Relationships between leaf color changes, pigment levels, enzyme activity, photosynthetic fluorescence characteristics and chloroplast ultrastructure of Liquidambar formosana Hance

Abstract

Liquidambar formosana Hance is an attractive landscape tree species because its leaves gradually change from green to red, purple or orange in autumn. In this study, the red variety of L. formosana was used to establish a quantitative model of leaf color. Physiological changes in leaf color, pigment levels, enzyme activity, photosynthetic fluorescence characteristics and chloroplast ultrastructure were monitored. The relationship between leaf color and physiological structure indices was quantitatively analyzed to systematically explore the mechanisms behind leaf color. Our data showed that with a decrease in external temperatures, chloroplast numbers and sizes gradually decreased, thylakoid membranes became distorted, and chlorophyll synthesis was blocked and gradually decreased. As a result, chloroplast membranes could not be biosynthesized normally; net photosynthesis, maximum and actual photochemical efficiency, and rate of electron transfer decreased rapidly. Excess light energy caused leaf photoinhibition. With intensification of photoinhibition, leaves protected themselves using two mechanisms. In the first, anthocyanin synthesis was promoted by increasing chalcone isomerase and flavonoid glycosyltransferase activities and soluble sugar content so as to increase anthocyanin to filter light and eliminate reactive oxygen species to reduce photoinhibition. In the second, excessive light energy was consumed in the form of heat energy by increasing the non-photochemical quenching coefficient. These processes tuned the leaves red.

Keywords

Anthocyanins / Leaf color parameter / Enzymatic activities / Chlorophyll fluorescence characteristics / Liquidambar formosana