Qianyu Jin

Nitrogen Metabolism in Adaptation of Photosynthesis to Water Stress in Rice Grown under Different Nitrogen Levels

To investigate the role of nitrogen (N) metabolism in the adaptation of photosynthesis to water stress in rice, a hydroponic experiment supplying with low N (0.72 mM), moderate N (2.86 mM), and high N (7.15 mM) followed by 150 g⋅L-1 PEG-6000 induced water stress was conducted in a rainout shelter. Water stress induced stomatal limitation to photosynthesis at low N, but no significant effect was observed at moderate and high N. Non-photochemical quenching was higher at moderate and high N. In contrast, relative excessive energy at PSII level (EXC) was declined with increasing N level. Malondialdehyde and hydrogen peroxide (H2O2) contents were in parallel with EXC. Water stress decreased catalase and ascorbate peroxidase activities at low N, resulting in increased H2O2 content and severer membrane lipid peroxidation; whereas the activities of antioxidative enzymes were increased at high N. In accordance with photosynthetic rate and antioxidative enzymes, water stress decreased the activities of key enzymes involving in N metabolism such as glutamate synthase and glutamate dehydrogenase, and photorespiratory key enzyme glycolate oxidase at low N. Concurrently, water stress increased nitrate content significantly at low N, but decreased nitrate content at moderate and high N. Contrary to nitrate, water stress increased proline content at moderate and high N. Our results suggest that N metabolism appears to be associated with the tolerance of photosynthesis to water stress in rice via affecting CO2 diffusion, antioxidant capacity, and osmotic adjustment.

Elevational Variation in Soil Amino Acid and Inorganic Nitrogen Concentrations in Taibai Mountain, China

Amino acids are important sources of soil organic nitrogen (N), which is essential for plant nutrition, but detailed information about which amino acids predominant and whether amino acid composition varies with elevation is lacking. In this study, we hypothesized that the concentrations of amino acids in soil would increase and their composition would vary along the elevational gradient of Taibai Mountain, as plant-derived organic matter accumulated and N mineralization and microbial immobilization of amino acids slowed with reduced soil temperature. Results showed that the concentrations of soil extractable total N, extractable organic N and amino acids significantly increased with elevation due to the accumulation of soil organic matter and the greater N content. Soil extractable organic N concentration was significantly greater than that of the extractable inorganic N (NO3−-N + NH4+-N). On average, soil adsorbed amino acid concentration was approximately 5-fold greater than that of the free amino acids, which indicates that adsorbed amino acids extracted with the strong salt solution likely represent a potential source for the replenishment of free amino acids. We found no appreciable evidence to suggest that amino acids with simple molecular structure were dominant at low elevations, whereas amino acids with high molecular weight and complex aromatic structure dominated the high elevations. Across the elevational gradient, the amino acid pool was dominated by alanine, aspartic acid, glycine, glutamic acid, histidine, serine and threonine. These seven amino acids accounted for approximately 68.9% of the total hydrolyzable amino acid pool. The proportions of isoleucine, tyrosine and methionine varied with elevation, while soil major amino acid composition (including alanine, arginine, aspartic acid, glycine, histidine, leucine, phenylalanine, serine, threonine and valine) did not vary appreciably with elevation (p>0.10). The compositional similarity of many amino acids across the elevational gradient suggests that soil amino acids likely originate from a common source or through similar biochemical processes.

Nitric oxide synthase-mediated early nitric oxide-burst alleviates drought-induced oxidative damage in ammonium supplied-rice roots

Ammonium (NH4+) can enhance rice drought tolerance in comparison to nitrate (NO3-). The mechanism underpinning this relationship was investigated based on the time-dependent nitric oxide (NO) production and its protective role in oxidative stress of NH4+-/NO3--supplied rice under drought. An early burst of NO was induced by drought 3h after root NH4+ treatment but not after NO3- treatment. Root oxidative damage induced by drought was significantly higher in NO3- than in NH4+-treatment due to its reactive oxygen species accumulation. Inducing NO production by applying NO donor 3h after NO3- treatment alleviated the oxidative damage, while inhibiting the early NO burst increased root oxidative damage in NH4+ treatment. Application of nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) completely suppressed NO synthesis in roots 3h after NH4+ treatment and aggravated drought-induced oxidative damage, indicating the aggravation of oxidative damage might have resulted from changes in NOS-mediated early NO burst. Drought also increased root antioxidant enzymes activities, which were further induced by NO donor but repressed by NO scavenger and NOS inhibitor in NH4+-treated roots. Thus, the NOS-mediated early NO burst plays an important role in alleviating oxidative damage induced by drought by enhancing antioxidant defenses in NH4+-supplied rice roots. Highlight NOS-mediated early NO burst plays an important role in alleviating oxidative damage induced by water stress, by enhancing the antioxidant defenses in roots supplemented with NH4+

Ammonium uptake and metabolism alleviate PEG-induced water stress in rice seedlings

Ammonium (NH4+) can enhance the water stress induced drought tolerance of rice seedlings in comparison to nitrate (NO3-) nutrition. To investigate the mechanism involved in nitrogen (N) uptake, N metabolism and transcript abundance of associated genes, a hydroponic experiment was conducted in which different N sources were supplied to seedlings growing under water stress. Compared to nitrate, ammonium prevented water stress-induced biomass, leaf SPAD and photosynthesis reduction to a significantly larger extent. Water stress significantly increased root nitrate reductase (NR) and nitrite reductase (NiR) activities, but decreased leaf NiR and glutamate synthetase (GS) activities under NO3- supply, causing lower nitrate content in roots and higher in leaves. In contrast, under NH4+ supply root GS and glutamine oxoglutarate aminotransferase (GOGAT) activities were significantly decreased under water stress, but remained higher in leaves, compared to NO3- treatment, which was beneficial for the transport and assimilation of ammonium in leaves. 15N tracing assays demonstrated that rice 15N uptake rate and accumulation were significant reduced under water stress, but were higher in plants supplied with NH4+ than with NO3-. Therefore, the formers showed higher leaf soluble sugar, proline and amino acids contents, and in turn, associated with a higher photosynthesis rate and biomass accumulation. Most genes related to NO3- uptake and reduction in roots and leaves were down-regulated; however, two ammonium transporter genes closely related to NH4+ uptake (AMT1;2 and AMT1;3) were up-regulated in response to water stress. Overall, our findings suggest that ammonium supply alleviated waters tress in rice seedlings, mainly by increasing root NH4+ uptake and leaf N metabolism.

Mixed-nitrogen nutrition-mediated enhancement of drought tolerance of rice seedlings associated with photosynthesis, hormone balance and carbohydrate partitioning

To investigate whether mixed-N (NO3− + NH4+) nutrition can enhance rice growth under water-deficit condition, a hydroponic experiment in which rice plants were supplied with different N forms (NO3−, NH4+ and mixed-N) was conducted, and the intrinsic mechanisms involved in photosynthesis, root-shoot carbon partitioning, and hormone signalling were investigated. Water stress was found to decrease rice biomass, leaf area, chlorophyll and Rubisco contents. However, mixed-N nutrition substantially alleviated these inhibitions compared with NO3− nutrition alone. Mixed-N nutrition also maintained a higher electron transport rate, actual photochemical efficiency of PSII, and non-photochemical quenching, causing higher photosynthesis and photochemical efficiency. Water stress up-regulated leaf sucrose-phosphate synthase (SPS), but down-regulated acid invertase (InvA). However, leaf InvA and root sucrose synthase in the cleavage direction (SSc) in NO3− nutrition was higher than that in mixed-N nutrition. Water stress decreased indole acetic acid (IAA) content in leaves and cytokinins content in roots, but their contents in mixed-N nutrition were higher than those in NO3− nutrition. In mixed-N nutrition, the up-regulation of SPS and IAA in leaves and the reduction of sucrose metabolism (SSc and InvA) in roots jointly resulted in the accumulation of sucrose in leaves and the inhibition of its transportation to roots, finally reducing the root:shoot ratio (R/S). The reduced R/S provides more photosynthates for shoots and increases the utilisation efficiency, thereby strengthening the water-deficit tolerance of plants. We concluded that the strengthened water-deficit tolerance in mixed-N-supplied rice was closely associated with higher accumulation of dry matter mainly via improvement of photosynthesis and photochemical efficiency, hormone balance, and coupling with root-shoot carbon partitioning.

Effects of salt stress on rice growth, development characteristics, and the regulating ways: A review

Abstract Rice (Oryza sativa L.) is highly susceptible to the rhizosphere salinity than other cereals. High sensitivity has been observed, mainly at vegetative and reproductive stages in rice. It is the duty of plant physiologists to comprehend the growth, development, and physiological processes of rice plants under stress. This paper includes the overview of rice growth and developmental processes influenced by salt stress and the regulation pathways involved in these processes. It also includes the promising salt tolerance strategies, i.e., genetic modification techniques, agronomic practices to improve rice growth, yield, and role of phytohormones and their management, especially inhibition of ethylene biosynthesis by using inhibitors 1-methylcyclopropene (1-MCP). Rice cultivation may be a first choice for improvement of salt tolerance through plant growth regulators and improved cultivation techniques. This study will significantly improve the understanding toward low rice grain yield and poor rice resistance under salt stress and will also stream scientific knowledge for effective utilization of salt affected soils by using different regulating ways.

Concentration and composition of soil amino compounds in major Chinese croplands

ABSTRACT The importance of organic nitrogen (N) in soil N cycle is difficult to assess because of uncertainties regarding its composition, sources, and bioavailability. The objective of this study was to characterise the distribution of soil inorganic N and amino compounds in major Chinese croplands. Results demonstrated that soil extractable N composition was dominated by inorganic N (), and the contents of different N forms widely varied across the 11 different soils. Free amino acid contents ranged from 0.26 to 1.03 mg N kg−1. In contrast, soil-adsorbed amino acids were approximately seven times greater than the free amino acids, which likely represent a potential important pool for free amino acids. Pearson analysis showed that soil free and -adsorbed amino acids were negatively related to soil pH (r = −.39 to −.81, p < .05), while extractable total N, , and hydrolysable amino acids showed the opposite trends. Irrespective of the significant differences in soil properties and environment, soil major amino acid composition was similar, with seven dominant amino acids: alanine, glycine, glutamic acid, aspartic acid, serine, threonine, and isoleucine. The similar composition suggests that the production and utilisation of amino acids likely rely on the same biochemistry or similar amino acid constituents.

Effects of ammonium application rate on uptake of soil adsorbed amino acids by rice

In recent years, excessive use of chemical nitrogen (N) fertilizers has resulted in the accumulation of excess ammonium (NH4+) in many agricultural soils. Though rice is known as an NH4+-tolerant species and can directly absorb soil intact amino acids, we still know considerably less about the role of high exogenous NH4+ content on rice uptake of soil amino acids. This experiment examined the effects of the exogenous NH4+ concentration on rice uptake of soil adsorbed glycine in two different soils under sterile culture. Our data showed that the sorption capacity of glycine was closely related to soils;’ physical and chemical properties, such as organic matter and cation exchange capacity. Rice biomass was significantly inhibited by the exogenous NH4+ content at different glycine adsorption concentrations. A three-way analysis of variance demonstrated that rice glycine uptake and glycine nutritional contribution were not related to its sorption capacity, but significantly related to its glycine:NH4+ concentration ratio. After 21-d sterile cultivation, the rice uptake of adsorbed glycine accounted for 8.8%;–22.6% of rice total N uptake, which indicates that soil adsorbed amino acids theoretically can serve as an important N source for plant growth in spite of a high NH4+ application rate. However, further studies are needed to investigate the extent to which this bioavailability is realized in the field using the 13C, 15N double labeling technology.概要目 的通过采用无菌土培培养方法, 阐明外源高铵态氮施用量与水稻幼苗生长、 土壤吸附态氨基酸吸收之间的关系。创新点借助无菌培养和 15N 同位素示踪方法, 揭示高铵态氮浓度条件下土壤吸附态氨基酸对水稻幼苗生长发育及其氮营养贡献的影响。方 法采集两种不同生态系统的土壤 A 和 B, 经 0.5 mol/L K2SO4 连续淋洗 5 次, 121 °C 灭菌 30 min, 15N-甘氨酸处理后, 根据甘氨酸吸附曲线 (图 1) 确定甘氨酸吸附饱和点和吸附半饱和点, 然后向土壤中添加一些不同浓度的铵态氮, 水稻幼苗无菌培养 21 天后, 用 MAT-271 质谱仪测定水稻幼苗氨基酸吸收量。结 论实验结果表明土壤甘氨酸吸附能力大小与土壤理化性质紧密相关, 有机质和阳离子交换量。 外源高铵态氮水平显著抑制水稻幼苗生长发育 (P<0.05;), 但甘氨酸吸收及其氮营养贡献与甘氨酸吸附能力大小无关, 而与土壤吸附态甘氨酸和铵态氮的浓度比值显著相关 (P<0.05;)。 经过 21 天的无菌培养, 土壤吸附态氨基酸对水稻的氮营养贡献率达 8.8%∼22.6%, 表明土壤吸附态氨基酸理论上可能作为植物的一种潜在重要营养氮源。