Glycinebetaine Improves Chilling Tolerance in Hybrid Maize

Plant growth and development is hampered by various environmental stresses including chilling. We investigated the possibility of improving chilling tolerance in hybrid maize by glycinebetaine (GB) seed treatments. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l^?1 (p.p.m.) aerated solution of GB 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. Germination and seedling growth was significantly hindered under chilling stress. Moreover, chilling stress significantly reduced the starch metabolism and relative water contents (RWC), and increased the membrane electrolyte leakage. However, activities of antioxidants (catalase, superoxide dismutase and ascorbate peroxidase) were increased under stress conditions. Seed treatments with GB improved the germination rate, root and shoot length, seedling fresh and dry weights, leaf and root scores, RWC, soluble sugars, α‐amylase activity and antioxidants significantly compared with untreated seeds under optimal and stress conditions. Induction of chilling tolerance was attributed to maintenance of high tissue water contents, reduced membrane electrolyte leakage, and higher antioxidant activities and carbohydrate metabolism. Seed treatment with 100 mg l^?1 GB was the best treatment for improving the performance of hybrid maize under normal and stress conditions compared with control and other levels used.     

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.     

Exploring the Role of Calcium to Improve Chilling Tolerance in Hybrid Maize

Abiotic stresses, including chilling, impede the plant growth and development mainly by oxidative damage. In this study, seed priming with CaCl₂ was employed to reduce the damage caused by chilling stress in hybrid maize. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l⁻¹ (ppm) aerated solution of CaCl₂ for 24 h and dried. Treated and untreated seeds were sown at 27 °C (optimal temperature) and 15 °C (chilling stress) under controlled conditions. Seed priming with CaCl₂ significantly reduced the chilling damage and improved the germination rate, root and shoot length, and seedling fresh and dry weights. Activities of antioxidants, including catalase, superoxide dismutase and ascorbate peroxidase, were also improved. Soluble sugars and α-amylase concentrations determined as general metabolic indicators of stress were also increased by seed priming with CaCl₂. Priming also improved the performance of maize at optimal temperature. Maintenance of tissue water contents, reduction in membrane leakage and increase in antioxidant activities, and carbohydrate metabolism seemed to induce chilling tolerance by CaCl₂. Seed priming with 100 mg l⁻¹ CaCl₂ was the optimal concentration in improving the performance of hybrid maize both under optimal and stress conditions.     

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.     

玉米耐低温冷害研究进展

玉米是典型的喜温C4作物,低温冷害胁迫是影响玉米生产的重要非生物逆境因素。为了研究低温对玉米生长发育的影响,归纳了玉米在低温胁迫条件下生理生化指标、光合作用参数的变化及耐冷遗传机制等方面的研究进展,并介绍了国内外抵御低温冷害所采取的方法,探讨了玉米耐低温研究的方向,提出玉米耐低温研究应更加注重玉米耐冷种质资源的创新及耐冷基因的挖掘利用。     

Effects of Exogenous Abscisic Acid on Antioxidant System in Weedy and Cultivated Rice with Different Chilling Sensitivity under Chilling Stress

Two chilling‐tolerant genotypes, that is, weedy rice WR03‐45 and cultivated rice Lijiangxintuanheigu and two chilling‐sensitive genotypes, that is, weedy rice WR03‐26 and cultivated rice Xiuzinuo were used in this study to investigate the effects of exogenous abscisic acid (ABA) on protection against chilling damage as well as on changes in physiological features. The results showed that under chilling stress the increased levels of superoxide radical (), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) in WR03‐45 and Lijiangxintuanheigu were lower than those in WR03‐26 and Xiuzinuo. Activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR)) and non‐enzymatic antioxidants (ascorbate acid (AsA) and reduced glutathione (GSH)) were enhanced in WR03‐45 and Lijiangxintuanheigu, whereas they were decreased significantly in WR03‐26 and Xiuzinuo. Application of exogenous ABA reduced the chilling damage in the four genotypes. The pre‐treatment with ABA decreased the levels of , H₂O₂ and MDA caused by chilling stress in the four genotypes through increasing the activities of SOD, CAT, APX, GR and the contents of AsA and GSH in the four genotypes under chilling stress. Moreover, pre‐treatment with Fluridone, the ABA biosynthesis inhibitor, prohibited the effects of ABA through enhancing the oxidative damages and suppressing the antioxidant defence systems under chilling stress. The results indicate the mechanism for rice with chilling tolerance is to enhance the capacity of antioxidant defence systems under chilling stress. Furthermore, ABA plays important roles in the tolerance of rice against chilling stress for it could induce the capacity of whole antioxidant defence systems including enzymatic and non‐enzymatic constitutions under chilling stress.     

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.     

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.     

玉米耐寒性鉴定研究进展

玉米是对低温逆境较为敏感的重要的禾谷类作物。早春低温冷害是影响玉米产量水平提高的重要因素之一。选育和创造耐寒玉米种质是减少此种危害的有效途径。耐寒性鉴定则是耐寒育种研究的基础。综述了国内外玉米耐寒性的鉴定方法和评价指标,分析了目前玉米耐寒性鉴定存在的问题,探讨了未来研究的方向,为深入开展玉米耐寒性研究提供参考。     

Brassinolide Application Improves the Drought Tolerance in Maize Through Modulation of Enzymatic Antioxidants and Leaf Gas Exchange

Brassinolides (BRs) are naturally occurring substances, which modulate plant growth and development events and have been known to improve the crop tolerance to abiotic stresses. In this study, possible role of exogenously applied brassinolide (BR) in alleviating the detrimental effects of drought in maize was evaluated in a rain‐protected wire‐house. Maize was subjected to drought at the start of tasseling for 6 days by withholding water application followed by foliar spray of BR (0.1 mg l^?1) to assess the changes in growth, gas exchange, chlorophyll contents, protein, relative leaf water contents (RLWC), proline, malonialdehyde (MDA) and enzymatic antioxidants. Drought substantially reduced the maize growth in terms of plant height, leaf area and plant biomass. Moreover, substantial decrease in gas exchange attributes (net photosynthetic rate (A), transpiration rate (E), stomatal conductance (g_s), water use efficiency (WUE), instantaneous water use efficiency (WUEi) and intercellular CO₂ (C_i) was also recorded. However, exogenous application of BR remarkably improved the gas exchange attributes, plant height, leaf area, cobs per plant, seedling dry weight both under drought and well‐watered conditions. BR‐induced promotion in growth and physiological and metabolic activities were mediated through increased protein synthesis enabling maintenance of tissue water potential and activities of antioxidant enzymes lowering the lipid peroxidation under drought.     

Improved Cold and Drought Tolerance of Doubled Haploid Maize Plants Selected for Resistance to Prooxidant tert‐Butyl Hydroperoxide

To improve the abiotic stress tolerance of maize (Zea mays L.), doubled haploid (DH) plants were produced by in vitro selection of microspores exposed to tert‐butyl hydroperoxide (t‐BuOOH) as a powerful prooxidant This study investigated the tolerance of the progenies of t‐BuOOH‐selected DH lines to oxidative stress, cold and drought in controlled environment pot experiments by analyses of photosynthetic electron transport and CO₂ assimilation processes, chlorophyll bleaching and lipid peroxidation of leaves. Our results demonstrated that the t‐BuOOH‐selected DH plants exhibited enhanced tolerance not only to oxidative stress‐induced by t‐BuOOH but also to cold and drought stresses. In addition, they showed elevated activities of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, catalase, glutathione reductase and glutathione S‐transferase when compared with the DH lines derived from microspores that were not exposed to t‐BuOOH and to the original hybrid plants. The results suggest that the simultaneous up‐regulation of several antioxidant enzymes may contribute to the oxidative and cold stress tolerance of the t‐BuOOH‐selected DH lines, and that the in vitro microspore selection represents a potential way to improve abiotic stress tolerance in maize.     

Coronatine Enhances Chilling Tolerance in Cucumber (Cucumis sativus L.) Seedlings by Improving the Antioxidative Defence System

Coronatine (COR) is a new plant growth regulator that mimics the biological activities of methyl jasmonate. We determined whether COR enhanced chilling tolerance of cucumber ( Cucumis sativus L. cv. Jinchun 4) seedlings and if such tolerance was correlated with changes in the activity of antioxidant enzymes. COR was applied to seedlings at two-leaf stage at 0 (Control), 0.1, 1, 10, and 100 n m . Seedlings were then subjected to chilling stress at 5 ± 1 °C for 4 days. Seedlings treated with COR showed significant higher tolerance to chilling stress and the optimal concentration was 1–10 n m . Compared with control, the chilling injury index (CII) of the seedlings treated with COR at 1 and 10 n m was decreased by 44.9 % and 24.5 %, respectively, while the membrane chilling stability (MCS) expressed as the change of relative conductance was increased by 37.2 % and 17.0 %, respectively. The malondialdehyde (MDA) content in leaves treated with COR at 1 n m was decreased by 39.7 %, and the O₂⁻ production rate and H₂O₂ content reduced by 28.6 % and 8.5 %, respectively. Treatment with COR at 1 n m increased the activities of superoxide dismutase (SOD) in leaves by 34.4 %, catalase (CAT) by 58.7 % and ascorbate peroxidase (APX) by 23.0 % under low temperature. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities were also significantly improved by 28.9 % and 21.3 % following treatment with COR at 1 and 10 n m , respectively. The overall results suggest that COR enhanced chilling tolerance in cucumber seedlings by improving the antioxidative defence system.     

Cadmium Enhances Generation of Hydrogen Peroxide and Amplifies Activities of Catalase, Peroxidases and Superoxide Dismutase in Maize

Maize (Zea mays L. cv. 777) plants grown in hydroponic culture were treated with 50 μm CdSO₄. Growth and metabolic parameters indicative of oxidative stress and antioxidant responses were studied in leaves of plants treated with Cd. Apart from increasing lipid peroxidation and H₂O₂ accumulation, supply of Cd suppressed growth, fresh and dry mass of plants and decreased the concentrations of chloroplastic pigments. The activities of catalase (CAT; EC 1.11.1.6), peroxidase (POD; EC 1.11.1.7), ascorbate peroxidase (APX; EC 1.11.1.11) and superoxide dismutase (SOD; EC 1.15.1.1) were increased in plants supplied 50 μm Cd. Localization of activities of isoforms of these enzymes (POD, APX and SOD) on native gels also revealed increase in the intensities of pre‐existing bands. Stimulated activities of CAT, POD, APX and SOD in maize plants supplied excess Cd do not appear to have relieved plants from excessive generation of reactive oxygen species (ROS). It is, therefore, concluded that supply of 50 μm Cd induces oxidative stress by increasing production of ROS despite increased antioxidant protection in maize plants.     

Effects of the Seed Film Coating Salicylic Acid on the Chilling Tolerance of Cotton Seedlings

The objective of this study was to investigate the effect of the different concentrations of the seed film coating salicylic acid on the cold tolerance of cotton seedlings using the sand culture method. The physiological response of cell membrane permeability, protective enzyme activity and osmotic adjustment of cotton seedling were measured before and after at low temperature stress and at normal temperature. The results showed that 1-10 mmol·L^－1 of seed film coating with salicylic acid seed coating treatment could effectively alleviate damage to cotton seedlings at low temperature, and the accumulation of the relative electrical conductivity and malondialdehyde were reduced on cotton seedlings. The activity of superoxide dismutase, peroxidase, catalase, and soluble protein, soluble sugar and proline contents increased sharply. These results indicate that film coating with salicylic acid can alleviate the effects of low temperature stress on seedling growth inhibition and improve the cotton seedlings by providing chilling tolerance, and the optimum treatment concentration salicylic acid is 5 mmol·L^－1.     

Fluorimetric Determination of the Genetic Variability Existing for Chilling Tolerance in Sweet Sorghum and Sudan Grass

Chilling temperatures drastically inhibited the photochemical quenching of chlorophyll fluorescence (q_Q) measured in intact leaves photosynthesizing under steady-state conditions. This effect appeared, however, to be characteristic of chilling-susceptible plant species and was not observed in plants which are known to be chilling-tolerant, indicating that the measurement of q_Q can serve in practice to estimate rapidly the relative chilling tolerance of crop plants. A large number (28) of sweet sorghum (Sorghum bicolor) and Sudan grass (Sorghum sudanense) genotypes were screened for chilling tolerance using this rapid q_Q method. Although sweet sorghum and sudan grass obviously behaved as chilling-sensitive plants, a considerable variation for chilling susceptibility was observed among the different genotypes tested. Some sweet sorghum varieties, such as ‘Dale’ and ‘Keller’, and most of the sudan grass varieties appeared to possess a certain degree of resistance towards low temperature stress, indicating the existence of useful germplasms in Sorghum for improving stress tolerance.     

烟草乙烯反应突变体的抗冷性及机理分析

为了深入研究乙烯在植物抵抗逆境胁迫中的作用,以烟草为模式植物,利用幼苗对外源乙烯的"三重反应",筛选得到了40多个乙烯不敏感突变体,其中多数突变体具有较强的抗冷性;从中选取4个突变体株系,对它们耐受低温胁迫的生理基础和作用机理进行了分析。结果表明,低温(0℃)胁迫下,烟草乙烯不敏感突变体的电解质渗透率显著低于野生型,而抗氧化酶活性(POD、SOD)以及过氧化氢酶(CAT)活性都高于野生型,说明突变体具有抵抗低温胁迫的优势生理基础。进一步研究发现,低温(0℃)胁迫下,烟草突变体中冷诱导基因Nt CBFs和Nt COR47呈现高水平表达,乙烯信号传导途径中下游基因ERFs的表达也发生显著变化。这些研究为烟草乙烯不敏感突变体株系具有较强的抗冷性提供了直接的分子证据。     

玉米耐旱性研究进展

干旱是目前影响玉米产量最重要的非生物胁迫因子。为了加快玉米耐旱性研究,提高育种效率,本研究归纳了近年来国内外玉米耐旱性研究现状将其总结为玉米耐旱性鉴定方法、遗传研究、品种选育以及耐旱性功能基因研究。对目前研究中存在的问题,如尚未有统一标准耐旱性鉴定体系、缺乏耐旱种质资源以及耐旱机理研究尚浅等进行了分析,并针对每个问题提出其解决对策,这为玉米耐旱性深入研究提供有力信息。     

不同种质杂交玉米品种间的耐旱性研究

选用3个不同种质的玉米品种迪卡007、桂单22号和农大108为试材,通过盆栽试验研究苗期水分胁迫下玉米的一系列生理生化指标的变化,并探讨了这些指标与玉米耐旱性之间的关系。结果表明,水分胁迫下,株高、叶绿素和光合作用速率下降,相对电导率、丙二醛(MDA)含量、SOD和POD活性升高,生物产量、穗粒数、百粒重随着干旱胁迫程度的加重而降低。这些指标在3个品种间的表现差异显著,在确定品种耐旱方面可以作为参考。     

6种玉米品种耐盐性筛选

针对不同玉米品种进行苗期耐盐性筛选,用以发掘和利用具有优良耐盐性状的玉米品种。本试验以蛭石为介质,设置0、45、95、145、195、245、295 mmol/L等7个NaCl浓度水平,进行耐盐性筛选。结果表明,6个玉米品种的生长临界NaCl浓度不同,‘潞玉39’和‘华农138’生长临界NaCl浓度约为 300 mmol/L,耐盐性较好;‘金苹618’的生长临界NaCl浓度为195.4 mmol/L,耐盐性较差。6种玉米品种叶片的POD活性、SOD活性、CAT活性约在195 mmol/L盐浓度下达到最大值,而且都随盐浓度的增大呈先升高后降低的趋势,但不同品种增加或降低的值有所差异。脯氨酸与丙二醛的含量都随盐浓度的增大呈上升趋势,但不同品种的增加值有所差异。综合分析,‘潞玉39’和‘华农138’耐盐性较好,更适宜在盐碱地上开展进一步田间研究。     

气候变化背景下吉林省春玉米冷害特征研究

为了研究气候变化背景下过去55年及未来35年吉林省春玉米冷害的时空变化特征,笔者利用气象行业标准《北方春玉米冷害评估技术规范》规定的指标和计算方法,分析了1961—2015年以及2种未来气候情景（RCP4.5和RCP8.5）下2016—2050年吉林省春玉米冷害的时空分布特征。结果表明：（1）1961–2015年及2种情景下2016—2050年各地区5—9月月平均气温之和均呈增加趋势,但RCP8.5情景下的5—9月月平均气温之和均高于RCP4.5情景。（2）1961—2015年吉林省西部和中部中度冷害发生频率较高,东部重度冷害发生频率较高。（3）RCP4.5情景下冷害频率高于RCP8.5情景,冷害均集中在东部。（4）1996年之前春玉米冷害范围以大范围冷害为主,之后均为局部冷害;RCP4.5情景下以区域性冷害发生为主;RCP8.5情景下以局部冷害为主。未来气候变暖背景下吉林春玉米冷害时空变化特征研究结果可为吉林省农业生产的防灾减灾工作提供技术支撑。