Mechanisms Of Adaptation To Ionic Toxicity And Their Regulation In Plants

Salinity(NaCI stress) and aluminum(Al) toxicity are two major stresses limiting crop productivity on saline and acid soils, which comprise up to 65% of the word抯 arable lands. Scientific utilization and development of these lands are beneficial to sustainable agriculture in the future. Therefore, it is important to study the mechanisms of salt and aluminum tolerance in plants. H~-ATPase in plasma membrane and lJ?ATPase(H~-PPase) in tonoplast are essential for the regulation of intracellular departmentation and tissue distribution of Na,K under salt stress. The H pump activities vary from no detectable change, decrease to significant increase. Several factors may contribute to this variation, including different plant species, different NaCI concentrations and treatment time. The reasons for the activation and the decline of H* pump activities are not yet well understood. In this paper, we studied the mechanisms of activation and the decline of [I pump activities with two barley cultivars(Hordeurn vu/gare L.) differing in salt tolerance(Tanyin 2, salt-tolerant, Kepin 7, salt-sensitive). Under NaCI stress for 2 d, W-ATPase activities increased both in plasma membrane and tonoplast of salt-tolerant harley(Tanyin 2) roots. La>( I mmol/L), an inhibitor of Ca2 channel in plasma membrane, and EGTA(5 mmol/L), Ca2~ chelator. inhibited this NaCI-induced increase in both H~-ATPase activities. Treatment of barley roots with CaM antagonist(tritluoperazine, TFP, 20~tmol/L) also diminished the increase of both H~-ATPase activities. La> or La) 4-TFP treatment resulted in the increase both in Na~ uptake and transport to shoots in barley seedlings under NaCl stress. These results suggested that influx of Ca> from apoplast was necessary for the activation of plasmalemma and tonoplast Ht-ATPase, and the regulation of ion uptake under NaCI stress. CaM was involved in the regulation of I-L-ATPase activities and ion uptake by Ca>. Iv V-ATPase activity increased in tonoplast vesicles isolated from salt-tolerant barley(Tanyin 2) roots under 200 mmol/L NaCI (containing 1/2 Hoagland solution) for 2 d, and decreased for 9 d , as compared with control(1/2 Hoagland solution). H4-PPase activity in tonoplast of roots decreased during 9 d NaC1 stress. Both W- ATPase and H~-PPase activities decreased in tonoplast vesicles isolated from salt- sensitive barley(Kepin 7) roots during NaCI stress as compared with control, and the later was more sensitive to NaCI than the former. ATP content increased in the Tanyin 2 roots under NaCl stress for 2 d, and decreased for 9 d, as compared with control. In Kepin 7 roots, ATP content decreased during NaC1 stress as compared with controL PPi (pyrophosphate) content increased slightly both in Tanyin 2 and Kepin 7 roots under NaCI stress. Tonoplast 1-V -ATPase activity was inhibited competitively by PPi. These results indicated that the decrease in ATP and the inhibition by PPI might result in the decrease in tonoplast W-ATPase activity in barley roots under NaCI stress. H?ATPase activities of tonoplast and plasma membrane in roots of Tanyin 2(salt- tolerant cultivar) increased when the roots were exposed to 50-~200 mmol/L NaCI for 2 days. then H~-ATPase activity of tonoplast decreased and H4 -ATPase activity of plasma membrane still increased when NaCI concentration was increased to 600 mmol/L. In Kepin 7(salt-sensitive cultivar), both tonoptast and plasma membrane H- ATPase activities in roots also increased at lower levels of Na...