Photosynthesis

About: Photosynthesis is a research topic. Over the lifetime, 19789 publications have been published within this topic receiving 895197 citations.

Impact of Heavy Metals on Photosynthesis

Abstract: Use of phytotoxicity of metallic compounds dates back to 1896, when the French farmers applied Bordeaux mixture (copper sulphate, lime and water) to control fungal pests (Martin and Woodcock 1983). Currently, global heavy metal (HM) pollution is a serious environmental concern. Photosynthetic functions have been invariably affected either directly or indirectly by HMs (Baszynski and Tukendorf 1984; Clijsters and Van Assche 1985; Baszytniski 1986; Sheoran et al. 1990; Greger and Ogren 1991; Krupa and Baszynski 1985, 1995; Prasad 1995a, 1997). A critical examination of the literature reveals that HMs react with the photosynthetic apparatus at various levels of organization and architecture i.e. accumulation of metals in leaf (main photosynthetic organ); partitioning in leaf tissues like stomata, mesophyll and bundle sheath; metal interaction with cytosolic enzymes and organics; alteration of the functions of chloroplast membranes; supramolecular level action, particularly on PS II, PS I, membrane acyl lipids, and carrier proteins in vascular tissues; molecular level interactions, particularly with photosynthetic carbon reduction cycle enzymes, xanthophyll cycle and adenylates.

Photosynthesis and Ribulose 1,5-Bisphosphate Carboxylase in Rice Leaves: Changes in Photosynthesis and Enzymes Involved in Carbon Assimilation from Leaf Development through Senescence

Abstract: Changes in photosynthesis and the ribulose 1,5-bisphosphate (RuBP) carboxylase level were examined in the 12th leaf blades of rice ( Oryza sativa L.) grown under different N levels. Photosynthesis was determined using an open infrared gas analysis system. The level of RuBP carboxylase was measured by rocket immunoelectrophoresis. These changes were followed with respect to changes in the activities of RuBP carboxylase, ribulose 5-phosphate kinase, NADP-glyceraldehyde 3-phosphate dehydrogenase, and 3-phosphoglyceric acid kinase. RuBP carboxylase activity was highly correlated with the net rate of photosynthesis ( r = 0.968). Although high correlations between the activities of other enzymes and photosynthesis were also found, the activity per leaf of RuBP carboxylase was much lower than those of other enzymes throughout the leaf life. The specific activity of RuBP carboxylase on a milligram of the enzyme protein basis remained fairly constant (1.16 ± 0.07 micromoles of CO 2 per minute per milligram at 25°C) throughout the experimental period. Kinetic parameters related to CO 2 fixation were examined using the purified carboxylase. The K m (CO 2 ) and V max values were 12 micromolar and 1.45 micromoles of CO 2 per minute per milligram, respectively (pH 8.2 and 25°C). The in vitro specific activity calculated at the atomospheric CO 2 level from the parameters was comparable to the in situ true photosynthetic rate per milligram of the carboxylase throughout the leaf life. The results indicated that the level of RuBP carboxylase protein can be a limiting factor in photosynthesis throughout the life span of the leaf.

Pyruvate,Pi Dikinase and NADP-Malate Dehydrogenase in C4 Photosynthesis: Properties and Mechanism of Light/Dark Regulation

Abstract: [Extract] C4 Cycle and its Significance in Photosynthesis This review considers two key enzymes of the C4 pathway of photosynthesis, pyruvate,Pi dikinase (PPDK) and NADP-malate dehydrogenase (NADPMDH). I Besides their critical roles in C4 photosynthesis, these enzymes also share in common the fact that their activity is rapidly modulated by changes in light intensity. We will describe the radically different mechanisms by which this light-mediated modulation of activity is achieved . The kinetic and physical properties of these enzymes, and other mechanisms by which they are regulated, will also be reviewed. There have been recent reviews of the biochemistry of C4 photosynthesis (28, 31) and the light modulation of other photosynthetic enzymes, particularly in C3 plants (1-3, 16-18), so these areas will not be covered here.