Hr Of Illumination Research Articles

Light and nutritional regulation of transcripts encoding a wheat protein kinase homolog is mediated by cytokinins.

Many metabolic processes in plants are regulated by phosphorylation of proteins by kinases, but little is known of the roles that specific protein kinase play in the various signal transduction pathways or the mechanisms by which these kinases themselves are regulated. We report here the isolation of a gene, wpk4, encoding a putative protein kinase from wheat that appears to belong to the SNF1 kinase subfamily and that shows increased transcript levels in response to multiple stimuli: light, nutrient deprivation, and cytokinin application. Although wpk4 mRNA is undetectable in etiolated seedlings, it rapidly accumulates within 1 hr of illumination. General nutrient deprivation also increases wpk4 mRNA levels, but only under light conditions. In addition, of the various phytohormones tested, cytokinin (N6-benzylaminopurine) specifically increases wpk4 mRNA levels regardless of the light conditions, whereas in the presence of a cytokinin antagonist the level of wpk4 mRNA is not increased by either light or nutrient deprivation. These results suggest that the light and nutrient signals that induce wpk4 mRNA accumulation may be mediated through cytokinins and provide a strong basis for examining the coordinated regulation of protein phosphorylation by light, cytokinins, and nutritional cues in a single transduction pathway.

Influence of 1,10-phenanthroline, a photodynamic herbicide, on the ultrastructure of mesophyll cells and photosynthetic activity in greening pea seedlings

We have examined the ultrastructure of mesophyll cells and photosynthetic activity induced by a photodynamic herbicide, 1,10-phenanthroline (Phe), in greening pea seedlings. Greening pea seedlings treated in darkness and subsequently illuminated were resistant to low doses (2 mM) of Phe. Pea plants treated with 10 or 20 mM Phe were susceptible to light, CO 2 evolution in Phe-treated plants proceeded at a much higher rate than the rate of CO 2 uptake. Net photosynthesis rate ( Pn) was extremely low in Phe-treated plants. Ultrastructure of mesophyll cells was the same in control, Phe 10 and Phe 20 plants before transfer of plants to light. Differences between control and Phe-treated plants became visible after 4 hr of illumination and increased during 9 hr of illumination. This difference was manifested in thylakoid swelling, dilation of endoplasmic reticulum (ER) cisternae, degeneration of internal mitochondrial membranes and disruption of chloroplast envelopes. There were starch grains in control but not in Phe-treated plant mesophyll cells. A standard photoinhibition mechanism might explain the destruction caused by phenanthroline and subsequent illumination. In the present paper we suggest another possible mechanism, also based on chelating properties of Phe, which could directly cause membrane depolarization and thus change membrane permeability. One of these mechanisms might explain the structural and functional effects of Phe action.

Light-mediated control of translational initiation of ribulose-1, 5-bisphosphate carboxylase in amaranth cotyledons.

In cotyledons of 6-day-old amaranth seedlings, the large subunit (LSU) and the small subunit (SSU) polypeptides of ribulose-1,5-bisphosphate carboxylase are not synthesized in the absence of light. When dark-grown seedlings were transferred into light, synthesis of both polypeptides was induced within the first 3 to 5 hr of illumination without any significant changes in levels of their mRNAs. In cotyledons of light-grown seedlings and of dark-grown seedlings transferred into light for 5 hr (where ribulose-1,5-bisphosphate carboxylase synthesis was readily detected in vivo), the LSU and SSU mRNAs were associated with polysomes. In cotyledons of dark-grown seedlings, these two mRNAs were not found on polysomes. In contrast to the SSU message, mRNAs encoding the nonlight-regulated, nuclear-encoded proteins actin and ubiquitin were associated with polysomes regardless of the light conditions. Similarly, mRNA from at least one chloroplast-encoded gene (rpl2) was found on polysomes in the dark as well as in the light. These results indicate an absence of translational initiation in cotyledons of dark-grown seedlings which is specific to a subset of nuclear- and chloroplast-encoded genes including the SSU and LSU, respectively. Upon illumination, synthesis of both polypeptides, and possibly other proteins involved in light-mediated chloroplast development, was induced at the level of translational initiation.

Light-Mediated Control of Translational Initiation of Ribulose-1,5-Bisphosphate Carboxylase in Amaranth Cotyledons

In cotyledons of 6-day-old amaranth seedlings, the large subunit (LSU) and the small subunit (SSU) polypeptides of ribulose-1,5-bisphosphate carboxylase are not synthesized in the absence of light. When dark-grown seedlings were transferred into light, synthesis of both polypeptides was induced within the first 3 to 5 hr of illumination without any significant changes in levels of their mRNAs. In cotyledons of light-grown seedlings and of dark-grown seedlings transferred into light for 5 hr (where ribulose-1,5-bisphosphate carboxylase synthesis was readily detected in vivo), the LSU and SSU mRNAs were associated with polysomes. In cotyledons of dark-grown seedlings, these two mRNAs were not found on polysomes. In contrast to the SSU message, mRNAs encoding the nonlight-regulated, nuclear-encoded proteins actin and ubiquitin were associated with polysomes regardless of the light conditions. Similarly, mRNA from at least one chloroplast-encoded gene (rpl2) was found on polysomes in the dark as well as in the light. These results indicate an absence of translational initiation in cotyledons of dark-grown seedlings which is specific to a subset of nuclear- and chloroplast-encoded genes including the SSU and LSU, respectively. Upon illumination, synthesis of both polypeptides, and possibly other proteins involved in light-mediated chloroplast development, was induced at the level of translational initiation.

Photodynamic inactivation of red cell uroporphyrinogen decarboxylase by porphyrins

1. 1. The effects of light and porphyrins on the activity of red cell uroporphyrinogen decarboxylase were studied. 2. 2. Photoinactivation of uroporphyrinogen decarboxylase was dependent on uroporphyrin concentration, irradiation time and temperature. Using 40 W/m 2 of UV light intensity, 40–45% decreased activity was produced with 200 μM uroporphyrin I, at 37°C and after 2 hr of illumination. 3. 3. It has been demonstrated that porphyrins photoinactivate uroporphyrinogen decarboxylase and a mechanism for this action in relation to skin lesions is proposed.

Glycerolipid synthesis in Avena leaves during greening of etiolated seedlings I. Lipid changes in leaves.

Etiolated seedlings of Avena sativa L. were illuminated under fluorescent light of 1,500 lux at 25°C and the lipid changes in their first leaves and isolated plastids were followed during 24 hr of greening. Lipid changes were divided into a degradation phase [0 hr of illumination (hr-L) to 3 hr-L] and a synthetic phase (3 hr-L to 24 hr-L). In the degradation phase, which paralleled prolamellar body transformation in the plastids, both plastidic lipids, monogalactosyldiglyceride (MGDG), digalactosyldiglyceride (DGDG), sulfoquinovosyldiglyceride (SQDG) and phosphatidylglycerol (PG), and extraplastidic lipids, phosphatidylcholine (PC), phosphatidylethanolamine (PE) and phosphatidylinositol (PI), were partially degraded. Plastidic lipids (except DGDG) began to increase at 1.5 hr-L without the de novo synthesis of fatty acids, at the same time that there was a temporary accumulation of diglyceride, whose fatty acids were similar to the fatty acids of phospholipids such as PC, PE and PI, but different from the fatty acids of DGDG. This suggests that there is conversion of phospholipids to plastidic lipids during the later degradation phase. During the later degradation phase and the early synthetic phase (until 6 hr-L), plastid division occurred, resulting in a 30% increase in the plastid number per cell. Plastidic lipids were synthesized rapidly during the synthetic phase, in accordance with the beginning of light-enhanced fatty acid synthesis and thylakoid proliferation. In addition, the fatty acid composition of the plastidic lipids changed markedly throughout the synthetic phase : in MGDG, DGDG and SQDG, α-linolenate increased as linoleate decreased at both the C-1 and C-2 positions of sn-glycerol; in PG, α-linolenate increased in compensation for the decrease in linoleate at C-1 and hexadecenoate (3t) appeared and increased in compensation for the decrease in palmitate at C-2. This is evidence of the parallel desaturation of linoleate to linolenate at both C-1 and C-2 of MGDG, DGDG and SQDG, and also of the position-specific desaturation of linoleate to linolenate at C-1 of PG and of palmitate to hexadecenoate at C-2 of PG. The formation of hexadecenoate was entirely light-dependent. Extraplastidic lipids increased slightly in the early synthetic phase (3 hr-L to 6 hr-L), but declined later.

Effect of Gibberellic Acid, Indole-3-Acetic Acid and 1-Ascorbic Acid on the Regulation of RNA Metabolism in De-etiolated Barley Shoot

Summary The effect of exogenous application of GA 3 IAA and I-ascorbic acid on free nucleotide pool, the content and synthesis of RNA and acid RNase activity was studied in intact barley shoot at the end of 96 hr of dark germination or 72 hr in darkness followed by 24 hr of illumination. Light was inhibitory to RNA synthesis, but enhanced RNase activity. The latter was further stimulated by all the three growth regulators which resulted into a fall in RNA level. Light and growth regulators acted in a synergistic manner in case of free nucleotide pool and RNase activity, whereas in case of RNA level their interaction was antagonistic.

Growth Regulation by Ethylene in Fern Gametophytes. III. Inhibition of Spore Germination

Spores of Onoclea sensibilis were investigated for inhibition of germination by ethylene. A curve of germination against ethylene concentration indicated a “threshold” type of response, but percentage of spore germination was not influenced either by the density of the inoculum or by the presence of 1 % sucrose in the culture medium. Ethylene totally inhibited dark germination, but in white light reversal of inhibition was possible in about 50% of the germinating spores. Time-course studies revealed that in imbibed spores ethylene inhibited germination in the first 3 ± 1 hr of illumination. Dose-response curves of light intensity vs. germination indicated that the response to light differed in the presence and absence of ethylene. Recovery from inhibition was possible once ethylene was allowed to escape, and the rate of recovery was accelerated by light.

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. III. INHIBITION OF SPORE GERMINATION

Spores of Onoclea sensibilis were investigated for inhibition of germination by ethylene. A curve of germination against ethylene concentration indicated a “threshold” type of response, but percentage of spore germination was not influenced either by the density of the inoculum or by the presence of 1 % sucrose in the culture medium. Ethylene totally inhibited dark germination, but in white light reversal of inhibition was possible in about 50% of the germinating spores. Time‐course studies revealed that in imbibed spores ethylene inhibited germination in the first 3 ± 1 hr of illumination. Dose‐response curves of light intensity vs. germination indicated that the response to light differed in the presence and absence of ethylene. Recovery from inhibition was possible once ethylene was allowed to escape, and the rate of recovery was accelerated by light.

Factors affecting vegetative growth and the production of perithecia in culture by Ophiobolus graminis. II. Variations in light and temperature

Sixty-one isolates of O. graminis were shown to be obligate photosporulators. Fertile perithecia developed only when the cultures were exposed to light of between 65 and 360 f.c., with a maximum at 200 f.c. The temperature range for the production of fertile perithecia was between 13 and 24°c, with the optimum at 20°. Studies on the interaction of light and temperature showed that when cultures received sufficient light, temperature controlled perithecial numbers. Light most effective in photosporulation was of wavelengths between 390 and 450 mμ. Red light neither inhibited nor stimulated reproduction. At least 12 hr of illumination was required, and perithecial numbers per unit area increased with increasing light period until the cultures dried out.

Light-dependent hydrogen evolution by Scenedesmus

The effect of glucose and the uncoupler Cl-CCP upon hydrogen production was studied in adapted cells of Scenedesmus obliquus D3. Cl-CCP at 10(-5)M concentration completely inhibited the evolution of H2 in the dark and increased the apparent rate of H2 evolution in the light. At 10(-5)M Cl-CCP, photosynthesis and photoreduction by anaerobically adapted algae were only temporarily inhibited; O2 evolution reappeared after approximately 1 hr of illumination if CO2 was present. Increasing the Cl-CCP concentration to 5 x 10(-5)M led to a maximum rate of photohydrogen production and fully inhibited H2 evolution, photoreduction and dark H2 evolution. H2 evolution was accompanied by a release of varying amounts of CO2 in the light, as well as in the dark. Dark CO2 production was stimulated by Cl-CCP. H2 evolution in the light was stimulated by adding glucose to autotrophically grown cells or by growing the cells heterotrophically with glucose; starvation had an opposite effect. Adapted cells released (14)CO2 from the 3 and/or 4 position of specifically labeled glucose, indicating that degradation occurred via the Embden-Meyerhof pathway. The amount of H2 released by autotrophically grown cells was the same either with continuous illumination or with short periods of light, followed by darkness. Scenedesmus mutant No. 11, which is unable to evolve O2 was not inhibited in its capacity to evolve H2 in the light. These data indicate that the evolution of H2 in the light by adapted Scenedesmus depends upon the degradation of organic material and does not require the production of free O2 by photosystem II.

Comparative indexes of thyroid function in sheep.

The effects of light and temperature on thyroid activity of sheep were assessed by four methods: thyroid secretion rate, zero time per cent uptake of I131, I131 output half-time, and measurement of the thyroid epithelial cell height. Increased ambient temperature inhibited thyroid activity as evaluated by all methods. Reduced temperatures consistently resulted in a depressed uptake of I131. I131 output half-time had no relationship with actual hormone secretion. Light alterations imposed the same trend on thyroid function when activity was assessed by secretion rate and cell height measurement. As evaluated by these two methods the lowest thyroid activity was observed at 12 hr of illumination per day and increased with both increasing and decreasing light beyond this 1:1 light-to-dark ratio. When the three isotopic measures of thyroid activity were correlated with the histological method the highest correlation was found between cell height and thyroid secretion.