PROLINE STATUS IN SALT-TOLERANT AND SALT-SENSITIVE ALFALFA CELL-LINESAND PLANTS IN RESPONSE TO NACL

We have investigated proline status in relation to salt-tolerance in c ell cultures of alfalfa and salt-tolerant plants regenerated from our salt-tolerant cell cultures. Selection for salt-tolerance in culture c orrelated in some, but not most cases with selection for constitutivel y high proline concentrations in callus grown on normal medium. Transf er of salt-tolerant lines with constitutively low proline concentratio ns to NaCl containing medium led to nearly ten fold increases in proli ne concentrations, with increased proline detectable in as little as t wo hours. One selected salt-tolerant cell line which showed a constitu tively high proline concentration showed no additional salt dependent increases in proline concentration. In our alfalfa plants, proline is accumulated more rapidly in shoots than in roots when plants are expos ed to salt, but both roots and shoots increase their proline concentra tions about ten fold in three to five days after growth conditions wer e chan ed to include 171 mM NaCl. Shoots from all plants showed signif icant increases in proline accumulation within 24 h of exposure to sal t. However, only roots from salt-tolerant plants showed a doubling in proline concentration within 24 h after exposure to salt. In contrast, the salt-sensitive plant roots showed no change in proline concentrat ions during this time. The rapid adjustment of proline concentration i n our salt-tolerant callus and plant roots may serve a protective func tion.