低温弱光下水杨酸对黄瓜幼苗光合作用及抗氧化酶活性的影响

为了探讨低温弱光下水杨酸（SA）对黄瓜光合功能的调控作用，以‘津优3号’黄瓜幼苗为试材，叶面喷施不同浓度的SA溶液，研究低温弱光下黄瓜幼苗气体交换参数、光化学效率、MDA含量及抗氧化酶活性的变化.结果表明：低温弱光胁迫使黄瓜幼苗叶片的光合速率（P_n）、气孔导度（G_s）、蒸腾速率（T_r）、PSⅡ光下实际光化学效率（Φ_PSⅡ）及暗下最大光化学效率（F_v/F_m）明显降低，胞间CO₂浓度（C_i）显著升高，说明低温弱光下黄瓜幼苗P_n下降的主要原因是非气孔限制;低温弱光还可引起黄瓜幼苗丙二醛（MDA）含量增加，超氧化物歧化酶（SOD）活性升高，过氧化氢酶（CAT）活性降低，过氧化物酶（POD）活性先升高后降低.而胁迫前用0.5～2.5 mmol·L^-1 SA预处理幼苗，其叶片的P_n、G_s、T_r、Φ_PSⅡ、F_v/F_m及SOD、POD和CAT活性与CK（水预处理）相比均有不同程度的提高，C_i和MDA含量有所降低.表明SA可有效调控低温弱光下黄瓜幼苗叶片的光合功能，提高其低温弱光耐性，其适宜浓度为1 mmol·L^-1.

Effects of salicylic acid on the leaf photosynthesis and antioxidant enzyme activities of cucumber seedlings under low temperature and light intensity.

In order to elucidate the regulation functions of salicylic acid (SA) o n the photosynthesis of cucumber under low temperature and light intensity, the seedlings of cucumber ‘Jinyou 3’ under low temperature and light intensity wer e foliar-sprayed with different concentration SA, and the leaf gas exchange par ameters, photochemical efficiency, MDA content, and antioxidant enzyme activitie s were measured. The results showed that under low temperature and light intensi ty, the leaf photosynthetic rate (Pn), stomatal conductance (Gs), tr anspiration rate (Tr), actual photochemical efficiency of PSⅡ(ΦP SⅡ), and maximal photochemical efficiency of PSⅡ (Fv/Fm) of the seedlings all decreased but the intercellular CO2 concentration (Ci) inc re ased, suggesting that non-stomatal limitation was the main cause of the decreas e of Pn under low temperature and light intensity stress. Low temperature and light intensity also led to the increase of leaf malondialdehyde (MDA) conte nt and superoxide dismutase (SOD) activity, the decrease of catalase (CAT) activ ity, and the decrease after an initial increase of peroxidase (POD) activity. Ho wever, foliar-spraying 05〖KG-*2〗-〖KG-*7〗25 mmol ·L-1 of SA before the stress increased the leaf Pn, Gs, T r, ΦPSⅡ, Fv/Fm, and activities of SOD, POD and CAT whi le decreased the Ci and MDA content, suggesting that SA could regulate the leaf photosynthetic functions of cucumber seedlings, and enhance the see dlings resistance against low temperature and light intensity. The optimum conce ntration of SA for the foliar-spraying was 1 mmol·L-1.