Qiangsheng Wang

Occurrence of perfect and imperfect grains of six japonica rice cultivars as affected by nitrogen fertilization

This study aims to quantify nitrogen (N) effect on occurrence of perfect rice kernel (PRK) and imperfect grains which includes white-belly rice kernel (WBRK), white-core rice kernel (WCRK), green rice kernel (GRK), opaque rice kernel (ORK), and other imperfect grains (OTHERS). Two-year field experiments involving six japonica rice cultivars and seven N treatments were performed. The structural differences between white-belly and white-core tissues were compared using scanning electron microscope. Averaged over cultivars, grain yield increased progressively with N rate. PRK increased with N rate in 2008, but decreased with increased N rate in 2009. WBRK and WCRK decreased as N rate increased for both years. High N input resulted in higher occurrence of GRK and OTHERS for both years. Most starch granules in white-belly tissues are intact and surrounded by globular protein bodies, with many air spaces between them; while in white-core tissues, starch granules are easily broken into many single granules and no protein bodies are visible. Our results suggest that N has suppressing influence on chalky grains but favorable effect on other imperfect grains, and indicate different mechanism between WBRK and WCRK.

The impact of relative humidity, genotypes and fertilizer application rates on panicle, leaf temperature, fertility and seed setting of rice

A series of field and plant growth chamber experiments were conducted in 2006 and 2007 to study how relative humidity (RH), genotypes and nitrogen application rates affect organ temperatures and spikelet fertility rates in rice. It was observed that organ temperatures varied with air temperature, RH, genotype and nitrogen application rate. Increases in RH at constant air temperature and increasing air temperature with a constant RH both increased organ temperatures significantly. Cultivars also exhibited differences in organ temperatures; those cultivars with erect panicles recorded lower organ temperatures than those with droopy panicles under similar climatic conditions. Similarly, cultivars with panicles above the flag leaf had lower temperatures at the panicle when compared to those plants with the panicle below the flag leaf. It was also found that panicle temperature showed a significant negative correlation with both grain filling rate and seed setting rate. Spikelet fertility could be maintained by reducing spikelet temperature under decreasing RH in a high-temperature environment. Panicle fertilizer application rates had a significant effect on the organ and canopy temperatures. The canopy temperature of rice grown with an ample supply of nitrogen was generally cooler than the canopy temperature of a nitrogen-deficient treatment.

Effects of external ABA, GA3 and NAA on the tiller bud outgrowth of rice is related to changes in endogenous hormones

Hormones play an important role in regulating the growth of rice tiller buds. However, little is known about the hormonal changes that occur during tiller bud growth and the mechanism of hormonal regulation of tiller bud growth. Here, two rice cultivars, Yangdao 6 (Indica) and Nanjing 44 (Japonica), were used to investigate the changes in plant hormones during tiller bud growth and the mechanism that underlies the hormonal regulation of tiller bud growth. In the present study, panicles were removed after heading to stimulate the growth of dormant tiller buds located at the elongated upper internodes. At the same time, external abscisic acid (ABA), gibberellic acid (GA3) and α-naphthalene acetic acid (NAA) were applied. The results demonstrated that auxin and cytokinin (CTK) play important and different roles in the regulation of tiller bud growth. Auxin in the nodes inhibits tiller bud growth, while CTK is transferred to the tiller buds to promote growth. The inhibitory effects of GA3 and NAA on tiller bud growth are mainly due to the control of the indole-3-acetic acid (IAA) or CTK contents in plants. As opposed to auxin and CTK, the ABA contents in nodes and tiller buds remained unchanged before tiller bud growth after panicle removal. Meanwhile, external ABA application only slightly slowed the growth of the tiller buds, suggesting that ABA may not be a key regulator of tiller bud growth. These results indicate that auxin, CTK and ABA together likely play roles in the regulation of tiller bud growth.

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.

Endosperm structure of white-belly and white-core rice grains shown by scanning electron microscopy.

Abstract: White-belly and white-core are the major two types of grain chalkiness in japonica rice. This study aims to compare the morphological features of white-belly and white-core using a scanning electron microcope (SEM). A japonica rice cultivar Wuyujing3 and its mutants were used as materials. Nearly 1000 SEM images were observed, and 12 representative photos were selected. SEM images showed contrasting differences between white-belly and white-core in endosperm microstructure including the shape of endosperm cell, the size distribution of starch granules, and the amount of protein bodies. White-belly and white-core also varied markedly in morphological features of the cracked compound starch granules. Our findings should help to advance our understanding of the multi-faceted nature of grain chalkiness from the perspective of starch and protein accumulation, and should be of value for future work on rice grain chalkiness.

Temperature Difference Between the Air and Organs of Rice Plant and Its Relation to Spikelet Fertility

Based on the experiment of measuring panicles and leaves, air temperature, and humidity above the canopy of rice cultivars after heading in 2005 and 2006, we investigated the temperature difference (TD) between the air and organs of rice plant and its relationship with spikelet fertility. The results showed that TDs between the air and organs of rice varied with air temperature, air humidity, and plant type. For similar air humidity, TDs were lower at the air temperature of 28.5℃ than at higher temperature of 35.5℃, whereas for the same air temperature, the TDs decreased as the air humidity increased. TDs were also affected by plant type of the cultivars. Erect panicle cultivars showed higher TDs than those with droopy panicles under similar climatic conditions, and cultivars with panicles above flag leaf (PAFL) had higher TDs than those with panicles below the flag leaf (PBFL). Cultivars grown in a location with lower air humidity and higher temperature, such as Taoyuan, China, had higher spikelet fertility than those in higher humidity under the similar air temperature during the grain filling stage. This is partially attributed to the larger TDs under the lower humidity. Row- spacing and the ratio of basal-tillering to panicle-spikelet fertilizer showed a significant influence on TD and subsequently on spikelet fertility, suggesting the possibility of increasing spikelet fertility by agronomic management.

Physicochemical and Sensory Properties of japonica Rice Varied with Production Areas in China

Northeast of China and Jiangsu Province are major production areas of japonica rice in China. Rice from northeast of China is well-known for its good-eating and appearance quality, and that from Jiangsu Province is viewed as inferior. However, little is known concerning the difference in physicochemical and sensory properties of rice between the major two production areas. Analysis of 16 commercial rice samples showed marked differences in physicochemical properties, including chalky grain rate, contents of amylose and protein and pasting properties between the two main areas. Northeastern rice contained more short-chain amylopectin as compared with Jiangsu rice. However, Jiangsu rice is comparable to northeastern rice in terms of sensory quality including overall acceptability and textural properties of springiness, stickiness and hardness as evaluated by trained panel. Our results indicated the limitation of conventional index of physicochemical properties, and suggested the necessity of identification of new factors controlling rice sensory property. In addition, the taste analyzer from Japan demonstrates limitation in distinguishing the differences between northeastern and Jiangsu rice, and therefore needs localization to fit China.

Effect of Nitrogen Applied Before Transplanting on NUE in Rice

Abstract Nitrogen (N) application before transplanting, where N fertilizers are applied in seedling-bed and carried to the paddy field with seedlings, is a novel method proposed in this article aiming for improving nitrogen utilization efficiency (NUE) in rice. The effect of this method on mineral N distribution in the rhizosphere soil was investigated in a field experiment with a japonica variety, Ningjing 2, in seasons of 2004 and 2005. There were four levels of N applied 16 h before transplanting: zero N (N0), 207 kg ha −1 (NL), 310.5 kg ha −1 (NM), and 414 kg ha −1 (NH). The result indicated that N fertilizer before transplantation had positive effect of increasing mineral N content in the rhizosphere soil of rice. Generally, N content in the rhizosphere soil of rice tended to increase with the amount of N fertilizer before transplanting, with the NH treatment having the largest effect. Additionally, N fertilizer before transplanting had significant influence on rice NUE and grain yield. Compared with other treatments, the NM treatment showed the largest influence, with basal-tillering NUE, total NUE, and grain yield being 15%, 12%, and 529.5 kg ha −1 higher than those of N0 treatment. This result indicated that N fertilizer before transplantation had positive effect on mineral N distribution in the rhizosphere soil of rice, thus improving NUE and grain yield.

Effect of Nitric Oxide on Alleviating Cadmium Toxicity in Rice (Oryza sativa L.)

Nitric oxide (NO) is a gaseous signaling molecule in plants that plays a key role in mediating a wide range of physiological processes and responses to biotic and abiotic stresses. The present study was conducted to investigate the effects of the exogenous application of sodium nitroprusside (SNP), an NO donor, on cadmium (Cd)-induced oxidative stress and Cd uptake in rice plants. Rice plants were exposed to Cd stress (0.2 mmol L -1 CdCl2) and different concentrations of SNP (0.05, 0.1, 0.2, and 0.4 mmol L-1). A SNP concentration of 0.1 mmol L-1 (SNP10) significantly reduced the Cd-induced decrease in shoot and root dry weights and leaf chlorophyll concentrations. The addition of NO also reduced the malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ) and ascorbic acid (ASA) concentrations. However, the reduction in glutathione (GSH) concentration was inhibited by NO treatment. Moreover, NO prevented the Cd-induced increase in antioxidative enzyme activity. The amount of Cd accumulation in rice plants was also influenced by the addition of NO. The NO supplied by the SNP enhanced the Cd tolerance of the rice by increasing the Cd uptake by the roots and decreasing the Cd accumulation by the shoots. However, the application of potassium ferrocyanide (Cd+Fe) or sodium nitrate and nitrite (Cd+N) (without NO release), did not exhibit the effects of the SNP. Furthermore, the effects of the SNP were reversed by the addition of hemoglobin (an NO scavenger). Our results suggested that exogenous NO was involved in the resistance of rice to Cdtoxicity.

Analysis of Variations in White-Belly and White-Core Rice Kernels Within a Panicle and the Effect of Panicle Type

Abstract This study aims to investigate the variation in occurrence of white-belly rice kernel (WBRK) and white-core rice kernel (WCRK) among different positions within a panicle. Twenty-four M4 mutants involved in four panicle types, namely the compact, intermediate, loose, and chicken foot panicle were used. They derived from a japonica rice cultivar Wuyujing 3. Considerable differences in morphological characters existed among the four types of panicle, especially in panicle length, the secondary branch number and ratio of grain number to total branch length. Marked differences were found in WBRK and WCRK among different positions within a panicle for all types of panicle. In general, grains located on the primary rachis and top rachis branches had higher WBRK and WCRK percentage than those on the secondary rachis and bottom rachis branches. WCRK exhibited larger variation among grain positions than WBRK did. Moreover, there was a significant difference in WCRK/WBRK among grain positions within a panicle, with primary rachis and top rachis branches having higher values than the secondary and bottom rachis. In addition, panicle type showed no significant effect on the pattern of WBRK and WCRK occurrence within a panicle. The results indicated the difference in mechanism of WBRK and WCRK formation in grain position within a panicle, and are valuable for breeding and agronomic practices aimed at lowering chalky grain rate.