Changes in the amino acid composition and protein modification in phloem sap of rice

Pure phloem sap was collected from insects feeding on rice (Oryza sativa L.) leaves by a laser technique similar to the aphid stylet technique. Rapid circulation of nitrogen in the sieve tubes was demonstrated directly using ¹⁵N as a tracer. Application to the roots of the metabolic inhibitors of amino acids, aminooxyacetate and methioninesulfoximine, changed the amino acid composition in the sieve tubes. Feeding methionine to leaf tips resulted in its bulk transfer into the sieve tubes. In vitro experiments confirmed the existence of protein kinases in the pure rice phloem sap. The phosphorylation status of the sieve tube sap proteins was affected by the light regime. The possibility that changes in chemical composition or protein modification such as phosphorylation in the sieve tubes might affect plant growth are discussed.Analysis of pure phloem sap collected from rice plants by insect laser technique has shown dynamic changes in the chemical composition and the quality of proteins in the sap.     

QTLs for nutritional contents of rice seedlings (Oryza sativa L.) in solution cultures and its implication to tolerance to iron-toxicity

Iron toxicity is one of the major constraints for lowland rice production in highly weathered soils, which are widely distributed in tropics and subtropics and often lack macronutrients such as potassium (K) and phosphorus (P). To analyze the genetic factors for excess iron accumulation under K or P deficiency, a set of seedlings in F₃ and F₈ generations from an Oryza sativa cross between a japonica cultivar ‚Gimbozu’ and an indica cultivar ‚Kasalath’ were raised and exposed to nutritional stresses in a short period under nutritional solutions. In the F₈ lines, contents of K, P, Fe, and Mg in dried shoots were measured. Quantitative trait loci (QTL) for the iron accumulation and related mineral contents in each plant were analyzed with composite interval mapping. QTLs for the Fe, P and Mg content in shoots were compared in the maps of F₃ and F₈. The QTLs for the Fe content in shoots varied in three types of nutritional conditions, but consistently indicated two overlapping regions on chromosome 3 and 4. The obtained QTLs were crosschecked with those reported before. Some of these QTLs were indicative of iron excluding the power of the root, which was expressed under reduced P content in solution.     

Accumulation of ammonium ion in cadmium tolerant and sensitive cultivars of Oryza sativa

Cd-tolerant and Cd-sensitive rice cultivars were used to study the role of NH₄ ⁺ accumulation in Cd-induced toxicity. NH₄ ⁺ accumulation seems to be involved in regulating the toxicity of rice seedlings caused by CdCl₂. This conclusion was based on the observations that (a) on treatment with CdCl₂, NH₄ ⁺ content increased rapidly in the leaves of the Cd-sensitive cultivar (cv. Taichung Native 1, TN1) but not in the Cd-tolerant cultivar (cv. Tainumg 67, TNG67), (b) pretreatment with abscisic acid (ABA) enhanced Cd tolerance and reduced Cd-induced NH₄ ⁺ accumulation in TN1 seedlings, (c) exogenous application of the ABA biosynthesis inhibitor, fluridone, decreased Cd tolerance and increased NH₄ ⁺ content in leaves of TNG67, (d) exogenous application of phosphinothricin, an inhibitor of glutamine synthetase (GS), which resulted in NH₄ ⁺ accumulation in the leaves, also induced toxicity similar to Cd in TN1 seedlings. Evidence is presented to show that Cd-induced NH₄ ⁺ accumulation in TN1 leaves is attributable to a decrease in GS activity. Since Cd-treated TN1 leaves had higher glutamine and glutamate contents than control leaves, it is unlikely that glutamine (or glutamate) depletion is the mechanism which regulates Cd-induced toxicity.     

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.     

Salt tolerance of rice cultivars

Summary The dry matter production and the concentration of nutrients in rice (Oryza sativa L.) cultivars from soil adjusted to different levels of salinity were evaluated under a greenhouse conditions. Soil salinity levels were produced by applying 0.34 mol l^–1 solution of NaCl which resulted in the following levels, control (0.29), 5, 10 and 15 dS m^–1 conductivity of saturation extract. The effect of salinity on dry matter production varied from cultivar to cultivar.The concentrations of P and K in the tops of rice cultivars decreased with increasing soil salinity. But the concentrations of Na, Zn, Cu and Mn increased.Significant varietal differences were found in relation to salinity tolerance. Based on dry matter yield reduction, rice cultivars were classified as tolerant, moderately tolerant, moderately susceptible or susceptible.     

Free proline contents in two different groups of rice mutants resistant to hydroxy-L-proline

Summary In four rice (Oryza sativa L.) mutants resistant to hydroxy-L-proline (Hyp), HYP101, HYP203, HYP205 and HYP210, and in their original variety, Nipponbare, free proline and Hyp contents in the seeds and in the 14-day-old seedlings have been determined. The four mutants can be divided into two groups: HYP101 and HYP203 are classified as to recessive gene and the levels of free proline are similar to that of the original variety; the second group includes mutants HYP205 and HYP210 where the Hyp resistance is transmitted heterozygously and, both in the seeds and in the seedlings, a remarkable increase in free proline content is observed. In particular, free proline contents in the seeds of HYP205 and HYP210 are, respectively, 24 and 12 times that of the original variety. Hyp is detected only in the seedlings cultured with Hyp solution. In the Hyp resistant seedlings of HYP205 and HYP210, Hyp contents are twice that of the original variety and less than half in the seedlings of HYP101 and HYP203. Hyp resistance and differential proline levels are also evident in the callus initiated from the mutants. This suggests that the Hyp resistant mutants are good genetic markers both in planta and in vitro. The Hyp mutants are also discussed with regard to stress resistance.     

Influence of aluminum in nutrient solutions on chemical composition in two rice cultivars at different growth stages

Summary A solution culture experiment was conducted using 2 rice cultivars (EEA 304, and CICA 4) to determine the effects of Al concentrations on chemical composition. The treatments consisted of five Al concentrations: 0, 10, 30, 40 and 60 ppm.Aluminum content in plant tissues way increased with increasing levels of Al in two cultivars. Increased Al concentrations in the nutrient solution exerted an inhibiting effect on the uptake of N, P, K, Ca, Mg, S, Fe, B, Cu, Zn, and Mn. Rice cultivars responded differently to Al treatments with respect to nutrients uptake. Tolerant cultivar, EEA 304, absorbed more phosphorus compared to susceptible cultivar CICA 4. Macro and micronutrients inhibiting effect was much lower in this Al tolerant cultivar. These results suggested that one of the Al tolerance mechanism in rice cultivars is associated with more efficient nutrients uptake.     

Somatic cell culture of rice cultivars with different grain types: Somaclonal variation in some grain and quality characters

Variations in some grain and quality characters in progenies of regenerated rice plants were studied. Grain length and weight decreased significantly, yet gel consistency increased. Variations in these quantitative characters of all cultivars studied were consistent, showing the tendencies of the variations. Grain protein contents of the somaclones were higher in one cultivar. Variability of most traits was increased by combining low-dosage radiation and tissue culture.     

Effect of aluminium on metabolism of starch and sugars in growing rice seedlings

The effect of increasing concentrations of Al₂(SO₄)₃ in situ on the content of starch, sugars and activity behaviour of enzymes related to their metabolism were studied in growing seedlings of two rice cvs. Malviya-36 and Pant-12 in sand cultures. Al₂(SO₄)₃ levels of 80 and 160 μM in the growth medium caused an increase in the contents of starch, total sugars as well as reducing sugars in roots as well as shoots of the rice seedlings during a 5–20 days growth period. The activities of the enzymes of starch hydrolysis α-amylase, β-amylase and starch phosphorylase declined in Al-exposed seedlings, whereas the activities of sucrose hydrolyzing enzymes sucrose synthase and acid invertase increased in the seedlings due to Al³⁺ treatment. The enzyme of sucrose synthesis, sucrose phosphate synthase showed decreased activity in Al³⁺ treated seedlings compared to controls. Results suggest that Al³⁺ toxicity in rice seedlings impairs the metabolism of starch and sugars and favours the accumulation of hexoses by enhancing the activities of sucrose hydrolyzing enzymes.     

Glutathione reduces the inhibition of rice seedling root growth caused by cadmium

We investigated the effects of agents known to affect cellular glutathione (reduced form, GSH) levels on the growth of rice seedlings treated with Cd. CdCl₂ was more effective than CdSO₄ in inhibiting root growth. However, CdCl₂ had no effect on shoot growth. GSH, a substrate for phytochelatin synthesis, was effective in counteracting growth inhibition of roots by CdCl₂. Root growth in the CdCl₂ medium was found also to be enhanced by the addition of L-glutamic acid and L-cysteine, both of which are substrates for GSH formation. Buthionine sulfoximine, an inhibitor of GSH synthesis, rendered the roots susceptible to growth inhibition by Cd. Our results suggest that GSH level may play a role in regulating Cd-inhibited growth of rice roots.Abbreviations BSO buthionine sulfoximine - GSH reduced form glutathione     

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.     

Disturbed ammonium assimilation is associated with growth inhibition of roots in rice seedlings caused by NaCl

The effects of NaCl on changes in ammonium level and enzyme activities of ammonium assimilation in roots growth of rice (Oryza sativa L.) seedlings were investigated. NaCl was effective in inhibiting root growth and stimulated the accumulation of ammonium in roots. Accumulation of ammonium in roots preceded inhibition of root growth caused by NaCl. Both effects caused by NaCl are reversible. Exogenous ammonium chloride and methionine sulfoximine (MSO), which caused ammonium accumulation in roots, inhibited root growth of rice seedlings. NaCl decreased glutamine synthetase and glutamate synthase activities in roots, but increased glutamate dehydrogenase activity. The growth inhibition of roots by NaCl or MSO could be reversed by the addition of L-glutamic acid or L-glutamine. The current results suggest that disturbance of ammonium assimilation in roots may be involved in regulating root growth reduction caused by NaCl.Abbreviations GDH glutamate dehydrogenase - GOGAT glutamate synthase - GS glutamine synthetase - MSO methionine sulfoximine     

Sodium chloride induced changes in leaf growth, and pigment and protein contents in two rice cultivars

Rice (Oryza sativa L.) seedlings were grown under NaCl stress. The leaf growth of resistant cv. Damodar was less affected than that of the susceptible cv. Jaya. The leaf protein content showed no distinct cultivar or age dependent differences under NaCl salinity. There was a significant increase in chlorophyll (Chl) and carotenoid (Car) contents of 25-d-oldseedlings of both cv. Jaya and cv. Damodar. However, Chl and Car content of 15-d-old seedlings of cv. Jaya decreased and that of cv. Damodar increased, under NaCl stress. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of low temperature on ethanolic fermentation in rice seedlings

Rice seedlings (Oryza sativa L.) were incubated at 5-30 degrees C for 48 h and the effect of temperature on ethanolic fermentation in the seedlings was investigated in terms of low-temperature adaptation. Activities of alcohol dehydrogenase (ADH, EC 1.1.1.1) and pyruvate decarboxylase (PDC, EC 4.1.1.1) in roots and shoots of the seedlings were low at temperatures of 20-30 degrees C, whereas temperatures of 5, 7.5 and 10 degrees C significantly increased ADH and PDC activities in the roots and shoots. Temperatures of 5-10 degrees C also increased ethanol concentrations in the roots and shoots. The ethanol concentrations in the roots and shoots at 7.5 degrees C were 16- and 12-times greater than those in the roots and shoots at 25 degrees C, respectively. These results indicate that low temperatures (5-10 degrees C) induced ethanolic fermentation in the roots and shoots of the seedlings. Ethanol is known to prevent lipid degradation in plant membrane, and increased membrane-lipid fluidization. In addition, an ADH inhibitor, 4-methylpyrazole, decreased low-temperature tolerance in roots and shoots of rice seedlings and this reduction in the tolerance was recovered by exogenous applied ethanol. Therefore, production of ethanol by ethanolic fermentation may lead to low-temperature adaptation in rice plants by altering the physical properties of membrane lipids.     

Alterations in root lipid peroxidation and antioxidative responses in two rice cultivars under NaCl-salinity stress

The comparative alterations of short term NaCl stress and recovery on growth, water relations, ionic composition, lipid peroxidation and antioxidants in roots of two rice cultivars differing in salt tolerance were studied. Exposed for 24 h to increasing (50, 100 and 150 mmol l⁻¹) concentrations of NaCl, roots of 12D Oryza sativa L. cv. Lunishree and cv. Begunbitchi decreased in fresh weight, dry weight and relative water content. Increased Na⁺ and decreased K⁺ ion were determined at increasing NaCl concentrations. Both peroxide content and lipid peroxidation measured in terms of MDA level increased and the ratio was higher in Begunbitchi compared to Lunishree. Recovered roots showed lower peroxide and MDA content. Ascorbate and glutathione contents increased in the stressed and recovered roots of Lunishree, but decreased in Begunbitchi with increasing NaCl concentrations. Although SOD, CAT and GR activities decreased in the stressed roots, CAT activity also increased in recovered roots of both the cultivars. The POX activity increased in stressed and recovered roots of both Lunishree and Begunbitchi. Higher free radicals scavenging capacity and more efficient protection mechanism of Lunishree against salt stress, as revealed by the lower level of lipid peroxidation and improved plant water status as well as activities of some of the antioxidants, suggest that significant cultivar differences in response to salt stress in rice are closely related to differences in the activities of antioxidants and ion content. Another possible conclusion is that improved tolerance to salt stress may be accomplished by increased capacity of antioxidative system.     

Changes in ammonium ion content and glutamine synthetase activity in rice leaves caused by excess cadmium are a consequence of oxidative damage

Ammonium ion accumulation and the decrease in glutamine synthetase (GS)activity induced by CdCl₂ were investigated in relation to lipidperoxidation in detached rice leaves. CdCl₂ was effective inincreasing ammonium ion content, decreasing GS activity and increasing lipidperoxidation. Free radical scavengers (glutathione, thiourea, sodium benzoate)and an iron chelator (2,2-bipyridine) were able to inhibit the decreasein GS activity and ammonium ion accumulation caused by CdCl₂ and atthe same time inhibit CdCl₂-induced lipid peroxidation. Paraquat,which is known to produce oxygen radicals, decreased GS activity, increasedammonium ion content, and increased lipid peroxidation. GS1 appears to be thepredominant isoform present. Excess Cd caused a decrease in GS1 but not in GS2in detached rice leaves. An increase in lipid peroxidation preceded ammoniumionaccumulation and the decrease in GS1 activity. These results suggest that thedecrease in GS activity and the accumulation of ammonium ions in detached riceleaves are a consequence of oxidative damage caused by excess Cd.     

籽粒镉低积累水稻地上部镉高积累遗传特性分析

农田土壤镉（Cd）污染日益严重,导致稻米Cd含量超标事件频繁出现,使粮食安全问题备受关注。因此,合理利用Cd污染农田、降低水稻籽粒Cd含量成为亟待解决的问题。籽粒Cd低积累水稻雅恢2816的地上部具有较强的Cd积累能力,研究旨在弄清其地上部Cd积累能力的遗传稳定性,进一步揭示控制该性状的遗传基础,为利用分子标记辅助选育地上部Cd富集能力强、籽粒Cd安全的水稻提供途径。以水稻雅恢2816和3个不同品种水稻分别组配获得的F₁为研究对象,分析地上部Cd积累相关性状的杂种优势。进一步以优势组合C268A/雅恢2816构建F₂作图群体,对地上部Cd积累相关性状进行QTL定位分析。结果表明：（1） F₁地上部Cd积累相关性状杂种优势明显,遗传稳定性强。地上部Cd积累相关性状属数量性状,F₂中/超亲分离现象明显。（2）在第4、6号染色体上共挖掘到1个控制水稻地上部生物量和3个控制地上部Cd积累量的QTL位点,分别为qSB-6、qSCdA-4、qSCdA-6-1和qSCdA-6-2,表型贡献率为10.6%—14.4%,且增效等位基因均来自雅恢2816。（3）地上部Cd积累量与地上部生物量、Cd含量,根、糙米的生物量、Cd积累量,根-地上部转移系数均呈极显著正相关,与地上部-籽粒转移系数呈极显著负相关,存在4个QTL集簇区Cl-4-1、Cl-6-1、Cl-6-2和Cl-6-3。（4）区间marker 04171-marker 04197控制着地上部生物量和Cd积累量,与控制糙米Cd含量的QTL不重叠。研究表明：籽粒Cd低积累水稻雅恢2816携带控制地上部Cd高积累的等位基因,可在世代间稳定遗传,QTL位点qSCdA-4、qSCdA-6-1、qSCdA-6-2是控制该性状的重要遗传基础,可为分子标记辅助选育地上部Cd高积累、籽粒Cd低积累水稻提供理论依据。     

Concentration and release level of momilactone B in the seedlings of eight rice cultivars

The release levels of a growth inhibitor, momilactone B, from rice (Oryza sativa L.) seedlings of eight cultivars were compared with the endogenous concentrations of momilactone B in their seedlings. All rice cultivars contained momilactone B in the seedlings, and their concentrations differed between the cultivars. Momilactone B was also found in all culture solutions in which these rice seedlings were grown, and the concentrations differed between the cultivars. The momilactone B concentrations in the culture solutions were reflected in the momilactone B concentrations in the seedlings. These results suggest that all rice cultivars may produce momilactone B and release momilactone B into the culture solutions. In addition, the release level of momilactone B may depend on the production level of momilactone B in the seedlings, which may affect allelopathic potential of these rice cultivars because as a growth inhibitor, momilactone B is able to act as an allelochemical.