Effect of Salt Stress on the Salicylic Acid Synthesis in Young Maize (Zea mays L.) Plants

The effect of salt stress on salicylic acid (SA) synthesis was investigated parallel with the induction of antioxidant enzymes in young maize plants. Two-week-old maize plants grown in hydroponic solution were treated with 50 or 100 m m NaCl for 7 days. Antioxidant enzyme activities, and the SA and o -hydroxy-cinnamic acid (oHCA) levels were measured on the 3rd and 7th day of treatment and after 4 days of recovery. Ascorbate peroxidase activity increased in the leaves, but changes in guaiacol peroxidase activity only could be detected in the roots after 7 days. Glutathione reductase activity increased both in the leaves and in the roots after the 3rd day of 100 m m NaCl treatment. Free SA only increased during recovery in the leaves and roots. In the leaves of plants treated with 100 m m NaCl, a slight increase was observed in the free oHCA level, which rose dramatically after recovery, while in the roots an increase could only be seen after recovery. These results suggest that oHCA may serve not only as a precursor of SA but may also have an antioxidant role during salt stress and recovery.     

苗期水分胁迫对玉米根系生长杂种优势的影响

以玉米杂交种高油115及其亲本(母本220、父本1145) 为材料, 研究了玉米苗期根系生长的杂种优势及水分胁迫的影响。试验设水分充足、轻度干旱和严重干旱3个处理, 田间持水量分别为75%、55%和35%。结果表明, 在水分充足条件下, 根长(RL)、根表面积(SA)和根干重(RDW)均表现出不同程度的中亲优势和超亲优势, 轻度干旱显著降低了各指标的杂种优势, 而严重干旱则完全抑制了根系生长的杂种优势。根系各性状中, RL的杂种优势最强。在水分充足条件下, 与中等根(根直径0.25~0.45 mm)和粗根(根直径>0.45 mm)相比, 细根(根直径0.05~0.20 mm)的RL、SA及其占总根系比例的杂种优势最高。轻度干旱胁迫虽然降低了根系的杂种优势, 但RL、SA仍表现出显著的超亲优势和中亲优势(粗根的超亲优势除外)。此外, 只有细根RL和SA占总根系的比例在轻度干旱胁迫下具有显著的中亲优势, 说明杂交种可以通过生成较亲本更高比例的细根来抵抗轻度干旱胁迫。     

Maize Genotypes Differing in Salt Resistance Vary in Jasmonic Acid Accumulation During the First Phase of Salt Stress

Plant hormones are considered to play an important role in plant adaptation to drought and salt stress. The objective of the study was to investigate the changes in endogenous jasmonic acid (JA) in relation to differences in the salt resistance of maize genotypes. Two maize genotypes (SR 03 and Across 8023) were compared for changes in water relations, growth and tissue JA levels in response to 100 mm NaCl. Salt stress significantly reduced the shoot growth of both genotypes; however, SR 03 exhibited significantly less reduction in relative shoot fresh weight than Across 8023. Both genotypes showed an identical response to salt stress regarding plant water relations; therefore, genotypic differences in the salt resistance could not be attributed to changes in shoot turgor and these results were further confirmed by the response of both genotypes under equiosmotic stress (?0.49 MPa) of either 100 mm NaCl or PEG‐6000. GC‐MS/MS analysis showed that salt stress did not alter shoot JA levels of both genotypes, however significantly increased the root JA levels of Across 8023. In contrast, root JA levels of salt‐resistant SR 03 did not change by salt stress. Increase in root JA levels in response to stress treatments does not coincide with the growth inhibition of shoot in Across 8023. In contrast, both PEG and NaCl did not change the JA concentrations in both root and shoot tissues of SR 03. Growth assays with maize seedlings showed that JA supply in root medium inhibits shoot extension growth and both maize genotypes were sensitive to the inhibitory effects of JA. These results suggest that maize genotypes differ in JA accumulation during the first phase of salt stress and JA may indirectly be involved in leaf growth inhibition of the salt‐sensitive genotype. In addition, our results also showed that treatment of salt‐stressed plants with exogenous JA improved the Na⁺ exclusion by decreasing the Na⁺ uptake at the root surface.     

Water Stress and Potassium Fertilization in Field Grown Maize (Zea mays L.): Effects on Leaf Water Relations and Leaf Rolling

Three cultivars of maize ( Zea mays L.) were grown in the experimental field at Hiroshima University, Japan under two levels of K fertilization with a non-irrigated water stress treatment and an irrigated control during June to August 1990. Leaf water potential, osmotic potential and stomatal conductance were measured 21 d after withholding water. Diurnal changes in degree of leaf rolling were measured on the 22nd day after withholding water. Leaf water potential and osmotic potential at full turgor were lower in the non-irrigated plants than irrigated and they were lower in the high K plants than the low K plants. Lowering of osmotic potential (osmotic adjustment) helped to maintain turgor under low water potential conditions. Turgor potential was increased by the higher K fertilization. Higher turgor potential may contribute to the higher stomatal conductance observed in non-irrigated high K plants. The degree of leaf rolling increased towards noon, and it was lower in high K plants than in low K plants. High K plants recovered from leaf rolling faster than the low K plants during the afternoon. High K. plants could maintain higher turgor potential throughout the day than the low K plants. Degree of leaf rolling was the lowest in the cultivar K-8388 which maintained the highest turgor potential via osmotic adjustment and it recovered from leaf rolling faster than the other two cultivars. Higher levels of K fertilization may be beneficial for maize plants to tolerate to water stress conditions.     

Agronomic Performance and Nutrient Concentration of Maize (Zea mays L.) as Influenced by Nitrogen Fertilization and Plant Density

A field experiment was conducted at Samaru, Nigeria to study the influence of nitrogen fertilization and plant density on the agronomic performance and nutrient concentration of maize ( Zea mays L.). The treatments were factorial combinations of five nitrogen fertilization rates (0, 50, 100, 150 and 200 kg N/ha) and three plant density levels (25000, 50000 and 75000 plants/ha).
Nitrogen fertilization up to 150 kg N/ha enhanced grain and stover yields and increased kernel number and weight up to 100 kg N/ha. Nitrogen supply also increased maize ear length. Increased N fertilization rates increased concentrations of N, K and Mg but had no effect on P and Ca concentrations. Higher grain yield was closely associated with higher N concentration in ear leaf; with 0.1 % change in N concentration causing 177 kg/ha change in grain yield. Increased plant density increased stover yield up to 50 or 75 thousand plants/ha but depressed kernel number and weight and ear length.     

Growth‐Related Changes in Subcellular Ion Patterns in Maize Leaves (Zea mays L.) under Salt Stress

Na⁺ accumulation in the leaf apoplast has been suggested to lead to dehydration, later wilting and finally, the death of the affected leaves. Our aim has been to evaluate whether the reduction in the plant growth of sensitive maize in response to salinity is correlated with higher amounts of Na⁺ and Cl^? concentrations in the leaf apoplast. Subcellular ion patterns in intact leaves were investigated by using deionised water infiltration. We found an increase in soluble Na⁺ and Cl^? concentrations of about 16‐ and 4‐fold, respectively, compared with the control. These concentrations characterized the apoplasts of expanding leaves that had entirely developed under salinity. Interestingly, the K⁺ concentration was significantly reduced by 64 % compared with its control in the symplast under salinity. Our finding of a significantly decreased Ca²⁺ concentration in shoots suggested a possible association of Ca²⁺ concentration with the reduction in leaf expansion under salinity. As the absolute increase in the apoplastic Na⁺ concentration during salt treatment was much lower compared with the increase in the symplastic Na⁺ concentration, salt treatment in maize appears not to result in osmotic stress imposed by a high apoplastic Na⁺ concentration as has been suggested for other plant species (Oertli hypothesis).     

The Influence of Plant Water Stress on Net Photosynthesis and Leaf Area of Two Maize (Zea mays L.) Cultivars

The effect of plant water stress on net photosynthesis and leaf growth were investigated in order to determine to what extent leaf water potential during vegetative growth and silking affects maize development.
Two commercial maize hybrids grown in pots in a glasshouse were subjected to leaf water potentials of -1300 and -1700 kPa during the eighth leaf stage and during silking to -1700 and -2300 kPa to previously unstressed, moderately and severely stressed plants. The effect of stress on inhibiting CO₂ uptake rates and leaf areas, as well as the recovery after alleviating stress, were compared to that of unstressed plants.
No substantial differences in CO₂ uptake rates were found between medium and long seasoned cultivars. The CO₂ uptake rates per unit leaf area decreased to negative values under both moderate and severe stress conditions during both growth stages. During silking, the recovery of CO₂ uptake rate was much lower than during the eight leaf stage. Leaf area decreased proportionally with increased stress but did not recover after alleviating stress on plants stressed during both the eighth leaf and silking stages.     

An Analysis of Seasonal Effects on Leaf Nitrate Reductase Activity and Nitrogen Accumulation in Maize (Zea mays L.)

The important enzyme in nitrogen (N) assimilation, nitrate reductase (NR), is an inducible enzyme influenced by many external (light, temperature, etc.) and internal (genotype) factors. The efficiency of the N assimilation system may vary with genotype and season. In the present study, the effects of season on NR activity in relation to N accumulation in maize plants were investigated. Six different cultivars of maize, namely Ganga-11, Deccan-103, Hi-starch (hybrids), Arun, Manjari and Vijay (composites), were sown during the monsoon (88-day crop duration) and in winter (150-day crop duration). In vivo NR activity in the last fully expanded leaf (LFEL), and the N contents of the whole plant and the LFEL were estimated at seven phenological growth stages. Three different states of N metabolism in maize, namely (i) low NR activity per unit leaf area per unit time coinciding with high accumulation of N, (ii) high NR activity coinciding with low N accumulation, and (iii) low NR activity coinciding with low N accumulation, were noted. These results clearly demonstrate that the relationships between N uptake and accumulation parameters change with the season and crop growth stage and are subject to a genotypic influence. Thus it is necessary to evaluate genotypes under similar environments to select a genotype with high N use efficiency. As these relationships are growth dependent, care must be taken to evaluate them at a particular phenological stage rather than on the basis of days after sowing.     

低磷胁迫对磷不同利用效率玉米叶绿素荧光参数的影响

盆栽试验在高磷（+P）和低磷(－P)条件下,于四叶期测定了磷高效利用型玉米KH5和磷低效利用型玉米齐201的老叶（第2叶）和新展开叶的（第4叶）叶绿素荧光诱导动力学参数。结果表明,低磷处理使玉米叶片PSⅡ关闭程度增加、光能转换和电子传递效率降低,过剩激发能增加。基因型间比较,磷高效利用型玉米的光能转换和电子传递效率     

QTL mapping for six ear leaf architecture traits under water‐stressed and well‐watered conditions in maize (Zea mays L.)

Morphological traits for ear leaf are determinant traits influencing plant architecture and drought tolerance in maize. However, the genetic controls of ear leaf architecture traits remain poorly understood under drought stress. Here, we identified 100 quantitative trait loci (QTLs) for leaf angle, leaf orientation value, leaf length, leaf width, leaf size and leaf shape value of ear leaf across four populations under drought‐stressed and unstressed conditions, which explained 0.71%–20.62% of phenotypic variation in single watering condition. Forty‐five of the 100 QTLs were identified under water‐stressed conditions, and 29 stable QTLs (sQTLs) were identified under water‐stressed conditions, which could be useful for the genetic improvement of maize drought tolerance via QTL pyramiding. We further integrated 27 independent QTL studies in a meta‐analysis to identify 21 meta‐QTLs (mQTLs). Then, 24 candidate genes controlling leaf architecture traits coincided with 20 corresponding mQTLs. Thus, new/valuable information on quantitative traits has shed some light on the molecular mechanisms responsible for leaf architecture traits affected by watering conditions. Furthermore, alleles for leaf architecture traits provide useful targets for marker‐assisted selection to generate high‐yielding maize varieties.     

玉米籽粒发育性状的遗传及与产量性状关系的研究

在含有 BA(6-苄基腺嘌呤)2.5毫克/升、NAA(萘乙酸)0.1毫克/升的 MS 培养基上诱导苎麻(Boehmeria niveaL.)试管苗未离体叶面生芽。比较了不同激素的效果,在诱导芽形成中 BA 优于 ZT(玉米素)和 KT(激动素)。在叶脉处,特别是在中脉维管束的薄壁细胞容易分裂和脱分化,且具有较强的分化能力。芽在叶面上发生有一定的规律,并对叶面     

玉米ZmPP6C基因的克隆及其响应光质和胁迫处理的表达模式分析

丝氨酸/苏氨酸蛋白磷酸酶6亚基(catalytic subunits of Ser/Thr protein phosphatase 6, PP6C)是PP6全酶的催化亚基。在模式植物拟南芥中的研究表明,PP6C参与生长素极性运输、脱落酸信号转导和光信号转导途径介导的开花调控。为了明确玉米丝氨酸/苏氨酸蛋白磷酸酶6亚基(ZmPP6C)的蛋白结构特征与同源蛋白间的进化关系,采用RT-PCR方法克隆了ZmPP6C的全长基因。序列分析表明,ZmPP6C开放阅读框为912个核苷酸,编码303个氨基酸残基,包含PP2A的催化亚基PP2Ac结构域;系统进化树分析表明,PP6C蛋白在进化上较为保守,并且与高粱的PP6C蛋白相似性更高。对玉米自交系B73的ZmPP6C基因进行器官特异性表达分析表明,其表达量在成株期叶片中最高,是根中的7.9倍;ZmPP6C能够响应不同光质处理,且受远红光和红光的影响较大;也能响应长日和短日处理,在长日条件下的光照和黑暗阶段各有一个明显的表达高峰,在短日条件下的光照和黑暗阶段分别有2个和3个表达峰值;同时,ZmPP6C还响应高渗透、盐渍和淹水等胁迫处理,出现明显的上调表达。结果表明,ZmPP6C在玉米光信号转导、开花诱导与胁迫应答中发挥重要作用,其分子与生化机制值得进一步探讨。     

Direct and Residual Contributions of Symbiotic Nitrogen Fixation by Legumes to the Yield and Nitrogen Uptake of Maize (Zea mays L.) in the Nigerian Savannah

Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha^–1, respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha^–1, respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha^–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah.     

不同基因型玉米硫素吸收利用差异研究Ⅰ.根系吸收动力学参数与品种对硫肥的响应

应用同位素示踪技术,测定了34个不同基因型玉米水培幼苗根系对硫素的吸收动力学参数,大田试验调查了参试基因型在不同硫肥处理后的籽粒产量表现,测定了植株硫素吸收总量.结果发现不同基因型玉米对硫肥的反应存在很大的差异,而苗期根系的硫素吸收动力学参数与该品种施用硫肥后硫素吸收总量和籽粒产量的变化有密切联系,可以作为     

Reduced Sink Activity in Growing Shoot Tissues of Maize under Salt Stress of the First Phase may be Compensated by Increased PEP‐Carboxylase Activity

The effects of salt stress (100 mm NaCl for 6 days) on growing tissues (shoot apex, growing leaf segments, root tips) of young maize plants (Zea mays L. cv. Pioneer 3906) were investigated in comparison to an unsalinized control, focusing on assimilate supply from source leaves and the activity of sucrolytic enzymes in the sink tissues. The objectives were to test whether (i) phloem unloading in growing tissues is mainly symplastic, (ii) salinity reduces sink activity, determined either as sucrose synthase activity (indicator for the symplastic pathway) or as acid invertase activity (indicator for the apoplastic pathway), and (iii) PEP‐carboxylase activity is increased under salinity to compensate for reduced sink activity. For growing tissues of young maize shoots, it can be assumed that phloem transport of sucrose is mainly driven by symplastic unloading into the sink cells. In maize root tips, both, apoplastic and symplastic pathways, contributed to carbohydrate supply to the sink cells. The activity of acid invertase in growing shoot tissues was very low, and the alkaline invertase contributed less than 10 % to the cytoplasmic sucrolytic activity. Salt stress of the first phase (mainly osmotic stress) caused a significant inhibition of acid invertase activity in the growing leaf segments and in the root tips, which was also true for alkaline invertase activity in the root tips as well as for sucrose synthase activity in root tips and shoot apex. The decrease of sucrose synthase activity in shoot apex might be particularly detrimental for the plant growth, as this tissue with a high cell division rate relied entirely on cytoplasmic enzyme activities. Under salt stress, PEP carboxylase activity was significantly increased in growing leaves and the shoot apex of maize, whereas no significant effect was observed in the root apex. In conclusion, PEP carboxylase can have an anaplerotic function supporting the demand for metabolites in growing shoot tissues of young maize plants under salt stress. In root tips, an additional supply of organic acids to the tricarboxylic acid cycle is probably not needed, as sucrolytic sink activity, which was high even under saline conditions, can meet the demand of the sink cells.     

Drought‐induced osmotic adjustment and changes in carbohydrate distribution in leaves and flowers of cotton (Gossypium hirsutum L.)

Research has indicated osmotic adjustment as a mechanism by which leaves and roots of cotton plants overcome a drought period. However, the relevance of this mechanism in reproductive tissues of modern cultivars under drought has not been fully investigated. The objectives of this study were to measure osmoregulation and carbohydrate balance in reproductive tissues and their subtending leaves grown under water‐deficit conditions. Two cotton cultivars were grown under controlled environment and field conditions. Plants were exposed to water‐deficit stress at peak flowering, approximately 70 days after planting. Measurements included stomatal conductance, proline concentration, soluble carbohydrates and starch concentration, and water potential components. Stomatal conductance of drought‐stressed plants was significantly lower compared to control, while osmotic adjustment occurred in reproductive tissues and their subtending leaves by different primary mechanisms. Pistils accumulated higher sucrose levels, maintaining cell turgor in plants exposed to drought at similar levels to those in well‐watered plants. However, subtending leaves lowered osmotic potential and maintained cell turgor by accumulating more proline. Soluble carbohydrates and starch concentration in leaves were more affected by drought than those of floral tissues, with corresponding reduction in dry matter, suggesting that flowers are more buffered from water‐deficit conditions than the adjacent leaves.     

Dissection of the genetic architecture for grain quality‐related traits in three RIL populations of maize (Zea mays L.)

To manipulate the composition of the maize kernel to meet future needs, an understanding of the molecular regulation of kernel quality‐related traits is required. In this study, the quantitative trait loci (QTL) for the concentrations of grain protein, starch and oil were identified using three sets of RIL populations in three environments. The genetic maps and the initial QTL were integrated using meta‐analyses. A total of 38 QTL were identified, including 15 in population 1, 12 in population 2 and 11 in population 3. The individual effects ranged from 2.87% to 13.11% of the phenotypic variation, with seven QTL each contributing over 10%. One common QTL was found for the concentrations of grain protein and starch in bin 3.09 in the three environments and the three RIL populations. Of the 38 initial QTL, 22 were integrated into eight mQTL by meta‐analysis. mQTL3 and mQTL8 of the key mQTL in which the initial QTL displayed R² > 10% included six and three initial QTL for grain protein and starch concentrations from two or three populations, respectively. These results will provide useful information for marker‐assisted selection to improve the quality of the maize kernel.     

Effects of Increasing Salinity Stress and Decreasing Water Availability on Ecophysiological Traits of Quinoa (Chenopodium quinoa Willd.) Grown in a Mediterranean‐Type Agroecosystem

Quinoa is a native Andean crop for domestic consumption and market sale, widely investigated due to its nutritional composition and gluten‐free seeds. Leaf water potential (Ψ_leaf) and its components and stomatal conductance (g_s) of quinoa, cultivar Titicaca, were investigated in Southern Italy, in field trials (2009 and 2010). This alternative crop was subjected to irrigation treatments, with the restitution of 100 %, 50 % and 25 % of the water necessary to replenish field capacity, with well water (100 W, 50 W, 25 W) and saline water (100 WS, 50 WS, 25 WS) with an electrical conductivity (EC_w) of 22 dS m^?1. As water and salt stress developed and Ψ_leaf decreased, the leaf osmotic potential (Ψ_π) declined (below ?2.05 MPa) to maintain turgor. Stomatal conductance decreased with the reduction in Ψ_leaf (with a steep drop at Ψ_leaf between ?0.8 and 1.2 MPa) and Ψ_π (with a steep drop at Ψ_π between ?1.2 and ?1.4 MPa). Salt and drought stress, in both years, did not affect markedly the relationship between water potential components, RWC and g_s. Leaf water potentials and g_s were inversely related to water limitation and soil salinity experimentally imposed, showing exponential (Ψ_leaf and turgor pressure, Ψ_p, vs. g_s) or linear (Ψ_leaf and Ψ_p vs. SWC) functions. At the end of the experiment, salt‐irrigated plants showed a severe drop in Ψ_leaf (below ?2 MPa), resulting in stomatal closure through interactive effects of soil water availability and salt excess to control the loss of turgor in leaves. The effects of salinity and drought resulted in strict dependencies between RWC and water potential components, showing that regulating cellular water deficit and volume is a powerful mechanism for conserving cellular hydration under stress, resulting in osmotic adjustment at turgor loss. The extent of osmotic adjustment associated with drought was not reflected in Ψ_π at full turgor. As soil was drying, the association between Ψ_leaf and SWC reflected the ability of quinoa to explore soil volume to continue extracting available water from the soil. However, leaf ABA content did not vary under concomitant salinity and drought stress conditions in 2009, while differing between 100 W and 100 WS in 2010. Quinoa showed good resistance to water and salt stress through stomatal responses and osmotic adjustments that played a role in the maintenance of a leaf turgor favourable to plant growth and preserved crop yield in cropping systems similar to those of Southern Italy.     

Effect of Chemical and Physical Stress Conditions on the Concentration and Composition of Essential Oil Components in Leaves of Full‐Grown Artemisia annua L.

Full‐grown Artemisia annua plants were subjected to chemical and physical stress conditions, and the effect of these on the concentration and chemical composition of essential oil components (EOC) in the leaves was studied. The chemical stress treatments were performed by foliar application of NaCl, H₂O₂, salicylic acid and chitosan oligosaccharide (COS). The EOC of the leaves were extracted with n‐hexane and identified and quantified by GC–MS and GC–FID, respectively. Approximately 96 % of EOC in the extracts were identified and quantified of which β‐pinene, camphene, germacrene D, camphor, coumarin and dihydro‐epi‐deoxyarteannuin B were the major EOC accounting for about 75 % of the total content of EOC in the extracts. The physical stress treatment, sandblasting of the plants resulted in a significant enhancement in the content of α‐pinene, camphene, coumarin and dihydro‐epi‐deoxyarteannuin B. The total yield of identified EOC in non‐treated plants (control) was 86.2 ± 13.8 μg g^?1 fresh weight (FW) compared with 104.0 ± 9.1 μg g^?1 FW in sandblasted plants. The chemical stress treatments did not affect the composition of EOC significantly. The results indicate that chemical stress treatments do not affect the concentration and composition of EOC in full‐grown A. annua plants to the same extent as physical stress treatment by sandblasting.