Showing papers on "Plant physiology published in 1991"

Endomycorrhizal fungi in nitrogen transfer from soybean to maize

Abstract: Using 15N as a tracer, interspecific N-transfer was studied during the course of plant development. The use of barriers of differing permeabilities between donor and receiver plants allowed separation of the effect of mycorrhizal colonization, root or hyphal contact and interplant hyphal bridging, on 15N-transfer from soybean (Glycine max (L.) Merrill) to maize (Zea mays L.). More transfer was measured between mycorrhizal plants, but transport of 15N from the labelled host plant to Glomus versiforme (Karsten) Berch did not seem to occur at the symbiotic interface, suggesting that the fungus is independent of its host for its N-nutrition, and that the role of hyphal bridges in N-transfer between plants, is not significant. Uptake by the receiver plant of the N excreted by the donor plant root system appears to be the mechanism of N-transfer between plants. The factor most affecting 15N-transfer between plants was found to be the extent of the contact between plant root systems. The presence of the endomycorrhizal fungus in plant roots reduced 15N-loss from soybean, but at the same time, its extensive hyphal network improved the efficiency of the maize root system for the recovery of the 15N excreted by soybeans. The net result was a better conservation of the N resource within the plant system. The transfer of N between mycorrhizal plants was particularly enhanced by the death of the soybean.

Molecular Activities of Plant Cells: An Introduction to Plant Biochemistry

Abstract: Plant growth and biochemistry - the connection The molecules of plant cells The structure of plant cells and their organelles Cellular energetics Enzymes and post-translational enzyme regulation Membrane structure, permeability and metabolite transport The aerobic oxidation to sugars and CO2 Secondary oxidative mechanisms in plants The light reactions of green plants The C3 carbon reduction cycle and associated processes Photorespiration C4 mechanisms of CO2 assimilation The assimilation of nitrogen from inorganic salts and gaseous N2 into amino acids Other light-coupled assimilatory and reductive mechanisms of plants Synthesis of N-containing compounds from amino acids Lipid biosynthesis and the assembly of membranes Synthesis of plant cell walls The plant genome and its replication Processes involved in the synthesis of protein The regulation of gene expression in plants The biogenesis of organelles.

The role of abscisic acid and plant growth regulators in tissue culture-induced rejuvenation of strawberry ex vitro

Abstract: Plant growth regulators applied in vitro affected strawberry plant performance ex vitro for a period of up to 4 months. Benzyl-adenine and gibberellin enhanced juvenile characteristics; in general, more runners and monofoliolate leaves were produced, net photosynthesis was reduced, leaf diffusive resistance was increased and, on occasion, flowering was delayed. In contrast, abscisic acid and a gibberellin biosynthesis inhibitor, paclobutrazol, resulted in a more adult phenotype; specifically, flowering was earlier, net photosynthesis and leaf diffusive resistance rates were equal to those of adult plants, and fewer leaves were monofoliolate. Tissue culture-produced plants reacquire the adult phenotype earlier than seedlings mature. Abscisic acid application to seedlings also resulted in earlier and increased flowering. Endogenous abscisic acid concentrations were greater in adult plants and less in tissue culture and seedling plants at 3 and 7 weeks ex vitro, after germination or after adult runner propagation. No flowering occurred at 3 weeks in any propagation type and only runner-produced plants flowered at 7 weeks. At 15 weeks, no statistical difference in abscisic acid concentrations existed among propagation treatments and all propagation types flowered. The endogenous concentrations of abscisic acid in plants propagated by all three methods were much higher at three weeks compared to concentrations at 7 or 15 weeks.

What's New in Plant Physiology The photoproteclive role of carotenoids in Mgher plants

Abstract: Andrew John YoungYoung, A. J. 1991. The photoprotective role of carotenoids in higher plants. -Physiol. Plant. 83: 702-708.Carotenoids have two important rotes in photosynthetic organisms. First, they ac! asaccessory light-harvesting pigments, effectively extending the range of light absorbedby the photosyntbetic apparatus. Secondly, they perform an essential photoprotec-tive role by quenching triplet state chlorophyll molecules and scavenging singletoxygen and other toxic oxygen species formed within the chloroplast. Only recentlyan additional, novel, protective role has been proposed for the carotenoid zeaxan-thin, involving the dissipation of harmful excess excitation energy under stress condi-tions. Zeaxanthin may be formed through de novo synthesis in response to long-termenvironmental stress, and through the rapid enzymic de-epoxidalion of the carote-noid violaxanthin (the xanthophyll cycle) in response to short-term alterations in theplant's light environment, interspecific differences occur in the ability of plants andalgae to produce zeaxanthin under stress conditions, and hence the ability to pho-toprotect the photosynthetic apparatus through this means varies from species tospecies. The ability of a plant to respond to light-mediated environmental stress byproducing zeaxanthin may therefore affect, at least in part, the ability of that plant toinhabit or colonise certain habitats (e.g. sun or shade conditions).Key words ~ Carotenoids, chlorophyll fluorescence, singlet-oxygen, xanthophyll cy-cle, zeaxanthin.A. J. Young, School of Natural Sciences, Liverpool Polytechnic, Byrom Street,Liverpool U 3AF, UK.