THE CARBON FIXATION CHARACTERISTICS OF ISOLATED CODIUM FRAGILE CHLOROPLASTS. CHLOROPLAST INTACTNESS, THE EFFECT OF PHOTOSYNTHETIC CARBON REDUCTION CYCLE INTERMEDIATES AND THE REGULATION OF RuBP+ CARBOXYLASE IN VITRO

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Abstract

Chloroplasts of the siphonaceous marine alga Codium fragile exhibit different carbon fixation characteristics in vitro from those of higher plants. A simple extraction medium, 0.8 M osmoticum and a saturating light intensity of 25 W.m−2 produced maximum rates of 40–60 μmoles CO2 fixed mg. chlorophyll−1 h−1 at 20°C, depending on the age and condition of the parent tissue. No marked lag phase was apparent and fixation proceeded at a linear rate for up to 60 min. Incubation with 10 mM PGA enhanced the fixation rate, as did 10 mM SBP, 10 mM FBP and 5 mM R5P to a lesser extent, whereas 6 PGlu, S7P, F6P, Ru5P and PEP produced no measureable effect. This lack of marked response to the addition of exogenous photosynthetic intermediates is correlated to a lack of induction by these chloroplasts. Using the retention of the soluble stromal enzyme RuBP carboxylase as a criterion of intactness, freshly isolated C. fragile chloroplasts were approximately 80% intact, and were still 40% intact after 96 h storage in the dark on ice. RuBP carboxylase was shown to resemble the higher plant carboxylase, existing in either an active or inactive form depending on the prevailing levels of RuBP and Mg2+, and to be metabolically regulated by PGA, 6PGlu, SBP, FBP and Pi. Maximum rates obtained with a chloroplast extract were 155 jumoles CO2 fixed mg chlorophyll−1 h−1, at 20°C. Copyright © 1978, Wiley Blackwell. All rights reserved

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COBB, A. H., & ROTT, J. (1978). THE CARBON FIXATION CHARACTERISTICS OF ISOLATED CODIUM FRAGILE CHLOROPLASTS. CHLOROPLAST INTACTNESS, THE EFFECT OF PHOTOSYNTHETIC CARBON REDUCTION CYCLE INTERMEDIATES AND THE REGULATION OF RuBP+ CARBOXYLASE IN VITRO. New Phytologist, 81(3), 527–541. https://doi.org/10.1111/j.1469-8137.1978.tb01626.x

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