INFLUENCE OF EXOGENOUS PROLINE ON EMBRYOGENIC AND ORGANOGENIC MAIZE CALLUS SUBJECTED TO SALT STRESS

The effect of exogenous proline (6 mM) and increasing NaCl doses (from 0.4 to 1.2% w/v) on the maintenance of organogenic and embryogenic ca llus lines derived from the salt-sensitive maize inbred W64Ao2 were st udied. To this end, total protein, free amino acid and polyamine conte nt were analyzed. The demand of exogenous nitrogen and especially of p roline, even in the presence of salt, differed in the two types of mor phogenic calluses. The total protein content of embryogenic calluses w as higher in the presence of proline than in its absence, in all the c ases studied. An opposite effect of proline was observed in organogeni c calluses: the presence of proline and salt decreased significantly t heir protein content. With respect to amino acid and polyamine content s, the organogenic calluses showed physiological characteristics of sa lt-adaptation, whereas the embryogenic calluses were more sensitive to NaCl. Although endogenous proline increased in the organogenic callus es cultured in the presence of salt, in embryogenic calluses it only r ose at the lowest salt concentration. Furthermore, the endogenous argi nine content under saline conditions was higher in organogenic calluse s. A compensatory effect between proline and polyamine metabolism rela ted to the endogenous arginine content in response to salt stress was also observed. This effect differed in the two types of calluses.