Physiological Response Mechanism Of Cucumber Seedlings To Red And Blue Light

Light is crucial to vegetable growth and development, it can significantly affects growth, quality and yield of vegetable. Therefore, it is important to define physiological response mechanism of cucumber seedlings to light quality in order to promote quality and yield of protected vegetable. In this study, we investigated effects of light qualities (white light, CK; red light, R; a combianation of red and blue light, RB; blue light, B) on photosynthetic electron transport capacity, the activity of photosystem Ⅱ (PSⅡ) and photosystem Ⅰ (PSⅠ), leaf morphology and physiological metabolism in cucumber (Cucumis sativus L.) seedlings. The results were as follows:1. We investigated the effects of different light qualities on photosynthetic electron transport capacity, and activity of photosystem Ⅱ (PSⅡ) and Ⅰ (PSⅠ) in cucumber plants. The results showed that the R treatment increased J step, I-step, L-band, K-band and WOI (WOI≥1) in OJIP curve, reduced most JIP-test parameters, and limited effective photochemical quantum yield of PSⅡ (φⅡ) and PSⅠ (φⅠ). These changes suggested that R treatment not only inhibited linear electron transport from PSⅡ to PSⅠ, but also induced suboptimal activity of PSⅡ and PSⅠ. However, these suppressions were effectively alleviated by blue light addition (RB). RB treatment significantly enhanced linear electron transport by elevating electron transport from QA to PSI, and increased φⅡ and <φⅠby 175.6% and 126.9%, respectively. B treatment plants exhibited normal photosystems activity and photosynthetic electron transport capacity similar to that of CK. These results indicated that blue light is more essential than red light for maintaining normal photosynthesis, as it dose effectively active photosystems activity and photosynthetic electron transport capacity.2. We explored leaf morphology, chloroplasts ultrastructure, accumulation and distribution of nutrients under different light qualities in cucumber plants. The results showed that R treatment decreased leaf thickness, palisade tissue and spongy tissue thickness, and palisade-sponpy tissue thickness ratio, chloroplast number and size, grana number and thickness, starch grain number and size. Moreover, R treatment enhanced accumulation of P, K, Mn and Zn in leaf. B treatment decreased leaf thickness and grana thickness, and increased accumulation of N, P, K, Ca, Mg and Mn. RB treatment showed similar leaf morphology, chloroplasts ultrastructure and accumulation of nutrients to that of CK. These results suggested that a combination of red and blue light benefited leaf and chloroplast morphogenesis, red light and blue light promoted accumulation of macronutrients and micronutrients.3. We investigated protected cultivation of cucumber plants which has been exposed to different light qualities. The results showed that R treatment had a negative impact on photosynthesis at first, and then these inhibitions were alleviated. Moreover, R treatment delayed flowering time of the 1 st female flower by 8 days. RB treatment delayed flowering time of the 1st female flower by 2 days and decreased its node by 2 nodes. B treatment accelerated flowering time of the 1 st female flower by 3 days and decreased its node by 4 nodes.4. R treatment decreased photosynthesis efficiency, inhibited leaf and chloroplast development and delayed flowering time of female flower of cucumber plant, suggesting that red light was not appropriate for cucumber seedling. However, B treatment and RB treatment promoted photosynthesis characteristics and leaf morphogenesis, what’s more, they increased female flowers of cucumber plants. These results indicated that blue light and a combination of red and blue light were suitable light source for cucumber seedlings.