Chengqiang Ding

The interaction between nitrogen availability and auxin, cytokinin, and strigolactone in the control of shoot branching in rice (Oryza sativa L.).

Key messageNitrogen availability and cytokinin could promote shoot branching in rice, whereas auxin and strigolactone inhibited it. The interaction between nitrogen availability and the three hormones is discussed.AbstractRice shoot branching is strongly affected by nitrogen availability and the plant hormones auxin, cytokinin, and strigolactone; however, the interaction of them in the regulation of rice shoot branching remains a subject of debate. In the present study, nitrogen and the three hormones were used to regulate rice tiller bud growth in the indica rice variety Yangdao 6. Both nitrogen and CK promoted shoot branching in rice, whereas auxin and SL inhibited it. We used HPLC to determine the amounts of endogenous IAA and CK, and we used quantitative real-time PCR analysis to quantify the expression levels of several genes. Nitrogen enhanced the amount of CK by promoting the expression levels of OsIPTs in nodes. In addition, both nitrogen and CK downregulated the expression of genes related to SL synthesis in root and nodes, implying that the inhibition of SL synthesis by nitrogen may occur at least partially through the CK pathway. SL did not significantly reduce the amount of CK or the expression levels of OsIPT genes, but it did significantly reduce the amount of auxin and the auxin transport capacity in nodes. Auxin itself inhibited CK synthesis and promoted SL synthesis in nodes rather than in roots. Furthermore, we found that CK and SL quickly reduced and increased the expression of FC1 in buds, respectively, implying that FC1 might be a common target for the CK and SL pathways. Nitrogen and auxin delayed expression change patterns of FC1, potentially by changing the downstream signals for CK and SL.

Nitrogen fertilizer increases spikelet number per panicle by enhancing cytokinin synthesis in rice

Key messageNitrogen fertilizer enhances local cytokinin synthesis to increase flower numbers in the panicles of rice. Localized cytokinin biosynthesis is an important response to nitrogen.AbstractFlower number per panicle is one of the most important traits in rice productivity determination. The number of flowers is established in the early stages of panicle development. Nitrogen fertilizer application before panicle initiation is well known to increase flower number. Nitrogen increases cytokinin (CKs) biosynthesis in plants, and CKs have very similar effects as nitrogen fertilizer on panicle branching. The effects of nitrogen fertilizer on panicle branching may be mediated by CKs, in which accumulation in the inflorescence meristem can regulate panicle development, resulting in increased numbers of flowers and branches. Adenosine phosphate-isopentenyltransferase (IPT) catalyzes the rate-limiting step of CKs biosynthesis. We analyzed the effect of nitrogen fertilizer (urea) on the expression of OsIPT genes (OsIPTs). The results showed that OsIPTs were markedly increased, and CKs accumulated in panicle when nitrogen fertilizer was applied. CKs biosynthesis in the roots and leaves was not up-regulated by nitrogen. These results suggest that nitrogen fertilizer enhances local CKs synthesis to increase flower numbers in the panicles of rice. Localized CKs biosynthesis is an important response to nitrogen.

A proteomic approach to analyze nitrogen- and cytokinin-responsive proteins in rice roots.

Nitrogen plays a central role in rice growth and development because it modulates a wide variety of processes, including cytokinin (CK) metabolism. CK-mediated signaling is also related to nitrogen metabolism. The functional relation between nitrogen and CK are extremely complex and unclear. In this study, a comparative proteomic analysis was carried out to analyze proteins regulated by nitrogen and CK in rice roots. Proteins extracted from rice roots are separated by two-dimensional polyacrylamide gel electrophoresis. Thirty-two protein spots that expressed similarly by nitrogen and CK treatments are selected for identification by mass spectrometry. Of these spots, 28 are successfully identified. These proteins were categorized into classes related to energy, metabolism, disease/defense, protein degradation, signal transduction, transposons, and unclear classification. Energy gives the largest functional category, suggesting that the glycolysis (two enzymes detected) and tricarboxylic acid cycle (six enzymes detected) are accurately regulated by nitrogen and CK, thus promoting the synthesis of amino acid. The identification of novel proteins provides new insights into the coordination of nitrogen and CK in rice. The possible role of these proteins is discussed.

Top-dressing nitrogen fertilizer rate contributes to decrease culm physical strength by reducing structural carbohydrate content in japonica rice

Abstract Lodging is an important factor limiting rice yield and quality by bending or breaking stem in japonica rice ( Oryza sativa L.) production. The objectives of this study were to determine the mechanism of lodging resistance in japonica rice as affected by carbohydrate components, especially its related arrangement in culm tissue and response to top-dressing nitrogen (N) fertilizer. Field experiments were conducted in Danyang County, Jiangsu Province, China, by using two japonica rice varieties Wuyunjing 23 (lodging-resistance variety) and W3668 (lodging-susceptible variety) with three top-dressing N fertilizer rates (0, 135 and 270 kg N ha −1 ) in 2013 and 2014. Lodging related physical parameters, morphological characteristics and stem carbohydrate components were investigated at 30 d after full heading stage. Results showed that with increasing N fertilizer rates, the lodging rate and lodging index increased rapidly primarily due to significant reduction of breaking strength in two japonica rice varieties. Correlation analysis revealed that breaking strength was significantly and positively correlated with bending stress, but negatively correlated with section modulus, except for significant correlation at W3668 in 2014. Higher stem plumpness status and structural carbohydrate contents significantly enhanced stem stiffness, despite of lower non-structural carbohydrate. With higher N fertilizer rate, the culm wall thickness was almost identical, and culm diameter increased slightly. The structural carbohydrates, especially for lignin content in culm, reduced significantly under high N rate. Further histochemical staining analysis revealed that high N treatments decreased the lignin deposition rapidly in the sclerenchyma cells of mechanical tissue, large vascular bundle and small vascular bundle region, which were consistent with reduction of bending stress, especially for W3668 and thus, resulted in poor stem strength and higher lodging index. These results suggested that structural carbohydrate plays a vital role for improving stem strength in japonica rice. N rate decreased lodging resistance primarily due to poor stem stiffness, by reducing structural carbohydrate content and lignin deposition in the secondary cell wall of lower internode culm tissue.

Methane emissions from rice fields under continuous straw return in the middle-lower reaches of the Yangtze River

A three-year experiment was conducted in the middle-lower reaches of the Yangtze River in China to study the influence of continuous wheat straw return during the rice season and continuous rice straw return in wheat on methane (CH4) emissions from rice fields in which, the rice-wheat rotation system is the most dominant planting pattern. The field experiment was initiated in October 2009 and has continued since the wheat-growing season of that year. The analyses for the present study were conducted in the second (2011) and third (2012) rice growing seasons. Four treatments, namely, the continuous return of wheat straw and rice straw in every season (WR), of rice straw but no wheat straw return (R), of wheat straw but no rice straw return (W) and a control with no straw return (CK), were laid out in a randomized split-plot design. The total seasonal CH4 emissions ranged from 107.4 to 491.7 kg/ha (2011) and 160.3 to 909.6 kg/ha (2012). The increase in CH4 emissions for treatments WR and W were 289% and 230% in the second year and 185% and 225% in the third year, respectively, in relation to CK. We observed less methane emissions in the treatment R than in CK by 14%-43%, but not statistically significant. Treatment R could increase rice productivity while no more CH4 emission occurs. The difference in the total CH4 emissions mainly related to a difference in the methane flux rate during the first 30-35 days after transplant in the rice growing season, which was caused by the amount of dissolved oxygen in paddy water and the amount of reducible soil materials.

Erratum to: ‘Lodging Resistance of Japonica Rice (Oryza Sativa L.): Morphological and Anatomical Traits Due to Top-Dressing Nitrogen Application Rates’

Background: Lodging in rice production often limits grain yield and quality by breaking or bending stems. Excessive nitrogen (N) fertilizer rates are the cause of poor lodging resistance in rice, but little is known about the effect of top-dressing N application rates on the mechanical strength of japonica rice plants, especially how the anatomical structure in culms is affected by N. In this study, field experiments on two japonica rice varieties with three top-dressing N application rates, 0 kg N ha −1 (LN), 135 kg N ha −1 (MN), and 270 kg N ha −1 (HN) as urea, were

Effect of Removing Superior Spikelets on Grain Filling of Inferior Spikelets in Rice

Large-panicle rice cultivars often fail to reach their yield potential due to the poor grain filling of inferior spikelets (IS). Thus, it is important to determine the causes of poor IS grain filling. In this study, we attempted to identify whether inferior grain filling of large panicles is restricted by superior spikelets (SS) and their physiological mechanism. SS were removed from two homozygous japonica rice strains (W1844 and WJ165) during flowering in an attempt to force photosynthate transport to the IS. We measured the effects of SS removal on seed setting rate, grain weight, grain filling rate, sucrose content, as well as hormone levels, activities of key enzymes, and expression of genes involved in sucrose to starch metabolism in rice IS during grain filling. The results showed that SS removal improved IS grain filling by increasing the seed setting rate, grain weight, sucrose content, and hormone levels. SS removal also enhanced the activities of key enzymes and the expression levels of genes involved in sucrose to starch metabolism. These results suggest that sucrose and several hormones act as signal substances and play a vital role in grain filling by regulating enzyme activities and gene expression. Therefore, IS grain filling is restricted by SS, which limit assimilate supply and plant hormones, leading to poor grain filling of IS.

Differential regulation of proteins in rice (Oryza sativa L.) under iron deficiency

Key messageSixty-three proteins were identified to be differentially accumulated due to iron deficiency in shoot and root. The importance of these proteins alterations on shoot physiology is discussed.AbstractIron (Fe) is an essential micronutrient for plant growth and its accumulation affects the quality of edible plant organs. To investigate the adaptive mechanism of a Chinese rice variety grown under iron deficiency, proteins differentially accumulated in leaves and roots of Yangdao 6, an indica cultivar, under Fe deficiency growth condition, were profiled using a two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/MS). The accumulations of seventy-three proteins were detected to be increased or decreased upon iron deficiency, and sixty-three of them were successfully identified. Among the sixty-three proteins, a total of forty proteins were identified in rice leaves, and twenty-three proteins were in roots. Most of these proteins are involved in photosynthesis, C metabolism, oxidative stress, Adenosine triphosphate synthesis, cell growth or signal transduction. The results provide a comprehensive way to understand, at the level of proteins, the adaptive mechanism used by rice shoots and roots under iron deficiency.

Triacontanol Reduces Transplanting Shock in Machine-Transplanted Rice by Improving the Growth and Antioxidant Systems.

Machine transplantation results in serious transplant shock in seedlings and results in a longer recover stage, which negatively impacts the growth of low-position tillers and the yield of machine-transplanted rice. A barrel experiment was conducted to examine the effect of the foliar application of triacontanol (TRIA) on machine-transplanted rice during the recovery stage. TRIA (0, 1, 5, and 10 μM) was sprayed over leaves 2 days before transplanting. The chlorophyll content, sucrose content, oxidative damage, antioxidant enzyme levels, glutathione (GSH), and ascorbate (ASA) redox states, tiller dynamics and yield components of the plants were investigated. The results show that foliar-applied TRIA significantly alleviates the growth inhibition and oxidative damage caused by transplant shock. Furthermore, the application of TRIA increased the chlorophyll and sucrose contents of the plants. Importantly, TRIA not only significantly improved the activity of catalase (CAT) and guaiacol peroxidase (POD), demonstrating that POD can play an important role in scavenging H2O2 during the recovery stage, but it also enhanced the redox states of ASA and GSH by regulating the activities of enzymes involved in the ASA–GSH cycle, such as ascorbate peroxidase (APX) and glutathione reductase (GR). A dose of 10 μM TRIA was the most efficient in reducing the negative effects of transplant shock, increasing the panicles, grain filling, and grain yield per hill by 17.80, 5.86, and 16.49%, respectively. These results suggest that TRIA acts to reduce transplant shock in association with the regulation of the redox states of ASA and GSH and antioxidant enzymes and serves as an effective antioxidant to maintain photosynthetic capacity and promote the occurrence of low tillers.

Shading Contributes to the Reduction of Stem Mechanical Strength by Decreasing Cell Wall Synthesis in Japonica Rice (Oryza sativa L.)

Low solar radiation caused by industrial development and solar dimming has become a limitation in crop production in China. It is widely accepted that low solar radiation influences many aspects of plant development, including slender, weak stems and susceptibility to lodging. However, the underlying mechanisms are not well understood. To clarify how low solar radiation affects stem mechanical strength formation and lodging resistance, the japonica rice cultivars Wuyunjing23 (lodging-resistant) and W3668 (lodging-susceptible) were grown under field conditions with normal light (Control) and shading (the incident light was reduced by 60%) with a black nylon net. The yield and yield components, plant morphological characteristics, the stem mechanical strength, cell wall components, culm microstructure, gene expression correlated with cellulose and lignin biosynthesis were measured. The results showed that shading significantly reduced grain yield attributed to reduction of spikelets per panicles and grain weight. The stem-breaking strength decreased significantly under shading treatment; consequently, resulting in higher lodging index in rice plant in both varieties, as revealed by decreased by culm diameter, culm wall thickness and increased plant height, gravity center height. Compared with control, cell wall components including non-structural carbohydrate, sucrose, cellulose, and lignin reduced quite higher. With histochemical straining, shading largely reduced lignin deposition in the sclerenchyma cells and vascular bundle cells compared with control, and decreased cellulose deposition in the parenchyma cells of culm tissue in both Wuyunjing23 and W3668. And under shading condition, gene expression involved in secondary cell wall synthesis, OsPAL, OsCOMT, OsCCoAOMT, OsCCR, and OsCAD2, and primary cell wall synthesis, OsCesA1, OsCesA3, and OsCesA8 were decreased significantly. These results suggest that gene expression involved in the reduction of lignin and cellulose in both sclerenchyma and parenchyma cells, which attribute to lignin and cellulose in culm tissue and weak mechanical tissue, consequently, result in poor stem strength and higher lodging risks. Highlights: (1) Shading decreases the stem mechanical strength of japonica rice by decreasing non-structural carbohydrate, sucrose, lignin, and cellulose accumulation in culms. (2) The decrease of carbon source under shading condition is the cause for the lower lignin and cellulose accumulation in culm. (3) The expression of genes involved in lignin and primarily cell wall cellulose biosynthesis (OsCesA1, OsCesA3, and OsCesA8) at the stem formation stage are down-regulated under shading condition, inducing defective cell wall development and poor lodging resistance.