Studies on the Kinetics of Photosynthetic Products Synthesized by Different Preparations of Intact Spinach Chloroplasts

Abstract

The earliest attempts to demonstrate CO2 fixation by isolated chloroplasts resulted in rates considerably lower than those supported by the intact leaf. While leaves may have a fixation capacity in the order of 180 ,moles/mg of chlorophyll-hr, the rate obtained by chloroplasts isolated in 0.35 M NaCl was usually less than 5%o of this value (1-3, 6). Then, Walker (11) observed rates as high as 25C-of those of the intact leaf by substituting 0.33 M sorbitol for 0.35 M NaCl in the isolation medium. Also with sorbitol, Jensen and Bassham (7) obtained a chloroplast preparation capable of fixing CO2 at a rate equal to that of the intact leaf. Both laboratories concluded, on the basis of microscopical observations, that chloroplasts isolated in sorbitol, in contrast to those prepared in NaCl, retained an intact membrane and possibly did not lose soluble proteins. However, the specific activities of the enzymes catalyzing the reductive pentose phos- The reason for the difference in the rates of photosynthesis between the two kinds of preparations remains unclear. It is possible that chloroplast preparations fixing CO2 at rates approaching those of the intact leaf were merely a larger population of chloroplasts which retained their structural integrity, or that the new preparation method enabled additional fixation abilities or opened up new pathways. The present work was, therefore, concerned with a comparison of the CO2 fixation processes of the

Isolation of chloroplasts from rice leaves using glutaraldehyde

“…Sorbitol was introduced as a component of the isolation medium by WALKER (21) and JENSEN and BASSHAM (11) and they could isolate chloro· plasts retaining a relatively high rate of COa fixation. The superiority of sorbitol was, sub· sequently, demonstrated by KALBERER et al (13), COCKBURN et a/, (14), and PLAUT and GJDDS (16). In this experiment, the sorbitol medium suggested by CoCKDURN et al (14) was employed.…”

“…In order to circumvent the inherent disad· vantage of the conventional aqueous media, modified isolation media have been proposed (10)(11)(12)(13)(14)(15)(16)(17). It has been shown that if glutaralde· hyde is added to a conventional isolation medi· um, structurally intact chloroplasts can be iso• lated easily (15), Glutaraldehyde has been used as a fixative for electron microscopy and cytochemistry (18).…”

Effects of Intermediates of the Photosynthetic Carbon Reduction Cycle on Carbon Metabolism in Spinach Chloroplasts Illuminated on Filter Paper Discs

“…However, the low activity of these chloroplasts cannot be due to the low level of PCR cycle intermediates alone, since in this case incubation with such compounds should restore their photosynthetic activity completely. The 0-chloroplasts would appear to be similar to the chloroplasts isolated in a salt-based medium by Plaut and Gibbs (10).…”