中文摘要：

为研究经霜对桑叶总黄酮积累量影响的机制,分析桑叶经霜前后总黄酮积累量合成关键酶苯丙氨酸解氨酶（phenylalnine ammonialyase,PAL）活力的动态变化,并对总黄酮积累量及气候温度进行相关性分析。在6 m L pH 8.8、0.1 mol/L硼砂-盐酸缓冲液中加入0.2 g桑叶叶片、0.2 g聚乙烯吡咯烷酮,底物L-苯丙氨酸浓度为0.04 mol/L,40℃条件下水浴反应40 min后测定经霜前后桑叶PAL活力,采用紫外分光光度法测定经霜前后桑叶总黄酮积累量。结果表明：PAL活力与平均气温呈极显著负相关,与总黄酮积累量呈极显著正相关,较低的温度有利于黄酮类物质的积累。

英文摘要：

In order to explore the mechanism underlying the influence of frost on the total flavonoid content in mulberry leaves,the dynamic changes in phenylalnine ammonia lyase（PAL） activity as a key enzyme in the biosynthesis of flavonoids was analyzed in mulberry leaves harvested before and after frost as well as the correlation between PAL activity and total flavonoid content or air temperature.For the determination of PAL activity in mulberry leaves,0.2 g mulberry leaf powder was homogenized with 0.1 mol/L borax hydrochloric acid buffer（6 mL,pH 8.8） added with 0.2 g of polyethylene（PVP） and centrifuged,and the supernatant was allowed to react with 0.04 mol/L L-phenylalanine as substrate at 40 ℃for 40 min.At the same time,the total flavonoid content of mulberry leaves was measured by UV spectrophotometry.The results showed that PAL activity in mulberry leaves harvested after frost was higher than in those harvested before frost.PAL activity showed a very significantly negative correlation with temperature,whereas it was significantly positively correlated with total flavonoid content.Lower temperature had a significant positive effect on the accumulation of total flavonoids.