Discussion on simultaneous measurements of leaf gas exchange and chlorophyll fluorescence for estimating photosynthetic electron allocation

The thylakoid electron (e super(-)) transport chain in plant chloroplasts is pivotal in coordinating the fluctuating supply of absorbed light energy with the varying demands of the photosynthetic metabolism. Photosynthetic electron allocation plays a key role in regulation of the photosynthetic metabolic processes. However, according to the biochemical process, there are some deficiencies in the current method; (1) the electron number required for one oxygenation cycle was underestimated; (2) the relative electron transport rate and the absolute electron transport rate were confused; (3) some electrons via PS II were used to CO sub(2) assimilation and photorespiration, whereas others associated with electron-consuming processes (e.g. O sub(2) acceptor cycle or water-water cycle) were ignored ; (4) mitochondrial respiration in the light (R sub(d)) was difficult to obtain, which led to inaccurate estimation of carboxylative reaction electron flow (J sub(c)) and photorespiration rate (R sub(p)). Simultaneous measurements of leaf gas exchange and chlorophyll fluorescence for wheat and bean were measured in this study. The results revealed that the electron transport rate and CO sub(2) assimilation synchronously reached the maximum values through fitting the rapid light curves and light response curve of plant photosynthesis in bean, but not in wheat. It's concluded that the difference seemed to be attributed to assimilation product output pattern. The difference of the electron allocations between the calculated values from photorespiration rate (12 x R sub(p)) and the measured ones ( Delta J sub(o)), and the difference of photorespiration rate between the estimation by traditional method (Eq.5) and the measurement, were all demonstrated that the difference between the relative electron transport rate and absolute electron transport rate.