Chloroplast respiration

Four types of oxygen consumption occur in plants dark respiration, photorespiration, chloroplast respiration, and cyanide-resistant respiration. Other reviews of photorespiration have been published 41, 42) therefore it will not be discussed here. Also, because knowledge of respiratory ETS in plants is based on the higher plants in contrast to the algae, this section will be confined largely to the higher plant literature. 

Chloroplast respiration is a novel form of respiration that has only recently been discovered. Chloroplast membranes exhibit a nonphosphorylation ETS that consumes oxygen (48). Ferredoxin and reduced nicotinamide adenine dinucleotide phosphate (NADPH) serve as electron carriers and glyceraldehyde-3-phosphate serves as the electron donor. This system probably originated in the respiratory ETS of the chloroplast s free-living ancestors, the cyanobacteria (49). 

The leaf structure has several important functions, three of which are photosynthesis, transpiration, and respiration (2). Photosynthesis is accomplished by chloroplasts in the leaf, which combine water and COj in the presence of sunlight to form sugars and release O2. This process is shown in Eq. (8-1). 

Ozone causes both quantitative and qualitative changes in carbon dioxide fixation patterns. Wilkinson and Bames, using carbon dioxide-found a reduction in radioactivity in soluble sugars and increases in free amino acids and sugar phosphates in white pine after a 10-min exposure to ozone at 0.10 ppm. Miller observed a decrease in carbon dioxide-fixation in ponderosa pines that correlated with loss of chlorophyll, after exposure to ozone at 0.30-0.35 ppm. The Hill reaction rates of chloroplasts isolated from healthy and ozone-injured ponderosa pine indicated that both light and dark reactions of the chloroplasts from ozone-injured plants were depressed. Barnes found depressed photosynthesis and stimulated respiration in seedlings of four pine species of the southeastern United States after exposure to ozone at 0.15 ppm. 

The toxic effects of ozone in plant systems have been studied for some time, yet the actual mechanisms of injury are not fully understood. In addition to visible necrosis which appears largely on upper leaf surfaces, many other physiological and biochemical effects have been recorded ( ). One of the first easily measurable effects is a stimulation of respiration. Frequently, however, respiration may not increase without concomitant visible injury. Furthermore, photosynthesis in green leaves as measured by CO2 assimilation, may decrease. It is well known that ozone exposure is accompanied by a dramatic increase in free pool amino acids ( ). Ordin and his co-workers ( ) have clearly shown the effect of ozone on cell wall biosynthesis. In addition, ozone is known to oxidize certain lipid components of the cell ( ), to affect ribosomal RNA (16) and to alter the fine structure of chloroplasts (7 ). 

Ozone has been shown to initiate many physiological and biochemical changes in sensitive plant species. Decreases in photosynthesis and increases and decreases in respiration have occurred in response to ozonation. The bioenergetic status of mitochondria and chloroplasts is disturbed by ozone. Decreases in oxidative- and photo- phosphorylation have been reported as have increases in adenosine triphosphate and total adenylate content of plant tissue. The variable physiological responses appear to be related to the stage of symptom development at the time of analysis and to the mode of ozone exposure, viz. in vivo and in vitro. 

Adenosine triphosphate is utilized in portions of the cell other than the mitochondria and chloroplasts therefore, the utilization as well as the production of ATP is of importance to total adenylate status. As a result, it became important to consider total ATP content of plants. When detached pinto bean leaves were exposed to 1,0 yl/1 ozone for 30 min total ATP content of the leaf decreased (12), Since ozone altered leaf ATP content it could also alter the leaf s adenylate status we wished to determine if a correlation existed between alteration in adenylates and the change previously reported in photosynthesis and respiration. Since ATP is readily broken down by adenosine triphosphatases, a reliable method of extraction and quantitative method of ATP analysis was designed for the study (8),... 

In most instances, either for mitochondrial suspensions or whole bacteria, ApH is less negative than -0.5 unit making a contribution of, at most, -30 mV to Ap. The exception is found in the thylakoid membranes of chloroplasts (Chapter 23) in which protons are pumped into the thylakoid vesicles and in which the internal pH falls dramatically upon illumination of the chloroplasts.185 The ApH reaches a value of -3.0 or more units and Ap is 180 mV, while Em remains 0. Reported values of Em for mitochondria and bacteria range from -100 to -168 mV and Ap from -140 to -230 mV.172 179 Wilson concluded that Em for actively respiring mitochondria, using malate or glutamate as substrates,... 

Starch production in leaves ceased after one to six days, depending on the species sucrose-14C could be substituted as a source of substrate for starch.190 Corn (maize) tolerates many of the triazine herbicides, but its isolated chloroplasts do not. Treatment did not influence catalase activity or respiration,191 but stopped oxygen output immediately.199... 

Extensive studies have been carried out on the proton-translocating ATPase of mitochondrial, bacterial and chloroplast membranes. This enzyme can also function in reverse to exploit the electrochemical potential of protons built up by respiration for the synthesis of ATP from ADP and P .298 The synthesis of ATP can be effected by the application of external electrical pulses to the ATPase vesicles in suspension with submitochondrial particles, showing that the diffusion potential of the protons (ApH) is not used. The yield of ATP was linearly dependent on the number of pulses.299... 

Iron has roles in enzyme systems and is necessary for the synthesis of chlorophyll (Hipkins, 1983). Chlorosis, the lack of chlorophyll is the first and obvious result of iron deficiency. Chloroplasts are reduced in size and without chlorophyll. Iron deficiency also has an effect on respiration and on cell division and thus growth. An excess of phosphate, bicarbonate, Cu, Zn, Co, Cd, Mn or Ni in the growth medium may cause Fe deficiency (Hewitt, 1948, 1953 Chaney and Giordano, 1977). 

The electron transfer processes that occur within the membrane, such as for example, phosphorylation (Fig. 17.6), are well known, but their mechanisms remain unexplained. These electron transfer processes are of primary importance in two types of membrane chloroplasts in photosynthesis, and mitochondria in respiration. 

Caspar, C, Huber. S. C., and Somerville, C. 1986. Alterations in growth, photosynthesis and respiration in a starch mutant of Arabidopsis thaliana (L.), Heynh deficient in chloroplast phosphoglucomutase activity. Plant Physiol. 79, 1-7. 

The activities of chloroplasts and mitochondria are related in various ways (Fig. 6-7). For instance, the O2 evolved by photosynthesis can be consumed during respiration, and the CO2 produced by respiration can be fixed by photosynthesis. Moreover, ATP formation is coupled to electron flow in... 

In Chapter 4 (Section 4.1D), we indicated that the radiation input of the sun to the earth s atmosphere averages 1366 W m-2 (the solar constant ). Some of the radiant energy is used to form ATP and NADPH in chloroplasts. In turn, these energy currencies lead to the reductive fixation of CO2 into a carbohydrate in photosynthesis (see Fig. 5-1). In the same photosynthetic cells, in other plant cells, and in animal cells, the carbohydrates formed during photosynthesis can serve as the energy source for mitochondrial respiration, which leads to the generation of ATP by oxidative phosphorylation. 

In the C4 pathway, CO2 in the form of HCO3- reacts with phosphoenol-pyruvate (PEP) via the enzyme PEP carboxylase located in the cytosol of the mesophyll cells (Fig. 8-15b).8 The initial product is oxaloacetate, which is rapidly converted to malate and aspartate. For all chloroplasts in photo-respiring (C3) plants, and for the chloroplasts in the bundle sheath cells of C4... 

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