Influences of ultra‐violet (UV)‐blue light radiation on the growth of cotton. II. Photosynthesis, leaf anatomy, and iron reduction

Abstract Cotton (Gossypium hirsutum L.) plants grown under low pressure sodium lamps (LPS) developed chlorosis which was similar in appearance to iron‐stress induced chlorosis, while plants under cool white fluorescent lamps (CWF) at the same level of photosynthetically active radiation (PAR) developed normally. These illumination sources differ in spectral irradiance; CWF lamps emit ultra violet (UV), whereas LPS lamps do not. Ultraviolet radiation is capable of reducing Fe3+ to Fe2+ through a chlorotic leaf which may be important in establishing an active iron fraction in the leaf. Root reduction of Fe3+ to Fe2+ was lacking in Fe‐stressed cotton under LPS light, but was present under CWF light. Net photosynthesis, photosynthetic electron transport, and leaf chlorophyll content were lower under LPS than CWF light in most of the growing media studies (soil or solutions with nitrate‐ or ammonium‐nitrogen supplied). Chloroplast ultrastructure and leaf thickness were also altered by LPS irradiance. Electron microscopic studies with plants grown in nutrient solutions for 4 weeks suggested that chioroplastic granal disorganization was more directly associated with diminished iron supplies than with light source. However, plants grown in soil for 6 weeks under LPS light had granal disorganization similar to that found in iron‐stressed plants. These studies suggest an important role for UV radiation in influencing the activity of iron in plants. Key words: ChlorophyllCool White FluorescentFerric Iron Root Reduction Gossypium hirsutum LLow Pressure SodiumLeaf MorphologyPhotosynthesisPhotosynthetic Electron Transport

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