A Comparison of the Effects of Chilling on Thylakoid Electron Transfer in Pea (Pisum sativum L.) and Cucumber (Cucumis sativus L.)

Experiments comparing the photosynthetic responses of a chilling-resistant species (Pisum sativum L. cv Alaska) and a chilling-sensitive species (Cucumis sativus L. cv Ashley) have shown that cucumber photosynthesis is adversely affected by chilling temperatures in the light, while pea photosynthesis is not inhibited by chilling in the light. To further investigate the site of the differential response of these two species to chilling stress, thylakoid membranes were isolated under various conditions and rates of photosynthetic electron transfer were determined. Preliminary experiments revealed that the integrity of cucumber thylakoids from 25°C-grown plants was affected by the isolation temperature; cucumber thylakoids isolated at 5°C in 400 millimolar NaCl were uncoupled, while thylakoids isolated at room temperature in 400 millimolar NaCl were coupled, as determined by addition of gramicidin. The concentration of NaCl in the homogenization buffer was found to be a critical factor in the uncoupling of cucumber thylakoids at 5°C. In contrast, pea thylakoid membranes were not influenced by isolation temperatures or NaCl concentrations. In a second set of experiments, thylakoid membranes were isolated from pea and cucumber plants at successive intervals during a whole-plant light period chilling stress (5°C). During wholeplant chilling, thylakoids isolated from cucumber plants chilled in the light were uncoupled even when the membranes were isolated at warm temperatures. Pea thylakoids were not uncoupled by the whole-plant chilling treatment. The difference in integrity of thylakoid membrane coupling following chilling in the light demonstrates a fundamental difference in photosynthetic function between these two species that may have some bearing on why pea is a chilling-resistant plant and cucumber is a chilling-sensitive plant.     

黄瓜的冷害及耐冷性

随着蔬菜反季节栽培面积的不断扩大,如何提高黄瓜(Cucumis sativus L.)耐冷性已成为选育新品种的研究重点。系统地综述近几年黄瓜耐冷性的鉴定、获得途径、冷害机理以及遗传和分子遗传学等方面的研究,以促进对黄瓜冷害机制的研究, 加速耐冷品种的培育。耐冷性鉴定时要从耐冷指数、低温发芽能力、MDA (丙二醛)含量和电解质渗漏率等几个方面综合鉴定。耐冷性的获得途径主要有冷驯化、激素处理、热激处理和培育耐低温品种,最重要的途径是耐冷品种选育。黄瓜冷害机理包括细胞膜的流动性降低及透性增加,光合作用被抑制,根系吸收减弱,可溶性糖含量减少,淀粉粒积累增加,微管的稳定性受到破坏等。黄瓜低温发芽能力由非加性基因决定,而幼苗时期主要由加性基因控制。黄瓜 耐冷的分子遗传学研究进展缓慢,目前已克隆出在低温锻炼中特异表达的功能未知的基因CCR18。今后还应研究黄瓜低温胁迫时的信号转导系统,以进一步揭示黄瓜的冷害机理;利用野生资源的抗逆性状,拓宽栽培黄瓜的遗传基础,选育适于保护地栽培的耐低温品种。     

黄瓜的冷害及耐冷性

随着蔬菜反季节栽培面积的不断扩大,如何提高黄瓜(Cucumis sativus L.)耐冷性已成为选育新品种的研究重点.系统地综述近几年黄瓜耐冷性的鉴定、获得途径、冷害机理以及遗传和分子遗传学等方面的研究,以促进对黄瓜冷害机制的研究,加速耐冷品种的培育.耐冷性鉴定时要从耐冷指数、低温发芽能力、MDA(丙二醛)含量和电解质渗漏率等几个方面综合鉴定.耐冷性的获得途径主要有冷驯化、激素处理、热激处理和培育耐低温品种,最重要的途径是耐冷品种选育.黄瓜冷害机理包括细胞膜的流动性降低及透性增加,光合作用被抑制,根系吸收减弱,可溶性糖含量减少,淀粉粒积累增加,微管的稳定性受到破坏等.黄瓜低温发芽能力由非加性基因决定,而幼苗时期主要由加性基因控制.黄瓜耐冷的分子遗传学研究进展缓慢,目前已克隆出在低温锻炼中特异表达的功能未知的基因CCRl8.今后还应研究黄瓜低温胁迫时的信号转导系统,以进一步揭示黄瓜的冷害机理;利用野生资源的抗逆性状,拓宽栽培黄瓜的遗传基础,选育适于保护地栽培的耐低温品种.     

Phosphorylation of Thylakoid Proteins of Oryza sativa: In Vitro Characterization and Effects of Chilling Temperatures

The phosphorylation of thylakoid proteins of rice (Oryza sativa L.) was studied in vitro using [γ-³²P]ATP. Several thylakoid proteins are labeled, including the light-harvesting complex of photosystem II. Protein phosphorylation is sensitive to temperature, pH, and ADP, ATP, and divalent cation concentrations. In the range pH 7 to 8.2, phosphorylation of the light-harvesting polypeptides declines above pH 7.5, whereas labeling of several other thylakoid polypeptides increases. Increasing divalent cation concentration from 3 to 20 millimolar results in a decrease in phosphorylation of the 26 kilodalton light-harvesting complex polypeptide and increased phosphorylation of several other polypeptides. ADP has an inhibitory effect on the phosphorylation of the light-harvesting complex polypeptides. Phosphorylation of the 26 kilodalton light-harvesting polypeptide requires 0.45 millimolar ATP for half-maximal phosphorylation, compared to 0.3 millimolar for the 32 kilodalton phosphoprotein. Low temperature inhibits the phosphorylation of thylakoid proteins in chilling-sensitive rice. However, phosphorylation of histones by thylakoid-bound kinase(s) is independent of temperature in the range of 25 to 5°C, suggesting that the effect of low temperature is on accessibility of the substrate, rather than on the activity of the kinase.     

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.     

微生物菌肥对设施黄瓜生长、产量及品质的影响

为探讨微生物菌肥在设施栽培黄瓜上的应用效果,以水果黄瓜为实验材料,设定施用"宁盾"A液(T1)、施用"宁盾"B液(T2)、同时施用"宁盾"A液与"宁盾"B液(T3)、对照(CK)4个处理,结果表明"宁盾"能够促进黄瓜植株生长、提高叶绿素含量和产量、改善果实营养品质;同时提高根际土壤蔗糖酶、脲酶的活性,增加根际土壤中氮、磷、钾等大量元素的含量,其中"宁盾"A液与B液配合使用效果最佳。     

微生物菌肥对设施黄瓜生长、产量及品质的影响

为探讨微生物菌肥在设施栽培黄瓜上的应用效果,以水果黄瓜为实验材料,设定施用"宁盾"A液(T1)、施用"宁盾"B液(T2)、同时施用"宁盾"A液与"宁盾"B液(T3)、对照(CK)4个处理,结果表明"宁盾"能够促进黄瓜植株生长、提高叶绿素含量和产量、改善果实营养品质;同时提高根际土壤蔗糖酶、脲酶的活性,增加根际土壤中氮、磷、钾等大量元素的含量,其中"宁盾"A液与B液配合使用效果最佳。     

Short- and Long-Term Effects of Salinity on Leaf Growth in Rice (Oryza sativa L.)

Addition of 50 mM NaCl to Oryza sativa L. had little effectupon the time of leaf initiation, but leaf mortality prior tothe normal phase of senescence was increased and the onset ofsenescence was advanced. There was no significant effect uponthe day-to-day pattern of growth, nor upon the ultimate length,of leaves that were developing at the time of, or shortly after,salinization with 50 mM NaCI. Leaves that developed after prolongedexposure of the plants to salinity were shorter. Addition ofNaCl, KC₁ or mannitol to the root medium brought about a cessationof leaf elongation within one minute. Growth at a reduced raterestarted abruptly after a lag period that depended upon theexternal concentration. Elongation rate recovered its originalvalue within 24 h after exposure to 50 mM NaCl, though not athigher concentrations. Addition of NaCl at concentrations upto 100 mM elicited no short-term effects upon photosyntheticgas exchange. Na uptake contributed to osmotic adjustment ofthe growing zone. When plants were rapidly exposed to 50 mMNaCl, no change in turgor pressure was detectable in the growingzone with the resolution of the miniature pressure probe used(about 70 kPa). It is concluded that the initial growth reductionin rice caused by salinization is due to a limitation of watersupply. A clear distinction is made between the initial effectsof low salinity which are recoverable and the long-term effectswhich result from the accumulation of salt within expanded leaves. Key words: Leaf elongation, gas exchange, photosynthesis, water relations     

5-Aminolevulinic Acid Induced Photodynamic Reactions in Thylakoid Membranes of Cucumber (Cucumis sativus L.) Cotyledons

The cucumber (Cucumis sativus L.) plants were sprayed with 20 mM 5-aminolevulinic acid or distilled water (control) and incubated in dark for 14 hr. The thylakoid membranes prepared from the intact chloroplasts, isolated from the above plants in dark, were illuminated with low light intensity (100 W/m2) for 30 min. Due 10 photodynamic reactions, the photochemical function of photosystem II was damaged by 50% in treated thylakoids whereas it was only slightly (8%) affected in control thylakoids. The photosystem I was, however, not affected. The exogenous electron donors, MnCl2, diphenyl carbazide and NH2OH failed to restore the photosystem II activity suggesting that the photodynamic damage had taken place very close to photosystem II reaction center. Singlet oxygen scavenger, histidine, could protect the photosystem II activity while superoxide radical scavengers, superoxide dismutase and 1, 2-dihydroxybenzene-3, 5-disulphonic acid disodium salt, and hydroxyl radical scavenger, formate, failed to protect the same.     

Effects of Potassium Deficiency on Cotyledon Photosynthesis and Seedling Development in Cucumis sativus L.

Seedlings of Cucumis sativus L. grew much less vigorously whencultured in potassium-deficient nutrient solution than in fullnutrients. The poorer growth was attributed to reduced CO₂ fixationby the cotyledons, which form the bulk of the photosyntheticsurface at this stage, and to a much lower level of export ofphotosynthetic products from the cotyledons. The magnitude ofthese effects increased as the seedlings aged and they werea major factor in the poorer development of the plumule in potassium-deficientplants. Electron microscopic examination of the cotyledons shows thatthe lower ¹⁴CO₂ fixation in potassiumstarved seedlings is associatedwith poorly-defined granal stacks and a proliferation of intergranalthylakoids. In plants grown in full nutrients the incorporationof radiocarbon into a cell wall fraction and into other insolublecomponents of the cell increased with cotyledon age whereasin potassium-deficient seedlings there was an increase in thepercentage of the total radiocarbon in the soluble fraction.This suggests either that the incorporation of photosyntheticproducts into cellular components was inhibited or that theability of the cotyledon to translocate photosynthetic productsto the rest of the seedling was reduced in plants grown in potassium-deficientconditions.     

超级杂交稻两优培九及其亲本低温强光适应特性

以超级杂交稻两优培九(培矮64S/9311)和母本培矮64S(PA64S)以及父本中籼9311为材料,以叶绿素荧光参数和活性氧代谢等指标研究生育后期亲本和后代对低温强光的适应特性。结果显示:低温强光处理后,与父母本相比,两优培九的叶绿素、PSⅡ原初光化学效率(Fv/Fm)和光化学猝灭系数(qP)和实际PSⅡ光能捕获的效率(φPSⅡ)的降低较少,说明在低温强光下,超级杂交稻两优培九吸收的光能较多地转化为化学能;同时两优培九的内源活性氧清除酶系如超氧化物歧化酶和过氧化物酶诱导的活性高,表现耐低温强光的特性,从而能有效清除叶片内的活性氧,因而膜脂过氧化较轻。试验结果表明:在生育后期超级杂交稻两优培九对低温强光适应的特性具有超双亲偏母本的现象。     

Influence of Chilling on Electrolyte Permeability, Oxygen Uptake and 2,4-Binitrophenol Stimulated Oxygen Uptake in Leaf Discs of the Thermophilic Cucumis sativus

The effect of chilling was studied in leaf discs from the chilling-sensitive Cucumis sativus L. by measurement of the electrolyte leakage from the discs, by oxygen uptake and by uncoupling of respiration with 2,4 dinitrophenol. Short periods of chilling are characterized by minor significant increases of electrolyte permeability, of respiration and of preserved ability to be uncoupled by 2,4-dinilrophenol. A longer period of chilling resulted in a strongly increased electrolyte permeability, in reduced oxygen uptake and in disappearance of uncoupling by 2,4 dinitrophenol. In general the induced changes in permeability and respiration were reversible within 4 days of chilling, if the discs were placed at 25°C after chilling.     

Effects of Simulated Acid Precipitation on Photosynthesis,Chlorophyll Fluorescence,and Antioxidative Enzymes in Cucumis sativus L.

The effects of simulated acid rain on gas exchange, chlorophyll fluorescence, and anti-oxidative enzyme activity in cucumber seedlings (Cucumis sativus L. cv. Jingchun No. 4) were investigated. Acid rain significantly reduced net photosynthetic rate and mainly non-stomatal factors contributed to the decrease of photosynthesis during the experimental period. The reduced photosynthesis was associated with a decreased maximal photochemical efficiency (F_v/F_m) and the average quantum yield of the photosystem 2 (PS2) reaction centres (_PS2). Meanwhile, acid rain significantly increased the activities of guaiacol peroxidase (GPX) and superoxide dismutase (SOD), but decreased the activity of catalase (CAT) together with an increased content of malonyldialdehyde (MDA), Hence the changes in photosynthesis in acid rain treatment might be a secondary effect of acidity damage probably due to lipid peroxidation of lipids and proteins in thylakoid membrane rather than direct effect on PS2 reaction centre.     

The Effects of Inhibition of Cotyledon Photosynthesis on Seedling Development in Cucumis sativus L.

The period during which cucumber cotyledons function purelyas storage organs is very brief and this role is supplementedand superseded shortly after emergence by their photosyntheticfunction. Inhibition of cotyledon photosynthesis by DCMU duringthe early post emergence phase prevented further plumule developmentalthough some cotyledon expansion still took place before seedlingdeath occurred. Seedlings did not survive DCMU application tothe cotyledons if the treatment was made before the first leafwas expanded. Reduction of the incident light intensity at the cotyledon surfaceto about 10 per cent of the control reduced the rate of growthof the seedlings but they did not die. Shading one cotyledonsubstantially reduced the weight and area of that cotyledonand of the seedling as a whole. There was little indicationthat the untreated cotyledon either increased its photosyntheticrate or its output of photosynthate-nor did it supply the inhibitedcotyledon with assimilates. There was some indication that sucroseapplied to the cotyledon surface was able to compensate forlight to a small extent especially when only one cotyledon wasshaded. However, in full light, sucrose tended to be inhibitory. After emergence cotyledon reserves are sufficient only for limitedcotyledon development. Survival and growth of the seedling beyondthis stage is dependent upon cotyledon photosynthesis.     

Estimation and Analysis of Cucumber (Cucumis sativus L.) Leaf Cellular Heat Sensitivity

Triphenyl tetrazolium chloride (TTC) reduction by cucumber (Cucumis sativus L. cv Poinsett 76 and cv Ashley) leaf discs was used as a viability assay to examine the effect of temperature pretreatment on the tissue response to acute hyperthermia. Semi-logarithmic plots of TTC reduction as a function of incubation time at different temperatures from 40 to 60[deg]C resembled the heat survival curves of animal cells. Heat inactivation rates were obtained and subjected to "quasi" Arrhenius analyses by analytical methods derived from the animal studies. The Arrhenius plots of TTC reduction rates for cv Ashley leaf discs preincubated at 25 or 37[deg]C and for cv Poinsett 76 preincubated at 37[deg]C were linear with the same activation energy (Ea) of about 80 kcal mol-1. The Arrhenius plot of cv Poinsett 76 preincubated at 25[deg]C was nonlinear with an Ea of about 80 kcal mol-1 at temperatures below 46[deg]C and an Ea of about 27.5 kcal mol-1 at temperatures above 47[deg]C. The significance of these differences is discussed in terms of the role of protein denaturation in the thermal sensitivity of cucumber disc reduction of TTC and the applicability of these methods to the analysis of plant cellular heat sensitivity.     

营养液温度和溶解氧浓度对黄瓜植株氮化合物含量的影响

常液温(25℃)下,当将营养液的溶解氧浓度(DO)降到1～2 mg/L时,黄瓜植株体内氮素代谢增强,根组织内各种氮素化合物含量有提高的趋势,叶和根内各种氨基酸含量显著提高,植株生长良好,对生长介质中的低氧逆境表现出较高的耐性;但高液温(33℃)下低溶解氧浓度(1 mg/L)处理,除植株可溶性氮和根组织内硝态氮含量不受影响外,叶和根中的其他各种氮素化合物含量均明显降低,而根组织内氨基酸含量则明显提高,植株生长不良,表明高液温下黄瓜植株耐低氧性明显降低.     

Effects of Low Temperature on Photosynthesis in Flag Leaves of Rice (Oryza sativa L.)

After low temperature (16℃) treatment, the net photosynthetic rate, chlorophyll content and FBPase activity tended to decrease and ratio of chlorophyll a/b, stomatal resistance, sucrose and starch content tended to increase in rice flag leaves at heading stage. However, the Pi content and water potential did not show pronounced change. The flag leaf chloroplasts contained large starch grains after three days at low temperature. The recovery of net photosynthetic rate in the flag leaves which had recieved stress at 16℃ for three days and transferred to normal nature condition was gradually increased. It almost came up to the value of control after five days. However, the decrease in stomatal resistance was rapid. It was almost lowered to the value of control after one day. Under normal nature comdition for five days, the chlorophyll content and FBPase activity reached near to the value of control. Meanwhile, the ratio of chlorophyll a/b, the sucrose and starch content almost declined to the value of control. The large starch grain in flag leaf chloroplast also disappeared. According to the experimental results, we discussed the relationship between the above-mentioned various changes and net photosynthetic rate We suggested that the effect of low temperature on photosynthesis might be one of factors in yield-reduction of rice.     

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

The control by phytochrome of hypocotyl elongation of light-grown Cucumis sativus L. after a white-light period was examined. The farred-absorbing form of phytochrome inhibits hypocotyl elongation. The response to phytochrome photostationary state () is not linear; all values of from 0.004 to 0.13 promote growth maximally, in the range of values of from 0.13 to 0.22 there is a linear growth response, between values of of 0.22 and 0.35 there is again no differential effect, and for values above 0.35 there is a strong (near linear) effect of on elongation. A kinetic examination of events following the white-light period shows that the major recovery from the photoperiod requires 8.5 h of darkness. End-of-day far-red treatment produces a very different response pattern, with a minor growth stimulation within 28 min of treatment followed by a major effect after 80 to 90 min. Three hours after far-red treatment there is a transient decline in growth rate which persists for about 2 h. Over the whole time course there is a great stimulation of growth rate compared with the controls. A similar growth-rate pattern also occurs if the end-of-day is 0.48, although the magnitude of the growth stimulation is less. Two components are affected by end-of-day , namely the time at which growth recovers and the subsequent growth rate. In the long term, the latter accounts for most of the differences in elongation growth. The dark recovery when only the hypocotyl is irradiated requires 4 h, but end-of-day far-red treatment reduces this to about 1.5 h. The persistence of the far-red-absorbing form of phytochrome for many hours in darkness in these light-grown plants is also demonstrated.Abbreviations and symbols D darkness - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - WL white light (from fluorescent lamps) - photostationary state of phytochrome - _c calculated      

Photocontrol of hypocotyl elongation in light-grown Cucumis sativus L.

An interaction is demonstrated between the effects of phytochrome and cryptochrome (the specific blue-light photoreceptor) in the inhibition of hypocotyl elongation of light-grown cucumber (Cucumis sativus L.) cv. Ridge Greenline seedlings. At certain fluence rates of blue light the total inhibition response is greater than the sum of the separate responses to each photoreceptor. The threshold for response to blue light is reduced at least 30-fold by additional red-light irradiation. The synergistic effect is demonstrated for two different fluence rates of red light. Synergism is mediated by phytochrome in both the cotyledons and the hypocotyl.Abbreviations and symbols BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - R red light - photostationary state of phytochrome - _c calculated