Cross-talk between sulfur assimilation and ethylene signaling in plants

Sulfur (S) deficiency is prevailing all over the world and becoming an important issue for crop improvement through maximising its utilization efficiency by plants for sustainable agriculture. Its interaction with other regulatory molecules in plants is necessary to improve our understanding on its role under changing environment. Our knowledge on the influence of S on ethylene signaling is meagre although it is a constituent of cysteine (Cys) required for the synthesis of reduced glutathione (GSH) and S-adenosyl methionine (SAM), a precursor of ethylene biosynthesis. Thus, there may be an interaction between S assimilation, ethylene signaling and plant responses under optimal and stressful environmental conditions. The present review emphasizes that responses of plants to S involve ethylene action. This evaluation will provide an insight into the details of interactive role of S and ethylene signaling in regulating plant processes and prove profitable for developing sustainability under changing environmental conditions.     

Phenotypic plasticity of the maize root system in response to heterogeneous nitrogen availability

Mineral nutrients are distributed in a non-uniform manner in the soil. Plasticity in root responses to the availability of mineral nutrients is believed to be important for optimizing nutrient acquisition. The response of root architecture to heterogeneous nutrient availability has been documented in various plant species, and the molecular mechanisms coordinating these responses have been investigated particularly in Arabidopsis, a model dicotyledonous plant. Recently, progress has been made in describing the phenotypic plasticity of root architecture in maize, a monocotyledonous crop. This article reviews aspects of phenotypic plasticity of maize root system architecture, with special emphasis on describing (1) the development of its complex root system; (2) phenotypic responses in root system architecture to heterogeneous N availability; (3) the importance of phenotypic plasticity for N acquisition; (4) different regulation of root growth and nutrients uptake by shoot; and (5) root traits in maize breeding. This knowledge will inform breeding strategies for root traits enabling more efficient acquisition of soil resources and synchronizing crop growth demand, root resource acquisition and fertilizer application during crop growing season, thereby maximizing crop yields and nutrient-use efficiency and minimizing environmental pollution.     

Exogenously-sourced ethylene increases stomatal conductance, photosynthesis, and growth under optimal and deficient nitrogen fertilization in mustard

In order to ascertain the stomatal and photosynthetic responses of mustard to ethylene under varying N availability, photosynthetic characteristics of mustard grown with optimal (80 mg N kg(-1) soil) or low (40 mg N kg(-1) soil) N were studied after the application of an ethylene-releasing compound, ethephon (2-chloroethyl phosphonic acid) at 40 days after sowing (DAS). The availability of N influenced ethylene evolution and affected stomatal conductance and photosynthesis. The effect of ethylene was smaller under deficient N where plants contained higher glucose (Glc) sensitivity, despite high ethylene evolution even in the absence of ethephon, potentially because the plants were less sensitive to ethylene per se. Ethephon application at each level of N increased ethylene and decreased Glc sensitivity, which increased photosynthesis via its effect on the photosynthetic machinery and effects on stomatal conductance. Plants grown with sufficient-N and treated with 200 μl l(-1) ethephon exhibited optimal ethylene, the greatest stomatal conductance and photosynthesis, and growth. These plants made maximum use of available N and exhibited the highest nitrogen-use efficiency (NUE).     

The role of ethylene in plant temperature stress response

Temperature influences the seasonal growth and geographical distribution of plants. Heat or cold stress occur when temperatures exceed or fall below the physiological optimum ranges, resulting in detrimental and irreversible damage to plant growth, development, and yield. Ethylene is a gaseous phytohormone with an important role in plant development and multiple stress responses. Recent studies have shown that, in many plant species, both heat and cold stress affect ethylene biosynthesis and signaling pathways. In this review, we summarize recent advances in understanding the role of ethylene in plant temperature stress responses and its crosstalk with other phytohormones. We also discuss potential strategies and knowledge gaps that need to be adopted and filled to develop temperature stress-tolerant crops by optimizing ethylene response.     

The carbon bonus of organic nitrogen enhances nitrogen use efficiency of plants

The importance of organic nitrogen (N) for plant nutrition and productivity is increasingly being recognized. Here we show that it is not only the availability in the soil that matters, but also the effects on plant growth. The chemical form of N taken up, whether inorganic (such as nitrate) or organic (such as amino acids), may significantly influence plant shoot and root growth, and nitrogen use efficiency (NUE). We analysed these effects by synthesizing results from multiple laboratory experiments on small seedlings (Arabidopsis, poplar, pine and spruce) based on a tractable plant growth model. A key point is that the carbon cost of assimilating organic N into proteins is lower than that of inorganic N, mainly because of its carbon content. This carbon bonus makes it more beneficial for plants to take up organic than inorganic N, even when its availability to the roots is much lower – up to 70% lower for Arabidopsis seedlings. At equal growth rate, root:shoot ratio was up to three times higher and nitrogen productivity up to 20% higher for organic than inorganic N, which both are factors that may contribute to higher NUE in crop production.     

Nitrogen deficiency increases volicitin-induced volatile emission,jasmonic acid accumulation,and ethylene sensitivity in maize

Insect herbivore-induced plant volatile emission and the subsequent attraction of natural enemies is facilitated by fatty acid-amino acid conjugate (FAC) elicitors, such as volicitin [N-(17-hydroxylinolenoyl)-L-glutamine], present in caterpillar oral secretions. Insect-induced jasmonic acid (JA) and ethylene (E) are believed to mediate the magnitude of this variable response. In maize (Zea mays) seedlings, we examined the interaction of volicitin, JA, and E on the induction of volatile emission at different levels of nitrogen (N) availability that are known to influence E sensitivity. N availability and volicitin-induced sesquiterpene emission are inversely related as maximal responses were elicited in N-deficient plants. Plants with low N availability demonstrated similar volatile responses to volicitin (1 nmol plant(-1)) and JA (100 nmol plant(-1)). In contrast, plants with medium N availability released much lower amounts of volicitin-induced sesquiterpenes compared with JA, suggesting an alteration in volicitin-induced JA levels. As predicted, low N plants exhibited greater sustained increases in wound- and volicitin-induced JA levels compared with medium N plants. N availability also altered volicitin-E interactions. In low N plants, E synergized volicitin-induced sesquiterpene and indole emission 4- to 12-fold, with significant interactions first detected at 10 nL L(-1) E. Medium N plants demonstrated greatly reduced volicitin-E interactions. Volicitin-induced sesquiterpene emission was increased by E and was decreased by pretreatment the E perception inhibitor 1-methylcyclopropene without alteration in volicitin-induced JA levels. N availability influences plant responses to insect-derived elicitors through changes in E sensitivity and E-independent JA kinetics.     

根系氮吸收过程及其主要调节因子

氮（N）是植物根系吸收最多的矿质元素之一．全球变化将使土壤中N的有效性发生改变,影响陆地生态系统碳分配格局与过程．研究根系N吸收及其调控对预测生态系统结构和功能具有重要理论意义．由于土壤中存在多种形态的N源,长期的生物进化和环境适应导致植物根系对不同形态N的吸收部位、机理及调控有较大差别．因此,植物长期生长在以某一形态N源为主的土壤上就形成了不同的N吸收机制和策略．本文简述了近年来在植物根系N吸收和调控方面的最新研究进展,重点评述了不同形态N在土壤中的生物有效性,根系N吸收部位,N在木质部中的装载和运输,不同形态N（NO3^-、NH4^＋和有机氮）的吸收机制,以及根系N吸收的自身信号调控和环境因子对根系N吸收的影响．在此基础上,提出了目前根系N吸收研究中存在的几个问题．     

Reliance on prey-derived nitrogen by the carnivorous plant Drosera rotundifolia decreases with increasing nitrogen deposition

? Carnivory in plants is presumed to be an adaptation to a low-nutrient environment. Nitrogen (N) from carnivory is expected to become a less important component of the N budget as root N availability increases. ? Here, we investigated the uptake of N via roots versus prey of the carnivorous plant Drosera rotundifolia growing in ombrotrophic bogs along a latitudinal N deposition gradient through Sweden, using a natural abundance stable isotope mass balance technique. ? Drosera rotundifolia plants receiving the lowest level of N deposition obtained a greater proportion of N from prey (57%) than did plants on bogs with higher N deposition (22% at intermediate and 33% at the highest deposition). When adjusted for differences in plant mass, this pattern was also present when considering total prey N uptake (66, 26 and 26 μg prey N per plant at the low, intermediate and high N deposition sites, respectively). The pattern of mass-adjusted root N uptake was opposite to this (47, 75 and 86 μg N per plant). ? Drosera rotundifolia plants in this study switched from reliance on prey N to reliance on root-derived N as a result of increasing N availability from atmospheric N deposition.     

Vertical leaf nitrogen distribution in relation to nitrogen status in grassland plants

Vertical gradients of leaf nitrogen (N) per unit leaf area (NLA) are viewed as plastic responses that optimize N utilization with respect to carbon assimilation. However, it has been shown that plant species, sowing density and N availability affect the steepness of the NLA gradient relative to the photon flux density (PFD) gradient. This paper tests the hypothesis that such variation is related to the N status of the plant. The N status was analysed using the concept of the critical N concentration (Ncrit) in which shoot N per unit dry mass (NSM) decreases with shoot mass, and a negative deviation of actual NSM from Ncrit indicates N shortage in the plant. The hypothesis was tested with contrasting grassland species Medicago sativa, Dactylis glomerata and Taraxacum officinale by varying PFD and N availability, plant density and hierarchical positions of individuals within stands. Combinations of all treatments showed a general negative correlation between the N allocation coefficient (i.e. the slope of the NLA-PFD relationship) and NSM for all three species. Thus, NLA, relative to PFD, gradients became steeper with increasing shoot mass and increasing N shortage in the plant. These data are consistent with the view that internal N availability is an important factor in modifying the NLA gradient.     

Soil nitrogen availability evaluations based on nitrogen mineralization potentials of soils and uptake of labeled and unlabeled nitrogen by plants

Summary Sudangrass [Sorghum sudanense (Piper) Stapf] was grown in a greenhouse pot experiment on 39 soils having a broad range of chemical and physical characteristics. Labelled N as sodium nitrate (9% excess N¹⁵) was applied at rates of 200 and 400 mg of N per pot (2kg of soil). After 6 weeks of growth, total N and N¹⁵ were determined on plant tops and roots and on the cropped soils. Maximum yield differed widely among the soils owing to variations in yield-limiting factors other than N. Despite the diversity of responses to N fertilizer, the experiment provided a meaningful basis for assessing soil nitrogen availability. Amounts of N taken up from soils were similar from pots receiving no fertilizer N and from pots receiving labeled N.Amounts of soil organic N mineralized during cropping plus the mineral N present initially in the soils correlated highly with amounts of soil N taken up by whole plants (tops and roots). Average recovery by whole plants of mineral N formed before and during the cropping period was about 85 per cent, a value corresponding closely to recovery of fertilizer N in this experiment. The similarity in recovery of N provided by soil and fertilizer suggests that mineral N from these sources comprised a common pool that behaved as an entity with respect to mineralization-immobilization relations or other reactions affecting N availability to plants.A-values, the amounts of soil N having an availability equivalent to that of applied fertilizer N, were similar for two levels of applied labeled N and for tops and whole plants. Moreover, A-values were similar to amounts of N mineralized before and during crop growth. This result is particularly significant, since amounts of N mineralized during crop growth were estimated from N mineralization potentials, taking into account the effects of temperature on the mineralization rate constant. Thus, the study provides preliminary evidence that the soil N mineralization potential offers a basis for reliably estimating amounts of soil N mineralized during selected periods of time under specified temperature regimes.     

Identification of the mulberry genes involved in ethylene biosynthesis and signaling pathways and the expression of MaERF-B2-1 and MaERF-B2-2 in the response to flooding stress

The phytohormone ethylene is essential to plant growth and development. It plays crucial roles in responses to biotic and abiotic stress. The mulberry tree is an important crop plant in countries in which people rear silkworms for silk production. The availability of the mulberry genome has made it possible to identify mulberry genes involved in ethylene biosynthesis and signal pathways. A total of 145 mulberry genes were identified by both homology-based and hidden Markov model (HMM) search, including 29 genes associated with ethylene biosynthesis and 116 genes in the AP2/ERF family. Studies on gene structure have provided a genetic basis for understanding the functions of these genes. The differences in gene expression were also observed in different tissues. The expression of two mulberry genes in the AP2/ERF family, MaERF-B2-1 and MaERF-B2-2, was found to be associated with the response to flooding stress.     

Progress of ethylene action mechanism and its application on plant type formation in crops

BackgroundThe plant hormone ethylene exerts a huge influence in the whole life cycle of plants, especially stress-resistance responses. With the development of functional genomics, that the action mechanism of ethylene takes part in mediated plant architecture has been clarified gradually, such as plant roots, stems, leaves, fiber elongation and so on. Accordingly, the application of ethylene on crops chemical control and genetic improvement is greatly expanded. From the view of ethylene mediated plant architecture in crops, here reviewed advances in ethylene biosynthesis and signal transduction pathway, stress-resistance responses and the yield potential enhance of crops in recently 20 years. On these grounds, the objectives of this paper were to provide scientific reference and a useful clue for the crop creation of ideal plant type.     

Omics of root-to-shoot signaling under salt stress and water deficit

Maximizing crop yield depends on the leaves receiving an optimal supply of water, mineral nutrients, small organic molecules, proteins, and hormones from the root system via the xylem. Soil drying and salinization alter these xylem fluxes, and modern omics techniques offer unparalleled opportunities to understand the complexity of these responses. Although absolute xylem concentrations of any constituent depend on the genotype and xylem sap sampling methodology, analysis of the relative changes in concentrations has revealed some conserved behavior. Typically, these stresses increase xylem concentrations of the plant hormone abscisic acid (ABA) that limits crop water loss, but decrease the concentrations of certain cytokinins that stimulate expansive growth and prevent premature leaf senescence. Further understanding of the ionic and biophysical alterations in the rhizosphere environment that cause increased xylem concentrations of the ethylene precursor (ACC) is needed. Interactions of these plant hormones with plant nutrient status and xylem nutrient delivery may be important in tuning plant responses to their environment. Xylem proteomics is an emerging area that will help understand mechanisms of plant stress adaptation. Using omics techniques to underpin rootstock-mediate plant improvement is likely to improve crop yields in dry or saline soil.     

Fruit-specific suppression of the ethylene receptor LeETR4 results in early-ripening tomato fruit

Tomato is an economically important crop and a significant dietary source of important phytochemicals, such as carotenoids and flavonoids. Although it has been known for many years that the plant hormone ethylene is essential for the ripening of climacteric fruits, its role in fruit growth and maturation is much less well understood. In this study, data are presented which indicate that fruit-specific suppression of the ethylene receptor LeETR4 causes early ripening, whereas fruit size, yield and flavour-related chemical composition are largely unchanged. Early fruit ripening is a highly desirable and valuable trait, and the approach demonstrated here should be applicable to any fruit species requiring ethylene to ripen. These results demonstrate that ethylene receptors probably act as biological clocks regulating the onset of tomato fruit ripening.     

Regulation of ethylene biosynthesis in plants

Ethylene is one of the plant hormones that controls growth and development. There are many responses regulated via ethylene in response to exogenous stimuli. Research on ethylene biosynthesis and the signalling pathway enabled us to understand the mechanism of the regulation of these responses. Different temporal and spatial expression of genes encoding enzymes involved in ethylene biosynthesis is of great importance for the regulation of ethylene responses. Also, post-translational regulation of the enzymes seems to be a key regulatory mechanism for the control of their activity. Because of versatile regulation of its production, ethylene can control plant development at many levels.     

Transgenic plants with altered ethylene biosynthesis or perception

The plant hormone ethylene is an essential signaling molecule involved in many plant processes including: germination, flower development, fruit ripening and responses to many environmental stimuli. Moreover, large increases in ethylene levels occur during plant stress responses, fruit ripening and flower wilting. Manipulation of ethylene biosynthesis or perception allows us to modulate these processes and thereby create plants with more robust and/or desirable traits, giving us a glimpse into the role of ethylene in the plant. Here, recent and landmark advances in genetic alteration of members of the ethylene pathway in plants and the physiological consequences of these alterations are examined.     

Preparation of ethylene gas and comparison of ethylene responses induced by ethylene,ACC, and ethephon

Ethylene is a gaseous plant hormone used in many physiological studies examining its role in plant growth and development. However, ethylene gas may not be conveniently available to many laboratories for occasional use, and therefore several chemicals can be used as replacements. Here we report that the kinetics of the ethylene response induced by ethylene and two widely-used ethylene replacements are different. ACC failed to efficiently replace prolonged ethylene treatments, while the decomposition products of ethephon may cause non-specific responses and the efficiency of ethephon conversion to ethylene was relatively low. A cost-effective method to prepare ethylene gas was developed. Analyzed by gas chromatography, the chemically produced ethylene exhibited an identical chromatogram to that from the commercial source. Our synthetic ethylene gave the same dose-response curve in Arabidopsis as gaseous ethylene. Our study shows that the use of the ethylene gas is essential to experiments that are sensitive to treatment duration and dosage. When ACC and ethephon are used as replacements, caution should be taken in the experimental design. For laboratories that do not have an ethylene tank, ethylene gas can be easily prepared by a chemical approach without further purification.     

N、P施肥对塔里木河上游绿洲棉花C、N、P生态化学计量特征的影响

施肥通过外源物质的添加直接干预了农田生态系统中作物元素的运移循环过程。通过野外N、P施肥试验,测定棉花各生育期碳(C)、氮(N)、磷(P)元素含量及其生物量,分析棉株C、N、P元素的分配规律,探讨棉株对生长速率调控的内在机制,获得棉株体内N、P元素的内稳性指数,并判断其限制性元素类型。结果表明:棉花C、N、P元素平均含量分别为388.7、20.97、3.43 g/kg;棉花比生长速率与N∶P、C∶P间均存在负相关关系,棉花生长符合生长速率假说;N、P元素内稳性指数H分别在1.02—5.28、1.01—4.55范围内。叶片N∶P可表征植物限制性元素类型,棉花最大生长速率所对应的叶片N∶P为13,是判断限制元素的标准;综合棉花生长速率和内稳性指数研究可知研究区棉花生长受到N、P元素的共同限制,同时,在生长前期更易受P元素的限制,生长后期更易受N元素的限制。     

Potassium deficiency in plants: effects and signaling cascades

Potassium (K⁺) is an important macronutrient for plant growth and productivity. It fulfills important functions and it is widely included in fertilization management strategies to increase crop production. Although K⁺ is one of the most abundant elements of the earth crust, its availability to plants is usually limited leading to severe reduction in plant growth and yield. In plants, K⁺ shortage induces several responses at different levels: morphological, physiological, biochemical, and molecular. Activation of signaling cascades including reactive oxygen species, phytohormones (ethylene, auxin, and jasmonic acid), Ca²⁺, and phosphatidic acid is also triggered. In this review, we summarize the main of these adaptive responses evolved by plants to cope with K⁺ deficiency in the rhizosphere.