Survival percentage, photosynthetic abilities and growth characters of two indica rice (Oryza saliva L. spp. indica) cultivars in response to iso-osmotic stress

The aim of this study was to investigate pigment degradation, chlorophyll fluorescence diminution, photosynthetic ability and growth reduction in two rice cultivars, in response to either iso-osmotic salt stress or water-deficit stress. Seedlings of rice cultivars RD6 and KDML105 were photo-autotrophically grown in MS media and subsequently exposed to -0.23 (control), -0.40 or -0.67 MPa iso-osmotic NaCl (salt stress) or mannitol (water-deficit stress) for 14 days. The survival percentage of the two rice cultivars reduced dramatically when subjected to -0.67 MPa NaCl treatment. Chlorophyll a (Chl(a)), chlorophyll b (Chl(b)), total carotenoids (Cx+c), maximum quantum yield of PSII (F-v/F-m) and photon yield of PSII (Phi(PSII)) in the stressed seedlings were significantly lower when compared to seedlings in the control group (without mannitol or NaCl), leading to low net-photosynthetic rate (P-n) and growth reduction. In addition, the growth characters of plantlets in the salt stress conditions were more sharply reduced, and the physiological changes greater than those in water-deficit stress conditions. On the other hand, non-photochemical quenching in the leaves of stressed plantlets increased significantly, especially in response to iso-osmotic salt stress. In the present study, overall growth performance and physiological characters of KDML105 grown under iso-osmotic stress were better than those of RD6.