SALT TOLERANCE IN CROP PLANTS - NEW APPROACHES THROUGH TISSUE-CULTUREAND GENE-REGULATION

Recent approaches to study of salinity tolerance in crop plants have r anged from genetic mapping to molecular characterization of gene produ cts induced by salt/drought stress. Transgenic plant design has allowe d to test the effects of overexpression of specific prokaryotic or pla nt genes that are known to be up-regulated by salt/drought stress. Thi s review summarizes current progress in the field in the context of ad aptive metabolic and physiological responses to salt stress and their potential role in long term tolerance. Specifically considered are gen e activation by salt, in view of proposed avenues for improved salt to lerance and the need to ascertain the additional influences of develop mental regulation of such genes. Discussion includes the alternate gen etic strategy we have pursued for improving salinity tolerance in alfa lfa (Medicago sativa L.) and rice (Oryza sativa L.). This strategy com bines single-step selection of salt-tolerant cells in culture, followe d by regeneration of salt-tolerant plants and identification of genes important in conferring salt tolerance. We have postulated that activa tion or improved expression of a subset of genes encoding functions th at are particularly vulnerable under conditions of salt-stress could c ounteract the molecular effects of such stress and could provide incre mental improvements in tolerance. We have proceeded to identify the ac quired specific changes in gene regulation for our salt-tolerant mutan t cells and plants. One particularly interesting and novel gene isolat e from the salt-tolerant cells is Alfin1, which encodes a putative zin c-finger regulatory protein, expressed predominantly in roots. We have demonstrated that this protein binds DNA in a sequence specific manne r and may be potentially important in gene regulation in roots in resp onse to salt and an important marker for salt tolerance in crop plants .