Lonchocarpus cultratus (Vell.) A.V.G. Azevedo & H.C. Lima (Fabaceae) growth under different shade and water availability conditions

ABSTRACT Light and water availability are among the environmental factors that most influence plant growth and development. The ability to acclimate to shade and tolerate drought can be assessed by growth characteristics. Thus, the objective of this study was to analyze the effect of water availability and shading on the initial growth of Lonchocarpus cultratus, a tree species, common name ‘embira-de-sapo’, abundant in several areas of South and Southeastern Brazil. The experiment was arranged in a 3x2 factorial completely randomized design. The plants were kept under 0%, 50%, and 80% shading and two conditions of water availability (daily irrigation - ID and twice a week - NDI). The variables height, root length, dry biomass of leaves, stem, and root were evaluated at 30, 60 and 90 days after emergence (DAE). Total, a, and b chlorophyll, mycorrhizal colonization, and nodulation were determined. Death of young plants maintained at 0% NDI occurred at the beginning of growth. At 90 DAE, plants kept under 80% shading and ID showed the highest height and etiolated plants due to the reduction of light intensity in this treatment. Over the experimental period, 0% and 50% shaded plants irrigated daily had the highest percentage of mycorrhizal colonization, and nodulation was observed in all plants regardless of the treatment.

Water-soluble chlorophyll protein is involved in herbivore resistance activation during greening of Arabidopsis thaliana

Water-soluble chlorophyll proteins (WSCPs) constitute a small family of unusual chlorophyll (Chl)-binding proteins that possess a Kunitz-type protease inhibitor domain. In Arabidopsis thaliana, a WSCP has been identified, named AtWSCP, that forms complexes with Chl and the Chl precursor chlorophyllide (Chlide) in vitro. AtWSCP exhibits a quite unexpected expression pattern for a Chl binding protein and accumulated to high levels in the apical hook of etiolated plants. AtWSCP expression was negatively light-regulated. Transgenic expression of AtWSCP fused to green fluorescent protein (GFP) revealed that AtWSCP is localized to cell walls/apoplastic spaces. Biochemical assays identified AtWSCP as interacting with RD21 (RESPONSIVE TO DESICCATION 21), a granulin domain-containing cysteine protease implicated in stress responses and defense. Reconstitution experiments showed tight interactions between RD21 and WSCP that were relieved upon Chlide binding. Laboratory feeding experiments with two herbivorous isopod crustaceans, Porcellio scaber (woodlouse) and Armadillidium vulgare (pillbug), identified the apical hook as Achilles’ heel of etiolated plants and that this was protected by RD21 during greening. Because Chlide is formed in the apical hook during seedling emergence from the soil, our data suggest an unprecedented mechanism of herbivore resistance activation that is triggered by light and involves AtWSCP.

Activities of amine oxidase, peroxidase and catalase in seedlings of Pisum sativum L. under different light conditions

The activities of amine oxidase, peroxidase and catalase were studied in 12 cultivars of field pea (Pisum sativum L.) and one accession of wild pea (Pisum sativum subsp. transcaucasicum). The influence of different light conditions on the enzyme activities was studied in extracts of 8-d-old seedlings. Substantially higher amine oxidase activity was detected in etiolated pea seedlings than in plants growing under controlled light conditions (12h photoperiod). Higher peroxidase and catalase activities indicate more intensive production of toxic hydrogen peroxide evolved by reactions of different type in green plants in comparison with etiolated ones. Significantly lower activity of peroxidases in etiolated plants could be related to a lower degree of lignification. Marked differences in enzyme activities between etiolated field pea and P. sativum subsp. transcaucasicum were observed for all studied enzymes. A very interesting result was the exceptionally low activity of amine oxidase in etiolated plants that was hardly detectable in green plants of Malton cultivar. Two bands with amine oxidase activity were found by the method of native PAGE in extracts of 8-d-old plants. A different relationship of these isoenzymes was detected in field pea and wild pea. Two isoenzymes were present in pea shoots but only one isoenzyme was detected in pea roots. Amine oxidase isoenzymes were studied in the roots and shoots of cv. Smaragd for three weeks. The profile of isoenzymes was opposite in 8- and 36-d-old stems of pea.

Effect of Norflurazon on Resorcinolic Lipid Metabolism in Rye Seedlings

Norflurazon is a selective pyridazinone herbicide excessively employed in the control of many annual grasses and broad-leaved weeds. This chemical causes plant bleaching due to the inhibition of the carotenoid pigment biogenesis as well as induces irreparable changes to chloroplasts, which are considered the organelles where the biosynthesis of resorcinolic lipids takes place. Resorcinolic lipids, a group of phenolic compounds, constitute not only an essential part of the plant antifungal defense system, but also are an important component of the human cereal diet. The aim of this study was to investigate the effect of norflurazon on the biosynthesis of resorcinolic lipids in 5-day-old rye plants (Secale cereale L.) that were grown at three different temperatures under light or dark conditions. At all tested temperatures, norflurazon decreased the fresh biomass of light-grown rye seedlings and increased the weight of plants grown in darkness. Compared with respective controls, this herbicide caused an increase in total content of alkylresorcinols in both green and etiolated plants with the exception of dark-grown norflurazon-treated rye at 29 °C. The general level of saturated homologues was markedly decreased by norflurazon in all etiolated plants and in light-grown seedlings at 15 °C. Independent of thermal and light conditions, in all norflurazon-treated samples two alkylresorcinol derivatives predominated: 1,3-dihydroxy-5-n-heptadecylbenzene and 1,3-dihydroxy-5-n-nonadecylbenzene. Thus, our results suggest that norflurazon affected the metabolism of alkylresorcinols in rye seedlings and its action was dependent on external stimuli.

Effect of chilling and acclimation on the activity of glutamine synthetase isoforms in maize seedlings

Effects of chilling and acclimation on the activity of cytosolic (GS1) and plastidic (GS2) isoforms of glutamine synthetase (E.C. 6.3.1.2) were studied in chilling-sensitive and acclimation-responsive maize inbred G50. Glutamine synthetase activity in mesocotyls and roots of chilled (7 d/4?C) and rewarmed (1 d/27?C) etiolated plants was "1/3 that of controls. In coleoptiles+leaves of light-grown plants, GS1 was reduced to 75%, and GS2 to 50%. Acclimation (3 d/14?C) increased GS activity and alleviated the effects of chilling. Exposure to H2O2 or menadione also reduced GS activity. Since chilling causes oxidative stress in maize, acclimation probably preserves GS activity by protecting GS from oxidative inactivation. .

15N NMR SPECTROSCOPIC STUDY OF AMMONIUM ION ASSIMILATION BY SPIRODELA OLIGORRHIZA—LEMNACEAE—AS AFFECTED BY LIGHT AND CARBON SUPPLY IN GREEN AND EXTOLIATED PLANTS

Nitrogen assimilation and amino acid production in Spirodela oligorrhiza plants exposed to 30 mM 15NH4Cl was studied using l5N NMR spectroscopy. Green and etiolated plants were studied under different light regimes and in the presence of added carbon, either as sucrose or as α-ketoglutarate. Etiolated plants are capable of ammonium assimilation and, as in green plants, this occurs via the glutamine synthetase/glutamine oxoglutarate amine transferase (GS/GOGAT) and the aspartate aminotransferase/asparagine synthetase pathways. The major assimilation products in both etiolated and green plants were glutamine and asparagine. Thus our results confirm that N-amides are key detoxification products when plants are exposed to external ammonium ion, and act as storage reservoirs or sinks for assimilated ammonium. In plants grown under continuous light, ammonium ion was taken up and assimilated to completion. L-methionine DL-sulfoximine, a GS inhibitor, inhibited ammonium ion assimilation but not its uptake. Addition of azaserine, a GOGAT inhibitor, resulted in the disappearance of α-amino signals, and l5N incorporation into the glutamine amide-N position only. This is evidence for the operation of the GS/GOGAT pathway, as opposed to the glutamate dehydrogenase (GDH) pathway, in both green and etiolated plants. Even in the dark and under various stress conditions, no sign of ammonium ion assimilation via the GDH pathway could be detected. The amount of amino acid metabolites strongly depended on the light regime and the extent of external carbon supply. Supply of α-ketoglutarate to the etiolated plants increased ammonium ion uptake and assimilation. Ornithine and arginine were also formed, consistent with the operation of the ornithine cycle.