(a) Effect of ABA on root elongation. Each value represents the mean of at least 30 measurements on 7-day-old seedlings grown for the last 2 days (from days 5–7) on ABA after transfer. Inhibition of root growth is expressed relative to the mean growth of the same genotype on medium without hormones. The standard errors on percentage inhibition are not represented because they never exceed 6%. Mean values for 100% root growth were: wild-type ± mm, sax1 ± mm. Dose–response curves are shown for one representative experiment out of three independent experiments.
Understanding the drivers of population divergence, speciation and species persistence is of great interest to molecular ecology, especially in the world's biodiversity hotspots. East Asia is one of regions harboring the most diverse temperate and subtropical flora in the world. Although this region has never been directly impacted by extensive and unified ice-sheets, it nonetheless experienced severe environmental change throughout the Late Tertiary and Quaternary with dramatic effects on the evolution and distribution of plants. By using phylogeographic, landscape genetic, and ecological modelling approaches, a steadily increasing number of phylogeographic studies in East Asia have documented the evolutionary web of population demographic, biogeographic, and speciation processes. This symposium will present recent remarkable studies concerning phylogeographic patterns, population demographic/biogeographic histories, speciation processes, as well as drivers of species diversification and persistence that have given rise to one of the world's most diverse floras in East Asia.
AB - Osmotic stress-induced accumulation of proline, an important protective osmolyte in higher plants, is dependent on the expression of Δ1-pyrroline-5-carboxylate synthase (P5CS) and proline dehydrogenase (PDH) enzymes that catalyze the rate-limiting steps of proline biosynthesis and degradation, respectively. Proline metabolism is modulated by differential regulation of organ specific expression of PDH and duplicated P5CS genes in Arabidopsis. Stimulation of proline synthesis by abscisic acid (ABA) and salt stress correlates with a striking activation of P5CS1 expression. By contrast, P5CS2 is only weakly induced, whereas PDH is inhibited to different extent by ABA and salt stress in shoots and roots of light-grown plants. Proline accumulation and light-dependent induction of P5CS1 by ABA and salt stress is inhibited in dark-adapted plants. During dark adaptation P5CS2 is also down-regulated, whereas PDH expression is significantly enhanced in shoots. The inhibitory effect of dark adaptation on P5CS1 is mimicked by the steroid hormone brassinolide. However, brassinolide fails to stimulate PDH, and inhibits P5CS2 only in shoots. Proline accumulation and induction of P5CS1 transcription are simultaneously enhanced in the ABA-hypersensitive prl1 and brassinosteroid-deficient det2 mutants, whereas P5CS2 shows enhanced induction by ABA and salt only in the det2 mutant. In comparison, the prl1 mutation reduces the basal level of PDH expression, whereas the det2 mutation enhances the inhibition of PDH by ABA. Regulation of P5CS1 expression thus appears to play a principal role in controlling proline accumulation stimulated by ABA and salt stress in Arabidopsis.