Chloroplast activity

DE Goldman (1943) Potential, impedance, and rectification in membranes. J Gen Physiol 27 37-60 P Grber, U Junesch and GH Schatz (1984) Kinetics of proton-transport-coupled ATP synthesis in chloroplasts. Activation of the A TPase by an artificially generated ApH and A F. Ber Bunsenges Physik Chem 88 599-608... 

Halliwell, B. Chloroplast Metabolism The Structure and Function of Chloroplasts in Green Leaf CeUs. New York Oxford Univ. Press, 1981. [A detailed description of chloroplast activity.]... 

Photoinactivation of isolated chloroplast activities is more pronounced under anaerobic treatment. 

Ozone has been shown to inhibit photosynthesis (8-10) and cause changes in the chloroplastic activated oxygen scavenging system (3, 11) implying action at the chloroplast level. 

Some authors(1) concluded that photosynthesis at low Fw was more limited by the loss of chloroplast activity than by increased difussive resistance. RBPC activity decreased in bean and cotton plants at water stress(2)(3) (4). PEPC and RBPC activities decreased at water stress in barley plants(5). In mesophyll cells from bean and tomato plants there was decreased in CO2 fixation at fairly low osmotic potentials which simultaneous with stomatal closure(6). Recently it was reported(7) that in soybean leaves a non stomatal limitations of leaf photosynthesis under drought stress conditions appears to be due in part to a reduction in the in vivo activity of RBPC. On the other hand it has been reported that chlorophyll content (8) (9) (10) shows alterations due to water stress. In the present work we pretend to compare the responses of carboxylase activities and chlorophyl content to water deficit in two maize hybrids (Ci ) (CPB2 and CPB8), two tomato cultivars (C3) (Pera Quibor, PQ and Rio Grande, RG) and two bean cultivars CC3)(Tacarigua,T and VUL-73-401,V). 

The lack of interaction between radiant flux density and salinity up to 130 mol.m" NaCl (Fig. 3) also suggest that the effect was not due to chloroplast activity. 

Cl8 l, Ci8 2 and Cl8 3 acids. TAGs of such composition are usually considered to occur only in the seeds (eg. flax, soybean etc.), which for the most part of the oil accumulation period include many chloroplasts actively forming polyenoic FAs. However, sea buckthorn cotyledons lack green plastids, are surrounded by an opaque seed coat and mature inside a fruit. Therefore, the... 

Light saturation curves for DCMU-sensitive PSII electron transport revealed two significant differences between TH and TNH chloroplasts (Fig. 1). First, TH chloroplast activity saturated at a much higher light intensity than TNH chloroplasts and, second, the quantum efficiency of the TH chloroplasts was lower at limiting light Sybesma, C. (ed.). Advances in Photosynthesis Research, Vol. II. ISBN 90-247-2943 2. 

FIGURE 22.27 Light-induced pH changes in chloroplast compartments. Illumination of chloroplasts leads to proton pumping and pH changes in the chloroplast, such that the pH within the thylakoid space falls and the pH of the stroma rises. These pH changes modulate the activity of key Calvin cycle enzymes. 

As discussed in Section 22.7, illumination of chloroplasts leads to light-driven pumping of protons into the thylakoid lumen, which causes pH changes in both the stroma and the thylakoid lumen (Figure 22.27). The stromal pH rises, typically to pH 8. Because rubisco and rubisco activase are more active at pH 8, COg fixation is activated as stromal pH rises. Fructose-1,6-bisphosphatase, ribulose-5-phosphate kinase, and glyceraldehyde-3-phosphate dehydrogenase all have alkaline pH optima. Thus, their activities increase as a result of the light-induced pH increase in the stroma. 

Smirnoff, J. Colombe, S.V. (1988). Drought influences the activity of enzymes of the chloroplast hydrogen peroxide scavenging system. Journal of Experimental Botany, 39, 1097-1109. 

Mayoral, M.L., Atsmon, D., Gromet-Elhanan, Z. Shimshi, D. (1981). Effect of water stress on enzyme activities in wheat and related wild species Carboxylase activity, electron transport and photophosphorylation in isolated chloroplasts. Australian Jourrml of Plant Physiology, 8, 385-94. 

Younis, H.M., Weber, G. Boyer, J.S. (1983). Activity and conformational changes in chloroplast coupling factor induced by ion binding Formation of a magnesium-enzyme-phosphate complex. Biochemistry, 22, 2505-12. 

Chlorophyll b occurs as an accessory pigment of the light-harvesting systems in land plants and green algae, and comprises one-third (or less) of total chlorophyll. The biosynthesis of chlorophyll b has been an area of active research particularly regarding its compartmentalization in chloroplast membranes, identification of the gene for chlorophyllide a oxidase, and characterization of the enzymes involved. ... 

A sequence of ten amino acids (ICS-D-KTGTLT) around the phosphorylation site of Na,K-ATPase (Asp ) is highly conserved among the Na,K-, H,K-, Ca-, and Id-pumps [6]. There is also homology with the subunit of FpATP synthetase of mitochondria and chloroplasts (see [6]) except that Asp is replaced by Thr. Accordingly a covalent phosphorylated intermediate is not formed in Fi-ATPase. Mutagenesis of the phosphorylated aspartate residue in Na,K-ATPase [82], Ca-ATPase [87], or H-ATPase [88] completely blocks activity. 

Both the intracellular and the plasma membranes are actively involved in the cell s vital functions. In the surface membranes of axons, processes of information transfer in the form of electrical signals (nerve impulses) lake place. Bioenergy conversion processes occur at the intracellular membranes of the mitochondria and chloroplasts. 

A well-known example of active transport is the sodium-potassium pump that maintains the imbalance of Na and ions across cytoplasmic membranes. Flere, the movement of ions is coupled to the hydrolysis of ATP to ADP and phosphate by the ATPase enzyme, liberating three Na+ out of the cell and pumping in two K [21-23]. Bacteria, mitochondria, and chloroplasts have a similar ion-driven uptake mechanism, but it works in reverse. Instead of ATP hydrolysis driving ion transport, H gradients across the membranes generate the synthesis of ATP from ADP and phosphate [24-27]. 

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