Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid inChenopodium rubrum L. as influenced by photoperiodic flower induction

Chenopodium rubrum plants, induced to flower by three cycles of 12 h darkness and 12 h light, produced 42% less ethylene than vegetative plants kept under continuous light. Plants that had each dark cycle broken by 2 h light in the middle did not flower and produced almost as much ethylene as the vegetative plants. Shoots and roots of plants of all three experimental treatments had a similar content of 1-aminocyclopropane-1-carboxylic acid (ACC), the mean amounting to about 2 nmol · g^–1 dry weight. Also the content of N-malonyl-ACC (MACC) was similar in shoots of all three treatments. MACC content in roots was shown to be much higher, especially in the treatments with three dark periods (about 85 nmol · g^–1 dry weight). When labeled [2,3-¹⁴C] ACC was administered, the relative contents of ACC and MACC were very similar among all three treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 36% less ACC than the vegetative ones. Plants subjected to night-break converted almost as much ACC to ethylene as vegetative plants. It is concluded that flower induction in the short-day plantChenopodium rubrum decreases ethylene production by decreasing their capability of converting ACC to ethylene.     

Ethylene production and metabolism of 1-aminocyclopropane-1-carboxylic acid in a long-day plant,Chenopodium murale L., as influenced by photoperiodic flower induction

Chenopodium murale plants, induced to flower by 5 days of continuous light, produced 43% more ethylene than vegetative plants kept under short days (16 h darkness, 8 h light). The 1-aminocyclopropane-1-carboxylic acid (ACC)-induced ethylene production, using saturating ACC concentration (10 mol·m⁻³) was also 55% higher in induced plants. Their ACC and N-malonyl-ACC (MACC) levels were also higher, the former increasing by 56% in both shoots and roots, the latter by 288% and 108% in shoots and roots, respectively. Administration of labeled [2,3-¹⁴C]ACC produced a very similar relative content of ACC and MACC in both treatments. The only process influenced by flower induction was ACC conversion to ethylene. Induced plants converted 66% more ACC than the vegetative ones. The effects of photoperiod on ethylene formation and metabolism in a long-day plant (LDP)C. murale and a short-day plant (SDP)C. rubrum are compared. Ethylene formation seems to be under photoperiodic control in both species, but its role in flower induction remains obscure.     

Accumulation of 1-(malonylamino)cyclopropane-1-carboxylic acid in ethylene-synthesizing tobacco leaves

During the hypersensitive reaction of Samsun NN tobacco to tobacco mosaic virus (TMV) the inoculated leaves synthesize large quantities of ethylene. At the same time, 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC), a conjugate of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) accumulates. Smaller amounts of MACC are formed concomitant with ethylene synthesis during the normal development of tobacco leaves. The conjugate appears neither to be hydrolysed to liberate ACC, nor to be transported to other plant parts. Its accumulation thus reflects the history of the operation of the pathway of ethylene synthesis in the leaf. In floating leaf discs exogenously applied ACC was converted only slowly to both ethylene and MACC. More ethylene and less MACC were produced in darkness than in light, suggesting that environmental conditions may influence the ratio at which ACC in converted to either ethylene or MACC.     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (TriticumaestivumL .)品种“8139”(抗旱性较弱 )和“5 0 4”(抗旱性较强 )叶片ACC和MACC含量于胁迫初期下降后期升高 ,ACC合酶活性持续升高 ,乙烯释放量在 8139中下降而在5 0 4中先大幅升高而后下降。两种作用效果相反的抑制剂MGBG (抑制SAMDC活性 )和AOA (抑制ACC合酶活性 )均明显影响了两品种春小麦叶片以上各指标的变化。结果表明 ,水分胁迫下作物乙烯的释放量并不与其合成直接前体ACC的量成正相关 ;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一 ,是一种干旱适应现象 ,可能与作物的干旱忍耐形成有关 ,而MACC具有调节胁迫乙烯释放的特殊生理作用。     

Impact of photoperiodic exposures during late gestation and lactation periods on the pineal and reproductive physiology of the Indian palm squirrel, Funambulus pennanti

Studies on the maternal transfer of photoperiodic information in mammals indicate that the daily photoperiod perceived by the mother during the gestation-lactation period is communicated to the fetus either through the placenta or via the milk. However, the impact of photoperiodic exposures during gestation and lactation on the maternal pineal and reproductive physiology has not been reported for any tropical rodent. The exposure of pregnant female Indian palm squirrels (Funambulus pennanti) to constant light (24 h light:0 h dark), constant dark (0 h light:24 h dark), long daylength (14 h light:10 h dark) or short daylength (10 h light:14 h dark) during early gestation (< 30 days) resulted in the resorption of pregnancy, while during late gestation (> 30 days), it did not interfere with the maintenance of pregnancy. Alterations in photoperiodic condition during late gestation and lactation altered the postpartum recovery process. Pineal gland activity, as assessed by pineal mass, protein content and plasma melatonin, was lowest during the breeding phase, but increased gradually after parturition until the next breeding phase. During gestation and lactation, constant light, long daylength and short daylength conditions were less effective, while constant dark condition had a profound effect in depressing pineal gland activity, which subsequently advanced postpartum recovery. Hence, lactating females under constant darkness prepare themselves for next mating much earlier than females under natural daylength (12 h light:12 h dark) conditions. Therefore, photoperiodic information, mediated via the pineal gland, may be important for maintaining gestation physiology as well as postpartum recovery in female rodents.     

Stimulation of ACC-dependent ethylene production in citrus leaf discs by light

The influence of light and darkness incubation on in vivo ethylene forming enzyme (EFE) activity in citrus ( Citrus sinensis L. Osbeck cv. Salustiana) mature leaf discs was studied. Leaf discs incubated in light produced higher amounts of ethylene than in darkness. Transfer of discs from light to the dark resulted in a marked inhibition of EFE activity, whereas transfer of discs from the dark to light enhanced ethylene forming activity considerably. Light did not affect 1-aminocyclopropane-l-carboxylie acid (ACC) uptake. Incubation in a CO₂-eniiched atmosphere enhanced EFE activity both in light and in darkness, but light stimulation of EFE activity was apparently not affected by CO₂. Effects of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU, inhibitor of photosynthetic electron flow) and KCN (inhibitor of cytochrome oxidase) were studied. DCMU at 0.2 m M inhibited EFE activity in light, whereas no effect was detected in the dark. On the other hand 1 m M KCN stimulated EFE activity in the light, and no significant effect was observed in the dark. CoCl₂ at 1 m M inhibited ACC-dependent ethylene production, suggesting that ethylene production from ACC is mediated by EFE in citrus leaf discs both in light and in the dark. Cycloheximide also inhibited EFE activity in the light and no effects were detected in the dark. Therefore protein synthesis in light (perhaps EFE synthesis) could be required for the light stimulation of the in vivo EFE activity.     

Regulation of ethylene biosynthesis after short-term heat treatment in etiolated pea stems

Incubation of plant tissues at a constant elevated temperature greatly inhibits both basal and wound ethylene production. However, recovery from heat treatment is relatively rapid and is followed by stimulated ethylene production. The present investigation examines the kinetics of ethylene production after short-term heal treatment and the regulation of heat-altered ethylene production. Subapical stem segments of 7-day-old etiolated pea L. cv. Alaska) seedlings were analyzed for ethylene production, 1-aminocyclopropane-l-carboxylic acid (ACC) oxidation, and ACC and l-(malonylamino)cyclopropane-l-carboxylic acid (MACC) content after a 2-min 40°C heat pulse. The short-term heat pulse transiently inhibited ethylene production and ACC oxidation accompanied by a slight ACC accumulation within a 30-min time period. Conjugation to MACC did not appear to play an integral role in heat-regulated ethylene production. It was concluded that the major factor affecting ethylene production after heat treatment is the temporary inactivation of ACC oxidation. The possible roles of ACC synthase, ACC oxidase and lipoxygenase in regulating ethylene production after heat treatment are discussed.     

Ethylene biosynthesis in Amaranthus caudatus seeds in response to methyl jasmonate

Methyl jasmonate (JA-Me) at 10^–3 M completely inhibited Amaranthus caudatus seed germination. Exogenous ethylene could totally reverse this inhibition. The inhibitor of ethylene action, 2,5-norbornadiene (NBD), increased the sensitivity of seeds to JA-Me. Methyl jasmonate inhibited ethylene production and also decreased both 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl ACC (MACC) content. Likewise, ACC oxidase activity in vivo was decreased by jasmonate. Similarly ACC oxidase activity in vitro isolated from seeds incubated in the presence of JA-Me was lower than that isolated from untreated seeds.The inhibitory JA-Me action on seed germination seems to be mainly associated with the inhibition of ethylene biosynthesis. Both inhibition of ACC synthase and ACC oxidase activity and/or synthesis can be involved.     

Photoperiodic control of cytokinin transport and metabolism in Chenopodium rubrum

Cytokinin (CK) levels in the short-day plant Chenopodium rubrum L. are known to fluctuate diurnally. The aim of this work was to investigate if the diurnal changes are brought about by changes in transport and/or metabolism of CKs. The effect of photo-period on cytokinin transport was studied by analysing CK concentrations in root, leaf and apical exudates, respectively, under constant light (CL), a 12-h photoperiod (DL) inductive for flowering, DL in which darkness was interrupted at the end of hour 6 by 15 min red light (R), or by 15 min R followed by 30 min far-red irradiation (R/FR). The concentrations of cytokinins (zeatin, zeatin riboside, isopentenyladenine, isopen-tenyladenosine) in all three types of exudates were significantly higher in the first 12-h period after the end of 12 h darkness than in CL. The R break almost fully negated the effect of darkness and its effect was reversed by FR, showing the involvement of phytochrome in the regulation of CK transport. In the next 12-h interval, i.e. 12–24 h after the end of darkness, the CK level remained high in the leaf exudate only, but to a much lower extent than in the previous 12 h. The highest CK concentration (increase by 108%) was observed in apical exudates during inductive darkness. A comparison of the CKs present in the individual exudates indicates that those arriving at the apical part are derived mostly from leaves with varying contributions by the xylem. The metabolism of applied [³H]-zeatin riboside (ZR) was studied using HPLC separation of the metabolites. Metabolism was found to be very rapid and different glucosides, adenine and adenosine were the main metabolites after 12 h incubation with labelled ZR in all regimes tested. The only metabolite that seems to be under photoperiodic control is ZR-5′-monophosphate. It is as yet not clear if photoperiod controls the phosphorylation or dephosphorylation reaction. The activity of the main cytokinin degradative enzyme, cytokinin oxidase, did not change during the photoperiodic regimes tested.     

Different circadian rhythms regulate photoperiodic flowering response and leaf movement in Pharbitis nil (L.) Choisy

The phase shifting effect of red light on both the leaf movement rhythm, and on the rhythm of responsiveness of photoperiodic flower induction towards short light breaks (10 min red light), has been studied in Pharbitis nil, strain Violet, and comparisons between the two rhythms have been made. The phase angle differences between the rhythms after a phase shift with 2 or 6 h of red light given at different times during a long dark period were not constant. The results indicate the involvement of two different clocks controlling leaf movement and photoperiodic flower induction.Abbreviations DD continuous darkness - l:D x:y light/dark cycles with x hours of light and y hours of darkness - PPR rhythm of photoperiodic responsiveness towards light break     

Influence of experimental illumination and seasonal variation on crossbreeding mating in the snail Biomphalaria glabrata

The crossbreeding activities of the Schistosoma mansoni vector snail Biomphalaria glabrata were counted in a laboratory aquarium throughout the year under two regimes of 12h light: 12h dark from 7 A. M. to 10 P. M. Mating increased significantly in Autumn and Winter and just missed a significant inverse correlation with temperature and a direct one with locomotion. Other similar experiments were carried out to compare mating under various illumination conditions in complete daily cycle measurements. Mating counts decreased under the regimes which submitted snail to a total exposure of 12h light and 12h dark during a daily cycle in the following sequence: 12h light:12h dark alternating hourly with light gradient, 12h light:12h dark, 1h light:1h dark and 12h dark:12h light. Under two constant illuminations, the mating scored less than under the previous conditions, except under 12h dark:12h light. Under darkness the mating count was lower than under light conditions. There was no way to differentiate the night and day rhythms of mating on different days in each regime, except for mating under 12h light:12h dark alternating with light gradient, constant dark and 12h dark:12h light conditions. Mating increased in certain light and temperature conditions, in which the intensities should have an optimum value.     

Rhythmicity in cotton seedlings

Ethylene production by detached cotyledons of cotton (Gossypium hirsutum L.) seedlings grown under cycles of 12 h darkness and 12 h light has been shown to be rhythmic, with a minimum and maximum 4 and 16 h, respectively after the start of the cycle (Rikin, Chalutz and Anderson, 1984, Plant Physiol. 75, 493–495). Treatment with silver ions stimulated the rhythmic ethylene production in both regular and inverted cycles (i.e. dark period changed to light period, and vice versa). The rate of the conversion of [3,4-¹⁴C]methionine into ethylene also followed the stimulation of rhythmic ethylene evolution by silver ions in both regular and inverted cycles, while treatment with aminoethoxyvinylglycine (AVG) decreased this stimulation. Conversion of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) into ethylene was not affected by silver ions, but was dependent upon the immediate light conditions, regardless of the time in the light-dark cycle, light decreasing and darkness increasing this process. It is concluded that silver ions stimulate the normal rhythmic ethylene production, and this stimulation is regulated at a step prior to the conversion of ACC into ethylene. The rhythmicity in other processes (cotyledon movement, phenylalanine ammonia-lyase activity, resistance to the herbicide 3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide [bentazon]) was not affected by a decrease in the rhythmic changes in ethylene production by AVG or interference in ethylene action by silver ions. Thus, these rhythmic changes were not regulated by the rhythmic changes in ethylene production.Abbreviations ABA abscisic acid - ACC 1-aminocyclopropane-1-carboxylic acid - AVG aminoethyoxyvinylglycine - PAL phenylalanine ammonia-lyase     

Changes m Ethylene Production in Relation to l-Aminocyclopropane-l-Carboxylic Acid and Its Malonyl Conjugate in Waterlogged Wheat Plants

When wheat seedlings were subjected to waterlogging, 1-aminocyelopropane-l-carboxylic acid (ACC), an ethylene precursor, accumulated in large quantity in roots. In shoots, ACC and ethylene production also increased, but declined with the prolonged periods of waterlogging. However, ACC content in roots maintained in high level during the whole period of waterlogging. Drainage caused a drastic drop in both ACC content and ethylene production in waterlogged plants to control level. 1-(malonylamino) cyclopropane-l-carboxylic acid (MACC) level in roots subjected to waterlogging showed little changes. However, MACC content in shoots kept increasing during the 9-days period of waterlogging. At later period of waterlogging (longer than 5 days) when ACC and ethylene production bad dropped, the. level of MACC continued to increase. Draining stopped this increasing, but did not reduced its level. When exogenous ACC was introduced into the leaves via transpiration stream, the ability of leaves of waterlogged plant to convert ACC to MACC was much higher than control. The data presented showed that at the later stage of waterlogging, the conversien of a great quantity of ACC to MACC in waterlogged wheat plants is the cause of the reduction of ethylene production and ACC content. It was suggested that the formation of MACC is another way of regulation in ethylene biosynthesis. Among leaves of different ages, the enhancement of ethylene, ACC and MACC content was more pronounced in older leaves than in younger laves during the waterlogging period. The physiological significance of adaptation to waterlogging stress was discussed.     

Chloroplast Biogenesis: XXII. Contribution of Short Wavelength and Long Wavelength Protochlorophyll Species to the Greening of Higher Plants

The contribution of short and long wavelength membrane-bound fluorescing protochlorophyll species to the over-all process of chlorophyll formation was assessed during photoperiodic growth. Protochlorophyll forms were monitored spectrofluorometrically at 77 K during the first six light and dark cycles in homogenates of cucumber (Cucumis sativus L.) cotyledons grown under a 14-hour light/10-hour dark photoperiodic regime, and in cotyledons developing in complete darkness. In the etiolated tissue, short wavelength protochlorophyll having a broad emission maximum between 630 and 640 nm appeared within 24 hours after sowing. Subsequently, the long wavelength species fluorescing at 657 nm appeared, and accumulated rapidly. This resulted in the preponderance of the long wavelength species which characterizes the protochlorophyll profile of etiolated tissues. The forms of protochlorophyll present in etiolated cucumber cotyledons resembled those in etiolated bean leaves in their absorption, fluorescence, and phototransformability. A different pattern of protochlorophyll accumulation was observed during the dark cycles of photoperiodic greening. The short wavelength species appeared within 24 hours after sowing. Subsequently, the long wavelength form accumulated and disappeared. The long wavelength to short wavelength protochlorophyll emission intensity ratio reached a maximum (~3:1) during the second dark cycle, then declined during subsequent dark cycles. Short wavelength species were continuously present in the light and dark. Primary corn and bean leaves exhibited a similar pattern of protochlorophyll accumulation. In cucumber cotyledons, both the short and long wavelengths species appeared to be directly phototransformable at all stages of photoperiodic development. It thus appears that whereas the long wavelength protochlorophyll species is the major chlorophyll precursor during primary photoconversion in older etiolated tissues, both long wavelength and short wavelength species seem to contribute to chlorophyll formation during greening under natural photoperiodic conditions.     

The Effects of Oxygen, Carbon Dioxide and Ethylene on Ethylene Biosynthesis in Relation to Shoot Extension in Seedlings of Rice (Oryza sativa) and Barnyard Grass (Echinochloa oryzoides)

Exposing dark-grown seedlings for 3 d to oxygen deficiency (0or 5 kPa) or to additions of carbon dioxide (10 kPa) or ethylene(0·1 Pa) slowed shoot extension in Echinochloa oryzoides,while in rice it was promoted by these treatments, except that5 kPa oxygen was without effect. In E. oryzoides this was dueto reduced growth of the mesocotyl, and in rice to enhancedgrowth of the coleoptile. These responses to carbon dioxideand oxygen deficiency were not consequences of increased ethyleneproduction, since this remained unchanged by carbon dioxideand depressed by oxygen shortage in both species. Furthermore,exogenous ethylene and the ethylene action inhibitor 2,5-norbornadieneeach failed to influence extension in anoxic seedlings, indicatingno regulatory role for ethylene in the absence of oxygen. However,concentrations of the ethylene precursor 1 -aminocyclopropane-1-carboxylic acid (ACC) were increased by carbon dioxide and0 kPa or 5 kPa oxygen, although after 72 h without oxygen totalACC production (i.e. changes in ethylene + ACC + MACC) was suppressedin both species. There was little effect on bound ACC [putativemalonyl-ACC (MACC)] formation. Transferring anaerobic (0 kPa)seedlings to oxygenated conditions (21 kPa) resulted in abnormallyfast rates of ethylene formation, possibly due to the accumulationof ACC under anoxia. This post-anoxic ethylene may have contributedto the faster extension by rice coleoptiles and slower extensionby mesocotyls of E. oryzoides compared with those of seedlingsmaintained continuously in air. Echinochloa oryzoides [Ard.] Fritsch, barnyard grass, Oryza sativa L, rice, oxygen shortage, carbon dioxide, ethylene biosynthesis, shoot extension, 1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC, GC-MS     

Effects of methyl jasmonate (MeJA) on the dark-induced senescence in oat (Avena sativa L.) leaf segments

To investigate the relationship between methyl jasmonate (MeJA) and ethylene in leaf senescence, we studied the effects of MeJA on ethylene production and ethylene biosynthetic enzyme activities in oat(Avena sativa L.) leaf segments incubated in darkness. MeJA promoted dark-induced senescence judged from the contents of chlorophyll and protein, and increased ethylene production 6 times of the control. MeJA also increased the activities of ethylene biosynthetic enzymes, 1-aminocyclopropane carboxylic acid (ACC) synthase and ACC oxidase as compared to control. In MeJA-treated leaf segments, ACC synthase activity reached its maximum level at 24 h of incubation and ACC oxidase activity peaked at 6 h of incubation. Aminoethoxyvinylglycine (AVG) and Co²⁺, inhibitors of ACC synthase and ACC oxidase respectively, reduced MeJA-induced ethylene production. They also delayed leaf senescence that was promoted by the treatment of MeJA. From these results, we can suggest that MeJA increased the activities of ACC synthase and ACC oxidase, these increased activities lead to increase in ethylene production and this increased ethylene production might promote dark-induced leaf senescence.     

Rhythmicity in ethylene production in cotton seedlings

Cotyledons of cotton (Gossypium hirsutum L.) seedlings grown under a photoperiod of 12 hour darkness and 12 hour light showed daily oscillations in ethylene evolution. The rate of ethylene evolution began to increase toward the end of the dark period and reached a maximum rate during the first third of the light period, then it declined and remained low until shortly before the end of the dark period. The oscillations in ethylene evolution occurred in young, mature, and old cotyledons (7 to 21 day old). These oscillations in ethylene evolution seemed to be endogenously controlled since they continued even when the photoperiod was inverted. Moreover, in continuous light the oscillations in ethylene evolution persisted, but with shorter intervals between the maximal points of ethylene evolution. In continuous darkness the oscillations in ethylene evolution disappeared. The conversion of [3,4-¹⁴C]methionine into [¹⁴C] ethylene followed the oscillations in ethylene evolution in the regular as well as the inverted photoperiod. On the other hand, the conversion of applied 1-aminocyclopropane-1-carboxylic acid into ethylene did not follow the oscillations in ethylene evolution, but was affected directly by the light conditions. Always, light decreased and darkness increased the conversion of applied 1-aminocyclopropane-1-carboxylic acid into ethylene. It is concluded that in the biosynthetic pathway of ethylene the conversion of 1-aminocyclopropane-1-carboxylic acid into ethylene is directly affected by light while an earlier step is controlled by an endogenous rhythm.     

Carbon dioxide-independent and -dependent components of light inhibition of the conversion of 1-aminocyclopropane-1-carboxylic acid to ethylene in oat leaves

Light inhibits while carbon dioxide enhances the conversion of 1-aminocyclopropane-1-carboxylic acid (ACC) to ethylene in oat ( Avena sativa L. cv. Victory) leaf segments. The possibility that the light inhibition is mediated through changes of carbon dioxide has been investigated. The level of CO₂ increases or decreases in the sealed incubation vial in darkness or in light, respectively, which can apparently account for the differences in ACC-dependent ethylene production between the dark and light treatments. However, although the evolution of ethylene from ACC in the dark is reduced upon depletion of CO₂, the difference between light and dark is still very noticeable. Moreover, the production of the ethylene in CO₂-free air in the dark was still higher than in the light, where the concentration of CO₂ was 0.01%. It is proposed that the light effect on the conversion of ACC to ethylene is composed of two distinguishable components: one CO₂-mediated and the other CO₂-independent.