XVI International Botanical Congess

Pre-treatment of etoilated mung bean seedlings with abscisic acid (ABA) induced resistance to a subsequent heat-shock of 50?C (2h), whereas the treatment with fluridone, an inhibitor of ABA biosythesis, caused thermosensitization. The Fluridone Effect was partially reversed by ABA, indicating the involvement of ABA in the acquisition of heat-shock tolerance ability. At the organ level, the major locus of ABA action was in the roots, which played an important role in the regulation of heat tolerance in the whole seedling. Similarly, Ca2 application afforded protection against heat-shock bur EGTA (a Ca2+ chelator) caused susceptibility. Ca2+ per se seemed more effective than the Ca2+: camodulin complex because treatment with trifluoperazine (a calmodulin antagonist) had a rather positive effect on thermotolerance. When used in combination, exogenously applied ABA and Ca2+ did not act synergistically but ABA effect on heat-shock tolerance was not seen in the presence of EGTA.