published_or_final_version / Botany / Master / Master of Philosophy

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Title page, contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Pre-harvest sprouting (PHS) is an important economic problem which affects a significant proportion of the Australian wheat crop through quality downgrading. Grain dormancy is the most effective means of overcoming germination in the wheat spikelet at harvest maturity. It has been a consistent observation over a long period of time that dormant red-grained wheat genotypes are almost more dormant than dormant white-grained genotypes. In white-grained wheat, there are two factors which contribute to dormancy, embryo sensitivity to abscisic acid (ABA) and an interacting and unknown seed coat factor. The proposed dormancy model is that complete dormancy can only be achieved with the coordinate expression of these two factors. This primary objective of this project was to determine the role of this putative seed coat factor in grain dormancy of white-grained wheat."--Abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1259900 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006

Title page, contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library. / Pre-harvest sprouting (PHS) is an important economic problem which affects a significant proportion of the Australian wheat crop through quality downgrading. Grain dormancy is the most effective means of overcoming germination in the wheat spikelet at harvest maturity. It has been a consistent observation over a long period of time that dormant red-grained wheat genotypes are almost more dormant than dormant white-grained genotypes. In white-grained wheat, there are two factors which contribute to dormancy, embryo sensitivity to abscisic acid (ABA) and an interacting and unknown seed coat factor. The proposed dormancy model is that complete dormancy can only be achieved with the coordinate expression of these two factors. This primary objective of this project was to determine the role of this putative seed coat factor in grain dormancy of white-grained wheat."--Abstract. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1259900 / Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2006

The effects of seed size on sprout growth of potato seed pieces were investigated in controlled temperature conditions. The objectives were to quantify the effects of seed size, plant growth regulators (gibberellin and paclobutrasol) and calcium availability on sprout length, sprout and root dry mass, as well as the fraction of seed reserves utilised for sprout development. The interactive effect between seed size and temperature was also investigated Sprout length did not differ among seed pieces ranging from 1 to 8g in mass. For larger seed pieces sprout length, dry mass and dry mass per unit length, and the root dry mass increased with increasing seed size, reaching a maximum at a seed mass of 24g after 40 days. The smaller the initial seed piece the larger was the fraction of assimilates utilised for sprout growth. Sprout length and dry mass as well as assimilate mobilisation for growth, were promoted by dipping seed pieces in gibberellin solutions, with the greatest effect obtained with 30 ppm GA, the highest concentration used in the experiment. Paclobutrasol showed inhibiting effects on all growth parameters except for sprout thickness. The root dry mass did not differ among treatments. Sprout growth was enhanced by calcium availability, with the greatest effect obtained with exogenous supply of calcium at 10 mmol/I as CaS04. A similar effect was noticed when complete nutrient solution was supplied. CaC03 was less effective than CaS04. Calcium availability to sprout tips affected sprout growth only when the roots were deprived of nutrients. Sprout length of the two seed pieces (3 and 5g in mass) was similarly affected by temperature over time, with the sprouts at the low temperature initially shorter, but reaching the same lengths as those at the high temperature after 30 and 40 days. Sprout dry mass and thickness of 3 and 5g seed pieces were similarly affected by temperature, with higher dry mass and greater thickening at 16°C than at 26°C. Exposure to low temperature (16°C) was associated with the transfer of a large fraction of seed reserves to the sprouts. / Dissertation (MSc (Agric): Agronomy)--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

KOSTRZEWA, R. M., J. W. KLARA, J. ROBERTSON AND L. C. WALKER. Studies on the mechanism of sprouting of noradrenergic terminals in rat and mouse cerebellum after neonatal 6-hydroxydopa. BRAIN RES. BULL. 3(5) 525-531, 1978.-The effect of various pharmacologic agents on the noradrenergic innervation of rat cerebellum was observed. It was found that the neurotoxin 6-hydroxydopa (6-OHDOPA), when given to rats at birth, caused a 46% reduction at 5 weeks of age in tyrosine hydroxylase activity in the locus coeruleus, the nucleus of origin for noradrenergic fibers innervating the cerebellum. At the same time, however, both tyrosine hydroxylase activity and NE content were elevated by 50% in the cerebellum. By treating gravid mice with the 6-OHDOPA, which crosses the placental barrier to affect the brains of developing pups, a dissociation has been shown between the elevated cerebellar NE levels and reduced telencephalic NE content. None of the other assorted pharmacological agents-namely amphetamine, metaraminol, apomorphine, α-methyl-ρ-tyrosine, L-dihydroxyphenylalanine and tyramine-when given at birth, caused a permanent elevation in cerebellar NE content. This series of studies suggests that a reduced number of noradrenergic perikarya are providing a greater innervation of the cerebellum than in control rats. Also, alteration of the telencephalic noradrenergic fibers, which are also derived from the locus coeruleus, does not appear to be a necessary event for the initiation of sprouting of noradrenergic fibers in the cerebellum. Because none of the acute-acting pharmacological agents caused a permanent elevation of NE in the cerebellum, it appears that damage, and not mere stimulation or blockade, is a necessary event for initiation of sprouting.

The effect of preharvest foliar applications of ethephon and postharvest curing on baked sweet potatoes (Ipomoea batata) were analyzed. Ethylene had negative effects on appearance of baked roots while curing increased the total phenolics in sweet potatoes. Panelists preferred the non-ethylene treated and green or cured over ethylene treated sweet potatoes with respect to texture, color and flavor. No differences in chemical or color properties were found between treatments. The effect of curing time (0, 7, 14 days) on baked sweet potatoes was studied. Curing caused more browning on flesh of sweet potatoes. Moreover, panelists preferred the texture of the green over the cured roots but did not find any differences in flavor sensory quality. The effect of hot water treatment on sprouting and spoilage of cured sweet potatoes was investigated. The most effective treatment was at 53-56 °C for less than 10 min, resulting in less than 60% (control=80%).

In malting barley, rapid germination is desirable and linked to end use quality. Modern malting varieties have been bred for low seed dormancy leading to issues with pre-harvest sprouting in wetter growing regions. To maintain malting capacity while minimizing germination on the maternal plant requires in-depth understanding of the genetic regulation of dormancy in malting barley. Currently, the major effect QTLs SD1 and SD2 have been shown to influence dormancy across multiple populations of barley, though the physiological mechanisms involved remain unclear. To search for novel genetic regions that influence primary dormancy, three mapping populations were assessed including two Canadian biparental populations (Synch and Legci) as well as a diversity panel sourced from multiple locations worldwide (ICARDA AM-14). The SD2 locus had a major effect in the Synch population while the SD1 locus had a major effect in the Legci population and neither SD1 nor SD2 were linked to dormancy in the diversity panel. Instead, 14 additional marker trait associations were identified in AM-14 suggesting that investigating a broader range of genetic regulation of dormancy outside of North American varieties may provide solutions to regulate this trait. Additional testing on SD1 revealed that variation at this locus did not affect ABA sensitivity during germination or GA or ABA-regulated gene expression during grain fill. Indeed, lines containing the non-dormant SD1 allele germinate at a similar rate as the dormant SD1 seeds when the glumella was removed from the embryo. This indicated that the effect of the alanine aminotransferase gene underlying the SD1 allele is dependent on physical restriction on the embryo or the hypoxic effects produced by the glumella. Imposing a hypoxic (5% oxygen) environment on exposed embryos revealed an association between non-dormancy at SD1 and reduced sensitivity to the suppressive effects of hypoxia on germination. This suggests that alanine aminotransferase regulates dormancy release during barley germination at least in part through regulation of the seed’s response to hypoxia.

Alpha-amylase synthesis can be induced in wheat and barley half-seeds by addition of gibberellic acid (GA) to the incubation medium. In maize, induction in de-embryonated kernels by exogenous GA has been reported in some studies but not others. Alpha-amylase induction was investigated in maize by measuring activity in extracts from whole and de-embryonated kernels incubated with and without GA during germination. Alpha-amylase activity was first detected on the 3rd day of germination in whole kernels and GA-treated endosperms and on the 4th day in the controls. Thereafter both whole kernels and GA-treated endosperms followed approximately the same time course in α-amylase activity with the control lagging a day behind. Studies indicated that maximum α-amylase activity occurred on the 7th day in whole kernels and GA-treated endosperms and the 8th in control endosperms. Maize α-amylase was purified using differential solubility, column chromatography, glycogen precipitation and polyacrylamide gel electrophoresis, of these, the best purification method was glycogen precipitation. Maize α-amylase exhibited isozymes. The isozyme patterns were qualitatively similar in all samples and throughout incubation. Wheat and barley α-amylase isozymes have been divided into two groups on the basis of a number of characteristics. Genetics analysis revealed these isozymes to be the result of two multigene families. To shed light on the genetic basis of the maize α-amylase isozymes, physicochemical characterization was initiated. Studies of pH and temperature profiles and optima showed no differences between maize isozymes. The pH optima was pH 5 and the temperature optima was about 37°C. / Master of Science