Nitric Oxide Enhances Desiccation Tolerance of Recalcitrant Antiaris toxicaria Seeds via Protein S-Nitrosylation and Carbonylation

The viability of recalcitrant seeds is lost following stress from either drying or freezing. Reactive oxygen species (ROS) resulting from uncontrolled metabolic activity are likely responsible for seed sensitivity to drying. Nitric oxide (NO) and the ascorbate-glutathione cycle can be used for the detoxification of ROS, but their roles in the seed response to desiccation remain poorly understood. Here, we report that desiccation induces rapid accumulation of H2O2, which blocks recalcitrant Antiaris toxicaria seed germination; however, pretreatment with NO increases the activity of antioxidant ascorbate-glutathione pathway enzymes and metabolites, diminishes H2O2 production and assuages the inhibitory effects of desiccation on seed germination. Desiccation increases the protein carbonylation levels and reduces protein S-nitrosylation of these antioxidant enzymes; these effects can be reversed with NO treatment. Antioxidant protein S-nitrosylation levels can be further increased by the application of S-nitrosoglutathione reductase inhibitors, which further enhances NO-induced seed germination rates after desiccation and reduces desiccation-induced H2O2 accumulation. These findings suggest that NO reinforces recalcitrant seed desiccation tolerance by regulating antioxidant enzyme activities to stabilize H2O2 accumulation at an appropriate concentration. During this process, protein carbonylation and S-nitrosylation patterns are used as a specific molecular switch to control antioxidant enzyme activities

Uniform Selection as a Primary Force Reducing Population Genetic Differentiation of Cavitation Resistance across a Species Range

Background: Cavitation resistance to water stress-induced embolism determines plant survival during drought. This adaptive trait has been described as highly variable in a wide range of tree species, but little is known about the extent of genetic and phenotypic variability within species. This information is essential to our understanding of the evolutionary forces that have shaped this trait, and for evaluation of its inclusion in breeding programs. Methodology: We assessed cavitation resistance (P 50), growth and carbon isotope composition in six Pinus pinaster populations in a provenance and progeny trial. We estimated the heritability of cavitation resistance and compared the distribution of neutral markers (FST) and quantitative genetic differentiation (QST), for retrospective identification of the evolutionary forces acting on these traits. Results/Discussion: In contrast to growth and carbon isotope composition, no population differentiation was found for cavitation resistance. Heritability was higher than for the other traits, with a low additive genetic variance (h 2 ns = 0.4360.18, CVA = 4.4%). QST was significantly lower than FST, indicating uniform selection for P50, rather than genetic drift. Putativ

Water use efficiency : what are the implications for plantation forestry? : evidence for sustainable plantation forestry

Water use efficiency (WUE) is the ratio of some measure of growth or carbon assimilation to water utilization. It can be considered at the level of the leaf, whole plant or stand, and can be expressed in terms of total plant biomass or that of harvestable stems. It is a ratio and will be influenced by changes in either or both of the components. WUE is extremely variable with climatic and local weather conditions, soil type and plant age. Increases in yield of harvestable stem would increase WUE, but breeding practices have probably already maximised stem yield. Reductions in transpiration are considered unlikely to be achievable in plants growing in well-watered soils, and any such reductions would probably also bring about reductions in productivity. 'Water conservation' strategies are also unlikely in plants in water-limited soils, as competing neighbours would utilise the conserved water. It is not known whether there are differences among genotypes in intrinsic WUE, but if there are, these are more likely to become apparent under conditions of low, rather than high water availability. However, high WUE may not be a good selection criterion for plants suitable for water-limited conditions; the ability to acquire water and the ability to survive periods without water may be more important than the efficiency with which water is utilised. Southern African Forestry Journal No.195 2002: 73-7

Tissue diversity in respiratory metabolism and free radical processes in embryonic axes of the white mangrove (Avicennia marina L.) during drying and wet storage

Species diversity in responses to desiccation in plants is well studied and documented. However, organ and tissue variability in plant dehydration responses is not as well investigated and understood. Therefore, the responses of whole axes, hypocotyls, root primordia and plumules of white mangrove to drying and wet storage were monitored. Increasing the rate of drying lowered the critical and lethal water concentrations for survival as assessed by germination capacity and tetrazolium staining. Dehydration and hydrated storage were generally associated with decrease in activities of phosphofructokinase (PFK) and malate dehydrogenase and levels of nicotinamide adenine dinucleotide and an increase in the levels of hydroperoxides in whole axes, hypocotyls, root primordia and plumules and membrane damage in axes. Increase in the activities of superoxide dismutase and catalase and decrease in the activities of glutathione reductase and amounts of ascorbate accompanied drying and moist storage in all tissues, in general. Apart from the activity of PFK, the plumules showed the highest activities and quantities of all the enzymes and compounds among the tissues during desiccation and wet storage. It is possible that this tissue, despite its relatively small size and volume plays disproportionately an important role in the events described. Nonetheless, it is likely that physical rather than metabolic damage underlined loss of viability as it occurred at high water concentration.Keywords: Antioxidant, Avicennia marina desiccation, drying rate, free radical processes, lipid peroxidation, metabolism, respiration seed survivalAfrican Journal of Biotechnology, Vol 13(17), 1813-182

Developmental rates and morphological properties of fibres in two eucalypt clones at sites differing in water availability

One of the ways in which the global forestry industry can remain competitive is to improve the predictability of properties of fibres produced, particularly in plantations. Since the properties of the fibres are determined by growth and developmental processes, it is of importance to understand these processes and how they are affected by changing environmental conditions. Using two Eucalyptus spp. clones growing at sites contrasting in available water, this study measured the rates of fibre production, fibre transverse radial enlargement and fibre secondary thickening and the duration of the cell cycle, as well as the duration for which the processes of fibre enlargement and wall thickening continued. Samples were taken from the cambial zone in late summer (February–March) and in winter(May–June). The study found that season had the greatest effects on characteristics of the developmental zones as well as on developmental rates and durations, although there were significant effects of both site and clone. This was complicated by significant interactions that occur between genotype, sitetype and short-term variations in environmental conditions. It was found, however, that dry sites, where trees are experiencing comparatively high levels of environmental stress, can be expected to experience greater extremes in developmental processes between seasons, or over relatively short periods, generally, than wetter sites. These sorts of fluctuations will also translate into greater wood quality variation, and hence different site-types should be managed accordingly. Results from this work will contribute to the development of models of xylogenesis which are currently in development.Southern Hemisphere Forestry Journal 2007, 69(2): 71–7

Analysis of differences in field performance of vegetatively and seed-propagated Eucalyptus varieties II: vertical uprooting resistance

The aim of this study was to establish whether roots of micropropagated Eucalyptus grandis × E. nitens differ in their vertical uprooting resistance and architecture when compared with those of macropropagated E. grandis × E. nitens and seed-propagated E. grandis and E. nitens. Uprooting resistance was significantly lower for micropropagated plants than in other plant types after 16 months of field growth. All vegetatively propagated plants produced few and thick I-beam shaped roots, compared with the thin and numerous T-beam shaped roots of seed-propagated plants. Thinner T-beam shaped lateral roots evenly distributed around the stem enhanced resistance to vertical extraction more efficiently than thicker and fewer I-beam shaped roots. Some of the uprooted macropropagated E. grandis × E. nitens trees had produced the equivalent of a taproot (i.e. tap-sinker), compared with none of the micropropagated trees. Vegetatively propagated plants without tap-sinkers showed little resistance during vertical extraction, and their roots were generally asymmetrical and established just below the soil surface. Although the best predictor of uprooting resistance was a combination of the number of roots and root cross-sectional area at the root–stem junction, the number of roots was the most significant predictor. Micropropagation yielded an inferior root system than macropropagation during the first 16 months of field growth. Therefore, trees propagated in vitro may be unsuitable for commercial planting across areas with strong winds. Keywords: anchorage; cold-tolerant; macropropagation; micropropagation; root architectureSouthern Forests 2010, 72(1): 31–3