Abstract
Malate is the first stable product after CO2 is fixed in NADP-dependent malic enzyme (NADP-ME) type of C4 plants, which transfers CO2 and the reducing equivalent from mesophyll cell (MC) to vascular bundle sheath cell (BSC) chloroplasts and affects the redox state of BSC. The aim of this experiment is to investigate the effect of exogenous malate on the activity of photosystem II (PS II) in C4 and C3 plants. The leaf discs from the 5th fully expanded leaves of maize (NADP-ME type C4 plants) and the 10th fully expanded leaves of tobacco (C3 plants) were treated with malate of 50, 100 μM and the chlorophyll fluorescence parameters were measured. Malate treatments decreased the photochemical reaction efficiency (FV/FM) in maize leaves, as a result of rising in initial fluorescence (FO) and decreasing in maximal fluorescence (FM). The number of active PS II reaction center (RC) per excited cross section (RC/CS) declined in malate-treated maize, suggesting that malate inactivated PS II RC. Malate treatments also increased Wk, representing the severity of oxygen-evolving complex (OEC) damage, and decreased the rate of photosynthetic oxygen evolution. We conclude that exogenous malate regulates the activity and structure of PS II in C4 plant maize. No significant changes in the activity of PS II were observed in malate-treated C3 plant tobacco. It is suggested that the short term malate treatment will inhibit PS II of leaves which have C4 anatomy and C4 enzymes.
Highlights
C4 plants possess elevated photosynthetic ability, water use efficiency and nitrogen use efficiency compared with C3 plants
Tobacco has no significant difference in FO and FM, but maize has a significant increase in FO and mild decline in FM (Table 1)
The results showed that malate promoted the change in structure of oxygen-evolving complex (OEC) in maize leaf discs
Summary
C4 plants possess elevated photosynthetic ability, water use efficiency and nitrogen use efficiency compared with C3 plants. In typical C4 plants, mesophyll cells (MC) and vascular bundle sheath cells (BSC) in the leaves are arranged to form the Kranz anatomy around vascular tissues These two types of cells are different in structure and in function. This suggests that the malate might contribute to the regulation in loss of grana and deficiency in PS II activity in BSC chloroplast of C4 plants. The aim of this experiment is to investigate the effect of exogenous malate on the activity of PS II in C4 plant maize and C3 plant tobacco. The discs from 5th leaves of maize and 10th leaves of tobacco were treated with malate of 50 μM and 100 μM, and the chlorophyll fluorescence parameters were measured
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