Regulation of Submergence-induced Enhanced Shoot Elongation in Oryza sativa L.

Rice (Oryza sativa L.) is the only cereal that can be cultivatedin the frequently flooded river deltas of South-East and SouthAsia. The survival strategies used by rice have been studiedquite extensively and the role of several phytohormones in theelongation response has been established. Deep-water rice cultivarscan diminish flooding stress by rapid elongation of their submergedtissues to keep up with the rising waters. Other rice cultivarsmay react by mechanisms of submergence tolerance. Aerenchymaand aerenchymatous adventitious roots are formed that facilitateoxygen diffusion to prevent anaerobic conditions in the submergedtissues. This paper discusses the molecular aspects of the mechanismthat leads to shoot elongation (leaves of seedlings and internodes),the regulation of which involves metabolism of, and interactionsbetween, ethylene, gibberellins and abscisic acid. Finally,the importance of new techniques in future research is assessed.Current molecular technology can reveal subtle differences ingene activity between tolerant and non-tolerant cultivars, andidentify genes that are involved in the regulation of submergenceavoidance and tolerance.     

Coronatine elicits phytoalexin production in rice leaves (Oryza sativa L.) in the same manner as jasmonic acid

The phytotoxin coronatine induced the accumulation of the flavonoid phytoalexins sakuranetin and momilactone A in rice leaves. Coronatine-inducible sakuranetin production was under the control of kinetin and ascorbic acid (AsA), as observed with jasmonic acid (JA). The effects of kinetin and AsA on the activity of coronatine indicated that coronatine might elicit sakuranetin production in a manner similar to JA. The similarity of both their structures and the manner of elicitation of coronatine and JA suggest that they might interact at the same active site(s) to lead to phytoalexin production.     

Phytochrome action in Oryza sativa L.

Summary In-vivo phytochrome determinations in totally etiolated rice seedlings with a dual-wavelength spectrophotometer showed that on a fresh weight basis phytochrome concentration was highest in the coleoptile apex (0.175 of mean) ( O.D.) g^-1 (fresh weight). The age of the seedlings had little effect on the pattern of phytochrome distribution in the coleoptiles.The extent of growth inhibition observed 2 days after the irradiations was proportional to the logarithm of P _fr amount in the coleoptiles at the time of initial exposure to either red or blue light. Ultraviolet irradiation, however, did not induce either reversible growth inhibition or optically detectable phytochrome changes in vivo.After the conversion of P _r to P _fr bya brief red irradiation, non-photochemical transformation of phytochrome was observed in intact coleoptile tissues. Most of the optically measurable P _fr disappeared within 6 hours at 27°, when the total ( O.D.) decreased to about one fifth of the original level. The optical data did not agree with the fact that 50% of the initial physiological reversibility was still observed 9 hours later. No significant difference in dark transformation rate was seen between intact and excised coleoptile tissues.Abbreviations P _r red light absorbing form of phytochrome - P _fr far-red light absorbing form of phytochrome - ( O.D.) the change in the optical density difference reading at two wavelengths, following irradiation of the sample with actinic sources of red and far-red light - UV ultraviolet light     

Phytochrome action in Oryza sativa L.

Summary The mechanical properties of the cell wall were measured in coleoptiles of totally etiolated rice seedlings. Coleoptiles were either decapitated or briefly exposed to red (R) and/or far-red (FR) light. The elastic and plastic extensibilities of the cell wall changed with age (length) of the coleoptiles. Decapitation and exposure to R induced changes in these properties, and the time-courses were similar. Following decapitation or R irradiation, the plastic extensibility of the cell wall decreased more conspicuously than elastic extensibility. Exogenous application of auxin immediately following decapitation alleviated the effect of removal of the tip. FR irradiation reduced both kinds of extensibilities, but its effect was much less than that of R, and it reversed the R-induced effect to the level of tissue treated with FR only. In repeated R-FR treatments, the decrease of elastic extensibility by R and its reversal by FR could be repeated, but the effect of a second irradiation with R after FR on plastic extensibility was not as apparent as that of the first. Reduction of cell-wall extensibility of etiolated rice coleoptiles caused by R light appeared, at least partly, to be due to a reduced auxin supply in the elongating region from the tip, similar to that caused by decapitation.     

Expression of glutamine synthetase during the anaerobic germination of Oryza sativa L.

Glutamine synthetase (GS; EC.6.3.1.2.) occurs as cytosolic (GS₁) and plastidic (GS₂) polypeptides. This paper describes the expression of GS isoenzymes in coleoptile during the anaerobic germination of rice (Oryza sativa L.) and the influence of exogenous nitrate on this. By immunoprecipitation with anti-GS serum, two polypeptides of 41- and 44-kDa were detected of which the former was predominant. After fractionation by ion-exchange chromatography, the 41 and 44 kDa bands were identified as GS₁ and GS₂, respectively. Northern blot analysis with specific probes showed the presence of mRNA for cytosolic GS but not for the plastidic form. The presence of exogenous nitrate did not alter the activity and expression of GS in the coleoptile. The role of GS during the anaerobic germination of rice seems to induce the re-assimilation of ammonia rather than the assimilation of nitrate.Abbreviations GS glutamine synthetase - GS₁ cytosolic glutamine synthetase - GS₂ platidic glutamine synthetase We are grateful to Dr. Julie V. Cullimore for providing GS anti-serum and clones. The research was supported by the National Research Council of Italy, special project RAISA, sub-project N. 2 paper N. 1586.     

百菌清对土壤微生物特性和水稻生物量的影响

农药是集约化农业保证农产品产量的重要因素之一,但不合理的施用方法会导致农药残留、土壤结构破坏和土壤微生物特性改变等一系列问题。许多研究发现,百菌清对作物和土壤微生物具有一定的毒害和抑制作用。通过温室试验探讨了百菌清不同施用量对土壤微生物生物量、呼吸强度、代谢熵和脱氢酶活性的影响,并测定了水稻生物量。结果表明,虽然微生物数量没有明显变化,但其活力受到显著抑制,且施用剂量越高抑制越明显。试验后期脱氢酶活性逐渐增加,但仍然低于对照。虽然,百菌清没有造成水稻生物量下降,但由于研究属于短期试验,且只施用了1次百菌清,因此其环境生态学影响有可能被低估。     

Regulation of Medicago sativa L. somatic embryogenesis by gibberellins

The influence of exogenous gibberellic acid (GA₃) andpaclobutrazol, an inhibitor of gibberellin biosynthesis, on growth of callusandsomatic embryogenesis in petiole-derived tissue cultures of Medicagosativa L. has been investigated. GA₃ (0.5–500M) or paclobutrazol(5–100 M) were added to either an induction (with 2,4 Dand kinetin) or a differentiation medium (without plant growth regulators).Gibberellin A₃, applied during the induction as well as thedifferentiation stage, reduced the weight of callus and increased the number ofsomatic embryos in Medicago sativa L. tissue cultures.Somatic embryo production was increased more by the presence of exogenousGA₃ in the differentiation than induction medium. The inclusion ofpaclobutrazol in the induction or differentiation medium caused the inhibitionof callus growth and embryo production. Callus growth was much less affectedthan embryogenesis. These results indicate that gibberellins are beneficial forboth embryoinduction and formation. The level of endogenous gibberellins is presumablysufficient for callus induction and growth. However, it seems not optimal forthe induction and particularly for the differentiation of embryos.     

Regulation of potato meristem development by jasmonic acid in vitro

The influence of jasmonic acid (JA) on differentiation of meristems of the potato,Solanum tuberosum cv. Vesna, was investigated in vitro. Meristems were grown on Murashige and Skoog (MS) medium supplemented with indole-3-acetic acid (IAA) (10 μM), kinetin (10 μM), gibberellic acid (3 μM), as modified by Bang. Addition of JA in concentrations of 0.5–10 μM increased the number of meristems that developed into buds, particularly in meristems isolated from shoots grown from tubers in the dark. JA had no noticeable effect on meristems from germs grown in light. All added concentrations of JA retarded callus and root formation. The inhibitory effect on rhizogenesis disappeared immediately after transfer of the developed buds to medium without JA.     

High amylose mutants of rice,Oryza sativa L.

Summary Five mutant lines of rice with increased amylose content in starch granules were identified among floury endosperm mutants. The amylose contents of the mutants ranged from 29.4% to 35.4% and were about twice as high as that of the normal counterpart. Starch properties of the high amylose mutants were analyzed by column chromatography, X-ray diffractometry, photopastegraphy and scanning electron microscopy. The high amylose mutants produced longer unit chains of amylopectin than those of the normal counterpart as well as an increased amount of amylose. A X-ray diffractogram of starch in the mutant was characterized by a type B pattern, while that in the normal counterpart showed a type A pattern which is typical for starches of common cereals. The temperatures at the initiation of gelatinization of the mutants were much higher than that for the normal counterpart. The endosperm cells of the mutant were loosely packed with irregular round-shaped starch granules, whereas those of the normal counterpart were densely packed with polyhedral starch granules. Judging from the results obtained, it was concluded that starch properties of the high amylose mutants of rice were similar to those of the amylose-extender (ae) mutant of maize.     

Regulation of potato meristem development by jasmonic acid in vitro

The influence of jasmonic acid (JA) on differentiation of meristems of the potato,Solanum tuberosum cv. Vesna, was investigated in vitro. Meristems were grown on Murashige and Skoog (MS) medium supplemented with indole-3-acetic acid (IAA) (10 M), kinetin (10 M), gibberellic acid (3 M), as modified by Bang. Addition of JA in concentrations of 0.5–10 M increased the number of meristems that developed into buds, particularly in meristems isolated from shoots grown from tubers in the dark. JA had no noticeable effect on meristems from germs grown in light. All added concentrations of JA retarded callus and root formation. The inhibitory effect on rhizogenesis disappeared immediately after transfer of the developed buds to medium without JA.     

Basis of selectivity of cyhalofop-butyl in Oryza sativa L.

Cyhalofop-butyl (CB), 2-[4-(4-cyano-2-fluorophenoxy)phenoxy]propanoic acid, butyl ester (R), is an aryloxyphenoxypropionate (AOPP) herbicide for postemergence use in rice to control grasses, mainly Echinochloa spp. Similar to other AOPP and cyclohexanedione herbicides, the site of action of CB is acetyl-coenzyme A carboxylase (ACCase), an enzyme in fatty acid biosynthesis. The mechanisms involved in the selectivity of CB in rice (Oryza sativa L.)—absorption, translocation, metabolism, and ACCase susceptibility—were studied. Studies of in vitro inhibition of ACCase in E. oryzoides and O. sativa L. species discounted any differential active site sensitivity as the basis of tolerance to CB. The O. sativa L. cuticle was uniformly covered by waxes, with predominantly unshaped large waxes randomly distributed, obtaining absorption values of under 30%, 24 h after application (HAA). The E. oryzoides cuticle formed a non-uniform covered reticule, with less wax density and areas lacking in waxes reaching maximum values of absorption rising to 73%, 24 HAA. Translocation studies revealed no significant differences, either between species, or between times, remaining in the treated leaf. There was a good correlation between the rate of metabolism and plant tolerance. Plant metabolism studies demonstrated that tolerant rice inactivated the esterases producing a lack of functionality thus reducing the conversion of CB to cyhalofop acid, which is the active form of the herbicide. Moreover, it increased the metabolism of the herbicide forming non toxic metabolites much faster than E. oryzoides. It was concluded that the basis of rice tolerance to CB was a lack of esterase functionality, a reduced absorption through the cuticle and an increase in cyhalofop acid metabolism.     

Identification of the silicon form in xylem sap of rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a typical silicon (Si)-accumulating plant, but the mechanism responsible for the translocation from the root to the shoot is poorly understood. In this study, the form of Si in xylem sap was identified by (29)Si-nuclear magnetic resonance (NMR) spectroscopy. In rice (cv. Oochikara) cultured in a monosilicic acid solution containing 0.5 mM Si, the Si concentration in the xylem reached 6 mM within 30 min. In the (29)Si-NMR spectra of the xylem sap, only one signal was observed at a chemical shift of -72.6 ppm, which is consistent with that of monosilicic acid. A (1)H-NMR study of xylem sap did not show any significant difference between the wild-type rice and mutant rice defective in Si uptake, and the components of the xylem sap were not affected by the Si supply. The Si concentration in the xylem sap in vitro decreased from an initial 18 mM to 2.6 mM with time. Addition of xylem sap to a solution containing 8 mM Si did not prevent the polymerization of silicic acid. All these results indicate that Si is translocated in the form of monosilicic acid through the xylem and that the concentration of monosilicic acid is high in the xylem only transiently.     

Electron-probe microanalysis of silicon in the epidermis of rice (Oryza sativa L.) internodes

Summary Electron-probe X-ray microanalysis showed that significant amounts of silicon are accumulated in the entire epidermal system of the rice internode except in the stomatal apparatuses. Thus, there is a lack of specific sites for Si deposition from levels just above the base to the tip of the rice internode. In the intercalary meristem region, 1 cm above the base of the internode, point-count data indicate more Si accumulation in the dumb-bell shaped silica cells than in the long epidermal cells. Above this region, Si is accumulated essentially in a uniform pattern in all epidermal cells. Such a pattern for Si accumulation in rice internodes markedly contrasts with that for Avena internodes and may explain, in part, why rice plants have a higher percentage Si (dry weight basis) in their shoots. The adaptive significance of this silicification pattern in rice is discussed.     

The physical location of fourteen RFLP markers in rice (Oryza sativa L.)

A biotin-labeled in situ hybridization technique was used in order to physically map RFLP markers to the chromosomes of rice (Oryza sativa L.). Fourteen RFLP markers, associated with the ends of the linkage groups on rice chromosomes 7, 8, 11, 12, were physically mapped onto specific regions of the chromosomes. The average detection rate of in situ hybridization was 5.91%. The markers were located on seven different chromosome arms. Ten of the fourteen markers were distributed near the chromosome ends. This demonstrated that the RFLP linkage groups involved covered a wide physical distance and that the centromeric region was bisected by all but one linkage group. Two markers covered a short genetic distance but were physically distant, while two covering a longer genetic distance were physically closer together. This indicates that considerable variation can, and does, exist between genetic and physical maps.This paper is a contribution of the U.S. Department of Agriculture, Agricultural Research Service, and Missouri Agricultural Experiment Station, Journal Series No. 11 882All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, age, marital status, or handicapThis paper reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a recommendation for its use by the U.S. Department of Agriculture or the University of Missouri     

水稻蔗糖转运基因家族研究进展

蔗糖是韧皮部同化碳运输的主要形式,植物蔗糖转运体(SUT,Sucrose transporters)在参与植物碳素分配中起着重要的作用.编码SUT蛋白的基因在许多双子叶和单子叶植物中都已被分离.目前已经在水稻中鉴定出了5个蔗糖共运体(Sucrose symporter)基因家族成员.对这5个成员在水稻中的鉴定、克隆和表达分析,以及其蛋白结构、分类与进化进行了综述.这些信息可用于探索杂交稻高产的同化物分配和运输的分子原因.