Steps in the Acquisition of Photosynthetic Competence by Plastids of Maize

Abstract

Coupling factor particles are associated with membranes of maize etioplasts (Lockshin et al., 1971. Biochim. Biophys. Acta 226: 366-382). In addition, several, but not all, of the polypeptides found in the photosynthetic lamellae of maize chloroplasts are present in etioplasts.During the photoregulated maturation of chloroplasts from etioplasts, the membranes of the organelie acquire the capacity to carry on acid to base phosphorylation. (9) have shown that the coupling factor required for photophosphorylation is associated with the membranes of the etioplasts of dark-grown maize. This demonstrated that the unit of membrane assembly in maize thylakoids is different from the unit of photosynthetic function of these membranes. The coupling factor for phosphorylation also occurs in bean etioplasts (6).A/B phos3 is the production by chloroplast thylakoids of ATP upon transfer of membrane vesicles from an acidic to an alkaline solution in the presence of ADP and inorganic phosphate (7). This reaction occurs in darkness and is entirely independent of the capture of quanta by Chl. Etioplast membranes are incapable of carrying out A/B phos even though they contain the coupling factor which is required for this process (5). However, the volume of these membranes fails to change regardless of the osmotic environment, unlike thylakoids of green plastids. Plastid fragments obtained from maize seedlings grown in the dark for 7 days and then illuminated for a few hours can carry on A/B phos. It has been shown (5) MATERIALS AND METHODSPlant material, growth and greening conditions, plastid isolation, and assay of A/B phos activity were the same as described previously (5).PPV determinations were made as previously described (5), except that in some instances thrombocytocrits were employed instead of Stafford-Shevsky and McNaught tubes. The former allow volume determinations with an accuracy of ±3% under the condition of the experiments.For protein and lipid determinations, plastid thylakoid preparations were purified by means of sucrose density gradients. The plastids were isolated as described earlier (5), ruptured osmotically in 10 mm NaCl and homogenized. The resulting suspension was layered onto continuous gradients which ranged from 25 to 68% (w/v) of sucrose in 0.05 M HEPES, pH 7.7, and 1 mm MgCl2. The gradients were centrifuged in a Beckman SW 27 rotor at 25,000 rpm for 90 min. The purified pigmented fragments were removed with a syringe, diluted with 10 mm NaCl, and sedimented by centrifugation in a Sorvall SS-34 rotor at 12,000g for 5 min. After resuspension of the resulting pellet in 10 mm NaCl, the fragments were ready for use. All steps were carried out at or near 0 C.The isolated and purified fragments to be used for fatty acid determinations were saponified under N2 with 50% methanolic KOH (50% methanol containing 5% KOH) for 2 hr at 100 C. The nonsaponifiable fraction was exhaustively extracted into petroleum ether and discarded. The KOH-methanol solution containing saponifiable lipids was acidified w...

Changes in the polypeptide composition of internal membranes of barley plastids during greening

“…The present results demonstrate that the etioplast internal membranes have a complex polypeptide composition although, in agreement with earlier results (2,4,6,8,10,13), they lack certain of the polypeptides present in chloroplast thylakoids. The appearance of the proteins found in chloroplast thylakoids within 3h of greening is consistent with the appearance of complete photosynthetic ability within this time (3,5,16).…”

“…In an earlier paper (6), the polypeptide composition of the internal membranes of wild-type barley etioplasts was compared with that of thylakoids isolated from chloroplasts. It was concluded in this, and other studies (2,4,8,10,13), that certain prominent polypeptide bands present in chloroplast membrane patterns were absent or reduced in intensity in patterns of etioplast membranes. Conversely, other bands were found only in the polypeptide pattern of etioplast membranes.…”

Comparison of the Molecular Weights of Proteins Synthesized by Isolated Chloroplasts with Those Which Appear during Greening in Zea mays

“…Prolamellar bodies ofetioplasts and thylakoids ofchloroplasts are comprised of different complements of proteins. Improved electrophoretic techniques have resulted in better resolution of membrane proteins than in an earlier study of maize plastids (15), permitting a more detailed analysis of developmental changes during greening (Fig. 1).…”

Biogenesis of thylakoid networks in angiosperms: knowns and unknowns

“…The CZ contains proplastids, which possess little or no internal membrane structures and lack photosynthetic capacity. The pathway by which the thylakoid network develops as proplastids mature into chloroplasts in the process of leaf formation of the periphery of the meristem is unknown Forger and Bogorad 1973;Griffiths 1978;Gunning 1965;Ryberg and Sundqvist 1982;Sperling et al 1998;Von Wettstein et al 1995, and references therein).…”