Proline profiles in aromatic rice cultivars photoautotrophically grown in responses to salt stress

The aim of this investigation is to monitor the proline profiles and green leaf percentage in Thai aromatic rice cultivars, relating to salt concentration and exposure times. Eleven aromatic, Pakkali (Pok) salt tolerant and IR29 salt sensitive rice cultivars were germinated and aseptically transferred to in vitro photoautotrophic conditions using vermiculite as supporting material for 7 days. Sodium chloride salts in the culture media were adjusted to 0, 171, 342, 512 or 684 mM for 4 days. Proline contents in the leaf tissues of salt-stressed seedlings were positively related to salt concentrations in the culture media. The high salt concentration progressively stimulated on proline accumulation in the leaf tissues. A unique proline profile in the aromatic rice cultivars was clearly classified into three classes, high, modulate and low accumulation classes using Hierarchical cluster analysis. The results evidently showed that the green leaf percentages in the high and modulate proline accumulation classes were higher than those in low proline class. The Pok and IR29 rice cultivars were defined as moderate and low proline accumulation classes, respectively. In addition to, the proline contents in salt stressed seedlings (342 mM NaCl) of all classes were positively correlated with salt exposure times. An increasing exposure period of salt stress directly enhanced the proline gathering. It should be demonstrated that the proline accumulation in Thai aromatic rice was depended on rice cultivars, salt concentrations and salt exposure time.