Engineered multi-functional, pro-angiogenic collagen-based scaffolds loaded with endothelial cells promote large deep burn wound healing.

The lack of vascularization associated with deep burns delays the construction of wound beds, increases the risks of infection, and leads to the formation of hypertrophic scars or disfigurement. To address this challenge, we have fabricated a multi-functional pro-angiogenic molecule by grafting integrin αvß3 ligand LXW7 and collagen-binding peptide (SILY) to a dermatan sulfate (DS) glycosaminoglycan backbone, named LXW7-DS-SILY (LDS), and further employed this to functionalize collagen-based Integra scaffolds. Using a large deep burn wound model in C57/BLK6 mice (8-10 weeks old, 26-32g, n = 39), we demonstrated that LDS-modified collagen-based Integra scaffolds loaded with endothelial cells (ECs) accelerate wound healing rate, re-epithelialization, vascularization, and collagen deposition. Specifically, a 2 cm × 3 cm full-thickness skin burn wound was created 48 h after the burn, and then wounds were treated with four groups of different dressing scaffolds, including Integra + ECs, Integra + LDS, and Integra + LDS + ECs with Integra-only as the control. Digital photos were taken for wound healing measurement on post-treatment days 1, 7, 14, 21, 28, and 35. Post-treatment photos revealed that treatment with the Intgera + LDS + ECs scaffold exhibited a higher wound healing rate in the proliferation phase. Histology results showed significantly increased re-epithelialization, increased collagen deposition, increased thin and mixed collagen fiber content, increased angiogenesis, and shorter wound length within the Integra + LDS + ECs group at Day 35. On Day 14, the Integra + LDS + ECs group showed the same trend. The relative proportions of collagen changed from Day 14 to Day 35 in the Integra + LDS + ECs and Integra + ECs groups demonstrated decreased thick collagen fiber deposition and greater thin and mixed collagen fiber deposition. LDS-modified Integra scaffolds represent a promising novel treatment to accelerate deep burn wound healing, thereby potentially reducing the morbidity associated with open burn wounds. These scaffolds can also potentially reduce the need for autografting and morbidity in patients with already limited areas of harvestable skin.

Interplay Impact of Exogenous Application of Abscisic Acid (ABA) and Brassinosteroids (BRs) in Rice Growth, Physiology, and Resistance under Sodium Chloride Stress.

The hormonal imbalances, including abscisic acid (ABA) and brassinosteroid (BR) levels, caused by salinity constitute a key factor in hindering spikelet development in rice and in reducing rice yield. However, the effects of ABA and BRs on spikelet development in plants subjected to salinity stress have been explored to only a limited extent. In this research, the effect of ABA and BRs on rice growth characteristics and the development of spikelets under different salinity levels were investigated. The rice seedlings were subjected to three different salt stress levels: 0.0875 dS m-1 (Control, CK), low salt stress (1.878 dS m-1, LS), and heavy salt stress (4.09 dS m-1, HS). Additionally, independent (ABA or BR) and combined (ABA+BR) exogenous treatments of ABA (at 0 and 25 µM concentration) and BR (at 0 and 5 µM concentration) onto the rice seedlings were performed. The results showed that the exogenous application of ABA, BRs, and ABA+BRs triggered changes in physiological and agronomic characteristics, including photosynthesis rate (Pn), SPAD value, pollen viability, 1000-grain weight (g), and rice grain yield per plant. In addition, spikelet sterility under different salt stress levels (CK, LS, and HS) was decreased significantly through the use of both the single phytohormone and the cocktail, as compared to the controls. The outcome of this study reveals new insights about rice spikelet development in plants subjected to salt stress and the effects on this of ABA and BR. Additionally, it provides information on the use of plant hormones to improve rice yield under salt stress and on the enhancement of effective utilization of salt-affected soils.

Unearthing the Alleviatory Mechanisms of Brassinolide in Cold Stress in Rice.

Cold stress inhibits rice germination and seedling growth. Brassinolide (BR) plays key roles in plant growth, development, and stress responses. In this study, we explored the underlying mechanisms whereby BR helps alleviate cold stress in rice seedlings. BR application to the growth medium significantly increased seed germination and seedling growth of the early rice cultivar "Zhongzao 39" after three days of cold treatment. Specifically, BR significantly increased soluble protein and soluble sugar contents after three days of cold treatment. Moreover, BR stimulated the activity of superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase; thereby alleviating cold-induced damage and increasing glutathione content and the GSH/GSSG ratio while concomitantly reducing H2O2 content. BR upregulated the expression levels of cold-response-related genes, including OsICE1, OsFer1, OsCOLD1, OsLti6a, OsSODB, OsMyb, and OsTERF2, and downregulated that of OsWRKY45, overall alleviating cold stress symptoms. Thus, BR not only upregulated cellular osmotic content and the antioxidant enzyme system to maintain the physiological balance of reactive oxygen species under cold but, additionally, it regulated the expression of cold-response-related genes to alleviate cold stress symptoms. These results provide a theoretical basis for rice breeding for cold resistance using young seedlings.

[Research advance in the roles of water-nitrogen-oxygen factors in mediating rice growth, photosynthesis and nitrogen utilization in paddy soils.] / ç¨»ç”°æ°´æ°®æ°§çŽ¯å¢ƒå› å­å¯¹æ°´ç¨»ç”Ÿé•¿å‘è‚²ã€å ‰åˆä½œç”¨å’Œæ°®åˆ©ç”¨çš„è°ƒæŽ§ç ”ç©¶è¿›å±•.

Water and nitrogen are two important factors controlling rice growth and development. Suitable water-nitrogen interaction can alter nitrogen forms and oxygen environmental factors via regulating water content in the rhizosphere of paddy soil, promote the construction of root morphology, improve leaf photosynthesis and the allocation equilibrium of the photosynthetic products between the source and sink organs, and consequently increase rice population quality and grain yield. The microbial regulation mechanisms driven by the environmental factors (e.g. water, nitrogen and oxygen) also play an important role in improving nitrogen utilization efficiency in rice-soil system. Here, we reviewed the research progress in water-nitrogen interaction, and briefly discussed the effects of water, nitrogen form, and dissolved oxygen on rice growth, photosynthesis, carbon and nitrogen metabolism, nitrogen conversion and the underlying microbiological mechanism. We proposed several key directions for future researches: 1) to quantitatively investigate the spatial and temporal variations of dissolved oxygen in rhizosphere and their dominant environmental drivers under different water and nitrogen regimes; 2) to evaluate the responses of root-sourced signal to rhizosphere dissolved oxygen in different rice genotypes, and uncover its intrinsic mechanisms involved in rice growth and development; 3) to investigate the effects of key microbial process driven by the rhizosphere oxygen environment on the soil nitrogen conversion and rice nitrogen utilization.

Pyridoxal 5'-phosphate enhances the growth and morpho-physiological characteristics of rice cultivars by mitigating the ethylene accumulation under salinity stress.

Salinity-induced ethylene accumulation caused by high production of 1-aminocyclopropane-1-carboxylic acid (ACC) hinders rice plant growth and development. Nevertheless, ACC deaminase may alleviate salt stress and high ethylene production in rice cultivars under salinity stress. Pyridoxal 5'-phosphate (PLP), an ACC deaminase co-factor, could be a useful ACC inhibitor in plants; however, it has not been studied before. In the present study, the effects of PLP on the growth and morphophysiological characteristics of rice cultivars (Jinyuan 85 (JY85) and Nipponbare (NPBA) were investigated under salinity stress (control (CK), low salinity (LS), and high salinity (HS) in hydroponic conditions. The experiment was laid out in a completely randomized design (CRD) under factorial arrangement of treatments. The results showed that, compared with no PLP, exogenous application of PLP significantly inhibited ACC and ethylene production in the roots, leaves and panicles of both cultivars under salinity, and PLP was more effective at improving the physiological characteristics of both cultivars under salinity stress. Further, root morphophysiological traits and pollen viability were triggered in the PLP treatment compared to the no-PLP treatment under various salinity levels. ACC production inhibited by PLP was useful for improving the 1000-grain weight, grain yield per plant, and total plant biomass under the CK, LS and HS treatments in both rice cultivars. These results revealed that PLP, as an ACC deaminase cofactor, is a key tool for mitigating ethylene-induced effects under salinity stress and for enhancing the agronomic and morphophysiological traits of rice under saline conditions.

Abscisic acid mediated proline biosynthesis and antioxidant ability in roots of two different rice genotypes under hypoxic stress.

BACKGROUND: Abscisic acid (ABA) and proline play important roles in rice acclimation to different stress conditions. To study whether cross-talk exists between ABA and proline, their roles in rice acclimation to hypoxia, rice growth, root oxidative damage and endogenous ABA and proline accumulation were investigated in two different rice genotypes ('Nipponbare' (Nip) and 'Upland 502' (U502)). RESULTS: Compared with U502 seedlings, Nip seedlings were highly tolerant to hypoxic stress, with increased plant biomass and leaf photosynthesis and decreased root oxidative damage. Hypoxia significantly stimulated the accumulation of proline and ABA in the roots of both cultivars, with a higher ABA level observed in Nip than in U502, whereas the proline levels showed no significant difference in the two cultivars. The time course variation showed that the root ABA and proline contents under hypoxia increased 1.5- and 1.2-fold in Nip, and 2.2- and 0.7-fold in U502, respectively, within the 1 d of hypoxic stress, but peak ABA production (1 d) occurred before proline accumulation (5 d) in both cultivars. Treatment with an ABA synthesis inhibitor (norflurazon, Norf) inhibited proline synthesis and simultaneously aggravated hypoxia-induced oxidative damage in the roots of both cultivars, but these effects were reversed by exogenous ABA application. Hypoxia plus Norf treatment also induced an increase in glutamate (the main precursor of proline). This indicates that proline accumulation is regulated by ABA-dependent signals under hypoxic stress. Moreover, genes involved in proline metabolism were differentially expressed between the two genotypes, with expression mediated by ABA under hypoxic stress. In Nip, hypoxia-induced proline accumulation in roots was attributed to the upregulation of OsP5CS2 and downregulation of OsProDH, whereas upregulation of OsP5CS1 combined with downregulation of OsProDH enhanced the proline level in U502. CONCLUSION: These results suggest that the high tolerance of the Nip cultivar is related to the high ABA level and ABA-mediated antioxidant capacity in roots. ABA acts upstream of proline accumulation by regulating the expression of genes encoding the key enzymes in proline biosynthesis, which also partly improves rice acclimation to hypoxic stress. However, other signaling pathways enhancing tolerance to hypoxia in the Nip cultivar still need to be elucidated.

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

BACKGROUND: Nutrition with ammonium (NH4+) can enhance the drought tolerance of rice seedlings in comparison to nutrition with nitrate (NO3-). However, there are still no detailed studies investigating the response of nitric oxide (NO) to the different nitrogen nutrition and water regimes. To study the intrinsic mechanism underpinning this relationship, the time-dependent production of NO and its protective role in the antioxidant defense system of NH4+- or NO3--supplied rice seedlings were studied under water stress. RESULTS: An early NO burst was induced by 3 h of water stress in the roots of seedlings subjected to NH4+ treatment, but this phenomenon was not observed under NO3- treatment. Root oxidative damage induced by water stress was significantly higher for treatment with NO3- than with NH4+ due to reactive oxygen species (ROS) accumulation in the former. Inducing NO production by applying the NO donor 3 h after NO3- treatment alleviated the oxidative damage, while inhibiting the early NO burst by applying the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) increased root oxidative damage in NH4+ treatment. Application of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester(L-NAME) completely suppressed NO synthesis in roots 3 h after NH4+ treatment and aggravated water stress-induced oxidative damage. Therefore, the aggravation of oxidative damage by L-NAME might have resulted from changes in the NOS-mediated early NO burst. Water stress also increased the activity of root antioxidant enzymes (catalase, superoxide dismutase, and ascorbate peroxidase). These were further induced by the NO donor but repressed by the NO scavenger and NOS inhibitor in NH4+-treated roots. CONCLUSION: These findings demonstrate that the 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+.

1-Methylcyclopropene Modulates Physiological, Biochemical, and Antioxidant Responses of Rice to Different Salt Stress Levels.

Salt stress in soil is a critical constraint that affects the production of rice. Salt stress hinders plant growth through osmotic stress, ionic stress, and a hormonal imbalance (especially ethylene), therefore, thoughtful efforts are needed to devise salt tolerance management strategies. 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor, which could significantly reduce ethylene production in crops and fruits. However, 1-MCPs response to the physiological, biochemical and antioxidant features of rice under salt stress, are not clear. The present study analyzed whether 1-MCP could modulate salt tolerance for different rice cultivars. Pot culture experiments were conducted in a greenhouse in 2016-2017. Two rice cultivars, Nipponbare (NPBA) and Liangyoupeijiu (LYP9) were used in this trial. The salt stress included four salt levels, 0 g NaCl/kg dry soil (control, CK), 1.5 g NaCl/ kg dry soil (Low Salt stress, LS), 4.5 g NaCl/kg dry soil (Medium Salt stress, MS), and 7.5 g NaCl/kg dry soil (Heavy Salt stress, HS). Two 1-MCP levels, 0 g (CT) and 0.04 g/pot (1-MCP) were applied at the rice booting stage in 2016 and 2017. The results showed that applying 1-MCP significantly reduced ethylene production in rice spikelets from LYP9 and NPBA by 40.2 and 23.9% (CK), 44.3 and 28.6% (LS), 28 and 25.9% (MS), respectively. Rice seedlings for NPBA died under the HS level, while application of 1-MCP reduced the ethylene production in spikelets for LYP9 by 27.4% compared with those that received no 1-MCP treatment. Applying 1-MCP improved the photosynthesis rate and SPAD value in rice leaves for both cultivars. 1-MCP enhanced the superoxide dismutase production, protein synthesis, chlorophyll contents (chl a, b, carotenoids), and decreased malondialdehyde, H2O2, and proline accumulation in rice leaves. Application of 1-MCP also modulated the aboveground biomass, and grain yield for LYP9 and NPBA by 19.4 and 15.1% (CK), 30.3 and 24% (LS), 26.4 and 55.4% (MS), respectively, and 34.5% (HS) for LYP9 compared with those that received no 1-MCP treatment. However, LYP9 displayed a better tolerance than NPBA. The results revealed that 1-MCP could be employed to modulate physiology, biochemical, and antioxidant activities in rice plants, at different levels of salt stress, as a salt stress remedy.

iTRAQ-Based Protein Profiling and Biochemical Analysis of Two Contrasting Rice Genotypes Revealed Their Differential Responses to Salt Stress.

Salt stress is one of the key abiotic stresses causing huge productivity losses in rice. In addition, the differential sensitivity to salinity of different rice genotypes during different growth stages is a major issue in mitigating salt stress in rice. Further, information on quantitative proteomics in rice addressing such an issue is scarce. In the present study, an isobaric tags for relative and absolute quantitation (iTRAQ)-based comparative protein quantification was carried out to investigate the salinity-responsive proteins and related biochemical features of two contrasting rice genotypes-Nipponbare (NPBA, japonica) and Liangyoupeijiu (LYP9, indica), at the maximum tillering stage. The rice genotypes were exposed to four levels of salinity: 0 (control; CK), 1.5 (low salt stress; LS), 4.5 (moderate salt stress; MS), and 7.5 g of NaCl/kg dry soil (high salt stress, HS). The iTRAQ protein profiling under different salinity conditions identified a total of 5340 proteins with 1% FDR in both rice genotypes. In LYP9, comparisons of LS, MS, and HS compared with CK revealed the up-regulation of 28, 368, and 491 proteins, respectively. On the other hand, in NPBA, 239 and 337 proteins were differentially upregulated in LS and MS compared with CK, respectively. Functional characterization by KEGG and COG, along with the GO enrichment results, suggests that the differentially expressed proteins are mainly involved in regulation of salt stress responses, oxidation-reduction responses, photosynthesis, and carbohydrate metabolism. Biochemical analysis of the rice genotypes revealed that the Na⁺ and Cl- uptake from soil to the leaves via the roots was increased with increasing salt stress levels in both rice genotypes. Further, increasing the salinity levels resulted in increased cell membrane injury in both rice cultivars, however more severely in NPBA. Moreover, the rice root activity was found to be higher in LYP9 roots compared with NPBA under salt stress conditions, suggesting the positive role of rice root activity in mitigating salinity. Overall, the results from the study add further insights into the differential proteome dynamics in two contrasting rice genotypes with respect to salt tolerance, and imply the candidature of LYP9 to be a greater salt tolerant genotype over NPBA.

Trade-off of within-leaf nitrogen allocation between photosynthetic nitrogen-use efficiency and water deficit stress acclimation in rice (Oryza sativa L.).

Nitrogen (N) allocation in leaves affects plant photosynthesis-N relationship and adaptation to environmental fluctuations. To reveal the role of leaf N allocation in water deficit stress acclimation in rice, the plants were grown in infertile soil supplying with low N (0.05 g N·kg-1 soil) and high N (0.2 g N·kg-1 soil), and then imposed to water deficit stress (∼75% relative soil water content). We found that the proportion of leaf N allocated in the photosynthetic apparatus was significantly positive correlated with photosynthetic N-use efficiency (PNUE), and that N allocation in the carboxylation system and bioenergetics were the primary two limiting factors of PNUE under the conditions of high N and water deficit stress. PNUE was not significantly affected by water stress in low N condition, but markedly reduced in high N condition. Under low N condition, plants reduced N allocation in the light-harvesting system and increased soluble protein and free amino acids, or reduced N allocation in the cell wall to maintain PNUE under water deficit stress. Under high N, however, plants decreased N allocation in bioenergetics or carboxylation, but increased N allocation in non-photosynthetic components during water stress. Our results reveal that the coordination of leaf N allocation between photosynthetic and non-photosynthetic apparatus, and among the components of the photosynthetic apparatus is important for the trade-off between PNUE and the acclimation of water deficit stress in rice.

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.

Heat stress induces spikelet sterility in rice at anthesis through inhibition of pollen tube elongation interfering with auxin homeostasis in pollinated pistils.

BACKGROUND: Pollen tube elongation in the pistil is a key step for pollination success in plants, and auxins play an important role in this process. However, the function of auxins in pollen tube elongation in the pistil of rice under heat stress has seldom been previously reported. RESULTS: Two rice genotypes differing in heat tolerance were subjected to heat stress of 40 °C for 2 h after flowering. A sharp decrease in spikelet fertility was found in the Nipponbare (NPB) and its mutant High temperature susceptible (HTS) under heat stress, but the stress-induced spikelet sterility was reversed by 1-naphthaleneacetic acid (NAA), especially the HTS. Under heat stress, the pollen tubes of NPB were visible in ovule, while those of HTS were invisible. However, we found the pollen tubes in ovule when sprayed with NAA. During this process, a significant increase in indole-3-acetic acid (IAA) and reactive oxygen species (ROS) levels was found in the pistil of heat-stressed NPB, while in heat-stressed HTS they were obviously decreased. Additionally, the peroxidase (POD) activity in pistil of NPB was significantly decreased by heat stress, whereas there was no difference between the heat-stressed and non-heat-stressed pistils of HTS. CONCLUSION: It was concluded that the enhancement of heat tolerance in plants by NAA was achieved through the increase of the levels of auxins, which prevented the inhibition of pollen tube elongation in pistil, and the crosstalk between auxins and ROS, which might be involved in this process. In addition, POD might be a negative mediator in pollen tube elongation under heat stress due to its ability to scavenge ROS and degrade auxin.

Nitrogen metabolism correlates with the acclimation of photosynthesis to short-term water stress in rice (Oryza sativa L.).

Nitrogen metabolism is as sensitive to water stress as photosynthesis, but its role in plant under soil drying is not well understood. We hypothesized that the alterations in N metabolism could be related to the acclimation of photosynthesis to water stress. The features of photosynthesis and N metabolism in a japonica rice 'Jiayou 5' and an indica rice 'Zhongzheyou 1' were investigated under mild and moderate soil drying with a pot experiment. Soil drying increased non-photochemical quenching (NPQ) and reduced photon quantum efficiency of PSII and CO2 fixation in 'Zhongzheyou 1', whereas the effect was much slighter in 'Jiayou 5'. Nevertheless, the photosynthetic rate of the two cultivars showed no significant difference between control and water stress. Soil drying increased nitrate reducing in leaves of 'Zhongzheyou 1', characterized by enhanced nitrate reductase (NR) activity and lowered nitrate content; whereas glutamate dehydrogenase (GDH), glutamic-oxaloacetic transaminase (GOT) and glutamic-pyruvic transaminase (GPT) were relative slightly affected. 'Jiayou 5' plants increased the accumulation of nitrate under soil drying, although its NR activity was increased. In addition, the activities of GDH, GOT and GPT were typically increased under soil drying. Besides, amino acids and soluble sugar were significantly increased under mild and moderate soil drying, respectively. The accumulation of nitrate, amino acid and sugar could serve as osmotica in 'Jiayou 5'. The results reveal that N metabolism plays diverse roles in the photosynthetic acclimation of rice plants to soil drying.

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.

Heat Stress Is More Damaging to Superior Spikelets than Inferiors of Rice (Oryza sativa L.) due to Their Different Organ Temperatures.

In general, the fertility and kernel weight of inferior spikelets of rice (Oryza Sativa L.) are obviously lower than those of superior spikelets, especially under abiotic stress. However, different responses to heat stress are seemed to show between the superior and inferior spikelet, and this response is scarcely documented that the intrinsic factors remain elusive. In order to reveal the mechanism underlying, two rice plants with different heat tolerance were subjected to heat stress of 40°C at anthesis. The results indicated that a greater decrease in fertility and kernel weight was observed in superior spikelets compared to inferior spikelets. This decrease was primarily ascribed to their different organ temperatures, in which the temperature of the superior spikelets was significantly higher than that of inferior spikelets. We inferred the differences in canopy temperature, light intensity and panicle types, were the primary reasons for the temperature difference between superior and inferior spikelets. Under heat stress, the fertility and kernel weight of superior and inferior spikelets decreased as the panicle numbers per plant were reduced, which was accompanied by significantly increasing the canopy temperatures. Thus, it was suggested that the rice plant with characteristic features of an upright growth habit and loose panicles might be more susceptible to heat stress resulting from their higher canopy and spikelets temperatures.

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.

[Advances in studies of absorption and utilization of amino acids by plants: A review].

Plant can directly take up the intact amino acids, thus bypass the microbial mineralization of organic nitrogen. As an excellent carbon and nitrogen source, there exists competition for amino acid absorption between plant roots.and soil microorganisms. And the total flux of amino acids in soil may be enormous due to the extensive sources and short half-life. Studies on amino acid nitrogen nutritional contribution for plant by the technique of nitrogen isotopic tracer, has become a research topic in recent years ,which will help us better understand the principle of soil fertility. This paper summarized the recent researches on amino acid morphological characteristics in soil and its metabolic mechanism and nitrogen nutritional contribution for plant in different ecosystems, and discussed the present status and development trend of the amino acid circulation mechanism in the plant-soil-microorganism ecosystem and its bioavailability for plant. Finally, the topics of environmental regulating mechanism of amino acid bioavailability, amino acid carbon-nitrogen metabolism, and how to improve the field organic nitrogen management were all the core issues to be resolved.

Creation of mixed beam from alloy target and couple of pure targets with laser.

To create mixed species ion beam with laser pulses, we investigated charge state distributions of plasma formed from both Al-Fe alloy targets and pure Al and Fe targets placed close together. With two targets, we observed that the two kinds of atoms were mixed when the interval of two laser pulses was large enough (40 µs). On the other hand, when the interval was 0.0 µs, we observed fewer Fe ions and they did not mix well with the Al ions. The two species were mixed well in the plasma from the alloy target. Furthermore, we observed that specific charge states of Fe ions increased. From the results, it was determined that we can use two pure targets to mix two species whose difference of the drift velocity is large. On the other hand, we must use an alloy target when the drift velocities of the species are close.

[Selenium cycling and transformation in paddy field and selenium nutrition of rice: a review].

Due to the alternate variation of soil redox potential and the particularity of soil components in paddy field, the selenium (Se) cycling and transformation in paddy soil are obviously different from those in upland soil, and can affect the Se availability in soil and the Se absorption and accumulation by rice. To deeply understand the Se cycling and transformation in paddy soil and the Se absorption and accumulation by rice is of great importance in studying the transformation of soil inorganic Se to organic Se. This paper summarized the researches on the cycling mechanisms and form transformation of Se in paddy soil and the metabolic mechanisms and absorption characteristics of Se by rice, and discussed the present status and development trend of the studies on the Se transformation in soil-rice system and the Se translocation in rice plant, which could provide references for the study of soil Se availability and the cultivation of Se-enriched rice.

[Effects of Sedum plumbizincicola--Oryza sativa rotation and phosphate amendment on Cd and Zn uptake by O. sativa].

In a pot experiment, hyperaccumulator Sedum plumbizincicola and low-cadmium accumulating Oryza sativa cultivar "Zhongxiang No. 1" were planted in rotation on a heavy metals-polluted soil, and calcium magnesium phosphate (Ca-P) and rock phosphate (P-R) were amended, aimed to study the effects of the rotation and phosphate amendment on the growth of the two plants and the zinc- and cadmium accumulation in their shoots. After the amendment of 50 g P-R x kg(-1), the Zn and Cd uptake by S. plumbizincicola was 11.5 mg x pot(-1) and 0 x 79 mg x pot(-1), respectively, being significantly higher than that after the amendment of 4 g Ca-P x kg(-1). After the planting of S. plumbizincicola, the Zn and Cd concentrations in "Zhongxiang No. 1" increased, but the amendment of Ca-P decreased the accumulation of Zn and Cd in rice shoot significantly. The rotation with S. plumbizincicola and the amendment of Ca-P and P-R could immobilize the Zn and Cd in the contaminated soil as indicated by the quantitative change of NH4OAc-extractable Cd and Zn, and the efficiency of amendment with Ca-P was better than that of amendment with P-R. Field trial showed that amendment with Ca-P could not only increase the rice yield, but also reduce the Zn and Cd accumulation in rice shoot to a certain extent.