Changes in Chlorophyll Fluorescence in Maize Plants with Imposed Rapid Dehydration at Different Leaf Ages

A comparison of the effects of a rapidly imposed water deficit with different leaf ages on chlorophyll a fluorescence and gas exchange was performed in maize (Zea mays L.) plants. The relationships between photosynthesis and leaf relative turgidity (RT) and ion leakage were further investigated. Leaf dehydration substantially decreased net photosynthetic rate (A) and stomatal conductance (G _s), particularly for older leaves. With dehydration time, F _v /F _m maintained a relatively stable level for youngest leaves but significantly decreased for the older leaves. The electron transport rate (ETR) sharply decreased with intensifying dehydration and remained at lower levels during continuous dehydration. The photochemical quenching of variable chlorophyll fluorescence (q _P) gradually decreased with dehydration intensity for the older leaves but increased for the youngest leaves, whereas dehydration did not affect the nonphotochemical chlorophyll fluorescence quenching (NPQ) for the youngest leaves but remarkably decreased it for the older leaves. The leaf RT was significantly and positively correlated with its F _v /F _m, ETR, and q _P, and the leaf ion leakage was significantly and negatively correlated with F _v /F _m and NPQ. Our results suggest that the photosynthetic systems of young and old leaves decline at different rates when exposed to rapid dehydration.     

Variations in the Photosynthesis Rate and Activity of Photosynthetic Enzymes in Maize Leaf Tissue of Different Ages

Highly good correlations for the extractable activities of ribulose-1,5-bisphosphatecarboxylase, pyruvate,P_i dikinase, phosphoenolpyruvate carboxylase,NADP-malate dehydrogenase and NADP-malic enzyme and the rateof photosynthesis were found in maize leaves of various ages.The activities of the first two enzymes were similar to, orslightly higher than, the photosynthesis rate, whereas the activitiesof the other enzymes were 2 to 6 times higher than the photosynthesisrate. These results suggest that pyruvate,P_i dikinase and ribulose-1,5-bisphosphatecarboxylase may be rate-limiting factors in maize. (Received May 12, 1984; Accepted July 5, 1984)     

Changes of Photosynthetic Characteristics in Relation to Leaf Senescence in Two Maize Hybrids with Different Senescent Appearance

A field experiment was conducted to investigate the changes in chlorophyll (Chl) and nitrogen (N) contents, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) contents and PEPC activity, and the photon-saturated net photosynthetic rate (P _Nsat), and their relationships with leaf senescence in two maize hybrids with different senescent appearance. One stay-green (cv. P3845) and one earlier senescent (cv. Hokkou 55) hybrid were used in this study, and we found that Chl and N contents and the P _Nsat in individual leaves of P3845 were greater than those in corresponding leaves of Hokkou 55 at the successive growth stages. In addition, larger contents of RuBPCO and PEPC, and a greater activity of PEPC were observed in P3845. Due to the lower rates of decrease of Chl, RuBPCO, and PEPC amounts per unit of N, and the lower net C translocation rate per unit of N in the stay-green hybrid, leaf senescence was delayed in comparison to the earlier senescent hybrid.     

植物对低温的光合响应

低温是影响植物生长和发育的主要环境因子之一.低温下,植物的许多生理生化过程受到影响,而其中光合作用是对低温最敏感的过程.光合作用是地球上最重要的生理生化过程,所以研究光合作用在低温下的响应机制具有重要意义.本文系统地总结了当前国内外最新研究进展,综述了低温下植物的光合响应,主要内容包括影响低温下光合响应的因素、低温下光合响应的关键问题--能量平衡的调节,以及植物的低温光合响应信号通路,并展望了低温光合响应研究的新方向.     

浑善达克沙地不同光合途径植物叶片气体交换和水势特征(英文)

以生长于浑善达克沙地上的C3植物白榆(Ulmus pumila)、C4植物沙米(Agriophyllum pungens)和CAM植物钝叶瓦松(Orostachys malacophyllus)3种不同光合途径植物为材料,测定了它们生长期叶片的光合气体交换参数、叶绿素荧光参数和水势,探讨它们对生长环境的生理响应特征.结果表明,白榆和沙米的净光合速率、气孔导度均高于钝叶瓦松,特别是在夏季高温(>40℃)和强光照(>2 100 μmol·m-2·s-1)条件下表现得更加明显.白榆和沙米的光合速率、叶片水势都发生了严重的午休现象,其白天光合速率的降低主要是由于气孔关闭造成的.钝叶瓦松的叶片水势在3种植物中最高,但是白天的光合速率很低;其Fv/Fm值在14:00最低,一天中此时光系统II受伤害最大;CAM物种瓦松的碳固定仅发生在夜间.研究发现,C3植物白榆和C4植物沙米比CAM植物钝叶瓦松对热和高光照有着更强的忍耐力,瓦松固定碳主要发生在生长最快的阶段;CAM植物瓦松为了能够在夏季强光和高温条件下生存,它必须进行高强度的呼吸,仅在早晨和夜间进行碳固定.     

Lipid Peroxidation and Antioxidant Enzyme Activity in Response to Interval Hypoxic Training

This study revealed the metabolic parameters of reactive oxygen species, including erythrocyte superoxide dismutase, catalase, and glutathione peroxidase activity, and oxidative stress markers, including total prooxidant activity and plasma concentration of thiobarbituric acid reactive substances, in response to 14-day interval hypoxic training (IHT). The study included healthy subjects and patients with essential hypertension, who had a decreased activity of the main antioxidant enzymes due to a marked oxidative stress, as revealed by previous studies. In all subjects, the oxidative stress markers decreased and the enzyme activity increased in four days after the IHT course. However, the differences in metabolism of the reactive oxygen species between the patients and the healthy subjects persisted. It is suggested that, even with a different antioxidant enzyme system baseline, IHT may contribute to adaptive activity of this system.     

Comparative Study of the Photooxidative Response in Leaf Discs from Plants with Different Photosynthetic Pathways

The effect of strong light in the presence of methyl viologen (MV) on the contents of souble protein and its free carbonyl, photosynthetic pigments, malondialdehyde (MDA), and ch]orophyil fluorescence parameters were investigated in the leaf discs from plants with different photosyn, thetic pathways. The photooxidafive degradation of soluble protein and ch]orophyll occurred after 1 h of treatment, and was accompanied by the increase of malondialdehyde content, and oxygen uptake in the light and dark, as well as the inactivation of PS Ⅱ in all test plants. Unlike the maize ( Zea mays ) and sugarcane ( Saccharum sinense Roxb. ) ( C4 plant ) or pineapple (Ananas comosus ( L. ) Mere. ) (CAM plant), a marked increase of carotenoid and non-photochemical chlorophyll fluorescence quenching(qN) was observed in peanut ( Arachis hypogaea L. ) leaves ( C3 plant), as the photochemical fluorescence quenching (qp) declined and Fo raised. It is suggested that photooxidafive stress induced the active dissipation of excessive excite energy by antenna quenching in C4 plant. The response of increasing 02 uptake in the dark was also found in C4 plants during photooxidation. However, the extents of protein and lipid destruction were larger in leaves of maize and sugarcane than in peanut leaves. Fo went up significantly as the C3 plant did, but qN dropped down to the lowest value (10% of control), which may regard as an obvious change of photooxidative damage in C4 plants. Among the three types of plants, the CAM plant, pineapple showed stronger antioxidative feature due to the relative small range of changes in the estimated items as compared with the control.     

Relationships Among Hormone Changes,Transmembrane Ca2+ Flux and Lipid Peroxidation During Leaf Senescence in Spring Maize

45Ca2+ absorption by plasma membrane vesicles isolated from maize (Zea mays L. ) leaves cultured in vitro was assessed to investigate the relationships among hormone changes, transmembrane Ca2+ flux and lipid peroxidation during leaf senescence. The results suggested that the possible process of leaf senescence in spring maize followed a sequence of endogenous hormonal change then transmembrane Caa + flux which further led to lipid peroxidation, with consequent degradation of chlorophyll and protein.     

七子花幼苗光合特性的温度响应

对七子花苗期光合特性的温度响应的研究结果表明：（1）净光合速率的最适温度为26-30℃。在19-40℃之间,暗呼吸速率与温度呈乘幂关系。蒸膳速率与温度呈线性关系。（2）饱和光强,表观量子效率和净光合速率在29℃时最高,在39℃时最低,但光补偿点和蒸滕速率程式高,光抑制加剧。（3）高温使七子花叶片的羧化效率下降。CO2补偿点上升,从而引起光合能力下降。     

Factors Associated with Depression of Photosynthetic Quantum Efficiency in Maize at Low Growth Temperature

The photosynthetic productivity of maize (Zea mays) in temperate regions is often limited by low temperatures. The factors responsible for the sensitivity of photosynthesis in maize to growth at suboptimal temperature were investigated by measuring (a) the quantum yields of CO2 fixation and photosystem II (PSII) photochemistry, (b) the pigments of the xanthophyll cycle, (c) the concentrations of active and inactive PSII reaction centers, and (d) the synthesis of core components of PSII reaction centers. Measurements were made on fully expanded leaves grown at 14[deg]C, both before and during the first 48 h after transfer of these plants to 25[deg]C. Our findings indicate that zeaxanthin-related quenching of absorbed excitation energy at PSII is, quantitatively, the most important factor determining the depressed photosynthetic efficiency in 14[deg]C-grown plants. Despite the photoprotection afforded by zeaxanthin-related quenching of absorbed excitation energy, a significant and more persistent depression of photosynthetic efficiency appears to result from low temperature-induced inhibition of the rate at which damaged PSII centers can be replaced.     

春玉米叶片衰老中激素变化,Ca^2＋跨膜运输和膜脂过氧化三者之间的关系

通过离体玉米（ZeamaysL．）叶片培养和叶肉质膜微囊45Ca2 吸收等实验,探索春玉米叶片衰老过程中激素变化、Ca2 跨膜运输及膜脂过氧化三者之间的联系。结果认为,玉米叶片衰老的可能过程首先是内源激素含量变化,继而影响到Ca2 跨膜运输,进而导致膜脂过氧化,由此引起叶绿素和蛋白质降解。     

豌豆叶绿体脂氧合酶活性与叶片衰老及膜脂过氧化作用的关系

豌豆叶绿体脂氧合酶(LOX)活性在连体叶片衰老过程中变化不大。ABA处理离体叶片2d叶绿体LOX活性升高,处理时间延长活性下降。抗氧化剂α-生育酚、谷胱甘肽、没食子酸丙酯抑制豌豆叶绿体LOX活性。脂质过氧化产物丙二醛对豌豆叶绿体LOX和大豆纯LOX-1的活性均有抑制作用,大豆LOX-1能促进离体豌豆叶绿体膜脂过氧化作用。因此,豌豆叶绿体LOX可能参与叶片衰老过程中叶绿体膜结构和功能的改变,又受膜脂过氧化产物的制约。     

Photosynthetic Oxygen Evolution at Low Water Potential in Leaf Discs Lacking an Epidermis

Land plants encountering low water potentials (low _w) closetheir stomata, restricting CO₂ entry and potentially photosynthesis.To determine the impact of stomatal closure, photosyntheticO₂ evolution was investigated in leaf discs from sunflower (Helianthusannuus L.) plants after removing the lower epidermis at low_w. Wounding was minimal as evidenced by O₂ evolution nearlyas rapid as that in intact discs. O₂ evolution was maximal in1 % CO₂ in the peeled discs and was markedly inhibited when_w was below –1·1 MPa. CO₂ entered readily at all_w, as demonstrated by varying the CO₂ concentration. Resultswere the same whether the epidermis was removed before or afterlow _w was imposed. Due to the lack of an epidermis and readymovement of CO₂ through the mesophyll, the loss in O₂ evolvingactivity was attributed entirely to photosynthetic metabolism.Intact leaf discs showed a similar loss in activity when measuredat a CO₂ concentration of 5 %, which supported maximum O₂ evolutionat low _w. In 1 % CO₂, however, O₂ evolution at low _w was belowthe maximum, presumably because stomatal closure restrictedCO₂ uptake. The inhibition was larger than in peeled discs at_w between –1 and –1·5 MPa but became thesame as in peeled discs at lower _w. Therefore, as photosynthesisbegan to be inhibited by metabolism at low _w, stomatal closureadded to the inhibition. As _w became more negative, the inhibitionbecame entirely metabolic.     

玉米根、叶质膜透性和叶片水分对土壤干旱胁迫的反应

利用大型活动式防雨旱棚 ,人工控制不同土壤含水量 ,全生育期系统研究了轻度及严重土壤干旱胁迫对夏玉米根系活力、叶片相对含水量、离体叶片保水力和根、叶质膜透性的影响 .结果表明 :土壤干旱胁迫下 ,玉米叶片相对含水量下降、离体叶片保水力降低 ;叶片及根系质膜透性上升 ,并且根的质膜透性比叶片上升快 ,根系活力下降 ;在干旱胁迫下 ,根系、叶片质膜透性与叶片相对含水量呈负相关 ,而根系、叶片质膜透性与离体叶片保水力呈显著正相关 ,根系膜透性与叶片膜透性也呈显著正相关 ,维持根系活力与保持较高的叶片含水量有密切关系 .另外 ,由于严重水分胁迫处理的上述特性和充分供水处理差异显著 ,而轻度胁迫和充分供水不显著 ,因此可以认为轻度水分胁迫 ,即土壤含水量为田间持水量的 6 0± 5 %为夏玉米正常生长发育的下限指标 ,可作为制定节水栽培措施的理论依据 .     

Diurnal Changes in Citrus Leaf Thickness, Leaf Water Potential and Leaf to Air Temperature Difference

Diurnal changes in leaf water potential and leaf thickness ofwell-watered citrus trees were found to be highly correlated.Midday decreases in leaf thickness of about 30–35 µm reflected midday decreases in leaf water potential of about1.1–1.3 MPa from predawn values. Leaf water potentialwas also correlated with changes in leaf-to-air temperaturedifference and ambient vapour pressure deficit. Leaf thicknessas well as leaf to air temperature difference could possiblybe used to monitor leaf water status continuously as an indicatorof citrus tree water stress.     

棉花叶片衰老过程中激素和膜脂过氧化的关系

以陆地棉品种辽棉9号的去根幼苗为材料,对其进行暗诱导衰老培养.在培养液中分别加入6-BA、ABA、GSH、H2O2、CaCl2、A23187 和A23187 CaCl2,测定在不同培养条件下棉花去根幼苗叶片内源激素、SOD酶活性和MDA含量的变化.结果表明:棉花叶片衰老表现为细胞分裂素含量的下降和ABA含量的上升.6-BA、GSH和钙离子均延缓叶片的衰老,ABA和H2O2促进叶片的衰老.     

Response of Chinese Wampee Axes and Maize Embryos to Dehydration at Different Rates

Survival of wampee (Clausena lansium Sksels) axes and maize (Zea mays L.) embryos decreased with rapid and slow dehydration. Damage of wampee axes by rapid dehydration was much less than by slow dehydration, and that was contrary to maize embryos. The malondialdehyde contents of wampee axes and maize embryos rapidly increased with dehydration, those of wampee axes were lower during rapid dehydration than during slow dehydration, and those of maize embryos were higher during rapid dehydration than during slow dehydration. Activities of superoxide dismutsse (SOD), ascorbate peroxidase (APX) and catalase (CAT) of wampee axes markedly increased during the sady phase of dehydration, and then rapidly decreased, and those of rapidly dehydrated axes were higher than those of slow dehydrated axes when they were dehydrated to low water contents. Activities of SOD and APX of maize embryos notable decreased with dehydration. There were higher SOD activities and lower APX activities of slowly dehydrated maize embryos compared with rapidly dehydrated maize embryos. CAT activities of maize embryos markedly increased during the eady phase of dehydration, and then decreased, and those of slowly dehydrated embryos were higher than those of rapidly dehydrated embryos during the late phase of dehydration.     

Response of Chinese Wampee Axes and Maize Embryos to Dehydration at Different Rates

Survival of wampee （Clausena lansium Skeels） axes and maize （Zea mays L.） embryos decreased with rapid and slow dehydration. Damage of wampee axes by rapid dehydration was much less than by slow dehydration, and that was contrary to maize embryos. The malondialdehyde contents of wampee axes and maize embryos rapidly increased with dehydration, those of wampee axes were lower during rapid dehydration than during slow dehydration, and those of maize embryos were higher during rapid dehydration than during slow dehydration. Activities of superoxide dismutase （SOD）, ascorbate peroxidase （APX） and catalase （CAT） of wampee axes markedly increased during the early phase of dehydration, and then rapidly decreased, and those of rapidly dehydrated axes were higher than those of slow dehydrated axes when they were dehydrated to low water contents. Activities of SOD and APX of maize embryos notable decreased with dehydration. There were higher SOD activities and lower APX activities of slowly dehydrated maize embryos compared with rapidly dehydrated maize embryos. CAT activities of maize embryos markedly increased during the early phase of dehydration, and then decreased, and those of slowly dehydrated embryos were higher than those of rapidly dehydrated embryos during the late phase of dehydration.     

Antioxidant Enzymes and Lipid Peroxidation in Different Stages of Breast Cancer

Oxidative stress resulting from an imbalance between pro-oxidants and anti-oxidants seems to play an important role in human breast carcinogenesis. There are conflicting reports regarding the tissue levels of malondialdehyde (MDA), ascorbic acid and superoxide dismutase (SOD) in breast cancer patients whereas few blood values have been reported. The present study was carried out to observe the changes in serum MDA, serum SOD and plasma ascorbic acid with the stage-wise progression of the disease. Serum MDA and serum SOD levels were found to be increased gradually from Stage I to Stage IV as compared to control group (?p<0.001). The maximum rise was in Stage IV patients. In contrast, mean plasma ascorbic acid levels were low in all stages compared to control group (?p<0.001). The decrease was more pronounced in Stage III and Stage IV. The study would be of immense help for establishing blood based biochemical marker in breast cancer patients.