Effect of mannitol- and salt-induced iso-osmotic stress on proline accumulation,photosynthetic abilities and growth characters of rice cultivars (Oryza sativa L. spp. Indica)

The aim of this study was to investigate the biochemical,physiological and morphological responses of rice cultivars to iso-osmotic water deficit and salt stress. seedlings of three rice cultivars were photoautotrophically grown in ms media and subsequently exposed to -0.23 (control),-0.42 or -0.94 mpa iso-osmotic mannitol (water-deficit stress) or nacl (salt stress). chlorophyll a (chla),chlorophyll b (chlb),total carotenoids (cx+c),maximum quantum yield of psii (fv/fm) and photon yield of psii (φpsii) in the osmotically-stressed seedlings were significantly reduced when compared to those of the control group (without mannitol or nacl),leading to net-photosynthetic rate (pn) and growth reduction with positive correlation. in addition,physiological changes and growth parameters of salt stressed seedlings were more sharply reduced than those of water-deficit stressed seedlings,especially in pt1 salt susceptible. on the other hand,the proline contents in the root and leaf tissues of osmotically-stressed seedlings increased significantly,especially in response to iso-osmotic salt stress. the chlorophyll pigments in isoosmotically-stressed leaves were significantly degraded,related to low water oxidation,low pn and growth reduction. those multivariate parameters were subjected to classify the salt tolerance,hj and salt susceptible,pt1 and rd6 as well as the water deficit tolerance,hj and rd6 and water deficit susceptible,pt1 using hierarchical cluster analysis.