Effects of 24-Epibrassinolide on DNA Methylation Variation in Soybean (Glycine max) Leaf and Root Under Saline-Alkali Stress

Saline-alkali stress is major stress that severely reduces plant growth and productivity, it is necessary to make clear whether exogenous 24-epibrassinolide (EBR) can improve the salt-alkali resistance of soybean (Glycine max) by affecting its DNA methylation. In this study, the effects of EBR on soybean adaptation to saline-alkali stress, genomic DNA methylation level and pattern changes in saline-alkali-stressed leaf and root with or without EBR treatment were compared using methylation-sensitive amplified polymorphism (MSAP). In the results, saline-alkali stress increased DNA methylation levels in leaf and root, with higher respective hemi-methylation and global methylation rates observed in leaf (6.22, 22.24%) than root (5.72, 21.76%). EBR application reduced leaf and root DNA methylation levels, with leaf hemi-methylation rate (6.15%) exceeding that of root (4.25%) and leaf global methylation rate (21.79%) below that of root (22.51%). There were distinct DNA remethylation and demethylation variations across different tissues and treatments, demethylation in leaves was dominant. Meanwhile, untreated saline-alkali-stressed roots exhibited major demethylation-based variations, while remethylation variations predominated post-treatment. Under saline-alkali stress, root remethylation and demethylation rates (6.17, 7.55%, respectively) both exceeded respective leaf rates (5.18 and 7.46%); however, post-EBR treatment, root methylation rate (6.45%) exceeded leaf rate (5.38%), while root demethylation rate (6.13%) fell below leaf rate (6.94%). In conclusion, exogenous EBR application to saline-alkali-stressed soybean can influence leaf and root genomic DNA methylation levels and patterns via distinct tissue-specific methylation mechanisms.

Differential gene expression in desiccation-tolerant and desiccation-sensitive tissue of the resurrection grass, Sporobolus stapfianus

The rare African grass Sporobolus stapfianus is capable of surviving total air-dryness. Little is known about the genetic factors associated with this remarkable trait. Several genes have been isolated from drought-stressed leaf tissue of S. stapfianus, including genes encoding a glycine-rich protein, another with similarity to a yeast glyoxalase I gene and one cDNA which does not show any similarity with known genes. Some of the genes have not previously been linked to desiccation tolerance while some have previously been reported as being upregulated in response to drought stress or expressed throughout all stages of desiccation [Blomstedt, C., et al., Plant Growth Regulation 24, 219–228 (1998)]. To provide insight into changes in gene expression which are important in drought resistance the transcript levels in both desiccation-tolerant and desiccation-sensitive tissues, in response to varying degrees of drought stress, have been analysed. Genes whose expression decreases in leaf tissue in response to desiccation were also characterised, such as those encoding chlorophyll a/b binding protein and catalase. This study indicates the complexity of the drought stress response in the resurrection grass, S. stapfianus, which involves co-ordinated positive and negative regulation of several genes throughout the dehydration process.

Volume and osmotic potential changes in relation to inhibition of photosynthesis by water stress in intact leaves

It has been reported that for osmotically stressed leaf slices of a wide range of species, carbon dioxide saturated photosynthesis is uniformly inhibited by stress when water status is expressed as relative volume. Comparable data for intact leaves of a range of species are lacking. It is also unknown whether the same pattern of response applies to carbon dioxide limited photosynthesis. For these reasons responses of photosynthesis to carbon dioxide partial pressure were determined at 21% oxygen at high irradiance in intact leaves of five species as water deficits developed slowly in intact plants. Relative water content (volume) and total and osmotic water potentials were measured at each level of water stress. Three species adjusted osmotically such that volume remained unchanged over a range of water potentials. Regardless of whether volume was maintained, carbon dioxide saturated photosynthesis decreased as water potentials decreased. In contrast to the data for osmotically stressed leaf slices, relative volume, relative osmotic potential, and total water potential did not indicate a uniform level of inhibition of either carbon dioxide saturated or carbon dioxide limited photosynthesis across species. In some species the carbon dioxide compensation point increased with stress. The initial slope of photosynthesis versus substomatal carbon dioxide partial pressure was relatively less inhibited by stress than was the saturated rate. This difference was greater in some species than in others.