title: Mitigative effects of spermidine on photosynthesis and carbon-nitrogen balance of cucumber seedlings under Ca(NO3)2 stress.
abstract: Ca(NO3)2 stress is one of the most serious constraints to plants production and limits the plants growth and development. Application of polyamines is a convenient and effective approach for enhancing plant salinity tolerance. The present investigation aimed to discover the photosynthetic carbon-nitrogen (C-N) mechanism underlying Ca(NO3)2 stress tolerance by spermidine (Spd) of cucumber (Cucumis sativus L. cv. Jinyou No. 4). Seedling growth and photosynthetic capacity [including net photosynthetic rate (P N), stomatal conductance (Gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr)] were significantly inhibited by Ca(NO3)2 stress (80 mM). However, a leaf-applied Spd (1 mM) treatment alleviated the reduction in growth and photosynthesis in cucumber caused by Ca(NO3)2 stress. Furthermore, the application of exogenous Spd significantly decreased the accumulation of NO3 (-) and NH4 (+) caused by Ca(NO3)2 stress and remarkably increased the activities of N metabolism enzymes simultaneously. In addition, photosynthesis N-use efficiency (PNUE) and free amino acids were significantly enhanced by exogenous Spd in response to Ca(NO3)2 stress, thus promoting the biosynthesis of N containing compounds and soluble protein. Also, the amounts of several carbohydrates (including sucrose, fructose and glucose), total C content and the C/N radio increased significantly in the presence of Spd. Based on our results, we suggest that exogenous Spd could effectively accelerate nitrate transformation into amino acids and improve cucumber plant photosynthesis and C assimilation, thereby enhancing the ability of the plants to maintain their C/N balance, and eventually promote the growth of cucumber plants under Ca(NO3)2 stress.
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Jing
authors.initials: J
authors.lastname: Du
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Shu
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Qiaosai
authors.initials: Q
authors.lastname: Shao
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Yahong
authors.initials: Y
authors.lastname: An
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Heng
authors.initials: H
authors.lastname: Zhou
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China. srguo@njau.edu.cn.
authors.forename: Shirong
authors.initials: S
authors.lastname: Guo
authors.affiliation: Key Laboratory of Southern Vegetable Crop Genetic Improvement, Ministry of Agriculture, College of Horticulture, Nanjing Agricultural University, Nanjing, 210095, People's Republic of China.
authors.forename: Jin
authors.initials: J
authors.lastname: Sun
mesh_terms: D002244:Carbon / Q000378:metabolism; D018553:Cucumis sativus / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism; D013095:Spermidine / Q000378:metabolism*; D013312:Stress, Physiological
chemical_list: D009566:Nitrates; D002244:Carbon; D009584:Nitrogen; D013095:Spermidine
keywords: Ca(NO3)2 stress; Carbon–nitrogen balance; Cucumis sativus L.; Photosynthesis; Spermidine