Responses of three soybean cultivars exposed to UV-B radiation
Abstract
To understand the responses of various soybean (Glycine max) cultivars to ultraviolet-B, Dongnong 42, Zhonghuang 57 and Jin 36 were cultured either under UV-B radiation (10.08 kJ / m-2 UV-B) or without UV-B for 25 days. Under UV-B irradiation, significant difference were observed in plant height, nodes length, contents of soluble sugar, proline, protein, flavionoids, GSH, ASA, relative content of anthocyanins, also the emzymes activities of APX ,SOD and GR. The lowest plant height was presented in Jin 36, followed Zhonghuang 57 and Dongnong 42. The node length of plant decreased from the first node to the fourth one, and the maximal reduction was observed in Jin 36. Contents of protein, flavionoids, GSH, ASA and anthocyanins as well as emzyme activities of APX, SOD and GR significantly increased under UV-B irradiation where content of protein and activities of emzyme APX, SOD and GR were higher in Zhonghuang 57 than those in Dongnong 42 and Jin 36; higher GSH, ASA, flavonoids, as well as the anthocyanins were showed in Donghong 42. Increased proline content was observed in the three cultivars upon UV-B (p<0.05) where Zhonghuang 57 >Dongnong 42 > Jin36; for the soluble sugar content, the order was Zhongnong 57>Jin 36>Dongnong 42 (p<0.05). Various soybean cultivars showed varied physiological responses upon UV-B.
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Introduction
Ultraviolet-B (wavelengths from 280 to 320 nm) radiance resulting from depletion in the stratospheric ozone layer affects plant growth and metabolism with morphological, physiological, and biochemical changes is well documented (1). UV-B is recognized as one of the major environmental regulators that control gene expression, celluar and metabolic activities (2).
Plants have adopted the specific ways to deal with UV-B radiation. Leaf thickening is one mechanism which may mitigate the detrimental effects of UV-B by greater tissue absorption (3). Epidermal flavonoid accumulation is known as another adaptive mechanism which can alleviate harm on mesophyll that related to photosynthesis (4, 5). Enzymatic and nonenzymatic antioxidants that defense reactive oxygen species (ROS) induced by enhanced UV-B radiation (6, 7) has been illustrated too (8). UVR8, plant photoreceptor of UV-B, was a newly discovered mechanism which involved in the UV-B induced pathway (9-11).
Different species showed various responses, so is the cultivars of the same species (12, 13). It has been well established that dicotyledonous plants are more sensitive to UV-B than monocotyledons. At the present study, three soybean cultivars (Glycine max) were exposed to UV-B radiation, the growth and physiological traits were investigated.
Conclusion
Various soybean cultivars showed varied physiological responses upon to UV-B, but the trend is consistent. The result further showed that enzymatic and non-enzymatic antioxidants SOD, APX, GR, ASA, GSH, increased in leaf of the three cultivars which developed a strong network defense system through UV-B radiation. Both flavonoids and protein contents significantly increased which may be related to the increased secondary metabolism of plants. The improvement of osmotic regulation substances as proline and anthocyanins may be a adjustment of plant to UV-B. The soluble sugar decreased among the three cultivars which suggested UV-B affect the photosynthesis, not negatively.