fruit arriving in the market with undesirable rind colour. An intermediate holding temperature of between 11 and 15 ºC resulted in the greatest improvement in rind colour after 2 weeks. A high holding temperature (20 ºC) caused colour degradation, whereas a low holding temperature (4.5 ºC) resulted in the maintenance of rind colour. By selecting the correct holding temperature, even after shipping at sub-zero temperatures, final colour can be improved. / AFRIKAANSE OPSOMMING: Tyd-temperatuur interaksie op na-oes skilkleur ontwikkeling by sitrus Skilkleur is een van die belangrikste eksterne kwaliteitseienskappe van die sitrusvrug en spëel ʼn belangrikke rol in wat verbruikers koop. Verbruikers verwag dat heldergekleurde vrugte soet en ryp sal wees, terwyl sitrus met ʼn groen skil geassosieer word met onrypheid en ʼn suur smaak. In teenstelling hiermee is daar egter ʼn swak korrelasie tussen skilkleur en interne kwaliteit. Aangesien ʼn heldergekleurde oranje skil verbruikersaanvaarding verbeter, is dit dus belangrik om te verseker dat die sitrusvrug ʼn goeie skilkleur het teen die tyd wat dit die mark bereik. Verskeie voor-oes bestuurspraktyke en na-oes tegnieke kan toegepas word om die skilkleur te verbeter. Ontgroening met etileen gas is die tegnologie wat mees algemeen gebruik word om skilkleur na oes te verbeter, maar dit het egter verskeie newe effekte tot gevolg. Ontgroende vrugte is meer vatbaar vir bederf en verwelkde skille met ʼn dowwe voorkoms. Afsmaake kan voorkom en ʼn verkorte rakleeftyd is al gerapporteer. Dit is dus noodsaaklik om ʼn alternatief vir etileen ontgroening te ontwikkel en die rakleeftyd van sitrusvrugte te verleng. Onder normale boordomstandighede word skilkleur ontwikkeling geassosieer met lae nag temperature wat gewoonlik in die herfs of na ʼn kouefront ondervind word. Om soortgelyke omstandighede na te boots, was ʼn “hydrocooler” en koelkamers gebruik om die temperatuur vinnig te laat daal tot by 4 °C en dit vir 6 uur daar te hou. Die vrugte was dan by 20 tot 22 °C geinkubeer vir 72 uur. Hierdie “koueskok” behandeling van ‘Nules Clementine’ mandaryn het skilkleur verbeter tot ʼn vlak vergelykbaar met ontgroende vrugte in die 2002 seisoen wat ontstaan het weens ʼn verlaging in chlorofil en ʼn toename in die karotinoïed inhoud van die skil. Opbergingstemperatuur is een van die belangrikste na-oes faktore wat skilkleur beinvloed. Sitrusvrugte wat verskeep word na uitvoermarkte wat lae temperature (-0.6 °C) vir disinfestasie vereis arriveer soms by die mark met ʼn swak skilkleur. Om die fitosanitêre vereistes vir die invoer van sitrus deur die VSA na tekom, was vrugte vir ʼn minimum van 22 dae by -0.6 °C gehou. Die effek van verskeping by verskeie temperature (-0.6 °C of 4.5 °C), tydperke en die invloed van aanvanklike skilkleur, “oranje” of “geel” was geevalueer by aankoms in die mark. Vrugte wat by hoër temperature (4.5 °C) verskeep was het ʼn effens beter skilkleur as vrugte by -0.6 °C getoon. Die verlies in skilkleur wat waargeneem word na verskeping onder vriespunt kan moontlik toegeskryf word aan karotenoiëd afbraak. Daarom speel aanvanklike skilkleur ʼn kritieke rol in finale produk kwaliteit. Die finale mark bestemming en verskepingstemperatuur sal bepaal of swakgekleurde vrugte verpak kan word. Opbergingstemperatuur na verskeping kan effektief gebruik word om die skilkleur van vrugte wat swak gekleur was met aankoms by die mark te verbeter. Matige temperature tussen 11 en 15 °C het na 2 weke die beste verbetering in skilkleur gelewer. Hoër temperature (20 °C) het skilkleur nadelig beinvloed, terwyl lae temperature skilkleur behou het. Deur die korrekte temperatuur te kies, selfs na verskeping by temperature onder vriespunt, kan uiteindelike skilkleur steeds verbeter word.

The South African Citrus Industry is the second largest exporter of citrus, after Spain. The industry is under pressure to supply high quality fruit as well as to expand into new, high paying markets. However, high paying markets such as Japan and the USA require cold sterilised fruit as obligatory quarantine treatments against Mediterranean fruit fly (Ceratitis capitata) in order to reduce any possible spread of the pest. Citrus fruit originated from tropical climates and hence are chilling susceptible. Chilling injury symptoms appear as dark brown spots, pitting and/or decay when fruit are transferred to shelf temperatures; thus reducing the marketability of citrus fruit. Therefore, there is need for methods to mitigate chilling injury. Previous studies have shown silicon to mitigate many forms of stress without any hazardous effect on human health. Thus, the aim of the study was to investigate the potential of post-harvest silicon dips in mitigating chilling symptoms in citrus fruit. Briefly, fruit from two sources (Ukulinga Research Farm and Ithala Farm) were dipped in different silicon concentrations (0, 50, 150, and 250 mg ℓ-1) for 30 minutes and thereafter stored at -0.5 or 2⁰C for up to 28 days with weekly evaluation for chilling injury symptoms. Total antioxidants were determined using FRAP, ABTS, and DPPH assays under spectrophotometer. In addition, sugars, ascorbic acid, phenolics and flavonoids were analysed using High Performance Liquid Chromatography (HPLC). Fruit from Ukulinga Research Farm showed significantly higher total antioxidants (ascorbic acid total phenolics and specific flavonoids hesperidin and naringin) and sugars relative to fruit from Ithala Farm. Low concentrations of silicon dips significantly reduced the appearance of chilling injury symptoms by inducing an enzymatic conversion of glucose to ascorbic acid, thereby increasing the antioxidant capacity of chilling susceptible fruit. Moreover, silicon increased the concentration of total antioxidants, total phenolics and total flavonoids. High silicon concentrations had a negative effect on post-harvest quality of lemons by increasing fruit weight loss and electrolyte leakage, resulting in appearance of chilling symptoms. In conclusion, the study showed that silicon had potential to reduce chilling injury. However, high silicon concentrations raised concern, in particularly, on fruit appearance. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.