外源ABA对黄瓜幼苗抗低温胁迫的作用

在光照下对黄瓜(Cucuntis sativus L.)离体子叶圆片和幼苗分别使用10~(-6)mol/l 与10~(-4)mol/l ABA 处理,有防御低温伤害的作用,表现为降低子叶圆片的电解质渗漏,阻抑幼苗子叶的谷胱甘肽含量的下降和膜脂过氧化产物丙二醛(MDA)的累积,减缓叶片的光合作用的下降和叶绿素荧光的猝灭,提高幼苗的存活率。但这种作用可被黑暗和光合抑制剂(DCMU)所限制。     

Chilling Injury in Cotton {Gossypium hirsutum L.): Light Requirement for the Reduction of Injury and for the Protective Effect of Abscisic Acid

Pretreatment by darkness increased chilling (4°C) injuryin whole cotton (Gossypium hirsutum L.) seedlings and isolatedcotyledonary tissue. Addition of sucrose in the dark periodprevented the effect of darkness. Application of the photosyntheticinhibitor DCMU in light simulated the effect of darkness. ABA(10^–5 M) decreased chilling injury when applied in lightas a pretreatment before the onset of chilling. The same pretreatmentin darkness was almost ineffective, unless sucrose was added.ABA applied in light together with DCMU was ineffective in decreasingchilling injury. Lower light intensity resulted in increasedchilling injury and a decreased effect of ABA in the preventionof chilling injury. The antimicrotubular drug colchicine increased the chillinginjury. Pretreatment with ABA in light decreased the chillingand colchicine injury while the same pretreatment in darknesswas ineffective. These results suggest that a deficiency of a photosyntheticproduct increases the chilling sensitivity of the tissue. ABAapparently increases chilling resistance through a metabolicprocess which depends on photosynthetic activity. ³ Incumbent of the Seagram Chair in Plant Sciences (Received November 20, 1980; Accepted January 31, 1981)     

光和暗条件下低温对黄瓜和水稻叶绿素蛋白质复合体的影响

本试验以黄瓜和水稻幼苗为材料,研究了光照和黑暗条件下低温对植物叶绿素蛋白质复合体的影响。SDS—PAGE电泳结果表明:5℃及12h 280μmol m~(-2)S~(-1)处理2d,Chl-蛋白质复合体的降解明显大于5℃暗低温处理;低温与光照对P700-CPa_1的影响大于LHCP。叶绿素荧光测定表明;5℃及12h 280μmol m~(-2)s~(-1)的处理对PSⅡ的影响亦大于暗低温处理。由此认为:低温与光对植物叶绿体的PSⅠ和PSⅡ都有明显的影响,其机理可能与常温下高光强引起的光抑制相类似;不同的是低温下中等光强就能引起光抑制。因此,在光照低温下往往加剧植物冷害的发生。     

Amelioration of chilling stress by triadimefon in cucumber seedlings

Cucumber (Cucumis satvus L.) seeds were imbibed in distilled water (control) and 10 mg l^–1 triadimefon (TDM) for 10 h and then grown in a plant growth chamber with a light/dark temperature of 28/20 °C and a photoperiod of 14 h with a light intensity of 60 µmol m^–2 s^–1. 14-day-old seedlings were exposed to chilling stress with a light/dark temperature of 6/3 °C for 4 d. TDM improved the growth rate of cucumber seedling subjected to chilling stress and increased photosynthetic pigments contents and relative water content compared with the control at the end of chilling stress. Chilling stress decreased protein content and the activities of SOD, CAT and POD, but it increased proline, H₂O₂ and MDA accumulation, and relative electrical conductivity. TDM ameliorated the injury caused by chilling stress by preventing decreases in protein content and the activities of SOD, CAT and POD and by inhibiting increases in proline, H₂O₂ and MDA contents, and relative electrical conductivity, which suggested that TDM ameliorated the negative effect of chilling stress.     

Role of carbohydrates in diurnal chilling sensitivity of tomato seedlings

Tomato seedlings (Lycopersicon esculentum Mill.) chilled starting at different times during the light/dark cycle were most chilling-sensitive at the end of the dark period (AI King, MS Reid, BD Patterson 1982 Plant Physiol 70: 211-214). Low-temperature tolerance was regained with as little as 10 minutes of light exposure. Low light intensities were less effective than high light intensities in reducing sensitivity, and the length of exposure to light directly influenced sensitivity. Seedlings kept at low night temperatures prior to chilling were also less injured following chilling. Light also restored chilling tolerance to seedlings whose roots were removed. Supplying cut shoots with sucrose, glucose, or fructose reduced chilling sensitivity and largely eliminated the diurnal difference in sensitivity. Endogenous carbohydrate content was correlated with changes in chilling sensitivity; starch and sugar content fell markedly during the dark period. Increased concentrations of sugars were detected 15 minutes after the start of the light period. This evidence all suggests that changes in chilling sensitivity over the diurnal period are regulated by the light cycle. It also suggests that increased sensitivity at the end of the dark period could be due to carbohydrate depletion, and that chilling tolerance following light exposure is likely due to carbohydrate accumulation or closely related events.     

Inhibition of photosystems I and II and enhanced back flow of photosystem I electrons in cucumber leaf discs chilled in the light

Pre-illumination of cucumber leaf discs at a chilling temperature in low-irradiance white light resulted in accelerated re-reduction of P700(+) [the special Chl pair in the photosystem I (PSI) reaction centre] when the far-red measuring light was turned off. Measurements (in +/- methyl viologen or +/- DCMU conditions) of the re-reduction half time suggest that accelerated re-reduction of P700(+) appeared to be predominantly due to charge recombination and only partly due to reductants sustained by previous cyclic electron flow around PSI. Apparently, charge recombination in PSI was greatly enhanced by inhibition of forward, linear electron flow. Inhibition of PSII electron transport was observed to occur to a lesser extent than that of PSI, but only if the measurement of PSII functionality was free from complications due to downstream accumulation of electrons in pools. We suggest that promotion of controlled charge recombination and cyclic electron flow round PSI during chilling of leaves in the light may partly prevent further damage to both photosystems.     

Carotenoid composition and down regulation of photosystem II in three conifer species during the winter

Seedlings and coppice shoots of Betula pubescens Ehrh. were grown under controlled conditions designed to simulate the annual growth cycle, and a water stress was introduced during the short day (SD). Alleviation of hud dormancy after increasing periods at chilling temperatures was tested under long day (LD) conditions. Abscisic acid (ABA) was analysed in leaf and bud samples by gas chromatography-mass spectrometry using [²H₄]ABA as the internal standard. Elongation growth of coppice shoots was faster than that of seedlings under both LD and SD conditions, while the final growth cessation occurred in a similar manner and was not affected by water stress, which significantly reduced growth rate in both plant types. Bud dormancy gradually decreased with increasing length of chilling, starting from the basal parts of the plant axis. Water stress did not retard hudhurst. but rather improved it in the chilled coppice shoots and in the non-chilled and partially chilled seedlings. Water content of buds was higher in coppice shoots than in seedlings, but after exposure to SD. it gradually decreased to 45% in both plant types and was not affected by water stress or chilling. The ABA level in both leaves and buds increased during SD treatment and was" enhanced by water stress. No clear differences in bud ABA level were found between the seedlings and coppice shoots under SD conditions, although coppice shoots had less ABA during the preceding LD conditions. There was, in general, no clear effect of chilling on bud ABA level. Budbursl in chilled, single-node cuttings was inhibited by external ABA treatment, which raised the internal ABA levels 10 to 150 times above normal. The observed correlation between ABA level and water content in buds during induction of dormancy under SD and water stress conditions indicates a possible role for ABA in the regulation of dormancy.     

Glycogen content and nitrogenase activity in Anabaena variabilis

Nitrogenase (=acetylene-reducing activity) was followed during photoautotrophic growth of Anabaena variabilis (ATCC 29413). When cell density increased during growth, (1) inhibition of light-dependent activity by DCMU, an inhibitor of photosynthesis, increased, and (2) nitrogenase activity in the dark decreased. Addition of fructose stabilized dark activity and alleviated the DCMU effect in cultures of high cell density.The resistance of nitrogenase towards oxygen inactivation decreased after transfer of autotrophically grown cells into the dark at subsequent stages of increasing culture density. The inactivation was prevented by addition of fructose. Recovery of acetylene-reducing activity in the light, and in the dark with fructose present, was suppressed by ammonia or chloramphenicol. In the light, also DCMU abolished recovery.To prove whether the observed effects were related to a lack of photosynthetic storage products, glycogen of filaments was extracted and assayed enzymatically. The glycogen content of cells was highest 10 h after inoculation, while light-dependent nitrogenase activity was at its maximum about 24 h after inoculation. Glycogen decreased markedly as growth proceeded and dropped sharply when the cells were transferred to darkness. Thus, when C-supply (by photosynthesis or added fructose) was not effective, the glycogen content of filaments determined the activity of nitrogenase and its stability against oxygen. In cells lacking glycogen, nitrogenase activity recovered only when carbohydrates were supplied by exogenously added fructose or by photosynthesis.Abbreviations Chl chlorophyll a - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

三唑酮对黄瓜幼苗生长及抗寒性的影响

研究了不同浓度三唑酮浸种对黄瓜幼苗生物量及抗寒性的影响。结果表明,20～100μmol·L^-1三唑酮能显著抑制黄瓜幼苗的株高、根长,增加了根重、根冠比和叶绿素含量,30d幼苗经过3d低温胁迫后,10～50μmol·L^-1三唑酮处理能保持较高的叶绿素含量,有效地降低质膜相对透性,维持较高的SOD活性,50μmol·L^-1三唑酮处理明显减缓低温胁迫过程中MDA的累积。另外,50μmol·L^-1三唑酮处理在低温胁迫第1d促进脯氨酸的累积,在第3d脯氨酸反而低于对照。但高浓度(>100μmol·L^-1)三唑酮不利于幼苗抵御低温伤害,总的来看,三唑酮增强了黄瓜幼苗的耐寒性。     

Promotion of 5-aminolevulinic acid on photosynthesis of melon (Cucumis melo) seedlings under low light and chilling stress conditions

When melon seedlings (Cucumis melo L. Ximiya No. 1) were cultured in a growth chamber with about 150 micro mol m(-2) s(-1) photon flux density, the leaf photosynthetic ability reduced dramatically as leaf position decreased from the top. The application of 5-aminolevulinic acid (ALA) solutions significantly increased the net photosynthetic rate (P(n)) as well as apparent quantum yield (AQY), carboxylation efficiency (CE) and stomata conductance (G(s)). After irrigation with 10 ml of ALA solution (10 mg l(-1) or 100 mg l(-1)) per container filled with approximately 250 g clean sand for 3 days, the leaf P(n) was about 40-200% higher than that of controls, and AQY, CE and G(s) increased 21-271%, 55-210% and 60-335%, respectively. Furthermore, ALA treatments increased leaf chlorophyll content and soluble sugar levels, as well as the rate of dark respiration, but decreased the rate of respiration under light. On the other hand, after melon seedlings that had been cultured in the chamber suffered chilling at 8 degrees C for 4 h and then recovered at 25-30 degrees C for 2 and 20 h, the P(n) of the water-irrigated plants was only 12-18% and 37-47%, respectively, compared with the initial P(n) before chilling treatment. If the seedlings underwent the same treatment but with ALA (10 mg l(-1)), the respective P(n) was 22-38% and 76-101%, compared with that of the control before chilling stress. If chilling was prolonged for 6 h, the ALA-pre-treated plants only showed a few symptoms in the leaf margins whereas all water-irrigated plants died, which suggested that ALA presumably promoted chilling tolerance of the plants under low light.     

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.     

Effect of Light and Chilling Temperatures on Chilling-sensitive and Chilling-resistant Plants. Pretreatment of Cucumber and Spinach Thylakoids in Vivo and in Vitro

The effects of chilling temperatures, in light or dark, on the isolated thylakoids and leaf discs of cucumber (Cucumis sativa L. “Marketer”) and spinach (Spinacia oleracea L. “Bloomsdale”) were studied. The pretreatment of isolated thylakoids and leaf discs at 4 C in the dark did not affect the phenazine methosulfate-dependent phosphorylation, proton uptake, osmotic response to sucrose, Ca²⁺-dependent ATPase activity, or chlorophyll content. Exposure of cucumber cotyledon discs and isolated thylakoids of cucumber and spinach to 4 C in light resulted in a rapid inactivation of the thylakoids. The sequence of activities or components lost during inactivation (starting with the most sensitive) are: phenazine methosulfate-dependent cyclic phosphorylation, proton uptake, osmotic response to sucrose, Ca²⁺-dependent ATPase activity, and chlorophyll. The rate of loss of proton uptake, osmotic response to sucrose, Ca²⁺-dependent ATPase activity and chlorophyll is similar for isolated cucumber and spinach thylakoids, whereas spinach thylakoids are more resistant to the loss of phenazine methosulfate-dependent phosphorylation. The thylakoids of spinach leaf discs were unaffected by exposure to 4 C in light. The results question whether the extreme resistance of spinach thylakoids treated in vivo is solely a function of the chloroplast thylakoid membranes and establish the validity of using in vitro results to make inferences about cucumber thylakoids treated in vivo at 4 C in light.     

A Comparison of the Effects of Chilling on Leaf Gas Exchange in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

The effects of chilling on the photosynthesis of a chilling-resistant species, pea (Pisum sativum L. cv Alaska) and a chilling-sensitive species, cucumber (Cucumis sativus L. cv Ashley) were compared in order to determine the differences in the photosynthetic chilling sensitivity of these two species. For these experiments, plants were chilled (5°C) for different lengths of time in the dark or light. Following a 1 hour recovery period at 25°C, photosynthetic activity was measured by gas exchange (CO₂ uptake and H₂O release), quantum yield, and induced chlorophyll fluorescence. The results show that pea photosynthesis was largely unaffected by two consecutive nights of chilling in the dark, or by chilling during a complete light and dark cycle (15 hours/9 hours). Cucumber gas exchange was reduced by one night of chilling, but its quantum yield and variable fluorescence were unaffected by dark chilling. However, chilling cucumber in the light led to reduced CO₂ fixation, increased internal leaf CO₂ concentration, decreased quantum yield, and loss of variable fluorescence. These results indicate that chilling temperatures in conjunction with light damaged the light reactions of photosynthesis, while chilling in the dark did not.     

Effect of BA upon the Amount of Pchlide and NPR protein and the Activity of NPR in Cucumber Cotyledons

When cucumber seedlings (Cucumis sativus L. cv. Aonagajibai) were treated with aqueous solution of BA (10–5mol/1 and 10–8mol/l) by spraying application, the amount of NPR protein was increased and the NPR activity was promoted. The contents of protochlorophyl, lide (Pchlide) and NADPH as the substrates of the enzyme reaction, were also increased remarkably. 2. The amount of Pchlide and NPR protein decreased rapidly when treated with red light. BA plays the role in the protection against the damage of enzyme activity by light and then decreasing the destruction of NPR protein. BA increased the content of Pchlide and NADPH, so the NPR activity was maintained at a higher level although in light condition. 3. Because that BA increased the content of NPR protein and the reaction substrate such as NADPH and Pchlide, the NPR activity was promoted. So, the rate of chlorophyll biosynthesis was rapid, and the content of chlorophyll increased. The leaf turns to dark green.     

ABA与GA_3对黄瓜离体子叶和石刁柏茎生根的影响

较高比值的内源ABA/GA_S有利于黄瓜黄化子叶和石刁柏茎不定根的发生。外源ABA具有增加组织内ABA含量并降低GA_S含量而促进生根的作用,而外源GA_S则与ABA效果相反。外源GA_S浓度为10~(-5)mol/L时,外源ABA对黄瓜子叶生根的诱导被明显抑制。子叶内GA_S含量较高的黄瓜1101品系其父本发根能力明显低于母本。ABA与GA_3对不定根发生的调控作用在黄瓜子叶离体培养的第一天最明显。     

外源Narciclasine对黄化植物中δ-氨基乙酰丙酸生物合成的抑制作用及其与6-BA和ABA作用的关系

从多花水仙鳞茎分泌物中提取的生物活性物质narciclasine(NCS)能够明显抑制叶绿素合成途径中叶绿素前体δ-氨基乙酰丙酸(ALA)的生物合成。NCS的这种抑制作用可为6-BA所逆转。NCS对ALA生物合成的作用与ABA的作用相类似,当以NCS与ABA同时处理时,其抑制效应具有一定的加成性。     

28-homobrassinolide improves growth and photosynthesis in <Emphasis Type="Italic">Cucumis sativus</Emphasis> L. through an enhanced antioxidant system in the presence of chilling stress

The ameliorative role of 28-homobrassinolide under chilling stress in various growth, photosynthesis, enzymes and biochemical parameters of cucumber (Cucumis sativus L.) were investigated. Cucumber seedlings were sprayed with 0 (control), 10⁻⁸, or 10⁻⁶ M of 28-homobrassinolide at the 30-day stage. 48 h after treatment plants were exposed for 18 h to chilling temperature (10/8°C, 5/3°C). The most evident effect of chilling stress was the marked reduction in plant growth, chlorophyll (Chl) content, and net photosynthetic rate, efficiency of photosystem II and activities of nitrate reductase and carbonic anhydrase. Moreover, the activities of antioxidant enzymes; catalase (E.C. 1.11.1.6), peroxidase (E.C.1.11.1.7), superoxide dismutase (E.C. 1.15.1.1) along with the proline content in leaves of the cucumber seedlings increased in proportion to chilling temperature. The stressed seedlings of cucumber pretreated with 28-homobrassinolide maintained a higher value of antioxidant enzymes and proline content over the control suggesting the protective mechanism against the ill-effect caused by chilling stress might be operative through an improved antioxidant system. Furthermore, the protective role of 28-homobrassinolide was reflected in improved growth, water relations, photosynthesis and maximum quantum yield of photosystem II both in the presence and absence of chilling stress.     

Light Induced Enhancement in Proline Levels Under Stress is Regulated by Non-Photosynthetic Events

Vigna radiata (L.) seedlings (5-d-old) were exposed to different concentrations of NaCl in light and in dark. The content of proline in the shoots increased with an increase in NaCl concentration, in light as well as in dark. But, irrespective of the concentration of NaCl, proline accumulation in the shoots was higher in light than in dark. Pretreatment of seedlings with dichlorophenyl dimethyl urea (DCMU) did not make any significant difference in light promoted stress induced proline accumulation. As DCMU is a potent inhibitor of photosynthetic electron transport, the light reaction of photosynthesis was not responsible for the observed light promotion of stress induced proline accumulation. In another set of experiments, 5-d-old green as well as etiolated seedlings were exposed to NaCl stress in the presence of different concentrations of sucrose. Irrespective of the concentration of sucrose used, proline content in shoots of stressed seedlings was higher in light than in dark. Although, sucrose enhanced NaCl stress induced increase in proline content in dark by about 32 %, this enhancement was not comparable to the 286 % increase in proline content brought about by light. These results showed that certain factors other than photosynthesis play a role in light promotion of stress induced proline accumulation.     

Effect of Cold Hardening on SOD and Glutathion Reductase Activities and on the Contents of the Reduced Form of Glutathion and Ascorbic Acid in Rice and Cucumber Seedlings

Rice and cucumber seedlings were employed in the study on changes of superoxide dismatase (SOD) and glutathion reductase (GR) activities, the contents of the reduced form of glutathion (GSH) and ascorbic acid (ASA) in leaves and the chilling resistance as well as the level of lipid peroxidation products after cold hardening and chilling stress under light. The seedlings hardened under a day/night temperature variation of 15 ℃/10 ℃ and photon flux density (PFD) of 250μmol · m-2 · s-1 for 12 h/d indicated an increase of the activities of SOD and GR, and the contents of GSH and AsA. The resistance of the seedlings to chilling and light stress was enhanced by cold hardening. Under the stress condition, the stabilities of SOD and GR activities, and contents of GSH and AsA in hardened seedlings were higher than those in the unhardened seedlings; the lipid peroxidation was also less than that in the latter. It was thus concluded that cold-hardening under appropriate light leads on to the enhancement of function of membrane protective system and increase of cell membrane stability which is an important part of chilling-resistance mechanism in the plant.     

Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO₂ uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 mol m^-2 s^-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO₂ uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PA photoacoustic - PFD photon flux density - PSII photosystem II