Plant Science Letters最新文献

The distribution of phosphoproteins within spinach chloroplasts was studied. Intact chloroplasts with good rates of CO₂-dependent oxygen evolution were fed [γ-³²P]ATP and then separated into stroma and membrane fractions. Only one major labelled stroma protein was identified by gel electrophoresis/autoradiography, with a mol. wt. of 66 000. The membranes were separated into envelopes and thylakoid fractions. Three labelled proteins were separated by gel electrophoresis in the envelope with mol. wt. of 50 500, 29 000 and 13 000.

RNase-gold complexes were applied to thin sections of glutaraldehyde-fixed and Spurr's resin-embedded corn root tips in order to assess the specificity of these gold complexes for RNA in meristematic cells. Numerous micrographs showed that among cellular compartments, nucleoli, nuclei and portions of the cytoplasm were densely labelled whereas cell walls and vacuoles were infrequently labelled. A number of controls used to test the specificity of the labelling showed that RNase-gold was bound to RNA in the cells. Quantitative evaluation of the labelling performed on the samples using morphometric and X-ray microanalysis confirmed the qualitative distribution of RNase-gold based on visual evidence. Minor discrepancies were apparent between morphometric and X-ray microanalysis results. These results show that corn root tissues fixed and embedded in this way retain RNA in a form which can be labelled effectively with RNase-colloidal gold complexes.

The isolation of cotton anther callus protoplasts is greatly enhanced when the amino acids arginine, serine or glycine, or the divalent cations Ca²⁺ or Mg²⁺ are included in the enzyme mixture. These compounds stabilize cotton protoplasts in the presence of RNase found in the cellulase enzyme mixture. The inhibition of RNase-induced lysis may involve cation or amino acid protection of critical membrane proteins during protoplast isolation. Using these protective agents, cotton protoplasts will give rise to macroscopic callus colonies after 3 weeks in culture.

Chlorella pyrenoidosa cells were grown with 22.5 μM cerulenin (Ce) (a specific inhibitor of fatty acid biosynthesis) for 72 h and the effects on the lipid and fatty acid compositions of the individual lipid classes were examined. Ce-treatment resulted in higher levels of palmitic and linolenic acids, while the level of linoleic acid was strongly reduced. A marked reduction in the galactolipid (GL) content, and especially that of digalactosyl diglyceride (DGDG), was found in Ce-treated cells. Phospholipids (PLs) in Ce-treated cells became richer in phosphatidylethanolamine (PE), whereas the levels of phosphatidyglycerol (PG) and phosphatidylcholine (PC) hardly changed. The monogalactosyldiglyceride (MGDG), DGDG and PC were richer in unsaturated fatty acids in treated cells. Fluorescence polarization of 1,6-diphenylhexa-1,3,5-triene (DPH) indicated more fluid membranes in Ce-treated cells, as assayed on isolated PL multibilayers.

The quantitative and qualitative differences in the lipid composition of Ce-treated Chlorella are discussed in relation to herbicide resistance, and confirm the importance of the native composition of thylakoids in the herbicide-binding function.

Epicuticular wax on the adaxial leaflet side of blackberry (Rubus fruticosus) occurred as wax knobs and irregular-shaped platelets. Removal of the epicuticular wax by a collodion film revealed the wax-free cuticle surface. This allowed the selective extraction of epicuticular wax from the film and subsequently of intracuticular wax from the cuticle. Epicuticular wax amounted to approx. 90% of total cuticular wax, only about 10% were present as intracuticular wax. The epicuticular wax contained mainly alcohol acetates, free alcohols and esters with lesser amounts of fatty acids and alkanes. Intracuticular wax was composed of free alcohols, alcohol acetates and fatty acids together with small proportions of triterpenoid acids, alkanes and esters.

In microsomes from Cucurbita hypocotyls a duroquinone (DQ) stimulated NADH oxidase was found which is strongly activated by addition of 0.01–0.1% Triton X-100. After density gradient centrifugation and polyethyleneglycol (PEG) fractionation this enzyme occurs in membranes carrying plasma membrane markers. Another NADH oxidase localized at the endoplasmic reticulum (e.r.) is not activated but inhibited by Triton. The data are consistent with closed and outside-out plasma membrane vesicles where the NADH site becomes accessible only after detergent permeabilization. A role of the enzyme in transmembrane transport of electrons and/or protons is discussed.

Early changes in the morphological organization of the ovary wall of Pisum sativum L. cv. Alaska during the transformation of the ovary into young developing fruit were studied. Changes in either pollinated or unpollinated and gibberellic acid (GA₃)-treated ovaries were very similar and were characterized by a rapid enlargement of mesocarpic cells and an increase in the number of cell ‘layers’ in the endocarp. Unpollinated and untreated ovaries in emasculated flowers continued growing slowly until 2 days after anthesis and then began to degenerate. Degeneration was initiated in the endocarp, and on day 4 after anthesis the endocarp cells were completely wrinkled and no cellular ‘layers’ were distinguishable. The beginning of endocarp degeneration was coincident with the loss of sensitivity of unpollinated ovaries in response to GA₃.

Starch phosphorylase from leaves of the C₄-plant corn (Zea mays L.) could be separated into two peaks of activity by chromatography on DEAE-cellulose (or by (NH₄)₂SO₄ gradient solubilization). Subsequent polyacrylamide gel electrophoresis under native conditions revealed a slowly migrating phosphorylase for the peak eluting first from DEAE-cellulose and a major, fast migrating phosphorylase for the peak eluting second. The latter peak contained also two very minor bands which migrated even faster than the other two phosphorylases. When phosphorylases were extracted from mesophyll protoplasts and from bundle sheath strands (isolated by the enzymatic isolation procedure) it was the slowly migrating phosphorylase which was associated with the mesophyll cells and the major, fast migrating phosphorylase which originated from the bundle sheath cells. The findings are discussed in view of similar isoenzymes of phosphorylase reported for chloroplasts and cytosol in leaves of C₃-plants.

Enrichment of air with carbon dioxide up to 1200 μl ṡ 1⁻¹ air results in lower transpiration rates from oat (Avena sativa) seedling leaves held in the light at 30% relative humidity. Carbon dioxide treatment also enhances the release of ethylene from leaves treated with 1-aminocyclopropane-1-carboxylic acid (ACC). Thus, while the uptake of ACC via the transpiration stream is depressed by 33% by carbon dioxide enrichment, the release of ethylene from a given amount of ACC is increased by 400%. Neither ethylene nor ACC appear to affect the transpiration rate. The enhancement of ACC-dependent ethylene release cannot be simply correlated with stomatal behaviour.

Callus was obtained from leaf sheath segments in barnyardgrass (Echinochloa oryzicola Vasing) cultured on Murashige and Skoog's (MS) inorganic medium containing 2, 5 or 8 mg/l of 2,4-dichlorophenoxyacetic acid (2,4-D) and 3% (w/v) sucrose. Callus was subcultured for over 18 months on the medium containing vitamins and 2,4-D, and was then transferred to media containing cytokinin or auxin at various concentrations. Shoot formation and root formation, through somatic embryogenesis from the callus, were stimulated by addition of cytokinin and auxin, respectively. Regenerated plants were diploid and tetraploid. Diploid plants were green and grew to maturity in soil. Tetraploid plants were albino and did not grow into mature plants.