IMMUNOLOGICAL KINSHIP OF CLASS-I LOW-MOLECULAR-WEIGHT HEAT-SHOCK PROTEINS AND THERMOSTABILIZATION OF SOLUBLE-PROTEINS IN-VITRO AMONG PLANTS

The antibody prepared against one of the soybean (Glycine max) 15 to 1 8 kDa heat shock proteins (HSPs) that cross-reacted with the 12 polype ptides of 15 to 18 kDa class I low molecular weight (LMW) HSPs in soyb ean, was also found to cross-react in Western blot analyses with the c lass I LMW HSPs of nine other plant species, i.e., mung bean, pea, cuc umber, tobacco, Arabidopsis, rice, maize, wheat, and barley. An antibo dy raised from the 16.9 kDa rice HSP also crossreacted with the same c lass I LMW HSPs of the ten plant species tested. HSPs-enriched fractio ns (70 to 100% ammonium sulfate saturation) prepared from mung bean an d rice heat-shocked seedlings were able to thermostabilize the homolog ous soluble proteins, as we have shown previously in soybean. Up to 50 % of the soluble proteins that are normally denatured by heating at 55 degrees C for 30 min was protected when an HSPs-enriched fraction was added to either mung bean or rice protein. Additionally, the HSPs-enr iched fractions were exchangeable among these three plant species for thermostabilization. The protection provided by these HSPs-enriched fr actions is effective mainly for membrane-associated proteins. In soybe an depletion of the 15 to 18 kDa HSPs in the HSPs-enriched fraction re sulted in the loss of the thermostabilizing ability and when the 15 to 18 kDa HSPs were recovered in this fraction, the thermostabilizing ab ility was again restored. Thus, the 15 to 18 kDa HSPs in plant, which shuttle between the cytoplasm and cellular organelles during heat shoc k (HS) and recovery from HS, are responsible for providing the thermos tabilization.