Membrane fragments released by French pressure cell treatment of whole chloroplasts and isolated by differential centrifugation have been characterized structurally and with respect to phosophorylating and proton transport activities. In agreement with results of other workers, the heavy fraction released by pressure treatment was found by electron microscopy studies to be made up of mostly intact grana stacks while the light fraction was comprised of vesicles derived from the stromal lamellae. Both fractions were found to carry out rapid rates of cyclic photophosphorylation catalyzed by phenazine methosulfate (PMS). However, only the grana membranes demonstrated active proton accumulation in the presence of PMS. No light induced H+ uptake could be detected in the stromal lamellae fraction; and as expected, proton gradient dissipating agents such as NH4Cl, nigericin in the presence of K+, and gramicidin were only slightly inhibitory to phosphorylation at concentrations which were very inhibitory in the grana membrane fraction. Further evidence that stromal lamellae do not have active proton transport in the intact chloroplast was obtained by comparing various chloroplasts having different amounts of stromal and grana membranes. Comparative studies on young and old chloroplasts from lettuce, mesophyll and bundle sheath cell plastids from sorghum, and greening plastids from etiolated corn seedlings revealed a direct correlation between the extent of grana formation and the amount of proton transport activity. Samples which had larger amounts of stromal lamellae had high rates of ATP formation but a reduced capacity for H+ accumulation.
ASJC Scopus subject areas
- Cell Biology