Effect of Low Temperature and High Humidity Stress on Physiology of Cucumber at Different Leaf Stages.

Low temperature (LT) and high humidity (HH) are important environmental factors in green house and plastic tunnel during cold season that hamper plant growth and development. Here, we studied the effect of LT (day/night: 9/5°C with 25/18°C as the control) and HH (95% with 80% as the control) on cucumber young plants at 2, 4 or 6 leaf stage. LT and HH stress resulted in decline of shoot, root and total fresh and dry weight, and decreased net photosynthesis (Pn), stomatal conductance (Gs), transpiration rate (Tr), photochemical efficiency (Fv/Fm), photochemical quenching (qP), electron transport rate (ETR) and chlorophyll pigments, and increased malondialdehyde (MDA), hydrogen peroxide (H2 O2 ), superoxide (O2 - ), non-photochemical quenching coefficient (NPQ) and intercellular CO2 rate (Ci) as compared to the control at 2 leaf stage. Super oxidase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were up-regulated under LT and HH stress as compared to the control at 6 leaf stage. Abscisic acid (ABA) and jasmonic acid (JA) were increased under LT and HH stress as compared to the control at 6 leaf stage, while indole-3-acetic acid (IAA) and gibberellic acid (GA) were decreased under LT and HH stress as compared to the control at 2 leaf stage. Our results recommended that LT and HH stress affects cucumber young plants photosynthetic efficiency, PSII activity, antioxidant defense system, reactive oxygen species (ROS) and hormonal profile. The plants at 6 leaf stage showed more tolerance than 2 and 4 leaf stages under stress conditions. This article is protected by copyright. All rights reserved.