‘红叶’杜仲叶色转变过程中叶片生理指标变化

Leaf physiological indicator changes in the transformation of leaves color of Eucommia ulmoides‘Hongye’

【目的】研究‘红叶’杜仲不同时期叶片生理指标变化规律,为揭示其特殊叶色转变机理提供理论依据。【方法】以‘红叶’杜仲和‘小叶’杜仲为材料,选择5个时期进行叶片色素含量测定。分别测定叶绿素a、叶绿素b、总叶绿素、类胡萝卜素、类黄酮和花色苷含量。使用CR2500型色差计(日本MINOLTA公司)测定L(明度值)、a*(变红度值)及b*(变黄度值),利用a*和b*计算出色泽饱和度(Chroma,C*)和色调角(hur angle,h),并进一步计算叶片颜色指数(color index)。对叶色转变过程及花色苷合成代谢途径中的关键酶苯丙氨酸裂解氨酶(PAL)和查尔酮异构酶(CHI)进行提取和酶活性测定,研究各时期差异显著性并通过相关分析研究各指标间的关联程度。【结果】①‘小叶’杜仲虽与‘红叶’杜仲变化规律相似,但两品种各指标的初始值及变化幅度均存在显著差异。‘小叶’杜仲颜色指数始终属于黄绿级,而‘红叶’杜仲第1、2阶段属于黄绿级,第3、4阶段属于粉红级,第5阶段达到深红级。②两个品种各种色素含量均为逐步上升,但在Ca(叶绿素a含量)、Cb(叶绿素b含量)、CT(总叶绿素含量)、CCar(类胡萝卜素含量)、Cf(类黄酮含量)和CA(花色苷含量)这几种物质含量变化中,叶片颜色变红过程中最关键的是花色苷含量。分别比较两品种第5时期(38 d)相对于第1时期(6 d)各色素含量的增幅,得到‘红叶’杜仲的CA增幅是‘小叶’杜仲的553.96%。③无论‘小叶’杜仲还是‘红叶’杜仲,不同时期的PAL酶活性无显著差异,且各时期两品种的酶活性值大小相近。而‘红叶’杜仲CHI酶活性随着叶色的转变直线上升,第5时期(38 d)为第1时期(6 d)的306.14%,不同阶段间差异达到极显著水平;‘小叶’杜仲CHI酶活性随着叶色转变也有逐步升高的趋势,但是增幅较小,不同时期的酶活性无显著差异。④L、a*及b*与类胡萝卜素含量、花色苷含量及类黄酮含量呈极显著相关,而与叶绿素a含量、叶绿素b含量、总叶绿素含量及叶绿素a与叶绿素b含量比无显著相关关系。CHI酶活性和杜仲叶片L、a*、b*、类胡萝卜素含量、花色苷含量及类黄酮含量间均存在显著或者极显著的相关关系,而PAL与叶片色差值间则无显著相关性。【结论】在‘红叶’杜仲叶片颜色转变过程中,花色苷含量变化幅度远大于叶绿素含量变化幅度,是其呈色的直接原因;‘红叶’杜仲CHI酶活性高在‘红叶’杜仲典型叶色转变过程中具有关键作用。

【Objective】In order to provide a theoretical basis for revealing the mechanism of leaf color formation,the consistency of leaf physiological indicators of Eucommia ulmoides‘Hongye’at different periods of time was studied.【Method】Chlorophyll a,chlorophyll b,total chlorophyll,carotenoids,flavonoids and anthocyanin in five periods were tested and compared between E.ulmoides‘Hongye’and E.ulmoides‘Xiaoye’.A CR2500 color difference meter(Konica Minolta,Japan)was used to measure brightness(L),redness(a*)and yellowness(b*)values.Color saturation(Chroma,C*)and hue angle(h)were calculated using the a*and b*values,where C*=(a*2+b*2)/2,h=arctan(b*/a*).The leaf color index(color index)was calculated as follows:color index=(180-h)/(L+C*).The key enzymes in the leaf color transition process and the anthocyanin synthesis and metabolism pathway,phenylalanine lyase(PAL)and chalcone isomerase(CHI)were extracted,and the enzyme activity was determined.The data were analyzed using SPSS 16.0.The analysis of variance was carried out to test the significance of differences within each period,and correlations among indicators were analyzed.【Result】①Although the variation law of E.ulmoides‘Xiaoye’was similar to E.ulmoides‘Hongye’,the initial value and variation range of each index of the two varieties were significantly different.The color index of E.ulmoides‘Xiaoye’was always in the yellow-green grade,while it was in the yellow-green grade only in the first and second stages for E.ulmoides‘Hongye’.After that,the color was in the pink grade in the third and fourth stages,and the deep red grade in the fifth stage.②The content of various pigments in the two varieties increased gradually.Among all the indicators,i.e.Ca(chlorophyll a content),Cb(chlorophyll b content),CT(total chlorophyll content),CCar(carotenoid content),Cf(flavonoid content)and CA(anthocyanin content),the anthocyanin content played the key role in the process of reddening.The comparison of the content of each pigment in the fifth period(38 d)to the first period(6 d)indicated that the CA in E.ulmoides‘Hongye’increased by 553.96%compared to that of E.ulmoides‘Xiaoye’.③There was no significant difference in PAL enzyme activity in different time periods between the two varieties.The enzyme activity values of the two varieties in each period were similar.The CHI enzyme activity of E.ulmoides‘Hongye’increased linearly with the change in leaf color by 306.14%in the fifth period(38 d)compared to the first period(6d)and differed significantly among different stages.The CHI enzyme activity of E.ulmoides‘Xiaoye’increased gradually with leaf color change,although there was no significant difference in enzyme activity among different periods.④The L,a*and b*values were significantly correlated with CCar,CA and Cf,while it was not significantly correlated with Ca,Cb,CT and Ca/Cb.CHI enzyme activity was correlated or significantly correlated with the L,a*and b*values,with CCar,CA and Cf of Eucommia leaves,while no significant correlation was found between the PAL and leaf color difference.【Conclusion】In the process of color changes in E.ulmoides‘Hongye’leaves,the change of CA was much greater than that of chlorophyll content,and this was the direct cause of their color appearance.The high activity of the CHI enzyme in E.ulmoides‘Hongye’leaves played a key role in the process of typical leaf color transformation.