This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Edwards, G. E. Articles by Walker, D. A. Search for Related Content PubMed PubMed Citation Articles by Edwards, G. E. Articles by Walker, D. A. Agricola Articles by Edwards, G. E. Articles by Walker, D. A.

Articles

Photosynthesis by Isolated Protoplasts, Protoplast Extracts, and Chloroplasts of Wheat

Influence of Orthophosphate, Pyrophosphate, and Adenylates

Department of Botany, The University of Sheffield, Sheffield S10 2TN, England

Protoplasts, protoplast extracts (intact chloroplasts plus extrachloroplastic material), and chloroplasts isolated from protoplasts of wheat (Triticum aestivum) have rates of photosynthesis as measured by light-dependent O₂ evolution of about 100 to 150 micromoles of O₂ per milligram of chlorophyll per hour at 20 C and saturating bicarbonate. The assay conditions sufficient for this activity were 0.4 molar sorbitol, 50 millimolar N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid KOH (pH 7.6), and 10 millimolar NaHCO₃ with protoplast, plus a requirement of 1 to 10 millimolar ethylenediaminetetraacetate (EDTA) and 0.2 to 0.5 millimolar inorganic orthophosphate (Pi) with protoplast extracts and chloroplasts. Protoplast extracts evolved approximately 6 micromoles of O₂ per milligram of chlorophyll before photosynthesis became largely dependent on exogenous Pi while photosynthesis by chloroplasts had a much stronger dependence on exogenous Pi from the outset.

Photosynthesis by chloroplasts from 6-day-old wheat plants under optimum levels of Pi was similar to that with the addition of 5 millimolar inorganic pyrophosphate (PPi) plus 0.2 millimolar adenosine-5'-diphosphate (ADP). Either PPi or ADP added separately inhibited photosynthesis. When chloroplasts were incubated in the dark for 2 to 6 minutes, photosynthesis was strongly inhibited by 5 millimolar PPi and this inhibiting was relieved by including adenosine-5'-triphosphate (ATP) or ADP (0.2 to 0.6 millimolar). Chloroplasts from 9-day-old wheat leaves were slightly less sensitive to inhibition by PPi and showed little or no inhibition by ADP.

Chloroplasts isolated from protoplasts and assayed with 0.3 millimolar Pi added before illumination have an induction time from less than 1 minute up to 16 minutes depending on the time of the assay after isolation and the components of the medium. In order to obtain maximum rates of photosynthesis and minimum induction time, NaHCO₃ and chelating agents, EDTA or PPi (+ATP), are required in the chloroplast isolation, resuspension and assay medium. With these inclusions in the isolation and resuspension medium the induction time decreased rapidly during the first 20 to 30 minutes storage of chloroplasts on ice. Requirements for isolating intact and photosynthetically functional chloroplasts from wheat protoplasts are discussed.

This article has been cited by other articles:

				G. Noctor, L. Gomez, H. Vanacker, and C. H. Foyer Interactions between biosynthesis, compartmentation and transport in the control of glutathione homeostasis and signalling J. Exp. Bot., May 15, 2002; 53(372): 1283 - 1304. [Abstract] [Full Text] [PDF]

				S. Suzuki, N. Murai, J. N. Burnell, and M. Arai Changes in Photosynthetic Carbon Flow in Transgenic Rice Plants That Express C4-Type Phosphoenolpyruvate Carboxykinase from Urochloa panicoides Plant Physiology, September 1, 2000; 124(1): 163 - 172. [Abstract] [Full Text]

				N Moran, G Ehrenstein, K Iwasa, C Bare, and C Mischke Ion channels in plasmalemma of wheat protoplasts Science, November 16, 1984; 226(4676): 835 - 838. [Abstract] [PDF]