Glycine metabolism in etiolated barley leaves on exposure to light

Of a large number of amino acids examined, changes in glycine were the only ones which were correlated with the ability of dark-grown barley leaves to synthesise protochlorophyllide, δ-aminolaevulinic acid and chlorophyll on exposure to light. A rapid depletion was found in endogenous glycine in barley leaves after day 7. Illumination of the leaves increased the rate of glycine depletion. Glycine concentrations were high throughout the young leaf. The top and middle leaf sections however, which had maximal chlorophyll synthesising potential exhibited the most pronounced decrease in glycine as the leaf aged. Using glycine-[¹⁴C] pulse techniques the half life of glycine in 7 and 14-day-old dark-grown leaves was 3.5 and 4.4 min respectively. Light treatment lengthened the half life to 6.9 and 12.1 min in 7 day and 14-day-old-leaves. Sustained illumination continued to decrease glycine turnover.     

The effect of haem on chlorophyll synthesis in barley leaves

Exogenously supplied bovine haemin, fed to etiolated barley leaves, inhibited chlorophyll synthesis in leaves exposed to light. Haemin inhibited the regeneration of protochlorophyllide (P650) and the conversion of exogenously supplied δ-aminolaevulinate (ALA) to protochlorophyll (P630). The effect of haemin on chlorophyll production was overcome by incubating the leaves in water in the dark before light treatment, suggesting the operation of a rapid haem destruction mechanism in leaves. Protohaem turnover in dark-grown leaves was between 8 and 9 hr, based on the rate of degradation of erogenous haemin and the rate of protohaem breakdown in laevulinic acid (LA) treated leaves. The rate constant for haem destruction was 85 pmol/nmol/hr in the dark and 45 pmol/nmol/hr after 4 hr light. There was no evidence that light affects the synthesis of protohaem. It appears that the regulation of endogenous levels of protohaem is by breakdown and it is this mechanism which is under light control. Haem considerably decreased the incorporation of radioactivity from glycollate-[¹⁴C], glycine-[¹⁴C] and glutamate-[¹⁴C] into accumulated ALA in the presence of LA.     

Haem and chlorophyll formation in etiolated and greening leaves of barley

The amounts of protochlorophyllide (P650) and protohaem were measured in ageing dark-grown barley leaves. Maximum amounts of P650 and protohaem were found in 6- to 8-day-old material after which P650 declined rapidly and protohaem more slowly. In leaves exposed to light maximum chlorophyll was produced in 6-day-old material with progressively less the older the leaves. Haem concentrations increased in seedlings of all ages exposed to light. A lag phase was observed for both chlorophyll and haem formation in leaves given a light treatment. Haem, however, showed a slight yet sig nificant decline as chlorophyll production commenced. The results indicate that chlorophyll and haem synthesis share a common pool of δ-aminolae vulinic acid (ALA). At a certain stage of development, the magnesium porphyrin pathway diverts precursors away from haem synthesis. It is only when the ALA synthesising system is well developed that the production of ALA can satisfy pathways to both haem and chlorophyll. The observed changes in haem under certain conditions suggest that, as in animal systems, haem levels may regulate porphyrin formation (chlorophylls) by controlling the supply of ALA.     

Chlorophyll formation and glycine metabolism in laevulinic acid treated barley leaves

Laevulinic acid (LA) inhibited chlorophyll formation and δ-aminolaevulinic acid (ALA) accumulation in dark-grown barley leaves. Mole ratios (ALA: chlorophyll × 8) indicate that LA decreased ALA production by about 30%. The turnover of glycine-[¹⁴C] in 7-day-old leaves treated with LA was 70% slower than in control tissue and this resulted in an increase in endogenous glycine. Total amino acid also increased in LA treated leaves. The data indicate that any contribution made by glycine to ALA synthesis in LA-treated barley leaves would be significantly restricted.     

The effect of kinetin on chlorophyll synthesis in ageing etiolated barley leaves exposed to light

Etiolated barley seedlings lose the ability to produce chlorophyll and soluble protein on exposure to light with increasing age. Similarly, the production of δ-aminolaevulinic acid-dehydratase and succinyl-CoA synthetase is decreased in older etiolated leaves exposed to light. The rate of protochlorophyllide₆₅₂ regeneration decreased well before the rates of exogenous δ-aminolaevulinic acid conversion to protochlorophyllide₆₃₂ was affected by ageing. Application of kinetin retarded these ageing symptoms in the etiolated leaves.     

Relationships between glycollate and formate metabolism in greening barley leaves

The activities of enzymes catalysing glycollate oxidation, formate production and folate-dependent formate utilization were examined in the primary leaves of Hordeum vulgare cv Galt. Seedlings were grown for 6 days in darkness and then transferred to continuous light (500 μinsteins/m² per sec) for up to 5 days. Cell-free extracts of the primary leaves contained glycollate oxidase (EC 1.1.3.1), 10-formyltetrahydrofolate synthetase (EC 6.3.4.3), 5, 10-methylenetetrahydrofolate dehydrogenase (EC 1.5.1.5) and ability to enzymically decarboxylate glyoxylate. These activities increased during greening and at the end of the light treatment were 70–450% higher than etiolated controls. Greened primary leaves also incorporated [¹⁴C]formate at rates that were three- to four-fold higher than shown by etiolated leaves. The specific activity of 10-formyltetrahydrofolate synthetase was decreased by 20–35% when the leaves were greened in the presence of 10 mM hydroxysulphonate. This inhibitor also reduced the incorporation of [¹⁴C]formate by up to 45%. A potential flow of carbon from glycollate to 10-formyltetrahydrofolate via glyoxylate and formate was suggested by the data.     

The turnover of chlorophyll in greening wheat leaves

A method for the estimation of chlorophyll turnover in wheat leaves is presented. This is based on the inhibition of chlorophyll synthesis by treatment of the cut leaves with laevulinic acid (LA), a competitive inhibitor of δ-aminolaevulinic acid dehydratase. The turnover of chlorophyll in young, greening leaves, given short periods of light was a relatively rapid process. However, in seedlings exposed to light for longer periods the turnover became progressively slower, and was measured in days rather than hours.     

Effect of carnitine on greening barley leaves

Carnitine increases chlorophyll production in greening barley leaves. [Methyl-¹⁴C]carnitine fed to greening leaves was not utilized as a carbon sou     

Phosphatidylethanolamine in wheat and barley leaves under water stress

Phosphatidylethanolamine could not be detected in the leaves of less drought-tolerant varieties of wheat (S-308) and barley (BG-25) when the plants wer     

Lipid metabolism in ageing leaves of dark-grown barley seedlings

The rapid senescence of the etiolated leaves of dark-grown barley seedlings in the dark is accompanied by the loss of those lipids associated with the plastids. The linolenate content of the plastid glycerolipids rapidly decreased whereas it tended to increase in the extraplastidic phospholipids. Kinetin treatment slowed down the loss of the plastid lipids and their constituent fatty acids. The hormone treatment brought about increased linolenate, particularly in phosphatidylcholine and monogalactosyldiacylglycerol. The senescing leaf attempts to adapt to ageing by increased membrane synthesis and/or membrane repair. Kinetin appears to control the sequential desaturation of oleate to linolenate.     

Metabolism of protein,peptides and aminoacids in ageing etiolated barley leaves

Both light- and dark-grown primary leaves of barley show a reduction in protein after about 7 days. With this reduction in protein there is a rise in t     

In vitro stability of nitrate reductase from barley leaves

Barley seedling nitrate reductase was stabilized in vitro without the use of extraneous protein by optimizing the buffer components. The extraction buffer (NRT 8.5) consists of 0.25 M Tris-HCl, pH 8.5, 3 mM DTT, 5 μM FAD, 1 μ M sodium molybdate and 1 mM EDTA. This buffer stabilizes the extracted nitrate reductase at O° and 30°, whereas the addition of extraneous protein to standard extraction buffers stabilizes the enzyme only at 0°.     

Glyceride metabolism and gluconeogenesis in barley endosperm

Endosperms of quiescent barley grains contained, on average, 54.5 μg of neutral glyceride-glycerol, equivalent to ca 480 μg glyceride. Of this probably 90% was located in the aleurone layer. During germination the level of glyceride-glycerol declined. It also declined in degermed grains and aleurone layers incubated in vitro. The fall was accelerated by GA₃, but indoleacetic acid, kinetin and glutamine were without effect. Increases in the levels of malate synthase and isocitrate lyase from very low initial values, and the results of incorporation studies with [¹⁴C]-labelled substrates, indicate that the glyoxylate cycle functions to convert glycerides to sucrose in germinating grains and degermed grains incubated with GA₃, but not in degermed grains without the hormone. In the absence of GA₃ the glyceride could be a respiratory substrate in degermed grains. The aleurone layers converted exogenous glucose to sucrose. Little label from [¹⁴C]-amino acids appeared in sucrose but in some cases considerable incorporation occurred into glutamine.     

Tissue localization of phytochrome in dark-grown barley leaves

Phytochrome was spectrophotometrically determined to be differentially concentrated among separated tissues of dark-grown, norflurazon-treated barley l     

Zinniol induces chlorophyll retention in barley leaves: the selective action of a non host-specific phytotoxin

A biologically active compound was isolated from liquid cultures of Alternaria tagetica and identified as zinniol. The selective action of zinniol, a non host-specific phytotoxin which induces necrosis in a number of unrelated plant species, has been demonstrated: enhanced chlorophyll retention occurs in zinniol-treated leaf tissue of three cereal species.     

Carnitine content of greening Barley leaves

The carnitine content of etiolated barley leaves doubled on exposure to light. After 24 hr exposure the carnitine content was the same as that of barle     

Desaturation of oleate-[14C] in leaves of barley

Etiolated barley leaves when exposed to light desaturate oleate-[¹⁴C] to linoleate. The production of substantial amounts of radioactive linolenate was found only in very young, tightly rolled leaves. In oleate-[¹⁴C] pulse experiments, radioactive linolenate first appeared in phosphatidylcholine (PC) and only after a lag period did it begin to accumulate in monogalactosyldiacylglycerol (MGDG). The results indicate that in young, immature barley leaves linolenate is synthesized from oleate on the parent lipid, PC, and is then transferred to MGDG.     

Effects of light and temperature on the composition of epicuticular wax of barley leaves

The amount of wax/cm² on expanding primary leaves of Bonus barley depends on both the photo- and thermoperiods in which the seedlings are grown. With a temperature cycle of 15–10°, transfer of dark grown leaves to the light stopped leaf expansion and after 24 hr yielded 2·5 times more wax/cm² than is characteristic for light grown leaves. This demonstrates that wax synthesis and extrusion is not directly correlated with leaf expansion. The relative amounts of the wax classes formed by the decarboxylation pathways (< 1%), the reductive pathways (89%) or only by elongation (10%) are the same in light and dark. Within the reductive pathways, however, light stimulates aldehyde formation. Both environmental parameters can strongly influence the chain length composition of the wax classes. In the light one chain length or one group of chain lengths dominates a given wax class. In the dark two prominent chain lengths or groups thereof are found. The major chain length in these two groups differs by two or more carbons.     

Control of carbohydrase formation by gibberellic acid in barley endosperm

α-Amylase, limit dextrinase and α-glucosidase were induced by gibberellic acid in barley grain from which the embryos had been excised. The responses to different concentrations of gibberellic acid were similar for the three carbohydrases. However α-glucosidase activity increased before the other two enzymes, and a low level of α-glucosidase was found in ungerminated grain. Experiments with cycloheximide and density-labelling in deuterium oxide suggest that the observed increases in activity are the result of de novo protein synthesis. The induction of these enzymes was reduced by pre-incubation in actinomycin D.     

Photochlorophyllide (P650) turnover in dark-grown barley leaves

Laevulinate (LA) induced an increase in protochlorophyllide (P650) in dark-grown ageing barley leaves. The increase was due to a suppression of a P650 breakdown mechanism. The LA inhibition of P650 destruction allowed an estimate to be made of turnover of P650 in ageing etiolated leaves. The rate constant for P650 destruction in 8-day-old dark-grown leaves was 139 pmol/nmol/hr with a half life of 5 hr.