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Compartmentation of labeled fixation products in intact mesophyll protoplasts from Avena sativa L. after in-situ inhibition of the chloroplast phosphate translocator

R. Hampp and M. Goller
Planta
Vol. 159, No. 4 (1983), pp. 314-321
Published by: Springer
Stable URL: http://www.jstor.org/stable/23376733
Page Count: 8
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Compartmentation of labeled fixation products in intact mesophyll protoplasts from Avena sativa L. after in-situ inhibition of the chloroplast phosphate translocator
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Abstract

Leaf mesophyll protoplasts of oat (Avena sativa L.) were allowed to fix 14C-labeled bicarbonate in the absence or presence of pyridoxal phosphate (PLP), a specific inhibitor of the phosphate translocator of the inner envelope membrane of chloroplasts. The incubation was terminated by a method of rapid integrated protoplast homogenization and fractionation, and compartmented levels of label contained in sugars, phosphate esters, amino acids and organic acids were determined. The results show that the addition of PLP to a suspension of intact protoplasts causes an accumulation of phosphate esters in the chloroplast stroma for up to 2.5 min of incubation, with a corresponding decrease in the cytosol. Prolonged treatment of protoplasts with PLP in the light resulted in a decrease of starch-associated label, combined with higher levels of labeled sugars in the cytosol, indicating a switch from phosphorolytic to hydrolytic starch degradation. Together with the determination of pool sizes of triose phosphates and of inorganic phosphate, the results demonstrate that the method employed is an important tool in investigating processes of intracellular regulation. They are discussed with respect to the permeability and possible side reactions of PLP, as well as in the light of reports on PLP action on isolated chloroplasts.

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