Effect of salts and electron transport on the conformation of isolated chloroplasts. I. Light-scattering and volume changes.
Whole chloroplasts isolated from the leaves of spinach (Spinacia oleracea L.) exhibit 2 types of conformational change during electron transport. Amine-uncoupled chloroplasts swell and atebrin-uncoupled chloroplasts shrink. Chloroplasts uncoupled by carbonylcyanide phenylhydrazones and by treatment with ethylenediamine tetraacetic acid do not change their volumes or light-scattering properties during electron transport. Phosphorylating chloroplasts shrink only slightly.The rate and extent of the conformational change parallel the rate of electron transport; both the decrease in turbidity with methylamine and the increase in turbidity with atebrin are rougly proportional to the Hill reaction rate. Consequently the great volume and light-scattering changes which occur in the presence of these uncouplers can be attributed, in part, to the very high rates of uncoupled electron transport. However, for a given rate of electron transport the atebrin-induced scattering increase is very much greater than the increase observed during photophosphorylation.When uncouplers are combined, the carbonylcyanide phenylhydrazone effect (no change) supercedes both the methylamine effect (swelling) and the atebrin effect (shrinking). The methylamine effect supercedes the atebrin (shrinking) and ethylenediamine tetracetic acid (no change) effects. The atebrin effect supercedes the ethylenediamine tetraacetic acid effect. A similar hierarchy of effects is observed with regard to the rate of the uncoupled electron transport.These light-scattering changes of whole chloroplasts reflect similar changes which occur in very small digitonin particles of chloroplasts. Therefore one must look among chloroplast substructures for the basic mechanism of swelling and shrinking.Many salts (including methylamine hydrochloride) cause the chloroplasts to shrink. This phenomenon is not osmotic since comparable osmolarities of sucrose are without effect. Magnesium chloride and calcium chloride are most effective but all salts tested gave major volume decrease when less than 0.05 m. The salt-shrunken chloroplasts show greater light-scattering changes during electron transport than do low-salt chloroplasts.
Izawa
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Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan.
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