Proline status of genetically stable salt-tolerant Brassica juncea L. somaclones and their parent cv. Prakash

Abstract

Three Brassica juncea L. somaclones (SR-1, -2 and -3) selected in vitro for NaCl-tolerance, non-selected somacone (CP-5) and parent cv. ‘Prakash’ were characterized for their free proline contents in the absence of stress and as a function of increasing salt stress. In the R₀ generation, ‘SR-3’ somaclone had ca. three times higher free proline as compared to parent ‘Prakash’ and other somaclones. Somaclone, SR-1, turned out to be sterile. The other somaclones were carried forward to the R₂ generation after making selections for yield and yield components in the R₁ generation. ‘SR-3’ bred true for its high proline accumulating characteristic. The somaclone ‘SR-3’ thus had a stable genetic variation for proline overproduction. Free proline content in 7-day-old whole seedlings and 6-week-old plant leaf tissue, increased with the increase in salt stress in all the lines but at differential rates. The magnitude of increase in free proline was much higher in ‘SR-3’ lines as compared to parent ‘Prakash’ and ‘SR-2’ salt-tolerant somaclones. Under salt stress, in leaf tissue, one of the ‘SR-3’ derived lines (SR3P6-2) accumulated as much as 269 μmoles of free proline as compared to ca. 20 μmoles per g dry weight in parent ‘Prakash’ and ‘SR-2’ line. It was interesting to note that there was a ‘critical point’ concentration of NaCl beyond which the endogenous level of free proline rose sharply. Somaclonal lines (SR3P6-2, SR2P1-2 and CP5-2) which were found to have higher salt-tolerance indices, also had higher ‘critical points’ as compared to the other relatively salt sensitive genotypes. The relationship between relative water content and osmotic potential of leaves under saltstress also showed a relatively higher degree of osmotic adjustment in the selected somaclones, the maximum being in SR-3 derived lines.