P. J. A. McCombs

Bio: P. J. A. McCombs is an academic researcher from University of Auckland. The author has contributed to research in topics: Kinetin & Phosphorylation. The author has an hindex of 2, co-authored 2 publications receiving 67 citations.

Evidence for modification of protein phosphorylation by cytokinins.

Abstract: Kinetin stimulated phosphorylation of protein in floated Chinese-cabbage leaf discs, but inhibited protein phosphorylation in nuclei+chloroplast extracts from Chinese-cabbage or tobacco leaves. Kinetin also inhibited protein phosphorylation in isolated tobacco nuclei or nuclei from carrot secondary-phloem tissue. Purified Chinese-cabbage leaf ribosomes exhibited protein kinase activity which was inhibited by kinetin and zeatin. The ribosome-associated kinase responded to kinetin and zeatin differently from that associated with nuclei+chloroplast preparations. Protein phosphorylation in vitro was not affected by adenosine 3′:5′-cyclic monophosphate, indol-3-ylacetic acid or gibberellic acid. It was only inhibited by N 9 -unsubstituted purines, among which the known cytokinins were the most effective inhibitors. The results are discussed in relation to possible similarities between the effects of cytokinins in plant tissues and the effects of adenosine 3′:5′-cyclic monophosphate in animal tissues. Both compounds appear to modify the activity of protein kinases and both affect many different cellular processes.

Protein, nucleic acid and starch metabolism in the duckweed, Spirodela oligorrhiza, treated with cytokinins.

Abstract: Bacteria-free cultures of Spirodela oligorrhiza continue to increase in frond number for 2 to 3 days after transfer to darkness. There is then no further increase in frond number for 3 to 4 weeks, although DNA, RNA and protein synthesis continue at decreased rates and starch accumulates in the plants. We refer to such ;non-growing' plants in darkness as dormant. Adding kinetin to dormant Spirodela initiated increased DNA, RNA and protein synthesis within 1h, although new fronds were not detected until 24h after the addition of kinetin. The frond number then continued to increase. Starch accumulated in dormant plants. Accumulation of starch appeared to be a consequence of inhibition of growth rather than the converse. No evidence was obtained for a block in [(14)C]glucose metabolism that might explain the lack of growth in darkness in the absence of kinetin. In darkness, more ribosomes were membrane-bound in dormant Spirodela than in Spirodela growing with kinetin. Similarities between the response of Spirodela to darkness, stringent control in bacteria and pleiotypic controls in animal cells are discussed. It is suggested that all three processes are ultimately controlled by specific protein kinases that are individually sensitive to different effectors.

Phosphorylation of chloroplast membrane polypeptides

Abstract: ILLUMINATION of chloroplast thylakoids leads to the formation of the so-called high energy state of the membrane1–3. The establishment of this state is accompanied by several structural changes within the membrane, including a conformational change in the coupling factor4, increased accessibility of photosystem II to the chemical probe p-diazonium benzene sulphonate5, and a reduction in the thickness of the partition between stacked thylakoids6. I describe here a rather different type of structural change that has not previously been reported for chloroplast membranes—protein phosphorylation. Like the above changes, protein phosphorylation is a reversible, energy-dependent membrane modification, but it differs from the other changes in that it takes the form of a specific chemical reaction involving certain identifiable chloroplast membrane polypeptides. The most conspicuous of these polypeptides is the light-harvesting chlorophyll a/b binding protein, the most abundant thylakoid polypeptide7.

Growing Duckweed to Recover Nutrients from Wastewaters and for Production of Fuel Ethanol and Animal Feed

Abstract: Lemnaceae or duckweed is an aquatic plant that can be used to recover nutrients from wastewaters. The grown duckweed can be a good resource of proteins and starch, and utilized for the production of value-added products such as animal feed and fuel ethanol. In the last eleven years we have been working on growing duckweed on anaerobically treated swine wastewater and utilizing the duckweed for fuel ethanol production. Duckweed strains that grew well on the swine wastewater were screened in laboratory and greenhouse experiments. The selected duckweed strains were then tested for nutrient recovery under laboratory and field conditions. The rates of nitrogen and phosphorus uptake by the duckweed growing in the laboratory and field systems were determined in the study. The mechanisms of nutrient uptake by the duckweed and the growth of duckweed in a nutrient-limited environment have been studied. When there are nutrients (N and P) available in the wastewater, duckweed takes the nutrients from the wastewater to support its growth and to store the nutrients in its tissue. When the N and P are completely removed from the wastewater, duckweed can use its internally stored nutrients to keep its growth for a significant period of time. A modified Monod model has been developed to describe nitrogen transport in a duckweed-covered pond for nutrient recovery from anaerobically treated swine wastewater. Nutrient reserve in the duckweed biomass has been found the key to the kinetics of duckweed growth. Utilization of duckweed for value-added products has a good potential. Using duckweed to feed animals, poultry, and fish has been extensively studied with promising results. Duckweed is also an alternative starch source for fuel ethanol production. Spirodela polyrrhiza grown on anaerobically treated swine wastewater was found to have a starch content of 45.8% (dry weight). Enzymatic hydrolysis of the duckweed biomass with amylases yielded a hydrolysate with a reducing sugar content corresponding to 50.9% of the original dry duckweed biomass. Fermentation of the hydrolysate using yeast gave an ethanol yield of 25.8% of the original dry duckweed biomass. These results indicate that the duckweed biomass can produce significant quantities of starch that can be readily converted into ethanol.

Diversity, classification and function of the plant protein kinase superfamily.

Abstract: Eukaryotic protein kinases belong to a large superfamily with hundreds to thousands of copies and are components of essentially all cellular functions. The goals of this study are to classify prote...