Zinc-deficiency symptoms in lowland rice as induced by modified-urea materials applied at different rates of nitrogen in calcareous soil

Summary Studies revealed that Zn-deficiency symptoms were induced markedly by the levels of nitrogen and its source in rainfed lowland rice grown on calcareous soil. Visual Zn-deficiency symptoms recorded 3 weeks after transplanting showed that increased supply of nitrogen at puddling resulted in significant increase in the extent of deficiency symptoms of this nutrient element. Zn-deficiency symptoms got aggravated with Mussorrie Rock Phos-coated urea (MRPCU) followed by sulphur-coated urea (SCU). Zn-deficiency symptoms induced by urea supergranules (USG) and prilled urea (PU) supplying two-thirds of nitrogen as basal were found to be of moderate level. No symptoms of Zn-deficiency were noted with no-nitrogen control.     

Aspects of the Fe and Mn nutrition of rice plants

Summary In three water-culture experiments, the effects of variations in pH, N form, and Si- and P level on the uptake and translocation of Fe and Mn, and on the chlorophyll contents of lowland rice were examined.It was found that Mn uptake increased with increasing pH, that it was not affected by variations in N form (NO₃ or NH₄), and that Si has a suppressive effect on Mn uptake. With increasing pH, the translocation of Fe to the shoots was reduced. This pH effect might be indirect, in that Fe translocation is hampered by excessive Mn uptake induced by high pH. Variations in N form and in Si level did not influence Fe uptake and- translocation.A combination of high P-and high Mn levels in solution proved to reduce the translocation of Fe to the rice shoots. Precipitation of Mn phosphate on the roots is likely to occur at high concentrations of both Mn and P in the root medium.A negative correlation was found between chlorophyll content and Mn content of the leaves. The chlorophyll content was not related to the iron content of the leaves. It is likely that chlorosis of rice leaves in an early growth stage can be caused by several combinations of the following factors: 1. high Mn supply, 2. NO₃ nutrition inducing an increase in solution pH favouring a further increase in Mn uptake, 3. absence of Si which exerts a suppressive effect on Mn uptake, and 4. high P supply. These factors can induce chlorosis, with and without exerting a concomitant influence on the uptake and translocation of Fe.     

Effects of N-fertilizers,straw, and dry fallow on the nitrogen balance of a flooded soil planted with rice

Summary Nitrogen balance studies were made on rice (Oryza sativa) grown in flooded soil in pots. A low rate of fertilizer (5.64 mg N. kg⁻¹ soil) did not depress the N gain, but a high rate (99.72 mg N. kg⁻¹ soil) elminated the N gain. Soil N loss was negligible since¹⁵N applied as ammonium sulfate and thoroughly mixed with the soil was recovered from the soil-plant system after 3 crops. The observed N gain, therefore, was caused by N₂-fixation, not by a reduction of soil N loss. Straw enhanced N gain at the rate of 2–4 mg per g straw. However, this gain was not observed when soil N availability was high. Dry fallow between rice crops decreased the N gain.     

Increased expression of OsPT1, a high-affinity phosphate transporter, enhances phosphate acquisition in rice

Most high-affinity phosphate transporter genes (OsPTs) in rice were highly induced in roots when phosphate was depleted. OsPT1, however, was highly expressed in primary roots and leaves regardless of external phosphate concentrations. This finding was confirmed histochemically using transgenic rice plants that express the GUS reporter gene under the control of the OsPT1 promoter, which exhibited high GUS activity even in the phosphate sufficient condition. Furthermore, transgenic rice plants overexpressing the OsPT1 gene accumulated almost twice as much phosphate in the shoots as did wild-type plants. As a result, transgenic plants had more tillers than did wild-type plants, which is a typical physiological indicator for phosphate status in rice.     

Genetic variation detected by DNA fingerprinting with a rice minisatellite probe in Oryza sativa L.

A rice minisatellite probe detecting DNA fingerprints was used to assess genetic variation in cultivated rice (Oryza sativa L.). Fifty-seven cultivars of rice, including 40 closely related cultivars released in the US, were studied. Rice DNA fingerprinting revealed high levels of polymorphism among distantly related cultivars. The variability of fingerprinting pattern was reduced in the closely related cultivars. A genetic similarity index (S) was computed based on shared fragments between each pair of cultivars, and genetic distance (D) was used to construct the dendrograms depicting genetic relationships among rice cultivars. Cluster analysis of genetic distance tended to group rice cultivars into different units corresponding with their varietal types and breeding pedigrees. However, by comparison with the coefficients of parentage, the criterion of relatedness based on DNA fingerprints appeared to overestimate the genetic relationships between some of the closely related US cultivars. Although this may reduce the power of fingerprints for genetic analysis, we were able to demonstrate that DNA fingerprinting with minisatellite sequences is simpler and more sensitive than most other types of marker systems in detecting genetic variation in rice.This paper reports the results of research only. Mention of a proprietary product does not consititute an endorsement or a recommendation for its use by the USDA or the University of Missouri. Contribution from the US Department of Agriculture, Agricultural Research Service, Plant Genetics Research Unit, and the University of Missouri Agricultural Experiment Station Journal Series No. 12178.     

Iron toxicity to rice in an acid sulfate soil as influenced by water regimes

Summary The effects of two water regimes: Continuous flooding and flooding with soil drying on iron toxicity to rice in an acid sulfate soil was studied by continuously growing 7 crops of IR-32 rice in pots under the two water treatments. There was no plant growth upto the second crop under both water treatments due to iron toxicity. But there was good growth of rice under the continuous water regime from third cropping onwards, however, there was no growth of rice in the flooding with soil drying treatment even upto the seventh crop due to iron toxicity.The results of the study bring out that keeping an acid sulfate soil flooded for a few weeks and then planting rice when iron in soil solution has dropped below toxicity level may be a possible management practice for lowland rice culture on such soils. Drying and reflooding an acid sulfate soil on the other hand aggravates soil acidity and keeps iron in solution in high amounts to be toxic to rice plant.     

RFLP tagging of a gene for aroma in rice

Summary We report here the identification of a DNA marker closely linked to a gene for aroma in rice. The DNA marker was identified by testing 126 mapped rice genomic, cDNA, and oat cDNA, clones as hybridization probes against Southern blots, consisting of DNA from a pair of nearly isogenic lines (NILs) with or without the aroma gene. Chromosomal segments introgressed from the donor genome were distinguished by RFLPs between the NILs. Linkage association of the clone with the gene was verified using an F₃ segregating for aroma. Cosegregation of the scented phenotype and donor-derived allele indicated the presence of linkage between the DNA marker and the gene. RFLP analysis showed that the gene is linked to a single-copy DNA clone, RG28, on chromosome 8, at a distance of 4.5 cM. The availability of a linked DNA marker may facilitate early selection for the aroma gene in rice breeding programs.     

Phosphate solubilization potential and stress tolerance of rhizobacteria from rice soil in Northern Thailand

Plant growth-promoting rhizobacteria (PGPR) are known to influence plant growth by various direct or indirect mechanisms. A total of 216 phosphate-solubilizing bacterial isolates were isolated from different rice rhizospheric soil in Northern Thailand. These isolate were screened in vitro for their plant growth-promoting activities such as solubilization of inorganic phosphate, ammonia (NH₃), catalase and cell wall-degrading enzyme activity. It was found that 100% solubilized inorganic phosphate, 77.77% produced NH₃ and most of the isolates were positive for catalase. In addition, some strains also produced cell wall-degrading enzymes such as protease (7%), chitinase (1%), cellulase (3%) and β-glucanase (3%), as evidenced by phenotypic biochemical test and quantitative assay using spectrophotometry. The isolates could exhibit more than two or three plant growth-promoting (PGP) traits, which may promote plant growth directly or indirectly or synergistically. Part of this study focused on the effect of NaCl, temperature, and pH on a specific the bacterial isolate Acinetobacter CR 1.8. Strain CR 1.8 was able to grow on up to 25% NaCl, between 25 and 55°C, and at pH 5–9. Maximum solubilization of tricalcium phosphate and aluminium phosphate was obtained at neutral pH, and 37°C. Strain CR 1.8 had protease activity but no cellulase, β-glucanase and cellulase activities.     

Molecular cloning, expression and characterization of a glycosyltransferase from rice

Secondary plant metabolites undergo several modification reactions, including glycosylation. Glycosylation, which is mediated by UDP-glycosyltransferase (UGT), plays a role in the storage of secondary metabolites and in defending plants against stress. In this study, we cloned one of the glycosyltransferases from rice, RUGT-5 resulting in 40–42% sequence homology with UGTs from other plants. RUGT-5 was functionally expressed as a glutathione S-transferase fusion protein in Escherichia coli and was then purified. Eight different flavonoids were used as tentative substrates. HPLC profiling of reaction products displayed at least two peaks. Glycosylation positions were located at the hydroxyl groups at C-3, C-7 or C-4′ flavonoid positions. The most efficient substrate was kaempferol, followed by apigenin, genistein and luteolin, in that order. According to in vitro results and the composition of rice flavonoids the in vivo substrate of RUGT-5 was predicted to be kaempferol or apigenin. To our knowledge, this is the first time that the function of a rice UGT has been characterized.     

Effects of deep placement and surface application of urea on the yield of wetland rice in pot trials

Summary The effects of deep placement and surface application of urea fertilizer on the yield of rice grown in pots of alluvial clay soil covered with 5 cm water was studied under controlled conditions. Application of two levels of urea supergranules and prills (2 g and 4 g urea/0.1 m²) on the surface of submerged soil increased the vegetative growth and enhanced the grain yield as much as 85%. However, no difference in yield was found between urea prills applied in three split doses and one application of urea supergranules.Deep placement of two levels of urea supergranules in the soil at four different depths (2.5, 5.0, 10.0 and 15.0 cm) resulted in the highest yields. The fertilizer was most efficient when the highest concentration was placed in the soil at a depth of 5.0 cm. This application method increased the grain yield by 20% as compared with the soil surface application.     

Iron nutrition affects cadmium accumulation and toxicity in rice plants

The effect of iron (Fe) nutrition on cadmium (Cd) toxicity and accumulation in rice plants was studied using a hydroponic system. The inhibitory effect of Cd on plant growth and chlorophyll content (SPAD value) was dependent on Fe level and the genotype. Malondialdehyde (MDA) content in leaves and roots was not much affected by an increased Cd stress at 0.171 mg l⁻¹ Fe, but it showed a rapid increase when the plants were exposed to moderate (1.89 mg l⁻¹) and high (16.8 mg l⁻¹) Fe levels. High Fe nutrition caused a marked reduction in Cd content in both leaves and roots. Fe content in plants was lower at high Cd (5.0 μM) stress than at low Cd (<1.0 μM) stress. Cd stress increased both superoxide dismutase (SOD) and peroxidase (POD) activities at low and moderate Fe levels. However, with high Fe level, it increased the POD activity, but reduced the SOD activity. Our results substantiate the hypothesis that cell membrane-bound iron transporter (carrier) involved in high-affinity iron transport systems can also transport Cd, and both these ions may compete for this common carrier. The study further showed that there were significant correlations between MDA and Fe contents in leaves and roots of rice plants. It is suggested that the occurrence of oxidative stress in plants exposed to Cd stress is mediated by Fe nutrition. The present results also show that Cd stress affects the uptake of Cu and Zn.     

Metabolic adaptation to flooding stress in upland and lowland rice seedlings

Ability of metabolic adaptation in upland and lowland rice (Oryza sativa L.) seedlings to flooding stress was compared. Flooding stress increased alcohol dehydrogenase (ADH) activity and ethanol concentration in shoots and roots of the upland and lowland rice seedlings. The difference in ADH activity and ethanol concentration in shoots between the upland and lowland rice was not apparent. However, both ADH activity and ethanol concentration in roots of the lowland rice were 2-fold greater than those in roots of the upland rice, suggesting that flooding-induction of ethanolic fermentation in lowland rice roots may be significantly greater than that in the upland rice roots. Since flooding often causes the anaerobic conditions in rooting zone than aerial part of plants and ethanolic fermentation is essential to survive in the anaerobic conditions, the ability of metabolic adaptation in lowland rice seedlings to flooding stress may be greater than that in upland rice seedlings.     

Influence of aluminum in nutrient solutions on chemical composition in upland rice cultivars

Summary Aluminum toxicity is an important growth limiting factor for upland rice production on oxisols of cerrado region in Brazil. Data related to the effect of Al on uptake of nutrients for rice crop are limited. The effect of five Al concentrations (0, 10, 20, 40 and 60 ppm) in culture solution on the chemical composition of 30 upland rice cultivars was studied.Aluminum concentration and content in plant tissues were increased with higher levels of Al in all cultivar. In the roots Al content was higher as compared with the tops. Critical toxic level of Al in the tops of 21 days old plants varied from 100 to 417 ppm depending on the cultivars. Rice cultivars responded differently to Al treatments with respect to nutrients uptake. Increased Al concentrations in the solution exerted an inhibiting effect on the concentrations and contents of N, P, K, Ca, Mg, S, Na, Zn, Fe, Mn, B and Cu. Thus the inhibition was more effective for macronutrients in the plant tops in following order: Mg>Ca>P>K>N>S>Na. Whereas for micronutrients it was in the order of Mn>Zn>Fe>Cu>B. Morphological, physiological and biochemical effects of Al, toxicity responsible for the reduction in plant nutrient uptake, are discussed.     

Effect of P and Mn on growth response and uptake of Fe,Mn and P by sorghum

Summary The effects of P and Mn on growth response and uptake of Fe, Mn and P by grain sorghum were investigated using nutrient culture. High P and Mn concentrations in solution (greater than 40 and 1 mg/l for P and Mn, respectively) markedly reduced plant height and shoot and root dry weight of 4-week-old sorghum plants. High Mn concentrations in solution increased the concentrations of Mn and P in shoot tissue and uptake of Mn, but depressed the uptake of P. High levels of P enhanced Mn uptake by sorghum and accentuated Mn toxicity at low Mn levels. The tissue Fe and total uptake of Fe were both reduced markedly by the high levels of P and Mn concentrations in solution. The increases of P, Mn and Fe concentrations in root tissue with a concomitant decrease of Fe in shoots suggested that the translocation of Fe from roots to shoots was hindered under high P and Mn conditions. Since coating occurred on root surfaces and intensified with increasing Mn concentrations in the substrate, part of the reduction of Fe in shoots could be attributed to the formation of high valent manganese oxides on the root surfaces which may retain Fe and reduce its absorption by sorghum.Contribution from the Department of Agronomy and Range Sci., University of California, Davis, CA.     

The growth and some physiological responses of rice to Cd toxicity as affected by nitrogen form

A hydroponic experiment was conducted to examine the effect of Cd stress on anti-oxidative enzyme activities at heading stage, yield components, root exudation and Cd and N uptake of rice plants grew in different N source i.e. (NH₄)₂SO₄, NH₄NO₃ and Ca(NO₃)₂. The results show that the effect of Cd stress on all measured parameters were N source dependent. Cd stress (1 μM) caused a remarkable reduction in grain yield and shoot biomass, an increase in root exudation, glutathione content, Cd concentration and catalase (CAT) and peroxidase (POD) activities of rice plants. In the plants under the control (without Cd addition) N source had no distinctive effect on the above measured parameters, but the differences among the three N forms in these parameters became significant when plants were exposed to Cd stress. Cd stress significantly increased POD and CAT activities, and gultathione content, with Ca(NO₃)₂-fed plants having the greatest POD and CAT activities and lowest glutathione content, and (NH₄)₂SO₄-fed plants being just opposite. Moreover, organic acid exudation varied also with N form for the Cd-stressed plants. In comparison with other two N forms, (NH₄)₂SO₄,-treated plants had higher grain yield, N concentration and lower Cd concentration in plants. The current results indicated that (NH₄)₂SO₄ is a better fertilizer for use in Cd contaminated soil.     

Aspects of the Fe-and Mn nutrition of rice plants

Summary The combination of low Mn levels and high Fe levels in tissues of lowland rice varieties, as often encountered when rice is grown on acid soils, is not likely to result from an antagonistic effect of Fe on the uptake of Mn.Experiments with rice plants growing on sand, supplied with Fe and Mn, and subjected to various pH levels and moisture regimes, made it clear that under acid anaerobic conditions the absorption of Mn by rice plants is little affected by the presence of large quantities of Fe, and that under acid aerobic conditions the absorption of Fe by rice plants is little affected by the presence of large quantities of Mn.     

Identification of microsatellite markers for fragrance in rice by analysis of the rice genome sequence

Several chemical constituents are important to the fragrance of cooked rice. However, the chemical compound 2-acetyl-1-pyrroline (AP) is regarded as the most important component of fragrance in the basmati- and jasmine-style fragrant rices. AP is found in all parts of the plant except the roots. It is believed that a single recessive gene is responsible for the production of fragrance in most rice plants. The detection of fragrance can be carried out via sensory or chemical methods, although each has their disadvantages. To overcome these difficulties, we have identified an (AT)₄₀ repeat microsatellite or simple sequence repeat (SSR) marker for fragrant and non-fragrant alleles of the fgr gene. Identification of this marker was facilitated through use of both the publicly available and restricted access sequence information of the Monsanto rice sequence databases. Fifty F₂ individuals from a mapping population were genotyped for the polymorphic marker. This marker has a high polymorphism information content (PIC = 0.9). Other SSR markers linked to fragrance could be identified in the same way of use in other populations. This study demonstrates that analysis of the rice genome sequence is an effective option for identification of markers for use in rice improvement.     

Allelochemicals released by rice roots and residues in soil

A few rice (Oryza sativa L.) varieties or rice straw produce and release allelochemicals into soil in which interfere with the growth of neighboring or successive plants. Allelopathic rice PI312777 and Huagan-1 at their early growth stages released momilactone B, 3-isopropyl-5-acetoxycyclohexene-2-one-1, and 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone into soil at phytotoxic levels, but non-allelopathic rice Huajingxian did not. Both allelopathic and non-allelopathic rice residues released momilactone B and lignin-related phenolic acids (p-hydroxybenzoic, p-coumaric, ferulic, syringic and vanillic acids) into the soil during residue decomposition to inhibit successive plants. The results indicated that allelochemicals involved in rice allelopathy from living and dead plants are substantially different. Interestingly, the concentrations of the allelochemicals released from the allelopathic rice seedlings in soil increased dramatically when they were surrounded with Echinochloa crus-galli. The concentrations of the allelochemicals were over 3-fold higher in the presence of E. crus-galli than in the absence of E. crus-galli. However, the same case did not occur in non-allelopathic Huajingxian seedlings surrounded with E. crus-galli. In addition to allelochemical exudation being promoted by the presence of E. crus-galli, allelopathic rice seedlings also increased allelochemical exudation in response to exudates of germinated E. crus-galli seeds or lepidimoide, an uronic acid derivative exuded from E. crus-galli seeds. These results imply that allelopathic rice seedlings can sense certain allelochemicals released by E. crus-galli into the soil, and respond by increased production of allelochemicals inhibitory to E. crus-galli. This study suggests that rice residues of both allelopathic and non-allelopathic varieties release similar concentrations and types of allelochemicals to inhibit successive plants. In contrast, living rice plants of certain allelopathic varieties appear to be able to detect the presence of interspecific neighbors and respond by increased allelochemicals.