Comparative Study On Absorption Spectrum And Chlorophyll Fluorescence Characteristics Among Three Types Of Leaves With Different Color From Ulmus Pumila Cv.Jinye

When the amount of light energy absorbed by the leaves exceeds the maximum converted by plant photosynthesis,the photosynthetic ability of the plant is reduced,which is called photoinhibition.Photoinhibition is an important mechanism of plant photosynthesis decline under environment stress.Ulmus pumila cv.jinye with colorful-leaf is bred in China.Its leaves with different content of lutein can appear green,light green,yellow and other colors.This provides us appropriate material to study the function of lutein in plant adaptation to photoinhibition.In this study,three types of leaves with different content of lutein from Ulmus pumila cv.jinye were used to determine photosynthetic pigment content,and the absorption spectrum and chlorophyll fluorescence characteristics at morning,noon and evening in summer,and the relationship between lutein content and photoinhibition was discussed;measure absorption spectrum and chlorophyll fluorescence characteristics of three types of leaves under strong light stress,the difference response to strong light was analyzed;detect the difference response to environment stress of three types of leaves under the condition of drought,salt,low temperature and high temperature stress.The results of this study will provide a reference for understanding the function of lutein in plant adaptation to photoinhibition and other stress.The main results are as follows:(1)There were no significant changes in the absorption spectra and fluorescence parameters of green leaves from Ulmus pumila cv.jinye at the morning,noon and evening in summer,indicating that the green leaves could resist the strong light at noon.The Fv/Fm decreased significantly in both light green leaves and yellow leaves under the strong light at noon in summer,indicating photoinhibition occureed at noon.Fv/Fm recovered at evening to the same level as that at morning,indicating that photoinhibition at noon was reversible.The degree of photoinhibition was more serious in yellow leaves.There was no significant difference in absorption spectrum under visible light in both two types of leaves with different color and among morning,noon and evening,Therefore,the decline of Fv/Fm was not due to the change in absorption of light energy.The decline of Fv/Fm was the result of significant increase in Fo.There were different mechanisms to defend photoinhibition in both two types of leaves.Light green leaves defended photoinhibition by increasing DIo/RC and decreasing RC/CSm;yellow leaves defended photoinhibition by increasing DIo/RC and decreasing RC/CSm and ETo/RC.Leaves from Ulmus pumila cv.jinye with color from green to yellow,the more lutein content,the more severe photoinhibition at the noon.The photoinhibition in light green leaves and yellow leaves at noon could recover at evening,therefore,serious photoinhibition in the leaves with higher lutein content was not lead to permanent hurt to leaf photosynthetic capacity,but instead lead to reversible inactivation of PS II reaction centers.The decline of Fv/Fm may be a protective response to adapt to strong light at noon for Ulmus pumila cv.jinye leaves.Thus the higher content of lutein in leaves is helpful to the protection response,and it is more beneficial to adapt to strong light in summer.(2)Photoinhibition did not occur in green leaves and light green leaves under strong light stress,but occurred in yellow leaves.In yellow leaves,Fv/Fm increased after stress,indicating photoinhibition was alleviated.The increase of Fv/Fm was the result of significant decrease Fo.There were no obvious photoinhibition in green leaves under strong light stress and at noon;light green leaves was inhibited by strong light at noon,but there was no obvious photoinhibition under strong light stress;photoinhibition occured in yellow leaves under strong light stress and at noon,but their mechanism is not consistent,Fv/Fm decreased and Fo increased at noon,Fv/Fm increased and Fo decreased under strong light stress.(3)There were no photoinhibition in three types of leaves with different color under drought and salt stress.Under low temperature stress,there was no significant change of Fv/Fm in green leaves and light green leaves,but yellow leaves had photoinhibition.Three types of leaves with different color all presented photoinhibition under high temperature stress,the most severe photoinhibition occurred in yellow leaves.The results show that,photoinhibition occourred in light green leaves and yellow leaves from Ulmus pumila cv.jinye under strong light at noon in summer,mainly caused by increasing the heat dissipation,reducing the energy of electron transfer and the number of active reaction center.With the increase in the lutein content,leaves presented the more severe photoinhibition,but the increase in the lutein content helps the recovery of potosynthesis from photoinhibition,so as to better adapt for leaves to the strong light.But the higher lutein content and less chlorophyll content is not benifit to the capture,transfer and conversion of light energy in leaves.Therefore,the light green leaves of Ulmus pumila cv.jinye can be well adapted to the strong light at noon in summer,and it also has good adaptability to drought,salt,low temperature and high temperature stress.