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.     

补充蓝光对设施栽培油桃光合性能及糖酸积累的影响

以设施曙光油桃(Prunus persica cv. ‘Shuguang’)为试材, 设置补充蓝光处理, 测定了生育期内5个关键时期叶片的光合性能相关参数及果实的糖酸组分, 并观察了叶片气孔的变化情况。结果表明: 补充蓝光后油桃叶片的净光合速率提高, 叶绿素a和b含量增加, 叶绿素a/b显著降低, 叶面积增大; 气孔开放提前并较早达到最大开度, 且关闭延迟。叶片中检测到的主要同化物为果糖、葡萄糖和山梨醇, 以山梨醇为主; 果实中则为果糖、葡萄糖、山梨醇和蔗糖, 成熟期以蔗糖为主。补充蓝光处理的叶片中3种同化物积累较少, 而果实中总糖和蔗糖含量较高, 表明蓝光处理提高了光合同化物从叶片到果实的转运转化能力。草酸是叶片和果实中主要的有机酸, 补充蓝光处理的果实中有机酸含量显著降低, 糖酸与对照相比提高了30.5%。硬核期后是蓝光处理提高果实糖酸比的关键时期, 此时补充蓝光可改善设施油桃光合性能及果实品质, 这一技术措施有望应用到设施果树的栽培中。     

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 flexible interrelation between AOX respiratory pathway and photosynthesis in rice leaves.

Alternative respiratory pathway was investigated in rice seedlings grown under total darkness, light/dark cycle, or continuous light. The capacity of the alternative pathway was relatively higher in leaves that had longer light exposure. An analysis of rice AOX1 multigene family revealed that AOX1c, but not AOX1a and AOX1b, had a light-independent expression. The alternative oxidase (AOX) inhibitor, salicylhydroxamic acid (SHAM, 1mM), inhibited nearly 68% of the capacity of the alternative pathway in leaves grown under different light conditions. The plants grown under different light periods were treated with SHAM and then were exposed to illumination for 4h. The transition from dark to 4h of light stimulated the capacity of alternative pathway in etiolated rice seedlings and in those grown under light/dark cycle, whereas the capacity of the alternative pathway was constant in seedlings grown under continuous light with additional 4h of illumination. Etiolated leaves did not show any CO(2) fixation after 4h of illumination, and the increase in chlorophyll content was delayed by the SHAM pretreatment. When seedlings grown under light/dark cycle were moved from dark and exposed to 4h of light, increases in chlorophyll content and CO(2) fixation rate were reduced by SHAM. Although these parameters were stable in plants grown under continuous light, SHAM decreased CO(2) fixation rate but not the chlorophyll content. These results indicate that the role and regulation of AOX in light are determined by the developmental stage of plant photosynthetic apparatus.     

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.     

叶黄素循环和D1蛋白周转在毛竹叶片光保护中的作用

利用叶绿素荧光技术,对强光胁迫下以及叶黄素循环抑制剂-二硫苏糖醇(DTT)和D1蛋白合成抑制剂-硫酸链霉素(SM)处理后毛竹(Phyllostachys edulis (Carr.) Lehaie)的光抑制特征进行研究。结果显示:在夏季中午强光或人为强光胁迫下,毛竹叶片最大光化学效率Fv/Fm均显著降低;在下午光强减弱或黑暗、弱光条件下,Fv/Fm可有效恢复。DTT和SM均可抑制毛竹叶片非光化学淬灭(NPQ),且DTT效果明显优于SM。另外,在强光下,DTT和SM处理均能使毛竹叶片Fv/Fm、实际光化学效率Y(Ⅱ)和光化学淬灭qP等荧光参数下降幅度增大。研究结果表明毛竹叶片具有完善的光破坏防御机制,NPQ与叶黄素循环和D1蛋白周转紧密关联,在叶片光保护机制中具有重要作用。     

Protoheme turnover and chlorophyll synthesis in greening barley tissue

Studies in which ¹⁴C-labeled precursors were fed to etiolated barley leaves (Hordeum vulgare L. var. Proctor) yielded chlorophyll and protoheme having similar specific radioactivities. These findings indicate: (a) there appears to be a rapid turnover of protoheme in the absence of net synthesis; (b) both pigments probably originate from a single 5-aminolevulinic acid pool; (c) the efficient utilization of glutamate-1-¹⁴C and the relatively poor utilization of glycine-2-¹⁴C suggest that 5-aminolevulinic acid is probably synthesized by a pathway other than 5-aminolevulinic acid synthetase (succinyl CoA-glycine succinyltransferase) in agreement with previously published work; (d) protoheme turnover appears to be faster under conditions which allow for rapid chlorophyll accumulation; (e) difference spectra indicate that mitochondrial cytochromes make a relatively minor contribution to the total heme in barley leaves. These findings are discussed in the light of current knowledge about tetrapyrrole regulation in photosynthetic organisms.     

Influence of Light of Different Spectral Compositions on Growth and Metabolism of Citrus Seedlings

Sour orange (Citrus aurantium L.) seedlings grown for six months under covers transmitting light of different spectral composition, were compared with others grown under a white cover (control) and outside in full daylight. The intensity of transmitted light was equalized under all covers and attained only 20% of full daylight. Seedlings grown in daylight were shorter, had more internodes, smaller leaves, less chlorophyll and more ascorbic acid than the others. Blue + far-red covers (no transmission between 560–700 nm) enhanced seedling length, the protein and chlorophyll content and peroxidase activity of leaves. When also the wave-range above 700 nm was cut out (blue) seedlings were the shortest, and leaves had very high protein and chlorophyll content, but much less ascorbic acid and lower peroxidase activity. Red + far-red covers (no transmission below 500 nm) enhanced seedling length more than blue + far-red; leaves contained as much protein as control, but had relatively high chlorophyll and peroxidase activity. Ascorbic acid was as low as in blue light.     

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.     

Phytochrome and hormonal control of expansion and greening of etiolated wheat leaves

Summary Unrolling of etiolated wheat leaf segments is stimulated by short periods of exposure to red light. Both gibberellic acid and kinetin will stimulate unrolling in the dark, whereas abscisic acid (ABA) inhibits the unrolling response to these two hormones and to red light. Exposure to 5 minutes of red light leads to a rapid increase in endogenous gibberellin levels in etiolated wheat leaves, and this increase is followed by a rapid decline. Pre-treatment with ABA inhibits the increase in gibberellin levels in response to red light, but the ihibitory effect of ABA on unrolling cannot be ascribed only to its effect on gibberellin levels. Pre-treatment with red light reduces the lag-phase in chlorophyll development when wheat leaf segments are subsequently exposed to white light; the effect of red light may be replaced by pre-treatment with kinetin, but gibberellic acid is relatively ineffective in this respect.     

Fate of the porphyrin cofactors during the light-dependent turnover of catalase and of the photosystem II reaction-center protein D1 in mature rye leaves

The apoprotein of the enzyme catalase (EC 1.11.1.6) was shown to exhibit a light-dependent turnover in leaves. Present results indicate that photoinactivation of the enzyme was not accompanied by a synchronous destruction and new synthesis of its heme moiety. In rye (Secale cereale L.) leaves the catalase content was not depleted in light when porphyrin synthesis was inhibited by gabaculine. Photoinactivation of purified bovine liver or rye leaf catalase in vitro was not accompanied by concomitant damage to the heme groups. Both the incorporation of -[³H]aminolevulinic acid ([³H]ALA) into catalase-heme and its apparent turnover increased with irradiance. However, the apparent half-life of the catalase-heme was much longer than that of its apoprotein. It is probable that not only degradation but also an exchange with the free heme pool contributed to the apparent turnover of radioactivity of the catalase-heme. Part of the chlorophyll (Chl) associated with photosystem II (PS II) had a preferential light-induced turnover, and repair of PS II appeared to require new Chl synthesis also in mature green rye leaves. The activity of PS II, indicated by the ratio of variable to maximal fluorescence (F_v/F_m), rapidly declined in the presence of gabaculine in light and the reaction-center proteins D1 and D2 were depleted. When segments of mature green rye leaves were labeled with [³H]ALA and incorporation into Chl-protein complexes analysed after electrophoretic separation in the presence of Deriphat, the highest radioactivity was observed in the core complex of PS II, while PS I and the light-harvesting complex of PS II (LHC II) were unlabeled. In greening etiolated leaves highest incorporation was observed in LHC II. Both the incorporation of [³H]ALA into the PS II core complex of green rye leaves and its turnover increased with irradiance. However, the apparent half-life of the PS II-bound labeled porphyrin compounds (mainly Chl) was considerably longer than that of the reaction-center protein D1 under identical conditions.Abbreviations ALA -aminolevulinic acid - CII Core complex of PS II - Chl chlorophyll - DMSO dimethyl sulfoxide - F_v/F_m ratio of variable to maximal chlorophyll fluorescence - LHC light-harvesting complex - PAR photosynthetically active radiation We thank the Deutsche Forschungsgemeinschaft for financial support. Technical assistence by B. Kramer and Ch. van Oijen is greatly appreciated. We are grateful to Dr. Johanningmeier and Dr. Godde (Lehrstuhl für Biochemie der Pflanzen, Universität Bochum, Germany) for providing antisera against the D1 and D2 proteins and Dr. M. Schmidt (Botanisches Institut, Universität Frankfurt am Main, Germany) for valuable advice. Deriphat 160 was kindly supplied by Henkel Corp., Hoboken, N.J., USA.     

Control of delta-Aminolevulinic Acid and Chlorophyll Accumulation in Greening Maize Leaves upon Light-Dark Transitions

The accumulation of δ-aminolevulinic acid (ALA) was studied in greening maize (Zea mays) leaves which were transferred to darkness and reilluminated after various periods of time. The system synthesizing ALA decays in the dark with a half-life of about 80 minutes. The onset of enzyme decay after transfer to darkness shows a 40-minute lag. The accumulation of ALA in the presence of levulinic acid in leaves transferred to darkness corresponds to that expected from the estimated half-life of the enzyme synthesizing ALA. On the other hand, the accumulation of protochlorophyll upon transfer to darkness in the absence of levulinic acid stops much earlier. It is suggested that a control point exists in the pathway between ALA and protochlorophyll, preventing utilization of the accumulated ALA upon transfer of greening leaves to darkness. This is supported by the observed effects of low intensities of monochromatic light (648 nm) on ALA and chlorophyll accumulation.     

The Effect of Phytohormones on Chlorophyll(ide), Protochlorophyll(ide) and Carotenoid Formation in Greening Dark Grown Wheat Leaves

The influence of phytohormones on chlorophyll and carotenoid formation during the greening of irradiated dark grown wheat leaves (Triticum aestivum L. cv. Starke II Weibull) was studied. Leaves were floated on solutions of abscisic acid, gibberellic acid and kinetin for 24 h. The chlorophyll and carotenoid contents were determined during a subsequent period of 48 h of continuous irradiation. Leaves treated with abscisic acid showed a longer lag phase and a lower rate of accumulation of chlorophyll as compared to the control than did leaves treated with gibberellic acid and kinetin. The carotenoid content was low both in leaves treated with abscisic acid and in those treated with gibberellic acid. Treatment with abscisic acid lowered the protochlorophyllide regeneration after a saturating light flash while gibberellic acid as well as kinetin had no effect. The influence of ABA was partly dependent on an increase of the wounded part of the cut leaf segments. The accumulation of protochlorophyllide in leaves treated with δ-aminolevulinic acid was not affected by the different hormonal treatments. These results suggest that the main effect of abscisic acid is probably outside the chloroplast, i.e. on the formation or transport of δ-aminolevulinic acid.     

Protochlorophyll/Chlorophyll Conversion by Single Flash Illumination

Previous studies (Smith and Benitez 1954) have shown the rate of the photochemical conversion of protochlorophyll to chlorophyil- a in etiolated leaves to be proportional to the product of the light intensity used and the duration of the illumination.
This relation, however, is considered to be valid only in the case of moderate light intensities and relatively short periods of illumination. Thus Koski (1950) found a reduction of the total content of pigments in etiolated corn leaves following 180 sec illumination of 150 fc (approximately 1600 lux); she considered this to be a destructive effect of the light. Virgin (1955) found a considerable destruction of chlorophyll to take place in etiolated barley leaves during illumination with 600 fc (about 6500 lux).
In the present paper it is shown that by using very high light intensities and very short periods of illumination it is possible to transform approximately 40 percent of the protochlorophyll of etiolated wheat leaves to chlorophyll- a without effecting any light induced loss of the total content of pigments.     

Control of chlorophyll production in rapidly greening bean leaves

The possible involvement of nucleic acid and protein synthesis in light-regulated chlorophyll formation by rapidly greening leaves has been studied.

Removing leaves from illumination during the phase of rapid greening results in a reduction in the rate of pigment synthesis; cessation occurs within 2 to 4 hours. Etiolated leaves which exhibit a lag in pigment synthesis when first placed in the light do not show another lag after a 4 hour interruption of illumination during the phase of rapid greening.

Actinomycin D, chloramphenicol, and puromycin inhibit chlorophyll synthesis when applied before or during the phase of rapid greening. Application of δ-amino-levulinic acid partially relieves the inhibition by chloramphenicol.

It is suggested that light regulates chlorophyll synthesis by controlling the availability of δ-aminolevulinic acid, possibly by mediating the formation of an enzyme of δ-aminolevulinate synthesis. This process may result from gene activation or derepression; the involvement of RNA synthesis of some sort is suggested by the inhibitory effect of actinomycin D on chlorophyll production by rapidly greening leaves.

     

Metabolism of Oat Leaves during Senescence : VII. The Interaction of Carbon Dioxide and Other Atmospheric Gases with Light in Controlling Chlorophyll Loss and Senescence

In air largely freed from CO₂, senescence of isolated oat (Avena sativa cv Victory) seedling leaves is no longer prevented by white light; instead, the leaves lose both chlorophyll and protein as rapidly as in the dark. Senescence in light is also accelerated in pure O₂, but it is greatly delayed in N₂; 100% N₂ preserves both protein and chlorophyll in light and in darkness. In light in air, most of the compounds tested that had previously been found to delay or inhibit senescence in darkness actually promote the loss of chlorophyll, but they do not promote proteolysis. Under these conditions, proteolysis can therefore be separated from chlorophyll loss. But in light minus CO₂, where chlorophyll loss is rapid in controls, two of these same reagents prevent the chlorophyll loss. Unlike the many reagents whose action in light is thus the opposite of that in darkness, abscisic acid, which promotes chlorophyll loss in the dark, also promotes it in light with or without CO₂. Kinetin, which prevents chlorophyll loss in the dark, also prevents it in light minus CO₂. In general, therefore, the responses to light minus CO₂ are similar to the responses to darkness, and (with the exception of abscisic acid and kinetin) opposite to the response to light in air.     

Alteration of photosystem II properties with non-photochemical excitation quenching

Oxygen yield from single turnover flashes and multiple turnover pulses was measured in sunflower leaves differently pre-illuminated to induce either 'energy-dependent type' non-photochemical excitation quenching (qE) or reversible, inhibitory type non-photochemical quenching (qI). A zirconium O2 analyser, combined with a flexible gas system, was used for these measurements. Oxygen yield from saturating single turnover flashes was the equivalent of 1.3-2.0 micromole(-) m(-2) in leaves pre-adapted to low light. It did not decrease when qE quenching was induced by a 1 min exposure to saturating light, but it decreased when pre-illumination was extended to 30-60 min. Oxygen evolution from saturating multiple turnover pulses behaved similarly: it did not decrease with the rapidly induced qE but decreased considerably when exposure to saturating light was extended or O2 concentration was decreased to 0.4%. Parallel recording of chlorophyll fluorescence and O2 evolution during multiple turnover pulses, interpreted with the help of a mathematical model of photosystem II (PS II) electron transport, revealed PS II donor and acceptor side resistances. These experiments showed that PS II properties depend on the type of non-photochemical quenching present. The rapidly induced and rapidly reversible qE type (photoprotective) quenching does not induce changes in the number of active PS II or in the PS II maximum turnover rate, thus confirming the antenna mechanism of qE. The more slowly induced but still reversible qE type quenching (photoinactivation) induced a decrease in the number of active PS II and in the maximum PS II turnover rate. Modelling showed that, mainly, the acceptor side resistance of PS II increased in parallel with the reversible qI.     

Effects of Cycloheximide and Light on Leaf Senescence in Maize and Hydrangea

The senescence of maize and hydrangea leaves after detachmentand darkening was studied in terms of the loss of chlorophylland protein. Chlorophyll contents of the detached leaves decreasedin the dark in both plants. Cycloheximide at 0.1 mM effectivelyinhibited the loss of chlorophyll in maize, but did not do soin hydrangea. Continuous irradiation with white light of 4.6Wm^–2 prevented the loss of chlorophyll in hydrangea leaves,while it caused bleaching of maize leaves. Reducing agents suchas ascorbic acid and glutathione did not prevent the bleachingby light. In maize leaves, the amount of protein decreased inthe dark more slowly than that of chlorophyll, and cycloheximideslightly prevented the protein decrease. Continuous light irradiationof 4.6 Wm^–2 delayed the loss of protein more effectivelythan cycloheximide did. (Received January 31, 1981; Accepted May 21, 1981)     

Chlorophyll accumulation and breakdown in light-grown barley transferred to darkness: effect of seedling age

Diurnally grown barley (Hordeum vulgare L. cv. Clipper) seedlings of various ages (3–4, 5–6 and 10–11-days-old) were transferred to darkness for 17 h and changes in leaf fresh weight, chlorophyll a, chlorophyll b and protochlorophyllide measured. The results were consistent with previous evidence of a light-independent chlorophyll biosynthetic pathway in light-grown barley. There was a net gain in chlorophyll (μg leaf^-1) in 5–6- and 10–11-day-old plants after 17 h dark treatment. The amounts of chlorophyll that accumulated were similar (5.9 and 4.3 μg Chl leaf^-1), despite a twofold difference in leaf size at T₀. The rate of leaf expansion in 5–6-day-old plants greatly exceeded the rate of chlorophyll accumulation and leaves were noticeably paler after dark treatment i.e. there was a reduction in chlorophyll concentration (μg g fresh weight^-1) in spite of an increase in chlorophyll content (μg leaf^-1). The ability of light-grown barley to accumulate chlorophyll in darkness was a function of seedling age. Very young seedlings (3–4-day-old) generally lost chlorophyll in darkness. The decrease in chlorophyll per leaf resulted mainly from loss of chlorophyll b. Preferential loss of chlorophyll b resulted in dramatic increases in the chlorophyll a:b ratio. Since 3–4-day-old seedlings (1) accumulated 5-aminolevulinic acid in the presence of levulinic acid at a rate comparable to older seedlings, and (2) converted exogenous 5-aminolevulinic acid to chlorophyll in the absence of light, it is unlikely that failure of the youngest plants to accumulate chlorophyll in darkness was due to blocks at these steps in the pathway. Net loss of chlorophyll (μg leaf^-1) in 3–4-day-old seedlings in darkness was eliminated by the addition of chloramphenicol, which occasionally produced a small, but significant, gain in total chlorophyll. These results imply that chlorophyll degradation in young barley leaves is strongly influenced by the chloroplast genome, and is a major factor influencing changes in chlorophyll levels in darkness. The present findings are consistent with the suggestion that the failure of 3–4-day-old barley seedlings to accumulate chlorophyll in darkness may be due to chlorophyll turnover in which the rate of degradation exceeds the rate of synthesis.     

The photosynthetic unit in chlorella measured by repetitive short flashes

Apparent size of the photosynthetic unit in Chlorella pyrenoidosa was estimated by the method of Emerson and Arnold: rate of oxygen evolution was measured under repetitive saturating flashes of about 10-microsecond duration separated by dark periods of 0.033 to 0.100 second. Cells used were taken from six steady state cultures maintained at different light intensities. Cell characteristics included a variation in chlorophyll content from 1 to 5%. Apparent size of the photosynthetic unit varied systematically with chlorophyll content in the range of 1560 to 2350 chlorophylls per O₂ per flash. Values for unit size showed no unusual statistical distribution and were not changed significantly by addition of low level background light at 645 or 705 nanometers. Maximal rate of unit turnover, calculated from light-saturated rate and unit size, varied inversely with chlorophyll content in the range of 70 to 180 per second.