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.

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In vitro selection of salt tolerant plants of Brassica juncea L. (Indian mustard) cv . Prakash has been accomplished by screening highly morphogenic cotyledon explant cultures on high NaCl media . Out of a total of 2,620 cotyledons cultured on high salt medium, 3 survived, showed sustained growth and regenerated shoots . They were multiplied by axillary bud culture on NaCl free medium . The salt-selected shoots retained salt tolerance following 3 month of growth and multiplication on control medium . While two of these somaclones flowered and set seeds, third one grew slowly, had abnormal leaf morphology and was sterile .The seed of the two fertile plants were sown in the field to raise R, segregating generation . Data were recorded for field, other agronomic components and oil content . The somaclonal lines, both selected salt-tolerant and non-selected, showed tremendous amount of variation for all the characters studied . One of the two tolerant somaclones invariably showed reduced height, longer reproductive phase and higher 1000 seed weight . Based on the agronomic performance of R, plants of these somaclones, some plants were selected and their progeny were evaluated for agronomic performance under standard field conditions and salt-tolerance in the greenhouse using sand pot culture method . Most of the lines bred true for their specific characteristics . In the greenhouse, selected salt-tolerant somaclones (SR-2 and SR-3) performed better for plant growth, yield and other agronomic traits at higher salt treatments, indicating thereby that salt-tolerance trait selected in vitro was expressed in the whole plants and is genetically stable and transmitted onto the progeny . The two tolerant lines, however, differed in their salt-tolerance during vegetative and reproductive phases as indicated by their salt-tolerance and stress susceptibility indices . The mechanism of salt-tolerance is not clear and needs to be further investigated .

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A NaCl-tolerant cell line of eggplant has been isolated, as a spontaneous variant, on agar solidified medium supplemented with 1% NaCl (Electrical conductivity -17.5 m mho/cm), a concentration lethal to the wild type cells. The stability of the altered response of the selected clone was confirmed by growing it on normal medium for 3 months and then bringing back to the stress medium. This cell line not only grew well on media containing upto 1% NaCl but also required 0.25% NaCl for its optimal growth. It is interesting to note that there is a certain concentration of NaCl (Critical point) above which the proline content of the cells rises sharply. A relationship between the NaCl stress and proline content has been found. The critical point in the wild type cultured cells (0.75% NaCl) lies below to that of the selected salt-tolerant variant (1.0% NaCl).