Effects of exogenous abscisic acid on growth, proline accumulation and delta 1 -pyrroline-5-carboxylate synthetase gene expression during drought- and salt-stress conditions in rice Oryza sativa L.
Abstract:
The effects of exogenous abscisic acid application on growth, proline accumulation and delta[superscript 1]-pyrroline-5-carboxylate synthetase (P5CS) gene expression were determined in two rice cultivar/line, which were Leung Pra Tew 123 (LPT123) and the salinity-tolerant line, Leung Pra Tew 123-TC171 (LPT123-TC171), under drought- and salt- stress conditions. It was found that salt stress inhibited growth of LPT123 more than LPT123-TC171. Shoot fresh weight of LPT123 was reduced significantly and the accumulation rates of shoot and root dry weight were decreased, while LPT123-TC171 grown in the same condition could maintain shoot fresh weight and the increase in shoot and root dry weight was detected. Growth of LPT123 was more affected by drought stress than LPT123-TC171. Under both salt- and drought-stress condition, the higher survival rate was detected in LPT123-TC171, when compared to the original rice cultivar, LPT123. These suggested the overlapping between salt- and drought-tolerant gene expression of LPT123-TC171. Spraying of abscisic acid to leaves of both rice lines resulted in improvement of tolerant ability to both salt- and drought-stress condition. However, the improvement of tolerant ability of rice seedling depended also on the concentration of abscisic acid. On the other hand, application of abscisic acid to rice seedlings, grown in normal condition, caused seedling growth retardation. Salt-stress condition had more impact on proline accumulation and induction of P5CS gene expression than drought-stress condition in both rice cultivar/line. LPT123-TC171 responded to the stress conditions faster than LPT123. ABA application to the stressed rice seedlings resulted in early accumulation of proline and induction of P5CS gene expression. These lead to the hypothesis that induction of P5CS gene expression together with early proline accumulation resulted from exogenous ABA application are responsible for the increase in stress-tolerant ability in rice seedlings