Expression of heat-stable and putative dehydrin proteins during nonacclimated and cold-acclimated conditions in several tuber-bearing Solanum species

Recent studies suggest cold-regulated heat-stable proteins mitigate the pot ential damaging effects of low water activity associated with freezing. A p roposed function of these proteins is stabilization of enzymes during expos ure of plants to subzero temperatures. To test this hypothesis for tuber-be aring Solanum L. species we determined the quantitative expression of heat- stable proteins, the qualitative changes in dehydrin proteins, and the capa city of heat-stable proteins to cryoprotect a freeze-thaw labile enzyme lac tate dehydrogenase (LDH), We used five tuber-bearing Solanum species (S. tu berosum L. 'Red Pontiac', S. acaule Bitter, S. sanctae rosea Hawkes, S, com mersonii Dunal, and S. cardiophyllum Bitter), which vary in nonacclimated r elative freezing tolerance (NA RFT), acclimated relative freezing tolerance (AC RFT), and acclimation capacity (ACC), The protein fraction containing a mixture of heat-stable proteins demonstrated cryoprotective capacities gr eater or equal to other cryoprotective compounds (bovine serum albumin, pol yethylene glycol, glycerol, and sucrose), Heat-stable proteins extracted fr om acclimated S. commersonii had superior cryoprotective capacity than thos e extracted from nonacclimated S. commersonii plants. Interestingly, in the presence of these proteins extracted from acclimated plants (in S. commers onii and S. sanctae rosea), LDH activity was elevated above that of unfroze n controls. No quantitative relationships were found between heat-stable pr otein concentration and NA RFT, AC RFT, or ACC among the five species. This was also true for dehydrin protein expression. Cold acclimation treatment resulted in increased dehydrin expression for acclimating and nonacclimatin g species. In three of the cold acclimating species (S. acaule, S. sanctae rosea, and S. commersonii), an increase in dehydrin expression may play a r ole in increased freezing tolerance during cold acclimation, In the cold se nsitive, nonacclimating species (S, tuberosum and S. cardiophyllum), howeve r, an increase in dehydrin level maybe related to the response of these spe cies to changed (perhaps stressful) environment during cold treatment, By e xploiting the genetic variation in NA RFT and ACC for five tuber-bearing sp ecies, we were able to gain new insight into the complexity of the relation ship between heat-stable protein and cold response.