Effects Of Drought Stress On Photosynthetic Characteristics And Active Oxygen Metabolism Of Cucumber Seedlings

Cucumber requires high soil moisture, it almost suffers drought stress by cultivating and managing improperly in actual production, leading to reduction of output and low quality. Drought stress is the one of most important factor which affecting photosynthesis and active axygen metabolism of plants. We tried to study the effect of drought stress on photosynthesis of cucumber and correlation between net photosynthesis rate and active axygen metabolism. We used two varieties cucumber which had different ecological characteristics, simulating different drought stress by weighting soil and sprinkling salicylic (SA) to ease drought stress. The physiological indices of photosynthesis, active axygen metabolism and nitrogen metabolism of cucumber seedlings were measured.Intercellular CO2 concentration, transpiration and stomatal conductance of cucumber seedlings had small difference with CK in medium and severe drought stress, but net photosynthesis rate was lower than CK; superxide ( O 2-) and hydrogen peroxide (H2O2) of two drought stress treatments were gradually accumulated. Superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were increased in prophase, but they were lower than CK after 12 d; nitrate reductase (NR) was lower than CK after 3 d, but protein contents was higher than CK in anaphase and protein band of drought stress treatments was more clear than CK after 3 d in SDS-PAGE of protein; malondialdehyde (MDA) of two drought stress treatments accumulated more than CK, praline (Pro) was accumulated more than CK, too; O 2- generating rate and MDA were negative correlation with net photosynthesis rate and NR. It indicated that drought stress notablely affected photosynthesis, active axygen metabolism and nitrogen metabolism of cucumber seedlings. O 2- accumulating more had leaded to decline net photosynthesis rate and nitrogen metabolism. Antioxidant enzymes affected photosynthesis and nitrogen metabolism indirectly.After SA treatment net photosynthesis rate of cucumber seedlings was declined retarded and SA had restrained the decline of transpiration and stomatal conductance; SA treatments could retard O 2- accumulating under drought stress, increasing SOD, CAT and POD activity; it also could retard NR activity. Prtein band was more clear than CK after 9 d; MDA and Pro were restrained by SA. The result showed that SA could increase the anti-drought capability of cucumber seedlings though reducing active oxygen, increasing the eliminated efficiency of antioxidant enzyme and restraining photosynthetic system damage by membrane-lipid peroxidation.