Ethylene and the Responses to Light of Rice Seedlings

The growth of rice seedlings (Oryza satira L.) in the presence of ethylene caused a change in the response to light of coleoptile elongation. In plants grown in air without added ethylene coleoptile elongation was promoted by red, far-red and yellow-green light only in very young seedlings; in older plants irradiation inhibited the growth of the coleoptile. The effect of growing plants in the presence of ethylene was to prolong the period during which light promoted coleoptile growth. Elongation of the first internode was inhibited by light whether or not the seedlings were grown in the presence of ethylene. A correlation existed between the growth effect of an irradiation and the initial decay rate of phytochrome which was established by the treatment. Regardless of wave length, light sources whose intensities were adjusted to produce a decay rate of about 10% per hour or less induced a moderate rate of coleoptile elongation which persisted for a relatively long period. Irradiation with red or yellow-green light of higher intensity which produced a higher rate of phytochrome decay induced a higher rate of coleoptile elongation, but growth stopped after several hours. Other observations, however, showed that one cannot establish a general simple correlation between the rate of elongation of rice coleoptiles under light and the status of measurable phytochrome in the plant.     

大麦氮敏感基因型苗期对氮饥饿的生理响应

以大田试验获得的大麦氮敏感基因型BI-45为材料,利用溶液培养方法,测定了苗期株高、根长、叶绿素含量、含氮量、谷氨酰胺合成酶和硝酸还原酶活性,以及与氮代谢相关的基因（GSI-GSl-2、GSI-3、GS2、Narl、NRT2．J、NRT2-2、NRT2-3和NRT2-4）的表达。结果表明：相对于正常供氮,氮饥饿胁迫下,BI-45根和叶中的氮素利用率提高,含氮量降低,叶绿素含量减少,根冠比增加;叶片中的谷氨酰胺合成酶活性和硝酸还原酶的活性高于根,但是,与叶中的相比,根中的谷氨酰胺合成酶活性升高及硝酸还原酶活性降低的差异性更显著;与正常供氮相比,氮饥饿处理下,根中基因傩家族,基Narl和硝酸盐转运蛋白基因NRT2家族的相对表达量皆达到显著性差异,其中GSl-I、GSl-2和NRT2-2在苗期大麦氮饥饿处理下表现尤为突出,并且在6h都有上调表达。     

Three-Year Soil Carbon and Nitrogen Responses to Sugarcane Straw Management

Green harvest sugarcane management has increased soil organic C and N stocks over time. However, emerging sugarcane straw removal to meet increasing bioenergy demands has raised concerns about soil C and N depletions. Thus, we conducted a field study in southeast Brazil over nearly three years (1100 days) for assessing soil C and N responses to increasing sugarcane straw removal rates. In order to detect the C input as a function of the different amounts of straw over three years, a field simulation was performed, where the original soil layer (0–0.30 m) was replaced by another from an adjacent area with low total C and δ¹³C. The treatments tested were as follows: (i) 0 Mg ha^?1 year^?1 (i.e., 100% removal), (ii) 3.5 Mg ha^?1 year^?1 (i.e., 75% removal), (iii) 7.0 Mg ha^?1 year^?1 (i.e., 50% removal), (iv) 14.0 Mg ha^?1 year^?1 (i.e., no removal), and (v) 21.0 Mg ha^?1 year^?1 (i.e., no removal + extra 50% of the straw left on the field). The results showed that sugarcane straw removal affected the soil C and total N pools. In the first 45 days of straw decomposition, a small but important straw-derived C portion enters into the soil as dissolved organic carbon (DOC). The lower the straw removal rate, the higher was straw-derived DOC content found into the soil, down to 0.50 m depth. After 3 years of management, keeping sugarcane straw on soil surface significantly increased C and N stocks within surface soil layer (0–0.025 m). Our findings suggest that under no straw removal management (i.e., 14 Mg ha^?1), approximately 364 kg ha^?1 of C and 23 kg ha^?1 of N are annually stored into this low-C soil. The contribution of the straw-derived C (C-C4) to the total soil C increases over time, which accounted for about 60% under no straw removal rate. The greatest contribution of the C storage preferentially occurs into the fraction of organic matter (<?0.53 μm) associated with soil clay minerals. We concluded that indiscriminate sugarcane straw removal to produce cellulosic ethanol or bioelectricity depletes soil C stocks and reduces N cycling in sugarcane fields, impairing environmental gains associated with bioenergy production. Therefore, this information, linked with other agronomic and environmental issues, should be taken into account towards a more sustainable straw removal management for bioenergy production in Brazil.     

Soil Carbon and Nitrogen Responses to Nitrogen Fertilizer and Harvesting Rates in Switchgrass Cropping Systems

The environmental sustainability of bioenergy cropping systems depends upon multiple factors such as crop selection, agricultural practices, and the management of carbon (C), nitrogen (N), and water resources. Perennial grasses, such as switchgrass (Panicum virgatum L.), show potential as a sustainable bioenergy source due to high yields on marginal lands with low fertilizer inputs and an extensive root system that may increase sequestration of C and N in subsurface soil horizons. We quantified the C and N stocks in roots, free particulate, and mineral-associated soil organic matter pools in a 4-year-old switchgrass system following conversion from row crop agriculture at the W.K. Kellogg Biological Station in southwest Michigan. Crops were fertilized with nitrogen at either 0, 84, or 196 kg N ha^?1 and harvested either once or twice annually. Twice-annual harvesting caused a reduction of C and N stocks in the relatively labile roots and free-particulate organic matter pools. Nitrogen fertilizer significantly reduced total soil organic C and N stocks, particularly in the stable, mineral-associated C and N pools at depths greater than 15 cm. The largest total belowground C stocks in biomass and soil occurred in unfertilized plots with annual harvesting. These findings suggest that fertilization in switchgrass agriculture moderates the sequestration potential of the soil C pool.     

Transcriptomic Profiling of Rice Seedlings Inoculated with the Symbiotic Fungus Trichoderma asperellum SL2

The fungal species Trichoderma is reported to have a significant impact on the growth and physiological performance of rice plants. However, the molecular mechanisms that induce these effects remain unspecified. Using next-generation sequencing technology, this study compared the differential expression of genes in rice seedlings that had been inoculated with Trichoderma asperellum SL2 with the gene expression in seedlings that had no such inoculation. The study showed that many genes related to plant growth enhancement and physiological functioning are differentially expressed in seedlings which have been symbiotically colonized by T. asperellum SL2. In these seedlings, specific genes related to photosynthesis, RNA activity, stomatal activity, and root development were found to be up-regulated as others were down-regulated. Although the exact causal mechanisms at the molecular level remain to be identified, the presence of Trichoderma versus its absence was associated with almost ten times more significant up-regulations than down-regulations for specific genes that have been identified from previous genomic mapping. Such analysis at the molecular level can help to explain observed phenotypic effects at the organismic level, and it begins to illuminate the observed beneficial relationships expressed phenotypically between crop plants and certain symbiotic microbes.

     

Mineral Elements of Subtropical Tree Seedlings in Response to Elevated Carbon Dioxide and Nitrogen Addition

Mineral elements in plants have been strongly affected by increased atmospheric carbon dioxide (CO₂) concentrations and nitrogen (N) deposition due to human activities. However, such understanding is largely limited to N and phosphorus in grassland. Using open-top chambers, we examined the concentrations of potassium (K), calcium (Ca), magnesium (Mg), aluminum (Al), copper (Cu) and manganese (Mn) in the leaves and roots of the seedlings of five subtropical tree species in response to elevated CO₂ (ca. 700 μmol CO₂ mol^-1) and N addition (100 kg N ha^-1 yr^-1) from 2005 to 2009. These mineral elements in the roots responded more strongly to elevated CO₂ and N addition than those in the leaves. Elevated CO₂ did not consistently decrease the concentrations of plant mineral elements, with increases in K, Al, Cu and Mn in some tree species. N addition decreased K and had no influence on Cu in the five tree species. Given the shifts in plant mineral elements, Schima superba and Castanopsis hystrix were less responsive to elevated CO₂ and N addition alone, respectively. Our results indicate that plant stoichiometry would be altered by increasing CO₂ and N deposition, and K would likely become a limiting nutrient under increasing N deposition in subtropics.     

Precipitation Pattern Regulates Soil Carbon Flux Responses to Nitrogen Addition in a Temperate Forest

Ecosystems - Changes in precipitation frequency and intensity are predicted to be more intense and frequent accompanying climate change and may have immediate or potentially prolonged effects on...     

水稻幼苗抗感性的动力学分析

通过3个品种的胁变过程的分析，表明：1.用向心力和切向力或离心力和切向力进行胁变分析是可行的。2.通过分析认为存在频率、阻尼和相位三种抗性因素。3.通过进一步分析认为阻尼与耐性相关，相位与避性相关，因此可以认为频率、耐性和避性是抗性的三个因素。4.继而认为存在避耐性抗性，避频抗性和耐频抗性三种抗性形成。5.在Levitt抗性理论中只有避耐一种抗性形式，本文突破了这种模式。     

Transcriptomic Analysis of Temperature Responses of Aspergillus kawachii during Barley Koji Production

The koji mold Aspergillus kawachii is used for making the Japanese distilled spirit shochu. During shochu production, A. kawachii is grown in solid-state culture (koji) on steamed grains, such as rice or barley, to convert the grain starch to glucose and produce citric acid. During this process, the cultivation temperature of A. kawachii is gradually increased to 40°C and is then lowered to 30°C. This temperature modulation is important for stimulating amylase activity and the accumulation of citric acid. However, the effects of temperature on A. kawachii at the gene expression level have not been elucidated. In this study, we investigated the effect of solid-state cultivation temperature on gene expression for A. kawachii grown on barley. The results of DNA microarray and gene ontology analyses showed that the expression of genes involved in the glycerol, trehalose, and pentose phosphate metabolic pathways, which function downstream of glycolysis, was downregulated by shifting the cultivation temperature from 40 to 30°C. In addition, significantly reduced expression of genes related to heat shock responses and increased expression of genes related with amino acid transport were also observed. These results suggest that solid-state cultivation at 40°C is stressful for A. kawachii and that heat adaptation leads to reduced citric acid accumulation through activation of pathways branching from glycolysis. The gene expression profile of A. kawachii elucidated in this study is expected to contribute to the understanding of gene regulation during koji production and optimization of the industrially desirable characteristics of A. kawachii.     

Why Nitrogen Use Efficiency Decreases Under High Nitrogen Supply in Rice (Oryza sativa L.) Seedlings

Hydroponic experiments were conducted in a greenhouse to examine the effects of different nitrogen (N) supply (low, 20 mg L⁻¹; intermediate, 40 mg L⁻¹; and high, 100 mg L⁻¹) on the growth, nitrogen use efficiency, and photosynthetic characteristics of rice seedlings (Oryza sativa L., cv. “Shanyou 63” hybrid indica. China). Leaf gas exchange was conducted to identify the photosynthetic-limiting factors in plants with high N supply. The results showed that (1) shoot biomass, leaf area, and tiller numbers per plant under low N were lower than under intermediate and high N supplies. No significant differences were observed between plants supplied with intermediate and high N. (2) About a 35% increase in leaf N content in plants fed by high N resulted in about a 15% increase in carboxylation efficiency (CE) and photosynthetic rate. (3) The noncorresponding increases in photosynthetic rate in rice seedlings fed by high N relative to low N resulted from Rubisco activity and/or CE. (4) The decreased Rubisco activity was induced by a relatively insufficient CO₂ supply under high N supply. These results indicated that insufficient CO₂ supply under high N supply accounted for the decreased Rubisco activity and the noncorresponding increases in photosynthetic rate to leaf N content, and as a result, decreased (photosynthetic) nitrogen use efficiency.