Origin and developmental changes of envelope proteins and translocator activities from plastids of Secale cereale L.
To determine the sites of synthesis of chloroplast-envelope proteins, we have analysed several enzyme and translocator functions ascribed to the envelope membranes, and investigated the envelope polypeptide composition of plastids isolated from 70S ribosome-deficient leaves of rye (Secale cereale L.) generated by growing the plants at a temperature of 32°C. Since the ribosomedeficient plastids are also achlorophyllous in light-grown leaves, not only were chloroplasts from mature, green leaves used for comparison, but also those from yellowing, aged leaves as well as etioplasts from dark-grown leaves raised at a temperature of 22° C. A majority of the plastidenvelope polypeptides appeared to be of cytoplasmic origin. The envelopes of ribosome-deficient plastids possessed ATPase (EC 3.6.1.3) activity; this was not, however, dependent on divalent cations, in contrast to the Mn(2+)- or Mg(2+)-dependent ATPase which is associated with chloroplast envelopes. Adenylate kinase (EC 2.7.4.3) was present in the stromal fraction of ribosome-deficient plastids and the stromal form of this enzyme is, therefore, of cytoplasmic origin. In contrast to previous findings, adenylate kinase was not, however, specifically associated with the chloroplast-envelope membranes, either in rye or in spinach. Measurements of the uptake of L-[(14)C]-malate into ribosome-deficient plastids indicated the presence and cytoplasmic origin of the dicarboxylate translocator. Malate uptake into rye etioplasts was, however, low. The phosphate translocator was assayed by the uptake of 3-phospho-[(14)C]glycerate. While rapid 3-phosphoglycerate uptake was observed for rye chloroplasts and etioplasts, it was hardly detectable for ribosome-deficient, plastids and rather low for chloroplasts from aged leaves. A polypeptide of M r approx. 30000 ascribed to the phosphate translocator was greatly reduced in the envelope patterns of ribosome-deficient plastids and of chloroplasts from aged leaves.
Botanisches Institut, Johann-Wolfgang Goethe-Universität, Postfach 111932, D-6000, Frankfurt am Main, Federal Republic of Germany.
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