Effects of various salts and of mannitol on ion and proline accumulation in relation to osmotic adjustment in rice (Oryza sativa L) callus cultures

Mature embryo-derived calli were obtained from three rice (Oryza sativa L.) cultivars differing in salinity resistance at the whole plant level [(I Kong Pao (IKP), (salt-sensitive), Aiwu (moderately resistant) and Nona Bokra (salt-resistant)] and exposed to three iso-osmotic concentrations of NaCl, KCl, Na2SO4, artificial Sea water (ASW) and mannitol. Relative growth rates, ion content and proline accumulation were quantified after 1, 2 and 3 months of stress. Among salt treatments, KCI was the most detrimental to callus growth in all genotypes and induced a strong increase in Cl content. The NaCl-induced inhibition of growth was lower in calli issued from Nona Bokra than in calli obtained From IKP; Na and CI accumulations as well as internal osmotic potential were lower in Nona Bokra and in Aiwu, thus suggesting a cellular component of salt resistance in these genotypes. Na obvious differences in growth were recorded among genotypes upon mannitol treatment, which appeared more detrimental than NaCl. Proline accumulation was higher in the salt-sensitive cultivar IKP, whatever the nature of the stressing agent: or the stress intensity, and did not appear to be involved in osmotic adjustment. It was concluded that specific ion toxicities are important aspects of salt stress effects on rice cells and chat proline is a symptom of injury in stressed rice calli rather than an indicator of resistance.