Genotypic differences in the heat-shock response and thermotolerance in four potato cultivars

We have studied the relationship between thermotolerance and heat-shock protein (HSP) expression in potato ( Solanum tuberosum L.), analyzing two reported heat sensitive cultivars (‘Russet Burbank’ and ‘Atlantic’) and two reported heat tolerant cultivars (‘Norchip’ and ‘Désirée’) under prolonged heat-stress conditions. A standard and quantitative assay for heat tolerance, based on electrolyte leakage, revealed that one of the “heat tolerant” cultivars, ‘Désirée’, is not nearly as heat tolerant as the other heat tolerant cultivar, ‘Norchip’. In addition, protein labeling and immunodetection analyses revealed that there were genotypic differences in HSP expression in potato cultivars; at 40 °C, ‘Norchip’, the most heat tolerant cultivar, synthesized small (sm) HSPs for a longer time period, than the other three cultivars. The levels of an 18 kDa smHSP increased up to 24 h in ‘Norchip’ and ‘Désirée’, whereas the levels started to decrease after 4 h in ‘Russet Burbank’ and 12 h in ‘Atlantic’. At 35 °C, a more moderate heat stress, we observed an unusual pattern of accumulation of the 18 kDa smHSP; the level initially increased, then decreased at 12–18 h, and, upon prolonged heat stress up to 40 h, increased again at 18–24 h. The possible mechanism behind this dynamic pattern is discussed. This is the first extensive study on heat-shock protein expression in potatoes using commercially important potato cultivars.