增强UV-B辐射和氮对谷子叶光合色素及非酶促保护物质的影响

Abstract

以谷子(<em>Setaria italica </em>(L.) Beauv.)为对象,从拔节期开始持续给予低氮(1.875 mmol/L)和高氮(15 mmol/L)两种氮供应条件并从抽穗期开始进行26 d两种强度(4.29、7.12 kJ·m^-2·d^-1)的增强UV-B辐射处理,研究了谷子叶中光合色素含量、类黄酮含量和苯丙氨酸解氨酶(PAL)活性的变化。结果表明:与高氮供应条件相比,低氮供应条件明显降低了谷子叶中光合色素含量但提高了类胡萝卜素/叶绿素含量比值;在开花期中段和灌浆期中段,高氮供应条件下谷子叶中光合色素含量对增强UV-B辐射比低氮供应条件下的谷子更敏感。从灌浆期开始到处理结束,两种影响因子对谷子叶中类黄酮含量均有显著影响,增强UV-B辐射导致谷子叶中类黄酮含量逐渐升高,且相同增强UV-B辐射强度下低氮供应条件下的谷子叶中类黄酮含量明显高于高氮供应条件下的谷子。谷子叶中PAL活性对两种影响因子的响应较类黄酮含量更加敏感,低氮供应条件使谷子叶中PAL活性明显提高。结合上述指标的相关性分析结果可知,低氮供应条件加强了处于繁殖期主要阶段的谷子叶中类黄酮的积累,并使谷子叶中的类胡萝卜素/叶绿素含量比值明显提高,进而有助于维持谷子叶中光合色素含量在增强UV-B辐射条件下的相对稳定性,对植株抵抗UV-B辐射伤害有利。;Enhanced UV-B radiation resulting from ozone depletion in stratosphere with the increase of human activities can harm plants greatly, whereas the change of nitrogen supply can affect the sensitivity and resistance to UV-B radiation in plants. Foxtail millet (<em>Setaria italica </em>(L.) Beauv.), a typical C₄ crop plant, was chosen as experimental model to investigate the effects of enhanced UV-B radiation and nitrogen supply on photosynthetic pigments and non-enzymatic protection system in leaves. The plants of foxtail millet were fertilized under two different nitrate-nitrogen conditions (1.875, 15 mmol/L) from the jointing stage to the grouting stage, and were stressed by two different intensities of enhanced UV-B radiation (4.29, 7.12 kJ·m^-2·d^-1) from the heading stage to the grouting stage (26 days). During this period, the photosynthetic pigments and flavonoids content and the phenylalanine ammonia-lyase (PAL) activity in leaves of foxtail millet were measured. The nitrogen supply showed significant effect on the photosynthetic pigments contents in leaves of both UV-B treated and non-treated foxtail millet. The leaves in low nitrogen supply group showed significantly lower photosynthetic pigments content but higher carotenoid/chlorophyll ratio when compared to those of high nitrogen supply group according to most of statistical test results (<em>P</em><0.05, least-significant difference, LSD). However, enhanced UV-B radiation treatment showed significant effects on the photosynthetic pigments contents in leaves of foxtail millet in only the 11th day and the 21st day, and the photosynthetic pigments were more sensitive to enhanced UV-B radiation treatment at the high nitrogen group compared to the low nitrogen group. The nitrogen supply showed significant effect on PAL activity in leaves of foxtail millet during the whole period of this experiment, whereas enhanced UV-B radiation showed significant effect on the PAL activity only after the 11th day. Meanwhile, most LSD results showed that the PAL activity in leaves of foxtail millet increased in the low nitrogen supply group compared to the high nitrogen group, whether treated by enhanced UV-B radiation or not. Furthermore, both the nitrogen supply and enhanced UV-B radiation affected the flavonoids content in leaves of foxtail millet significantly after the 16th day, and the flavonoids content in leaves increased significantly in the low nitrogen supply in the 26th day independent of enhanced UV-B radiation. There was a significant positive correlation between the flavonoids content and the PAL activity, but both the flavonoids content and the PAL activity had a significantly negative correlation with the chlorophyll content. Moreover, there was a significant correlation between the chlorophyll content and the carotenoid content. This study indicated that in leaves of foxtail millet, low nitrogen supply treatment could enhanced accumulation of flavonoids and the carotenoid/chlorophyll ratio, thus caused more stability of photosynthetic pigments contents when foxtail millet was stressed by enhanced UV-B radiation compared to the high nitrogen supply during the breeding period. Therefore, low nitrogen supply treatment may improve the resistance to UV-B radiation in plants.