Effects of a Daily Short-Term Temperature Drop on Chilling-Sensitive and Cold-Resistant Plants

Abstract

A set of physiological and biochemical parameters (leaf growth rate, plant biomass, chlorophyll content, rates of photosynthesis and transpiration, relative water content, leakage of electrolytes, lipid peroxidation intensity, and leaf cold tolerance) were examined with the example of typical cold-resistant (wheat, Triticum aestivum L.) and chilling-sensitive (cucumber, Cucumis sativus L.) plants subjected daily to a short-term temperature drop (DROP treatments) under controlled environmental conditions. For comparison, the plant responses to prolonged chilling were studied with the same species. To accomplish these aims, the cucumber and wheat plants were subjected to: (a) continuous (round-the-clock) cooling at 4°C (wheat), 9°C (cucumber), and 12°C (wheat and cucumber); (b) short-term (3 h) daily cooling to the same temperatures at the end of night periods over 6 days. Although cold-resistant and chilling-sensitive plants showed quantitatively and qualitatively different responses during and after long-term cooling, the plant responses to DROP treatments were qualitatively similar and differed only in their extent depending on cooling temperature. The DROP treatments retarded linear growth of plant organs in both chilling-sensitive and cold-resistant species. They also induced a range of favorable physiological changes promoting plant capability of adaptation. Specifically, photosynthetic rates in DROP-treated plants at chilling temperatures were higher than in untreated plants. In addition, DROP treatments improved the plant chilling tolerance.