Demonstration of Photophosphorylation by Maize Chloroplasts

Abstract

Photoplhosphorylation by isolate(i chlioroplasts has been reportedl and studied in several species (21), but no publislhed evidence of the reaction by maize chlioroplasts coul(l )e foundl. In a stu(ly of this reaction by maize chlioroplasts initial experiments using existing isolation techniques (2,12) (90 v). The homogenate was then filtered through eight layers -of cheesecloth and centrifuged at 2,000 X g for 7 minutes. The pellet was resuspended in 10 ml of grinding medium and recentrifuged at the same speed. The chloroplast pellet was finallv taken up in 1.5 ml of grinding medium. Although this procedure was satisfactory for spinach tisstue, mlaize chloroplasts isolated by the i(lentical

Stimulation of Photoreactions of Isolated Chloroplasts by Serum Albumin

“…Inhibition of chloroplast photoreactions, presunably due to inhibitors released during the isolation of chloroplasts was observed in several plant species (10,17,19), including Phaseolus. In the latter, photoreactions were strongly inhibited when chloroplasts were isolated at pH 6.0 (16) or wheni homogenized by mortar and pestle at pH 8.0 (15).…”

“…The increase in phosphorylation is supposedly due to inhibition of the rate of decay of the high energy non-phospiorylated intermediate, XE. it is postulated that serum albumin affects chloroplast photoreactions by binding endogenously released unsaturated fatty a-cids.The rates of electron transport and ATP formation of chloroplasts isolated from various plants differ appreciably (6,10,17), possibly because of the release of interfering substances during homogenization. Bean leaves, when homogenized at pH 6.0 release large quantities of linolenic acid, which totally inhibits normal chloroplast photoreactions (16).…”

“…The rates of electron transport and ATP formation of chloroplasts isolated from various plants differ appreciably (6,10,17), possibly because of the release of interfering substances during homogenization. Bean leaves, when homogenized at pH 6.0 release large quantities of linolenic acid, which totally inhibits normal chloroplast photoreactions (16).…”

Germ Plasm Manipulations of the Future

“…Other aspects of nitrogen metabolism presumably also have a genetic basis but adequate evidence is still largely lacking. Miflin and Hageman (1963) have developed a technique for isolating chloroplasts from young corn leaves capable of carrying on photophosphorylation. In subsequent studies the same authors (1966) compared three assays: Hill reaction, noncyclic and cyclic photophosphorylation.…”

Photophosphorylation and Carbon Dioxide Fixation by Chloroplasts Isolated from Populus deltoides

“…Second, enzyme inhibitors in high concentrations are released during the grinding process including polyphenols, tannins, and terpenes (10). In some systems it has been possible to avoid loss of activity by the addition of antioxidants (3,7) or adsorption and precipitation (11) 5 ,umoles of Pi, an adequate amount of 32P (1 X 1W0-1 X 106 cpm), chloroplasts containing less than 20 ,ug of chlorophyll, and water to a total volume of 1.7 ml. The reaction mixture was added to small round bottom test tubes and placed in a water bath maintained at 20 C. The reaction was started with light and terminated by addition of 0.3 ml of 20% trichloroacetic acid.…”