Response of the photosynthetic apparatus in cucumber leaves to daily short-term temperature drops

Responses of the photosynthetic apparatus in cucumber (Cucumis sativus L.) leaves were examined after exposing the plants to daily short-term temperature drops to 12°C (for 2 h at the end of night periods, DROP treatment) during active leaf growth (DROPI) and at the mature leaf stage (DROPII). The DROP treatment induced adaptive changes in the photosynthetic apparatus that were evident in elevated photosynthetic activity at low temperature, modified composition of pigments, altered water content in leaves, and altered ratio of leaf dry matter to leaf area. The stage of leaf development had a significant influence on the responses of photosynthetic apparatus to DROP treatments. The leaves subjected to DROP during active growth were capable of large structural rearrangements, which provided a larger increase in resistance of photosynthesis to low temperature, whereas the leaves exposed to temperature drops at the mature leaf state were characterized by the reduced capacity for acclimation.