Changes in Leaf Water Relations and Injuries in Maize Seedlings Induced by Different Chilling Conditions

The time course of injuries and electrolyte leakage as well as changes in leaf water content and relative turgidity during chilling at 5°C, 65 or 100 % relative humidity (RH) were determined for seedlings of two maize hybrids differing in chilling tolerance.
In the course of chilling of entire seedlings the statistically significant injuries and increased leakage of electrolytes occurred first, followed by significant water deficit in leaves which was independent of RH and genotype. However, during prolonged chilling high and significant correlation between the level of chilling-induced water stress and the extent of injuries was observed. Thus it has been assumed that the main factor responsible for primary chilling injuries in maize seedlings is the immediate influence of chilling temperatures on the cell membranes, and not the secondary water stress. The level of the water stress and the extent of the dehydration injuries under chilling conditions depended on the chilling sensitivity of the genotype. Differences between the examined genotypes consisted not only in delayed chilling injuries in a chilling tolerant hybrid, but also in significantly lesser effects of these injures on water relations.
However, exposure to low temperature of the aboveground part or of the roots of the seedlings only, caused first the chilling-induced marked water deficit in the leaves and next increased leakage of electrolytes. A direct effect of chilling temperature on the membranes in a situation when only a part of the seedling is being chilled, may be less harmful to the plant as a whole owing to normal functioning of the non-chilled part.     

ACC处理对不同基因型玉米幼苗响应氮素供给的调控效应

乙烯对玉米生长发育与形态建成具有重要调控作用,但乙烯对玉米氮素吸收与积累调控效应缺乏深入研究,局限了乙烯在玉米丰产高效栽培中的应用。本研究以郑单958、瑞福尔1号和德美亚3号3个玉米品种为试验材料,比较研究不同基因型玉米植株对氮素供给的响应差异,结合外源添加乙烯合成前体1-氨基环丙烷-1-羧酸(1-aminocyclopropane-1-carboxylicacid,ACC),分析乙烯对不同基因型玉米氮素吸收的调控效应。研究结果表明,在低氮条件下,氮素敏感型品种(德美亚3号和瑞福尔1号)比郑单958叶片缺氮表型明显,对ACC处理敏感,而且ACC处理抑制玉米植株地上和地下部的生长和干物质积累;ACC处理抑制了低氮下叶片叶绿素合成,降低叶片可溶性蛋白积累,促进玉米叶片早衰,其中ACC处理郑单958叶片叶绿素和可溶性蛋白含量均显著高于德美亚3号和瑞福尔1号;进一步研究发现,低氮处理抑制乙烯合成关键酶基因ZmACS7和ZmACO15的表达,降低乙烯含量,ACC处理促进低氮条件下ZmACS7和ZmACO15基因的表达,提高乙烯含量;低氮处理抑制玉米根系中ZmNRT2.1表达,但ACC处理促进低氮下玉米根系中ZmNRT2.1表达,其中郑单958根中ZmNRT2.1表达在低氮条件下显著高于德美亚3号和瑞福尔1号。研究结果表明乙烯通过调控玉米植株乙烯合成关键酶基因和ZmNRT2.1表达,调节了氮素吸收与分配,影响了植株生长,其中氮素敏感性品种比持绿型品种对乙烯更为敏感。     

The Effect of Short Warm Breaks during Chilling on Photosynthesis and the Activity of Antioxidant Enzymes in Plants Sensitive to Chilling

The effect of short warm breaks (from 15 min to 5 h) during chilling of three chilling-sensitive species (tomato, maize and soybean) was investigated. Injuries, intensity of net photosynthesis and antioxidant enzyme activity were measured. Throughout chilling treatment, plants were warmed by transferring them during the last few hours of the light phase from chilling temperature (5 °C for tomato and maize, 2 °C for soybean) to 20 °C. After warming, seedlings were moved back to chilling conditions. Warm breaks of 5 h almost entirely prevented the appearance of injuries, as measured by changes in leakage of electrolytes and tissue water content, during 12 days of chilling. Even a 15-min warm break ensured a significant decrease in injuries in chilled maize seedlings compared to continuously chilled seedlings. Inhibition of gas exchange and fluorescence in seedlings of two maize genotypes differing in chilling resistance was, to a small extent, prevented by 1-h warm breaks, while 4-h warm breaks reduced inhibition significantly. The length of the warm break (1 or 4 h) had no influence on changes in SOD activity compared to continuously chilled plants, but warm breaks of 4 h produced a significant increase in CAT activity. The possible influence of an alternative pathway in preventing injuries is discussed.     

The Effect of Chilling Maize Shoots and Roots on the Electric Potential, Composition of Fatty Acids and the ATPase Activity in the Non-chilled Organs of Seedlings

The effect of separate chilling (5°C for 2 and 4 days) on the shoots and roots of two maize hybrid seedlings on the electric potential, the composition of fatty acids and the ATPase activity in the microsomes of non-chilled leaves and roots (20°C) was investigated. It has been found that the low temperatures induced on the non-chilled organs gave similar changes to organs exposed to a reduced temperature. The changes consisted of a parallel depolarization of leaf and root membranes and similarly a decrease in the ATPase activity as well as changes in the unsaturation of the membranes' fatty acids. The reduction of the acid content 18:2 was particularly significant, which in the leaf microsomes correlated with a drop in the ATPase activity.
The similarity between the reactions of the chilled and non-chilled parts of the plant gives evidence of a communication' between the organs which may facilitate a coordinated reaction of the entire organism to stress. The background for these phenomena could be die action potential of die chilled parts of seedlings which, in the non-chilled parts, might produce changes in the structure of biomembranes and in the activity of enzymes.     

Chilling Tolerance of Maize Seedlings in the Field during Cold Periods in Spring is Related to Chilling-Induced Increase in Abscisic Acid Level

Recent studies on chilling tolerance mechanisms in maize revealed a significant positive correlation between genotypic chilling tolerance and chilling‐induced accumulation of the stress hormone abscisic acid (ABA) under controlled growth chamber conditions. Based on this and other results, the hypothesis was developed that chilling tolerance in maize is related to the ability to accumulate large amounts of ABA rapidly, as a protection against chilling injury. The objective of the present study was to test this hypothesis under field conditions during natural cold weather periods in spring, which often cause severe chilling injury in maize fields. In two experiments at two locations in Europe with contrasting climates, eight maize genotypes with different genotypic chilling tolerance were cultivated in spring in the field according to agronomic practice for maize. Before and at the end of cold weather periods, ABA levels and water contents were determined in the third leaves. It was found that chilling‐tolerant genotypes accumulated higher amounts of ABA during the chilling period than chilling‐sensitive genotypes. A significant positive correlation between chilling tolerance and the levels of ABA in the leaves was found. These results support the above‐mentioned hypothesis. In contrast to earlier studies performed under growth chamber conditions, the water content in chilled leaves was mostly higher than in non‐chilled leaves. The increase in ABA is therefore not attributable to chilling‐induced water deficit, but probably to the low temperature itself.     

Chilling Tolerance in Hybrid Maize Induced by Seed Priming with Salicylic Acid

The optimum temperature for maize germination is between 25 and 28 °C. Poor and erratic germination at suboptimal temperature is the most important hindrance in its early sowing. This study was conducted to induce chilling tolerance in hybrid maize (Zea mays L.) by seed priming with salicylic acid (SA) and to unravel the background biochemical basis. For seed priming, maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 ppm (mg l^?1) aerated solutions of SA for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Performance of maize seedlings was hampered under chilling stress. But seed priming with SA improved the seedling emergence, root and shoot length, seedling fresh and dry weights, and leaf and root score considerably compared with control both at optimal and chilling temperatures. However, priming in 50 mg l^?1 SA solution was more effective, followed by priming in 100 mg l^?1 SA solution. Seed priming with SA improved the chilling tolerance in hybrid maize mainly by the activation of antioxidants (including catalase, superoxide dismutase and ascorbate peroxidase). Moreover, maintenance of high tissue water contents and reduced membrane permeability also contributed towards chilling tolerance.     

Relationships between mineral content, lipoxygenase activity, levels of 1-aminocyclopropane-1-carboxylic acid and ethylene emission in apple fruit flesh disks (cv. Jonagold) during storage

Lipoxygenase activity (LOX), levels of 1-aminocyclopropane-1-carboxylic acid (ACC) and of 1-malonyl-aminocyclopropane-1-carboxylic acid (MACC) and the capacity of isolated fruit disks to evolve ethylene were examined during storage of apples having different fruit mineral content. The internal ethylene concentration (IEC) of the whole fruit was also measured before removing discs of tissue. The results show that all these activities depend on the fruit mineral content and confirm general knowledge on the relations between minerals and fruit storage. For instance, fruits rich in calcium and/or phosphorus presented a lower LOX activity, a lower ACC content and a lower ethylene emission while fruits rich in potassium and/or with a relatively high K/Ca presented a higher LOX activity, a higher ACC level and a higher ethylene emission. Results are discussed in an attempt to explain the effects of minerals on storage quality.     

The Effect of Short Warm Breaks during Chilling on Water Status, Intensity of Photosynthesis of Maize Seedlings and Final Grain Yield

The effects of short-term exposure of seedlings to suboptimal temperature (14 °C for 1 or 4 h in 24 h cycles) during chilling (5 °C for 12 days) on the water status and intensity of photosynthesis of tolerant (TG) and chilling-sensitive (SG) maize genotypes were studied. Daily warming for 1 or 4 h resulted in a decrease in the hydration of the seedlings to 31.1 % and 61.5 % (SG) and 14.8 % (TG) and 39.1 % (SG), respectively, in comparison with the continuously chilled control. During warming for 4 h, both genotypes absorbed water from soil in amounts that partly compensated for its loss through transpiration, after the plants had been moved to the lower temperature. A protective effect of shorter warming (1 h) on the hydration of the seedlings was a result of a strong, stomatal limitation of transpiration during the initial days of chilling. Warming for 1 or 4 h also increased the ability of TG stomata to close in reaction to water deficit in chilling conditions. The effect of increased temperature delayed the decrease of P_N in leaves and limited RGR inhibition of the seedling mass caused by chilling. Daily warming of plants at the seedling phase (14 and 20 °C for 1 or 4 h) reduced the unfavourable effect of chilling (5 °C for a period of 8 days) on the final yield, the filling of caryopses and their number in a cob after growth in natural conditions.     

玉米籽粒发育早期的乙烯代谢研究

本文对籽粒败育与乙烯的关系进行了探讨。采用两类不同基因型(果穗顶端败育类型和正常类型)玉米杂交种为材料,对籽粒发育前期乙烯的代谢变化进行了双向比较研究。结果表明：籽粒的乙烯释放量在授粉后的0~8天((0~8DAA)出现高峰。同期败育类型玉米籽粒的乙烯释放量显著高于正常类型;在同一类型中又表现为顶部高于中部。这种乙     

Effects of Exposure to Short Periods of Suboptimal Temperature during Chill (5 °C) on Gas Exchange and Chlorophyll Fluorescence in Maize Seedlings (Zea Mays L.)

The effect of various periods of exposure to suboptimal temperature ('warm breaks'– WB: 14 °C for 4 h, 1 h and 0 h – control in 24 h cycles) during chilling (5 °C) of maize seedlings on the photosynthesis, the photochemical efficiency of photosystem II (Fv/Fm) and on the injuries of the cell membranes of leaves and water content in plants was compared. The measurements were conducted after 1, 3, 7 and 12 chill cycles. It was found that WB of either length distinctly diminished the chill-induced inhibition of net photosynthesis and the decrease of photochemical efficiency of PSII. The protective effect on WB on these parameters was observed shortly after completion of chilling of the plant as well as an after-effect. Daily warming up of the plants also reduced the leakage of electrolytes and diminished the water deficit of the chilled seedlings. The protective effect of WB on the measured parameters of the plants was greater in the chill-sensitive genotype than in the chill-tolerant one, especially when plants were warmed up for 4 h. The results obtained are an indication that short periods of warm weather during cold spring may diminish the injuries of the photosynthetic apparatus, as well as reduce the disturbance of water status of seedlings, contributing in this way to better condition of maize crops.     

Effect of Low Night Temperatures on Photosynthetic Activity of the Maize Seedlings (Zea mays L.)

Night chilling (5 °C) subsequently lowered photosynthetic intensity in the leaves of maize seedlings at 20 °C through an increase in leaf diffusive resistance brought on by lower tissue water content in morning hours. A more significant increase in leaf diffusion resistance was observed when soil temperature was lowered than in the case of lower air temperature.
The unfavorable effect of soil and air cooling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature from 5 °C to 1 °C, the efficiency of the protective influence of higher atmospheric humidity was decreased. This demonstrates that the participation of factors unrelated to plant water status in inhibiting photosynthesis increases with lower night temperatures.
An additional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 μg per 1 cm² of leaf area.     

The Effect of Chilling Temperature on the Permeability of Membranes to K+, Mg2+, Ca2+ ions and on the Electric Potential of Leaves in the Seedlings of Maize (Zea mays L.)

The relations between the extent of injuries in seedlings caused by a few day-long exposures to chill (5°C) and the leakage of K⁺, Mg²⁺ and Ca²⁺ ions from the leaves as well as the electric potential in seven maize hybrids, were investigated. The permeability of cells to ions was defined based on their absolute concentration in a water diffusate (C_t) and concentration expressed in relation to the total ion content in the leaves (IL index).
At lowered temperature the hybrids of higher resistance to chilling temperature were characterized by a lower value of the IL index for K⁺ and Mg²⁺ ions than the chill-sensitive hybrids. On the other hand, absolute concentration of the ions (C_t) Mg²⁺ and Ca²⁺ leaking from the leaves before chill exposure of the seedlings was positively and highly correlated with the extent of injuries in hybrids caused by 4 day-long exposures to chill. This observation is evidence that the chill injuries were predetermined through increased cell permeability to the mentioned ions at room temperature.
Changes in the electric potential of leaves in conditions of lowered temperature preceded the injuries of leaves, which became apparent after a longer period of exposure to chill. Thus, as the leakage of Mg²⁺ and Ca²⁺ ions occurs, changes in the electric potential may supply early information about the predisposition of the particular maize hybrids to chilling injuries. Leakage measurements of Mg²⁺ and Ca²⁺ ions from the leaves at room temperature may find application in the selection of chill-tolerant maize genotypes.     

Electrolyte Leakage, ATP Content in Leaves and Intensity of Net Photosynthesis in Maize Seedlings at Permanent or Different Daily Exposure to Low Temperatures

Changes were determined in electrolyte leakage (EL), ATP content in leaves and intensity of net photosynthesis (FJ in maize seedlings as a result of continued exposure to low temperatures for several days or, after a cold night (5 °C, 9 h), alternating application of 5 °C and 20 °C temperatures during the lit phase of the day (h of chilling during day/night: 0/9, 5/9, 10/9, 15/9).
At continuous exposure to low temperatures, permanent reduction of ATP content occurred between days 7 and 10, while EL increased significantly between days 4 to 7 (depending on experimental conditions). Of three leaves differing in age, most injuries were found in the oldest leaf. An increased intensity of irradiation from 150 to 500 μE. m⁻².s⁻¹ caused an earlier decrease in the ATP content and a further increase in electrolyte leakage. ATP content showed a 24 h rhythm, it increased at the end of the night and decreased at the end of the day. The rhythm was particularly noticeable in the control plants (20 °C), as well as, however to a lesser extent, in plants exposed to daily fluctuating chilling temperatures. It has also been observed that higher temperatures occurring in day time may diminish electrolyte leakage induced by previous low temperatures
The intensity of F_n determined at 20 °C, 4 h after withdrawal of chilling, decreased with the prolongation of the chilling period during the day.
Thus, it may be assumed that the EL and F_n values as indicators of the plants' sensitivity are in better agreement with the induced chill doses than the ATP content in leaves, which to a greater extent depends on the interaction between chilling and other experimental factors, such as irradiation intensity or the sequence of light and darkness.     

水稻籽粒中乙烯和ACC对土壤水分的反应及其与籽粒灌浆的关系

以武运粳8号(粳稻)和扬稻6号(籼稻)为材,自抽穗后9 d至成熟期进行保持浅水层(WW)、土壤轻度落干(MD)和土壤水分严重亏缺(SD)3种处理。观察在不同土壤水分条件下灌浆期籽粒中乙烯和1-氨基环丙烷1-羧酸（ACC）浓度的变化及其与籽粒灌浆的关系,并使用化学调控物质进行验证。结果表明,MD显著提高籽粒灌浆速率和粒重,SD明显降低籽粒灌浆速率和粒重。籽粒中乙烯释放速率和ACC浓度在MD中降低,在SD中增加。籽粒乙烯释放速率及根系伤流液中ACC浓度与籽粒中ACC浓度呈极显著的正相关。籽粒灌浆速率与乙烯释放速率呈极显著负相关。在花后9~13 d喷施乙烯合成的抑制物质氨基－乙氧基乙烯基甘氨酸(AVG),明显降低籽粒中ACC的浓度和乙烯的释放速率,显著提高了籽粒灌浆速率和粒重以及籽粒中的蔗糖合成酶（SuSase）、ADP葡萄糖焦磷酸化酶（AGPase）和可溶性淀粉合成酶（SSSase）活性;喷施乙烯释放的促进物质乙烯利,结果则相反。表明结实期土壤轻度落干或适度干旱处理可以抑制水稻体内乙烯的产生,促进籽粒灌浆。     

脱落酸对低温胁迫下玉米幼苗生长和光合特性的影响

脱落酸（ABA）是作物生产中广泛应用的一种植物激素。探究ABA对低温胁迫下玉米幼苗光合特性的影响,为阐明低温胁迫下玉米幼苗叶片光合结构的防御保护机制提供理论依据。以玉米品种“久龙5号”为试验材料,采用盆栽试验,探讨了低温胁迫0、2、4、6、8d下不同浓度脱落酸对玉米幼苗生长及光合特性的影响。结果表明,低温胁迫显著抑制玉米幼苗的正常生长,导致SPAD值下降,叶片净光合速率（P_n）、蒸腾速率（T_r）、气孔导度（G_s）、PSⅡ光化学最大效率（F_v/F_m）和潜在光化学效率（F_v/F_o）水平下降,初始荧光（F_o）显著升高。外源喷施适当浓度的ABA能够显著缓解由低温胁迫导致的玉米叶片P_n、T_r和G_s下降幅度,提高F_v/F_m和F_v/F_o,降低F_o水平。由此可见,外源施加适当浓度的ABA能提高幼苗叶片的光合能力,提高PSⅡ反应中心活性,促进物质积累,提高玉米幼苗的耐冷性。同时,外源施加ABA存在一定的浓度效应,即“低促高抑”。本研究所设计浓度范围中15mg/L ABA浓度对光合抑制缓解效果最显著。     

盐胁迫下不同玉米品种在苗期叶片和根中Na~+、K~+、Ca~(2+)及脯氨酸含量变化的研究

选用自有耐盐专用品种山大耐盐1号和国审普通玉米品种浚单20在0～300mmol/L不同浓度NaCl溶液的胁迫下萌发生长,测定玉米苗期叶片和根中Na~+、K~+、Ca~(2+)及脯氨酸含量.结果表明,随着NaCl溶液浓度的不断提高,玉米叶片和根中Na+含量逐渐升高,K+和Ca~(2+)含量逐渐降低,根中各测定离子含量高于叶片中各离子含量.同时脯氨酸含量逐渐升高,而且存在一个极限值,超过这个极限值脯氨酸含量出现下降,但仍然维持较高水平.两个玉米品种间在以上测定项目中表现出的差异非常明显,可以作为耐盐品种选育的借鉴和品种耐盐性强弱的评价.     

硅对玉米种子萌发和幼苗生长作用机制初探

研究硅对玉米种子萌发和幼苗生长代谢的影响, 结果表明: 在Si浓度从1.0 mmol/L到2.5 mmol/L范围内, Si能提高玉米种子萌发过程中淀粉酶、蛋白酶、脂肪酶活性, 促进呼吸代谢, 提高种子发芽率和增加单株鲜重. 在幼苗生长阶段, Si能增加叶绿素含量, 提高光合强度, 增强根系活力和硝酸还原酶活力, 降低蒸腾强度, 提高蒸腾比率、叶     

水稻品种对几种逆境的多重耐性及与ABA的关系

从一些耐旱和耐冷品种中筛选出几个具多重耐性的品种,其中大黄谷耐渗透胁迫和盐胁迫,芝麻糯耐盐和冷胁迫,桂溪和湘中籼2号耐渗透胁迫,也较耐冷胁迫.以大黄谷、芝麻糯和桂溪为材料,研究了多重耐性与ABA积累的关系.在渗透胁迫、盐胁迫和冷胁迫下,各水稻品种内源游离ABA含量迅速积累,耐性品种积累的ABA量都较敏感品种高,     

外源谷胱甘肽对低温胁迫下玉米幼苗的影响

试验旨在研究外源谷胱甘肽增强玉米幼苗防御低温胁迫的效应。选取生产上大面积推广的‘郑单958’品种为试验材料,采用土培法,设置6组处理,分别为CK、LT、G1、G2、G3、G4,每个处理3次重复。将培养至三叶一心的玉米幼苗分别进行叶面喷施3天后,在人工气候箱中采用10℃低温胁迫,并对玉米幼苗生长及相关生理指标进行分析。结果表明,喷施外源谷胱甘肽能够显著减轻低温胁迫对玉米幼苗苗高、叶片含水量及叶绿素含量的影响。低温胁迫5天后,谷胱甘肽通过增强过氧化物酶活性缓解低温胁迫对玉米幼苗的伤害,G3与LT处理存在明显差异,提高了79.25%;在低温天数的增加下,玉米叶片细胞内可溶性糖及丙二醛含量逐渐升高,胁迫7天后,LT处理与胁迫后第5天相比,可溶性糖及丙二醛含量分别增加了106.97%、25.33%。综合来看,外源谷胱甘肽能提高低温胁迫下玉米的生长能力,主要通过提高抗氧化酶和光合调控能力,保持细胞渗透平衡。     

Abscisic Acid May Alter the Salicylic Acid‐Related Abiotic Stress Response in Maize

The effect of 0, 0.05 or 0.1 mm abscisic acid treatment on chilling tolerance and salicylic acid‐related responses was investigated in young maize seedlings (Zea mays L., hybrid Norma). Although the pre‐treatment of maize seedlings with abscisic acid slightly decreased the chlorophyll content, it also reduced the level of chilling injury caused by 6 days of cold treatment at 5 °C. Under normal growth conditions, increased levels of bound salicylic acid and of bound ortho‐hydroxycinnamic acid were observed in the leaves during abscisic acid treatment. In the roots, abscisic acid did not affect the free and bound salicylic acid levels, but increased the amount of free and bound ortho‐hydroxycinnamic acid. The activity of glutathione‐S‐transferase increased on the 3rd day of abscisic acid treatment, whereas it did not change when followed by cold stress, compared with the control leaves. In the roots, the activities of glutathione reductase, glutathione‐S‐transferase and ascorbate peroxidase increased during the abscisic acid treatment, and those of glutathione‐S‐transferase and ascorbate peroxidase were also stimulated when abscisic acid pre‐treatment was followed by cold stress, compared with the control roots. Our results suggest that an overlap may exist between the abscisic acid‐induced cold acclimation and the salicylic acid‐related stress response.