Susceptibility to low-temperature photoinhibition and the acquisition of freezing tolerance in winter and spring wheat : The role of growth temperature and irradiance

• Five winter and five spring wheat (Triticum aestivum L.) cultivars were grown under either control conditions (20 degreesC/250 photosynthetic photon flux density (PPFD) [mu mol m(-2) s(-1)]), high irradiance (20 degreesC/800 PPFD) or at low temperature (either 5 degreesC/250 PPFD or 5 degreesC/50 PPFD). To eliminate any potential bias, the wheat cultivars were arbitrarily chosen without any previous knowledge of their freezing tolerance or photosynthetic competence. We show that the differential susceptibilities to photoinhibition exhibited between spring and winter wheat cultivars, as assessed by chlorophyll fluorescence cannot be explained on the basis of either growth irradiance or low growth temperature per se. The role of excitation pressure is discussed. We assessed the correlation between susceptibility to low-temperature photoinhibition, maximum ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) and NADP-dependent malate dehydrogenase (EC 1.1.1.82) activities, chlorophyll and protein concentrations and freezing tolerance determined by electrolyte leakage. Susceptibility to photoinhibition is the only parameter examined that is strongly and negatively correlated with freezing tolerance. We suggest that the assessment of susceptibility to photoinhibition may be a useful predictor of freezing tolerance and field survival of cereals.

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