Photoinhibition at low temperature in chilling-sensitive and -resistant plants

Photoinhibition resulting from exposure at 7°C to a moderate photon flux density (300 micromoles per square meter per second, 400-700 nanometers) for 20 hours was measured in leaves of annual crops differing widely in chilling tolerance. The incidence of photoinhibition, determined as the decrease in the ratio of induced to total chlorophyll fluorescence emission at 693 nanometers (F_v/F_max) measured at 77 Kelvin, was not confined to chilling-sensitive species. The extent of photoinhibition in leaves of all chilling-resistant plants tested (barley Hordeum vulgare L.], broad bean Vicia faba L.], pea Pisum sativum L.], and wheat Triticum aestivum L.]) was about half of that measured in chilling-sensitive plants (bean Phaseolus vulgaris L.], cucumber Cucumis sativus L.], lablab Lablab purpureus L.], maize Zea mays L.], pearl millet Pennisetum typhoides (Burm. f.) Stapf & Hubbard], pigeon pea Cajanus cajun (L.) Millsp.], sesame Sesamum indicum L.], sorghum Sorghum bicolor L. Moench], and tomato Lycopersicon esculentum Mill.]). Rice (Oryza sativa L.) leaves of the indica type were more susceptible to photoinhibition at 7°C than leaves of the japonica type. Photoinhibition was dependent both on temperature and light, increasing nonlinearly with decreasing temperature and linearly with increasing light intensity. In contrast to photoinhibition during chilling, large differences, up to 166-fold, were found in the relative susceptibility of the different species to chilling injury in the dark. It was concluded that chilling temperatures increased the likelihood of photoinhibition in leaves of both chilling-sensitive and -resistant plants. Further, while the photoinhibition during chilling generally occurred more rapidly in chilling-sensitive plants, this was not related directly to chilling sensitivity.