紫外线辐射与土壤干旱胁迫对紫花苜蓿叶表皮蜡质晶体结构及含量的影响

选用紫花苜蓿强抗旱品种敖汉和弱抗旱品种三得利为材料,在紫外线辐射与土壤干旱胁迫下,分析紫花苜蓿叶表皮蜡质含量、晶体结构、叶片水势及紫外线吸光产物等的变化规律。结果表明,敖汉品种叶表皮蜡质含量高于三得利;在紫外线与干旱复合胁迫时敖汉叶表皮蜡质含量和叶片水势均较对照显著增加,而三得利叶水势较对照无显著变化。说明在复合胁迫下,强抗旱品种通过增加叶表皮蜡质的沉积来维持较高的叶水势。复合胁迫和单独紫外线辐射下(0.05 W/m²),紫花苜蓿叶表皮片状蜡质晶体结构发生熔融,扩大了叶表面积的覆盖率,减少角质层蒸腾失水;在0.1 W/m²紫外线辐射下,敖汉叶表皮蜡质晶体结构出现平行于叶表而垂直分布于其他晶体之上的片层结构,提高了紫外线辐射反射率,有效减少强辐射对植株生理的影响。单独土壤干旱处理对紫花苜蓿蜡质晶体结构无显著影响。紫外线辐射对植株紫外线吸光产物含量无显著影响,说明紫花苜蓿叶表皮蜡质晶体结构对紫外线辐射有直接防御作用,这可能部分程度地推迟、替代通过生理代谢途径对紫外线的防御。

Effect of soil water deficit and enhanced ultraviolet radiation on contents and crystal structure of cuticular waxes in alfalfa (Medicago sativa) leaf

Enhanced ultraviolet radiation induced by human activities widely influenced plant adaptation,which accompanied with drought stress severely reduced crop yields.In the current study,two alfalfa(Medicago sativa) cultivars with different drought resistances,Aohan(high resistance) and Sanditi(low resistance),were used to analyze the responses of leaf cuticular wax content and crystal structure,leaf water potential(LWP),and ultraviolet absorbing compounds under soil water deficit and enhanced ultraviolet radiation(UVR) stresses.The results showed that the leaf wax content in Aohan was significantly higher than that in Sanditi.Compared to well-watered plants,leaf wax content and LWP in Aohan with combined treatments of UVR and soil water deficit increased,while LWP in Sanditi changed insignificantly.This indicates that high-drought resistant cultivar might maintain higher level of LWP to control water loss by increasing wax deposition on leaf surface.Under the conditions of 0.05 W/m2 UVR dose or combined treatments of UVR and soil water deficit,the platelet wax crystalloid on leaf surface of both alfalfa cultivars melted,which increased covering areas and UVR reflection rate,and thus would reduce cuticular water loss.Under 0.1 W/m2 UVR dose,some crystal platelets paralleling leaf surface while vertically distributing above other crystalloid,appeared on leaf surface of Aohan,which efficiently reduced the effect of UVR on plant physiology,while the wax crystalloids of Sanditi further melted.The structure of wax crystalloids had no significant response to solely water deficit treatment.The contents of ultraviolet absorbing compounds had no significant response to enhanced UVR,indicating that the wax crystalloid structure on alfalfa leaf surface had direct defense mechanism to UVR,which partly might delay or replace the defense mechanisms from secondary metabolic compound such as ultraviolet absorbing compounds.