LEAF POSITION-DEPENDENT CHANGES IN PROLINE, PYRROLINE-5-CARBOXYLATE REDUCTASE-ACTIVITY AND WATER RELATIONS UNDER SALT-STRESS IN GENETICALLYSTABLE SALT-TOLERANT SOMACLONES OF BRASSICA-JUNCEA L

The magnitude of the effect of salt stress on proline content, pyrroli ne-5-carboxylate (P5C) reductase activity and water relations was foun d to be leaf position dependent in an advance generation (R4) of two B rassica juncea L. somaclones (SR-2 and SR-3) selected in vitro for NaC l-tolerance and the parent cv. Prakash. Free proline content and P5C r eductase activity increased with increase in salt stress in all the li nes but at different rates; the maximum increase being in the SR-3 der ived somaclonal line. At 100 mM NaCl, SR-3 showed a nearly 19 fold inc rease in proline content compared to a 4-5 fold increase in the other two genotypes. The proline level and P5C reductase activity of the fir st (youngest) leaf was higher than in the other leaves and decreased l inearly with increase in age of the leaf in all the lines. The relatio nship between relative water content and osmotic potential of the leav es at different positions also varied. The results indicate that a sig nificant effect of salt may appear non-significant if the position of the leaves is not taken into account while sampling.