In this study adaptations of bryophytes and lichens to desiccation stress were examined. The aim was to test whether desiccation tolerance in the selected species is constitutive or if desiccation tolerance could be induced by various hardening treatments. In addition, some putative tolerance mechanisms were investigated, including the accumulation of sugars, increase in ROS scavenging systems and other mechanisms e.g. energy dissipating processes. To determine if hardening treatments prior to desiccation stress increased desiccation tolerance, mosses and lichens were partially desiccated or treated with ABA. The effect of hardening treatments on the physiology of the moss Atrichum androgynum and lichens Peltigera polydactyla, Ramalina celastri and Telochistes capensis during a desiccation-rehydration cycle was investigated. Photosynthesis, respiration and chlorophyll fluorescence measurements were used as rapid tools to determine the metabolic activities in these lichens and moss species. In A. androgynum partial desiccation following slow drying at 52% RH increased the rate of recovery of net photosynthesis. Net photosynthesis recovered almost completely following slow drying in the material that was partially dehydrated and/or treated with ABA. This suggests that partial dehydration hardens the moss, and that ABA can fully substitute for partial dehydration. In R celastri and P. polydactyla both partial dehydration and ABA treatments displayed some improvement in desiccation tolerance depending on the duration and severity of stress. The reduction in the re-saturation respiration burst in P. polydactyla, although not quite significant, strongly suggests that hardening increases mycobiont tolerance. However, it is more difficult to establish whether the hardening treatments improve photobiont performance. In the moss A. androgynum ABA treatment increased the rate of recovery of photosynthesis and PSII activity, and also doubled non-photochemical quenching (NPQ). Increased NPQ activity will reduce ROS formation, and may explain in part how ABA hardens the moss to desiccation. In ABA treated, but not untreated mosses, desiccation significantly increased the concentration of soluble sugars in A. androgynum. Sugar accumulation may promote vitrification of the cytoplasm and protect membranes during desiccation. Starch concentrations in freshly collected A. androgynum and R. celastri were only c. 40 and 80 mg g ¯¹ dry mass respectively, and slightly rose during desiccation, but were only slightly affected by ABA pretreatment. ABA did not reduce chlorophyll breakdown during desiccation. In P. polydactyla ABA pretreatment had little effect on any of these parameters. Changes in the activities of the free radical scavenging enzymes ascorbate peroxidase, catalase and superoxide dismutase were measured during wetting and drying cycles in the moss A. androgynum and in the lichens P. polydactyla, R. celastri and T capensis. These species normally grow in the understorey of the Afromontane forest, moist, xeric, and extremely xeric miicrohabitats respectively. In A. androgyum, enzyme activity was measured shortly after collection, after 3 d storage following hardening by partial dehydration and/or 1 h treatment with ABA or distilled water and during desiccation and rehydration. In A. androgynum enzyme activities of CAT and SOD in untreated material were always higher than in the hardened treatments, while both partial dehydration and ABA treatments tended to reduce both CAT and the induction of SOD activity, although these effects were not significant between the treatments. This suggests that ABA may not be involved in the induction of free radical scavenging enzymes and probably these enzymes are not important in desiccation tolerance of A. androgynum. In lichens, the enzyme activity was measured shortly after collection, after hydration for 48 hat 100% RH, after desiccation for 14 d and 28 d, and during the first 30 min of hydration with liquid water. Enzyme activities tended to rise or stay the same following rehydration in all the species tested. After desiccation for 14 d, enzyme activities decreased, and then decreased further to very low values after 4 weeks desiccation. In all species, including T capensis from an extremely xeric habitat, the activities of all enzymes remained at very low values during the 30 min following rehydration, and were therefore unavailable to remove any reactive oxygen species accumulating in lichen tissues as a result of desiccation. Results suggests that the enzymic antioxidants are more likely to be involved in removing reactive oxygen species produced during the normal metabolic processes of lichens than having a role in desiccation tolerance. The Afromontane understorey moss Atrichum androgynum displayed an oxidative burst of H₂O₂ during rehydration following desiccation. Maximum rates of H₂O₂ production occur during the first 15 min of rehydration. While the production of H₂O₂ increases with increasing desiccation times, the moss produced significant amounts of H₂O₂ during rehydration after desiccation for times that did not inhibit photosynthesis or cause K⁺ leakage. A. androgynum may produce more H₂O₂ during desiccation than rehydration, because desiccation artificially induced using polyethylene glycol strongly stimulates production. Experiments involving inhibitors and exogenously supplied reductants indicate that peroxidases are responsible for the synthesis of H₂O₂. Factors that influence the rate of H₂O₂ production during rehydration include light and the hormone ABA. Patterns of H₂O₂ production are discussed in terms of their possible role as a defence against pathogenic fungi and bacteria. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2002.

Environmental stresses such as drought, salinity and low temperature have been major selective forces throughout plant evolution and are important factors which limit crop plant distribution and agricultural productivity. An understanding of how crops adapt to adverse conditions is not only of theoretical interest, but also has considerable practical value . Low-temperature stress subtraction libraries were constructed in a pBluescript vector with the two-step-PCR amplified cDNAs using subtractive hybridization. One insert cs18 was obtained and the sequence analysis of insert cs18 revealed that the insert cDNA had a 76% homology with the sequences of the corresponding portion of glucose dehydrogenase from Thermoplasma acidophilum and 62.0% homology with a genomic DNA of Arabidopsis. Four clones, cs18-13, cs18-14, cs18-15, and cs18-16 from low-temperature stress soybean root conventional cDNA library have been confirmed to have inserts that could hybridize to the cs18 insert. One cDNA with a Xba I and Xho I fragment of approximately 3,500 bp in length corresponded to the insert cs18 , which probably encodes for glucose dehydrogenase, was obtained. Northern blot analysis indicated that cs18 mRNA was highly expressed in soybean root but moderately expressed in leaves under low temperature. Changes in the nuclei of meristematic root cells in response to severe salinity were studied. Roots are in direct contact with the surrounding solution . Thus, they are the first to encounter the saline medium and are potentially the first site of damage or line of defence under salt stress. Nuclear deformation or degradation in the soybean root meristem with 150 mM or higher NaCI led to sequential cell degradation, cell death and cessation of plant growth . However, this study indicates that an increase in CaCI[2] concentration up to 5 mM could partially prevent salt injury to the cells. Tissue culture is an excellent tool for elucidat ing the correlation between plant organizational levels and salt tolerance because of the possibility it offers for studying the physiology of intact plantlets together with that of organs and single cells using homogenous plant material under uniform environmental conditions. One NaCI-tolerant cell line (R100) was isolated during this study. The R100 callus cell line was significantly more tolerant to salt than the salt-sensitive line (S100) during exposure to salt stress. Salt tolerance in this culture was characterized by an altered growth behaviour, reduced cell volume and relative water content, and accumulation of Na+, Cl ¯, K+, proline and sugars when grown under salt stress and with its subsequent relief. The selection of this salt tolerant cell line has potential for contributing new genetic variability to plant breeders. Sugars are not only important energy sources and structural components in plants , they are also central regulatory molecules controlling physiology, metabolism, cell cycle , development, and gene expression in plants. The concentrations of glucose and fructose increased during salt stress and after relieving salt stress, at a rate closely corresponding to the increase in relative water content. Their accumulation was the earliest response detected during the removing of salt stress indicating that glucose and fructose may play important roles during salt-stress. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.

An infusion technique was used with an aqueous radiocalcium ( 45CaCl2) solution during the seed-filling stage of well-watered and moisture-stressed soybean in a greenhouse. The kinetics of infusion volume showed a quadratic reduction in absorption which approached zero on the sixth day for non-irrigated plants. The concentration of 45Ca increased quadratically from the point of injection towards the apex independent of both water status and plant parts. The difference in concentration of 45Ca between irrigated and non-irrigated plants was significant (P < 0.05) and concentrations attained the maximum values at the sixth node from the plant base. Seeds contained considerably less 45Ca than either stem or leaves. / The effects of a long (LD, 16h) and a short (SD, 12h) photoperiod with two water stress levels (SL) of stress (ST) and no stress (NS) on the distribution of 45Ca in plant organs (PO) of leaves, petioles, and stem at different node number (NN) of soybean were studied during the seed-filling stage. The univariate and Manova analyses showed the main effects of photoperiod (PP), SL, and PO to be highly significant (P < 0.001) on Ca distribution. The long PP increased Ca concentration in top leaves compared with the short PP regardless of SL. Water stress significantly (P < 0.001) modified the Ca distribution and reduced its concentration in PO within NN irrespective of the photoperiod (a measure of light stress). A possible mechanism for the regulation of Ca distribution is discussed in terms of nitrate reduction. / Ca uptake was also studied by immersing the central tip of a trifoliate leaf in various concentrations of 45CaCl2 solutions and drought conditions during the seed-filling period of soybean. The beta-ray gauging and the diurnal leaf temperature variation showed similar characteristics for leaf water status. The activities of 45Ca were significantly higher (P < 0.0001) at 5, 10, 20, and 30 mM concentrations for water-stressed and non-stressed leaves compared with the control. 45Ca activities at 5, 10, and 20 mM Ca concentrations between stressed and non-stressed leaves were not significant, but the difference in their mean values at 30 mM Ca concentration was significant (P = 0.0159). The relationship between 45Ca uptake and Ca concentration was parabolic for both stressed (R 2 = 0.77) and non-stressed (R2 = 0.81) leaves. Autoradiograms indicated Ca movement through the mid-rib and veins of the tip-immersed trifoliate leaf but showed no activity in other plant parts. An activity gradient developed between seeds when a pod-tip was immersed in the radioactive solution. Solutions of ruthenium red (RR, 0.01 mM), Ethylene Glycol-bis-(beta-aminoethyl ether)- N,N,N,N-Tetraacetic Acid (EGTA, 0.1 mM), calcium (Ca, 1 mM), and double distilled water (control) were fed through a bottom branch of soybean with (ST) and without (NS) water stress. The volume absorptions and transpiration rates were significantly higher for NS than ST plants and decreased almost linearly with time for all treatments. The transpiration rates of Ca-feeding ST plants and the control overlapped while the NS plants approached the same rate of transpiration by the third week. Ca was implicated in stomatal closure for the reduction in the transpiration rates. The relative amounts of chlorophyll decreased with time but chlorophyll was least affected for Ca-absorbing plants for both ST and NS plants. The use of RR (Ca transport blocker), and EGTA (Ca chelator) indicated the role of intracellular Ca conce

The effect of salinity on phosphorus (P) absorption kinetics by 'Russet Burbank' cv. potato propagated by tissue culture technique was studied in the laboratory. Nine clones of the cultivar were evaluated for their salt tolerance at the vegetative stage by using in vitro culture. Four concentrations of NaCl (0, 40, 80, and 120 mM) were used in the experiments. The first experiment was carried out to study the effect of salinity on P absorption by using radiophosphorus ($ sp{32}$P) as a marker. P absorption showed a quadratic relationship with time. In general, there was a significant reduction in P absorption as the NaCl concentration increased in the nutrient medium. However, the root tip concentration of $ sp{32}$P increased with increased salt concentration. When P concentration in the nutrient medium was increased, $ sp{32}$P activity was also increased with time at 120 mM salt concentration. The activity of radiophosphorus decreased on root tips when P concentration in the nutrient medium was increased to 2.5 mM P. The second experiment was conducted in tissue culture using nodal cutting bioassay. The plant morphological parameters of shoot length, shoot fresh weight, shoot dry weight, root length, root fresh weight, and root dry weight were reduced for all nine clones as salinity increased. The clone PEI#1 (tu) exhibited high salt tolerance characteristics.

This study was conducted to improve knowledge of the impact of chronic soil water deficit and to test a novel technique of water management consisting of Lipo-chitooligosaccharides (LCO) spray application. It also aimed at evaluating changes in canopy reflectance due to water stress and LCO spray. Water stress during reproductive development resulted in an important decrease of plant physiological activity, vegetative growth, and productivity, and accelerated plant senescence at both water stress levels. Water deficit increased leaf reflectance in the visible and decreased it in the infrared ranges of the spectrum at both imposed stress levels. Foliar application of LCO affected overall plant physiological activity, increased flower and pod numbers. LCO treatment had the largest positive effect on the growth pattern of soybean at the medium stress level, which is the stress level most commonly observed in standard farm-field conditions. LCO treatment constitutes a potential technology for reducing water deficit effects. (Abstract shortened by UMI.)

Plants possess highly sensitive perception systems by which they recognize signal compounds originating from microbes. These molecular cues play an important role in both symbiotic and pathogenic relationships. Establishment of the soybean (Glycine max)-Bradyrhizobium symbiosis is orchestrated by specific signal molecules exchanged between appropriate plant and microbe partners: flavonoids as plant-to-bacteria signals, and Nod factor as bacteria-to-plant signals. How this signaling process interacts with stress conditions (abiotic and biotic) is the subject of this thesis. The abiotic stresses were suboptimal growth temperature, low pH, and salinity. Suboptimal growth temperatures affected the ability of the microsymbiont, Bradyrhizobim japonicum, to perceive nod gene inducers (genistein) and produce Nod factor. Nod Bj-V (C18:1, MeFuc) production by B. japonicum strains 523C and USDA110 was strongly affected by suboptimal growth temperature. Nod factor production declined with temperature, from 28 to 15°C. Strain USDA110 was more affected by decreased temperature than strain 532C. Decreased Nod factor production at low temperature was due to both decreased bacterial growth and lower production efficiency (Nod factor per cell). When a 1:1 mixture of Nod factor Nod Bj-V (C18:1, MeFuc) and Nod Bj-V (Ac, C16:0, MeFuc) was applied to soybean roots, root hair deformation increased as Nod factor concentration increased under stressfully low temperature and low pH conditions. High salinity stress strongly reduced the root hair deformation caused by Nod factor, and increasing the concentrations of added Nod factor did not over come this. Exogenous application of Nod Bj-V (C18:1, MeFuc), from strain 532C, to soybean root systems under two root zone temperatures (RZTs---17 and 25°C) reduced the progression of disease (powdery mildew---Microsphaera difussa) development on soybean leaves; this effect increased with Nod factor concentration and was gr

The effects of early season and late season drought stress on various carbohydrates, calcium and/or nitrogen content at apical, central and basal tuber locations were studied for Russet Burbank and A082260-8 potatoes. Drought stress which occurred early in the stage of tuber development appeared to have more detrimental effect than later season stress. Interactions between treatment and sampling date and variety x position x date were significant during early season stress. Generally, percent total solids increased during potato development for both varieties. The central portion of tuber had the lowest total solids. Total reducing sugar content generally decreased during potato development for both varieties with significant (P<.05) differences at early season stress due to the interaction effects of treatment x date and variety x position. No significant difference in reducing sugar at later season stress was found regardless of treatment. Variety difference in reducing sugar content occurred at the apical end. Russet Burbank had more reducing sugars than A082260-8 at this end. The exploration of fructose, glucose and sucrose individually showed the same developing pattern as total reducing sugar. Sucrose made up over 50% of the total sugars with glucose and fructose the next in order of importance. The apical end had more sucrose and glucose than the basal end. The interaction of variety and position for both nitrogen and dietary fiber may be a result of growth pattern differences in the two treatments. Total dietary fiber content was generally the highest at the basal portion for both varieties. Russet Burbank appeared to have higher total dietary fiber than A082260-8 at this end. The level of calcium in Russet Burbank was significantly higher than that in A082260-8. Basal and apical portions had higher calcium content than the central portion. / Graduation date: 1990

Graduation date: 1993

Orientador: Jairo Osvaldo Cazetta / Banca: Samira Domingues Carlin Cavallari / Banca: Cesar Martoreli da Silveira / Resumo: Pesquisas científicas focadas em identificar genótipos tolerantes a estresse abiótico são altamente desejáveis, pois, o uso desses genótipos diretamente no campo, ou indiretamente em processos de melhoramento genético, permite reduzir custos de manejo do solo, da cultura e perdas de produtividade. O objetivo desse trabalho foi determinar a tolerância de 24 genótipos de cana-de-açúcar sob elevados teores de Al3+ e Mn2+, associado a baixa disponibilidade de nutrientes. Para trabalhar com elevado número de unidades experimentais, um novo sistema de hidroponia foi adaptado e testado neste trabalho. O ensaio foi instalado e conduzido em casa de vegetação em delineamento inteiramente casualizado, num esquema fatorial 24x2, correspondendo a 24 genótipos, dois tratamentos (com e sem estresse), com quatro repetições, totalizando 192 unidades experimentais. No tratamento sem estresse, as plantas foram cultivadas em solução nutritiva completa e no tratamento com estresse foi utilizada a mesma solução nutritiva com elevada acidez (4,0 ± 0,1) e com apenas 5% da sua concentração original, além da elevada concentração de alumínio (60 mg L-1) e manganês (700 mg L-1) ambos na forma de cloreto. Os genótipos RB966928, RB855443, IACSP96-3060, SP81-3250, RB867515, CTC 21, RB965902 e IAC91-1099 foram os que tiveram suas características biométricas menos afetadas pelo estresse proposto e consequentemente foram considerados os mais tolerantes. Por outro lado, os genótipos RB965917, CTC 15, CTC17, RB... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The scientific research focused on identifying and understanding abiotic stress-tolerant genotypes is highly desirable since their use directly in the field or indirectly in breeding processes may reduce costs of soil and crop management and productivity losses. This aim of this study was to determine the tolerance of 24 sugarcane genotypes under high contents of Al3+ and Mn2+ associated with the low availability of nutrients. In order to work with a great number of experimental unities, a new way of hidroponic method was adapted and tested in this research. The experiment was carried out in a greenhouse in a completely randomized design, in a 24 × 2 factorial scheme, consisting of 24 genotypes, two treatments (with and without stress), and four replications, totaling 192 experimental units. In the treatments without stress, plants were grown in a complete nutrient solution whereas in the treatments with stress, a nutrient solution with a high acidity (4.0 ± 0.1) and only 5% of its original concentration, as well as a high concentration of aluminum (60 mg L-1 ) and manganese (700 mg L-1 ), was used, both in the form of chloride. The genotypes RB966928, RB855443, IACSP96-3060, SP81-3250, RB867515, CTC 21, RB965902 and IAC91- 1099 were those that had their biometric characteristics less affected by the proposed stress and consequently were considered the most tolerant. genotypes RB965917, CTC 15, CTC17, RB855536, CTC 2, CTC 20, and CTC99-1906 were identified as the most sensiti... (Complete abstract click electronic access below) / Mestre

Cellular redox states mediate various physiological and developmental processes. Mechanisms involved in sensing cellular redox state and linking it to an appropriate physiological response remains poorly understood in plants. Arabidopsis bZIP68 was previously found to undergo reversible oxidation in its Cys320 in cells under oxidative stress. In this study, it was found that bZIP68 was localized in the nucleus in Arabidopsis seedlings under normal conditions. Upon treatment of oxidative stress, bZIP68 underwent nucleocytoplasmic shuttling and accumulated in the cytoplasm. This stress-dependent nucleocytoplasmic shuttling depends on the redox-sensitive Cys320 and its nuclear export signal. bZIP68 suppresses expression of stress response genes under normal conditions and its loss-of-function mutation of bZIP68 leads to elevated expression of genes involved in oxidative stress defense including genes encoding for antioxidant proteins and for enzymes involved in biosynthesis of small molecule antioxidants. The bzip68 mutant also showed enhanced responses to stress treatment such as the oxidative stress and cold stress. Our study suggests that bZIP68 directly or indirectly senses perturbation of cellular redox states and links the redox change to activation of oxidative stress defense genes through redox regulation of transcription.