Stomatal conductance in Cucumis sativus upon short-term and long-term exposures to low temperatures

We studied stomatal conductance (g(s)) in leaves of cucumber plants (Cucumis sativus L., cv. Zozulya) subjected at early developmental stages to either short-term daily cooling (2 h at the end of night periods) or continuous chilling (12A degrees C throughout the day and night). Irrespective of the irradiance during measurements, continuous chilling either lowered g(s) or had no effect, as compared to g(s) of control plants (23A degrees C). In plants subjected to periodic short-term cooling, the g(s) was found to increase at low temperatures both at moderate and high irradiance; it also increased at high temperature (33A degrees C) but only at photosynthetically active irradiance of 800 mu mol/(m(2) s). It is supposed that heat-loving plants, subjected to different types of low-temperature treatment, mobilize different mechanisms of stomatal regulation and employ different strategies of adaptation in response to low- and high-temperature treatments. The unusual behavior of stomata, manifested in stomatal opening at both low and high temperatures, extends the adaptive potential of plants subjected daily to short-term low-temperature treatments. This leads to a high level of photosynthesis, biomass accumulation, and supports high physiological activity in plants.