Glutathione levels in phloem sap of rice plants under sulfur deficient conditions

Glutathione which is an abundant reduced sulfur compound in plants is considered to play important roles in the transmission of the sulfur nutrient status between organs within the plant body and in the long-distance transport of reduced sulfur. We determined the concentrations of glutathione, γ-glutamylcysteine (γ-EC), sulfate in the rice phloem sap collected by the insect laser technique. Phloem sap was collected from the plants cultured in sulfur-deficient and control solutions. The concentration of glutathione in the rice phloem sap was higher than that of sulfate in both control and sulfur-deficient plants. Under sulfur-deficient condition, the concentration of glutathione in the phloem sap did not decrease, whereas the sulfate concentration decreased significantly. The pattern of changes in γ-EC concentration was similar to that of glutathione. These data indicate the presence of mechanisms for the maintenance of a constant glutathione concentration in the phloem sap in rice plants under sulfur deficiency, whereas the sulfate concentration was found to be relatively unstable.     

Exogenous abscisic acid promotes the nitrogen use efficiency of Brassica napus by increasing nitrogen remobilization in the leaves

The effect of exogenous abscisic acid (ABA) on the nitrogen use efficiency (NUE) of Brassica napus was studied by pot experiments using ABA (1 mg L^?1) daubed on the leaves at the early siliquing stage. The results showed that activities of proteases and glutamine synthetase (GS) were significantly promoted by the ABA treatment, which increased the capacity of degradation of foliar proteins and biosynthesis of glutamine (N-transport compounds), both of which promote decreased N in leaves of the ABA treatment. L-glutamine, other free amino acids, and soluble sugar content in the phloem sap of the ABA treatment were significantly higher than those of the control. A ¹⁵N label trial showed that more ¹⁵N was distributed from leaves to the grain by the ABA treatment, which resulted in a significantly higher NUE in the ABA treatment relative to the control.     

Cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.) treated with a nutrient solution containing cadmium

To obtain direct evidence for the translocation of cadmium (Cd) via the phloem, we measured the Cd concentrations in the phloem sap of 5-week-old rice plants (Oryza sativa L. cv. Kantou) treated with a nutrient solution containing Cd. The phloem sap was collected from the leaf sheaths through the cut ends of stylets of the brown planthopper (Nilaparvata lugens Stål.). Cd concentrations in the phloem sap from the plants treated with 10 and 100 µM Cd for 3 d were 4.6 ± 3.4 and 17.7 ± 9.8 µM, respectively. Detection of Cd in the phloem sap indicated that Cd was translocated via sieve tubes in rice plants. Cd concentrations in the xylem exudate collected from the cut basis of the leaf sheaths of the plants treated with 10 and 100 µM Cd for 3 d were 18.9 ± 6.4 and 64.2 ± 14.6 µM, respectively. Cd concentrations in the phloem sap were significantly lower than those in the xylem exudate, indicating that Cd is not concentrated during the transfer from xylem to phloem. To our knowledge, this is the first determination of Cd concentrations in the phloem sap of plants, and the first direct proof that Cd is translocated via sieve tubes in rice plants.     

Analysis of phloem exudate collected from fruit-bearing stems of coconut palm: Palm trees as a source of molecules circulating in sieve tubes

Sieve tubes have been attracting widespread research interest because of their possible role in mediating physiological signals within the whole plant. However, progress in research into the function of sieve tubes has been limited by the low volume of sap available. To overcome this problem, we attempted to collect phloem exudate from tropical coconut palm trees (Cocos nucifera L. cv. Namhom). As much as 3 to 15 mL of exudate per hour was collected from the cut surface of the plant's fruit-bearing stem. Our analyses revealed that the characterized profiles of sugars (sucrose: 339 mM), amino acids (total concentration: 17.1 mM), cations (potassium: 48.3 mM), and proteins (total concentration: 0.1 /-lg /-lL-1) in the exudate were mostly consistent with those of phloem sap or phloem exudate collected from rice plants, castor bean plants, etc. This exudate was assumed to reflect the composition of the phloem sap from the source organs of coconut palm trees. The large volume of exudate collected contributed significantly to the analyses of the various compounds in the stream of sieve tubes.     

Glutamine synthetase of roots and leaves in response to nitrogen application at different growth stages in field‐grown rice

Information on glutamine synthetase (GS) activity of roots and leaves in response to nitrogen (N) application at different growth stages is limited for field‐grown rice. Root and leaf GS activity was measured on field‐grown rice plants to compare the effects of fertilizer‐N application at midtillering, panicle initiation, and flowering. Leaf GS activity was greater than root GS activity, regardless of N application. Root and leaf GS activity generally declined as plant aged, and the decline was greater in roots than leaves. Leaf and root GS activity were significantly increased by urea‐N applied at different growth stages. Root GS activity was maximum three days after N application, while leaf GS activity peaked one day after N application. Root GS activity showed greater response to N application at midtillering and panicle initiation than leaf GS activity, but the opposite was found at flowering. The stimulation of GS activity by N was greatest at midtillering and reduced with plant age.     

地表水NH4和NO3随水体入渗在土壤和地下水中输送过程的土槽试验研究

The infiltration of water contaminants into soil and groundwater systems can greatly affect the quality of groundwater. A laboratory-designed large soil tank with periodic and continuous infiltration models, respectively, was used to simulate the migration of the contaminants NH4 and NO3 in a soil and groundwater system, including unsaturated and saturated zones. The unsaturated soil zone had a significant effect on removing NH4 and NO3 infiltrated from the surface water. The patterns of breakthrough curves of NH4 and NO3 in the unsaturated zone were related to the infiltration time. A short infiltration time resulted in a single sharp peak in the breakthrough curve, while a long infiltration time led to a plateau curve. When NH4 and NO3 migrated from the unsaturated zone to the saturated zone, an interracial retardation was formed, resulting in an increased contaminant concentration on the interface. Under the influence of horizontal groundwater movement, the infiltrated contaminants formed a contamination-prone area downstream. As the contaminants migrated downstream, their concentrations were significantly reduced. Under the same infiltration concentration, the concentration of NO3 was greater than that of NH4 at every corresponding cross-section in the soil and groundwater tank, suggesting that the removal efficiency of NH4 was greater than that of NO3 in the soil and groundwater system.     

双季早稻氮素亏缺补偿效应的形成及其生理机制初探

为探明双季早稻氮素亏缺补偿效应的形成及其生理机制,采用桶栽方式,以超级杂交早稻品种淦鑫203为试验材料,于氮素亏缺敏感期分蘖期,设置5个氮肥处理:T0(各生育阶段均不施用氮肥,即空白对照)、T1(各生育阶段氮肥按常量分配)、T2(分蘖期氮肥亏缺后幼穗分化期不恢复供氮)、T3(分蘖期氮肥亏缺后幼穗分化期常量恢复供氮)和T4(分蘖期氮肥亏缺后幼穗分化期倍量补偿供氮),比较各氮肥处理稻株产量及其构成因素、单株分蘖数、成穗率和净光合速率、SPAD值、氮代谢酶(硝酸还原酶NR和谷氨酰胺合成酶GS)活性、内源激素含量、根系伤流量等有关生理指标的差异性。结果表明,T4单株产量与T1十分接近,补偿指数CI=0.99,无显著差异,呈现出等量补偿效应。与T1相比,T4叶片净光合速率、SPAD值、NR和GS活性均能维持在较高水平,而且随着生育推进,至补偿后期,T4该4项生理指标仍维持在较高水平,表现出较为明显的氮素亏缺补偿效应。至补偿后期,氮素补偿处理的T4和T3稻株叶片脱落酸(ABA)含量显著低于T0、T1和T2,以T4最低,生长促进类激素之和(GA3+IAA+ZR)与生长抑制类激素(ABA)比值则显著高于T0、T1和T2。氮素亏缺补偿后第10天根系伤流量以T0最低,T4、T3均高于T1,且T4与T1间差异达显著水平。至补偿后期,T4单株分蘖数及成穗率高于T1、T3。本研究结果进一步明确了双季超级杂交早稻分蘖期氮素亏缺补偿效应的形成,有助于诠释水稻氮素亏缺补偿效应形成的生理机制,为水稻氮肥施用不当时进行追补及双季早稻高产稳产栽培提供了科学依据。     

不同硼效率棉花品种木质部和韧皮部汁液中矿质养分的差异

溶液培养条件下研究硼对2个硼效率不同的棉花品种木质部、韧皮部中硼及其它矿质养分运输的影响。结果表明,缺硼使2个棉花品种木质部汁液硼含量及溢出量明显降低,低效品种降低幅度大于高效品种。供硼充足(0.5mg/L)时,2个棉花品种木质部汁液中硼浓度均小于培养液中硼浓度;缺硼(0.002mg/L)时,高效品种与低效品种木质部汁液硼浓度分别是培养液硼浓度的32.0和20.5倍。缺硼使2个棉花品种木质部汁液中钾、锰、铜、锌含量均升高,高效品种升高幅度较大;钙含量均降低,低效品种降低幅度较大;高效品种镁含量增高,低效品种降低。而2个棉花品种木质部各养分(钾、镁、钙、锰、铜、锌)溢出量均降低,低效品种降低更明显。无论在缺硼或供硼充足时,2个棉花品种韧皮部中硼浓度均极低,但韧皮部溢泌液中其它养分受缺硼影响品种间表现不同,高效品种韧皮部钾、镁、锰、铜溢出量升高,低效品种则降低;2个品种钙、锌溢出量均降低,低效品种降低幅度更大。     

Ammonium assimilation in rice based on the occurrence of 15N and inhibition of glutamine synthetase activity

Assimilation of ammonium (NH₄) into free amino acids and total reduced nitrogen (N) was monitored in both roots and shoots of two‐week old rice seedlings supplied with 5 mM 99% (¹⁵NH₄)₂SO₄ in aerated hydroponic culture with or without a 2 h preincubation with 1 mM methionine sulfoximine (MSX), an inhibitor of glutamine synthetase (GS) activity. ¹⁵NH₄ was not assimilated into amino acids when the GS/GOGAT (glutamate synthase) cycle was inhibited by MSX. Inhibition of glutamine synthetase (GS) activity in roots with MSX increased both the amount of NH₄ and the abundance of ¹⁵N labeled NH₄. In contrast, the amount of Gln and Glu, and their proportions as ¹⁵N, decreased in roots when GS activity was inhibited. This research confirms the importance of GS/GOGAT in NH₄ assimilation in rice roots.

¹⁵N‐labeled studies indicate that NH₄ ions incorporated by roots of rice are transformed primarily into glutamine (Gln) and glutamic acid (Glu) before being converted to other amino acids through transamination (15). The formation of amino acids such as aspartic acid (Asp) and alanine (Ala) directly from free NH₄ in roots also has been reported (4,15). Translocation of free NH₄ to plant shoots, based on the concentration of free NH₄ in xylem exudate, has been reported in tomato (13), although NH₄ in shoots primarily originates from nitrate reduction in the shoot. Photorespiration also can contribute to the accumulation of NH₄ in leaves (7).

The GS/GOGAT cycle appears to be primarily responsible for the assimilation of exogenously supplied NH₄ and NH₄ derived from nitrate reduction in leaves, as well as NH₄ derived from photorespiration (2,3,6,8). Genetic evidence cited to support this conclusion includes the lethal effect of photorespiratory conditions on plant mutants deficient in chloroplast‐localized GS and GOGAT activities (2,3,9), and the rapid accumulation of free NH₄ in GS‐deficient mutants under photorespiratory conditions (2,3,5).

The present study was initiated to quantify the in vivo amino acid synthesis in rice roots and shoots by analysis of ¹⁵N labeling, and should provide a more complete understanding of this important system for NH₄ utilization.     

Transfer of zinc from xylem to phloem in the peduncle of wheat

Maturing wheat grains represent major sinks for solutes in the phloem, while the xylem sap entering the ear is mainly delivered to the glumes. Nutrients and assimilates transported in the phloem may either be exported from source organs or loaded into the sieve tubes by a xylem‐to‐phloem transfer in the stem. The transfer of zinc from xylem to phloem in the peduncle of wheat was investigated by feeding radiolabelled zinc into the cut xylem of detached shoots. The label accumulated in grains of shoots with an intact phloem but not in those steam‐girdled below the ear. These findings indicate that zinc fed in low concentrations (0.1 ‐ 10 μM) entered the ear mainly via the phloem. After feeding high zinc concentrations (100 ‐1000 μM), the label was mainly retained in the stem and steam‐girding below the ear was rather ineffective. These results led to the conclusion that at these high concentrations zinc was still eliminated from the xylem sap, but loaded only in a minor percentage into the phloem. The interactions between the two long distance transport systems may play an important role in the regulation of zinc transport to the maturing grains of cereals.     

蘖穗氮肥追施比例对水稻灌浆成熟期 Rubisco 和 GS 同工型基因表达量的影响

【目的】 氮素营养影响着水稻灌浆过程中核酮糖-1, 5-二磷酸羧化酶/加氧酶 (Rubisco) 和谷氨酰胺合成酶 (GS) 基因转录表达量,研究其变化动态及其与不同形态氮含量的关系,旨在为阐明氮素营养对光合效率和籽粒蛋白质积累的影响分子调控机理提供理论依据。 【方法】 选用寒地粳稻穗数型高产品种和穗重型超级稻品种进行盆栽试验。施肥比例为 N∶P₂O₅∶K₂O = 1∶0.5∶1,氮肥 50% 作为基肥,其余作分蘖肥和穗肥追施,分蘖肥和穗肥比例为 10%∶40%、20%∶30%、30%∶20%、40%∶10%。分析了水稻灌浆过程中 Rubisco 和 GS 基因转录表达量及不同形态氮的积累动态。 【结果】 增加穗肥氮素施用量可显著提高水稻灌浆过程中叶片和籽粒的全氮、铵态氮、硝态氮含量;增加穗肥比例不同程度的上调了 Rubisco 大亚基和小亚基基因的 mRNA 表达量,其中OsRBCSL、OsRBCS2 和OsRBCS4 表达上调显著,OsRBCS3 和OsRBCS5 表达上调较小;穗肥比例增加延长了 Rubisco 各亚基基因高表达持续时间,增加了水稻灌浆中期和后期叶片中OsGS1;1 和OsGS2 基因的转录表达量以及籽粒OsGS1;1 基因的转录表达量和整个灌浆过程中OsGS1;3 基因的转录表达量。Rubisco 五个亚基基因的转录表达量与叶片 NO₃–-N 和全氮含量间以及叶片和籽粒中 GS 基因的转录表达量与 NH₄+-N 和全氮含量间均呈显著或极显著的正相关。 【结论】 在灌浆过程中OsRBCL 基因和 GS 基因的转录表达量变化动态不因品种或氮素营养不同而发生质的变化,不同基因对氮素营养的响应程度并不相同,增加叶片 NO₃–-N 和全氮含量,可以显著提高 Rubisco 基因的转录表达量,增加灌浆成熟期叶片和籽粒的 NH₄+-N 和全氮含量,可以显著提高叶片和籽粒的 GS 基因转录表达量。      

低氮胁迫下大麦谷氨酰胺酶基因的表达分析

谷氨酰胺酶是氮代谢中的关键酶,在氨同化和谷氨酰胺生物合成中起着重要的作用。为研究谷氨酰胺酶基因在大麦耐低氮中的作用机理,本研究利用荧光定量PCR技术检测了大麦中这两类谷氨酰胺酶基因（GS1和GS2）在低氮胁迫下的表达情况,并分析了谷氨酰胺酶基因在耐低氮大麦基因型BI-04和低氮敏感大麦基因型BI-45间的表达差异。结果表明,GS1基因在BI-04中表现为上调表达,而在BI-45中表现为下调表达,但随着时间的延长其表达量恢复并超过对照;而GS2基因在两种大麦基因型中的表达差不多,都表现为下调表达。另外,本文也观察到大麦谷氨酰胺酶基因的表达在黑暗条件下受到抑制,因此推测其也受到光照条件的影响。     

节水栽培水稻某些氮代谢生理特性研究

田间试验研究了节水栽培对水稻某些氮代谢生理特性的影响。结果表明,覆膜旱作水稻产量比常规水作显著降低,与裸地旱作相比则显著提高;3种栽培模式水稻叶片中氨基酸态氮和硝态氮含量、硝酸还原酶、谷氨酰胺合酶、谷草转氨酶和谷丙转氨酶活性均表现为生育前期较高、生育后期较低的动态特征。与常规水作相比,生育前期覆膜旱作水稻叶片中氨基酸态氮和硝态氮含量、硝酸还原酶和谷丙酰胺合酶活性均有所增加;整个生育期间谷草转氨酶活性有所提高而谷丙转氨酶活性则降低。与裸地旱作相比,覆膜旱作对水稻叶片中氨基酸态氮和硝态氮含量、硝酸还原酶、谷氨酰胺合酶、谷草转氨酶和谷丙转氨酶活性都有提高。水分胁迫对氮代谢生理特性及产量具有一定的负效应,而覆膜旱作能不同程度缓解这种效应,甚至有所促进;适量增加氮肥用量可以提高覆膜旱作氮代谢生理活性（尤其生育早期）及产量。     

盐胁迫下氮素形态对油菜和水稻幼苗离子运输和分布的影响

【目的】土壤盐碱化是制约农作物产量的主要因素之一,盐胁迫影响养分运输和分布,造成植物营养失衡,导致作物发育迟缓,植株矮小,严重威胁着我国的粮食生产。在必需营养元素中,氮素是需求量最大的元素,NO-3和NH+4是植物吸收氮素的两种离子形态。植物对盐胁迫的响应受到不同形态氮素的调控,研究不同形态氮素营养下植物的耐盐机制对提高植物耐盐性及产量具有重要的意义。【方法】本文以喜硝植物油菜(Brassica napus L.)和喜铵植物水稻(Oryza sativa L.)为试验材料,采用室内营养液培养方法,研究了NO-3和NH+4对Na Cl胁迫下油菜及水稻苗期生长状况、对Na+运输和积累的影响,以对照与盐胁迫植株生物量之差与Na+积累量之差的比值,评估Na+对植株的伤害程度。【结果】1)在非盐胁迫条件下,硝态氮营养显著促进油菜和水稻根系的生长;盐胁迫条件下,油菜和水稻生物量均显著受到抑制,Na Cl对供应铵态氮营养植株的抑制更为显著。2)盐胁迫条件下,两种供氮形态下,油菜和水稻植株Na+含量均显著增加,硝态氮营养油菜叶柄Na+显著高于铵态氮营养,叶柄Na+含量/叶片Na+含量大于铵营养油菜,硝态氮营养水稻根系Na+含量显著低于铵营养,地上部则相反。3)铵营养油菜和水稻Na+伤害度显著高于硝营养植株。4)盐胁迫条件下,硝态氮营养油菜地上部和水稻根系K+含量均显著高于铵态氮营养。5)盐胁迫条件下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株。【结论】与铵营养相比,硝营养油菜和水稻具有更好的耐盐性。硝态氮处理油菜叶柄Na+显著高于铵态氮处理,能够截留Na+向叶片运输。同时,供应硝态氮营养更有利于油菜和水稻吸收K+,有助于维持植物体内离子平衡。盐胁迫下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株,表明硝态氮营养油菜和水稻木质部-韧皮部对离子有较好的调控能力,是其耐盐性高于铵营养的原因之一。     

不同水、氮条件对水稻苗生长及伤流液的影响

为探明不同水分供应和氮素形态对水稻根苗及伤流液的影响,设正常水分及50 g/L PEG模拟水分胁迫和3种不同质量比例的NH4+-N/NO3--N（9/1,5/5,1/9）氮素营养处理,测定了水稻幼苗生物量,根系形态指标,根系活力及根基伤流量。结果表明,正常水分条件下,NH4+-N促进水稻根系平均直径增大,有利于水稻地上部物质累积;NO3--N则使水稻根系总吸收面积增大,促进根系物质累积;NH4+-N/NO3--N为5/5处理的水稻活跃吸收面积最大,活跃吸收面积比亦最高。水分胁迫条件下,NH4+-N/NO3--N为5/5的处理更有利于水稻地上部分的生长,NO3--N有利于水稻鲜重和干重增加,促进根系平均直径增大,水稻的根系总吸收面积、活跃吸收面积均随NO3--N供应比例的增加呈上升趋势。正常水分条件下,水稻幼苗白天的耗水量随NH4+-N/ NO3--N比例降低呈下降趋势,水分胁迫条件降低了水稻对水分的吸收。水分胁迫显著降低各处理水稻伤流量,正常水分条件下,NH4+-N/NO3--N为5/5处理的水稻伤流量最大;水分胁迫后,9/1处理的水稻伤流量相对较多。     

Arsenic uptake is suppressed in a rice mutant defective in silicon uptake

Possible mechanisms of the effects of silicon (Si) on arsenic (As) uptake were explored using a wild‐type rice and its low‐Si mutant (lsi1). Hydroponic experiments were carried out to investigate the effects of internal and external Si on the As accumulation and uptake by rice in excised roots (28 d–old seedlings) and xylem sap (61 d–old plants). The presence of Si significantly decreased the As concentrations in both shoots and roots of the wild type but not in the mutant with 13.3 μM–arsenite or 10/20 μM–arsenate treatments. The Si‐defective mutant rice (lsi1) also showed a significant reduction in arsenite or arsenate uptake. Moreover, As concentrations in xylem sap of the wild type were reduced by 51% with 1 mM Si– and 15 μM–arsenate treatments, while Si had no effect on As concentrations in the xylem sap of the mutant. Arsenic‐species analysis further indicated that the addition of 1 mM Si significantly decreased As(III) concentrations but had little effect on As(V) concentrations in the xylem sap of the wild type with 15 μM–arsenate treatments. These results indicated that external Si‐mediated reduction in arsenite uptake by rice is due to the direct competition between Si and arsenite during uptake. This is because both share the same influx transporter Lsi1. In addition, internal Si‐mediated reduction in arsenite uptake by rice is due to competition of the Si/arsenite efflux transporter Lsi2 during the As(III)‐transportation process. Silicon also inhibited arsenate uptake by rice. It is proposed that this could actually be due not to the inhibition of arsenate uptake per se but rather the inhibition of arsenite transformed from arsenate, either in the external solution or in rice roots.     

绿茶施用铵态氮和硝态氮后木质部导管中N运移模拟

An experiment was carried out to study the transport process of nitrogen （N） assimilation from tea roots by monitoring the dynamic composition of N compounds in xylem sap after 15^N-NO3 and 15^N-NH4 were fed to the root of tea plants （Camellia sinensis L.）. Results showed that the main amino acids were glutamine, theanine, axginine, asparic acid and glutamic acid, which accounted for 49%, 17%, 8%, 7%, and 4%, respectively, of the total amino acids in the xylem sap. After the tea plants were fed with 15^N-NO3 and 15^N-NH4 for 48 h, the amount of total amino acids in xylem sap significantly increased and those fed with 15^N-NH4 had higher increment than those with 15^N-NOa. Two hours after 15^N- NO3 and 15^N-NH4 were fed, 15N abundance in glutamine, asparagine, glutamic acid, alanine, and arginine were detected and increased quickly over time. This indicated that it took less than 2 h for NO3-N and NH4-N to be absorbed by tea roots, incorporated into the above amino acids and transported to the xylem sap. Rapid increase in 15^N-NO3 in the xylem sap of tea plants fed with 15^N-NO3 indicated that nitrate could be directly transported to the xylem sap. Glutamine, theanine, and alanine were the main amino acids transported in xylem sap of tea plants fed with both 15^N-NO3 and 15^N-NH4.     

植物汁液化学组成及其与菜心抗性和Cd累积的关系

Sap mixtures of the xylem, phloem, and vacuoles from low and high Cd accumulator varieties of Brassica parachinensis L. H. Bailey were analyzed under Cd stress to understand the biochemical mechanisms of Cd accumulation in plants. Low Cd accumulator （‘Teqing-60＇） and high Cd accumulator （‘Chixin-2＇） plants were grown in Cd-treated soil in pots in a greenhouse. Percentage of cell wall-bound Cd was estimated, pH level and the concentrations of amino acids, organic acids, anions, and cations in both stem and root saps were determined for the calculation of Cd speciations using the computer program GEOCHEM. The results showed that ‘Teqing-60＇ had a significantly higher （P ≤ 0.05） percentage of Cd bound to cell walls in roots and a significantly higher （P ≤ 0.05） pH in the root sap. ‘Teqing-60＇ also contained a higher concentration of total amino acids in both roots and stems compared with the high Cd accumulator variety ‘Chixin- 2＇. However, between the two accumulators, for stems and for roots, there were no significant differences in non-amino organic acids. GEOCHEM calculations showed that Cd in the root sap of ‘Teqing-60＇ mainly combined with amino acids, especially alanine. Compared with ‘Chixin-2＇, in the root sap of ‘Teqing-60＇, much lower levels of Cd as free ions or bound to simple ligands were found, indicating that less ‘Teqing-60＇ is transferred to stems and leaves. Cadmium activity in the shoot sap of ‘Teqing-60＇ was much lower than that in ‘Chixin-2＇; therefore, ‘Teqing-60＇ exhibited higher Cd resistance. However, direct determination of the Cd complexes from xylem and phloem sap is needed to verify these results.     

氮磷钾不同配比对饲用稻威优198产量及糙米蛋白含量的影响

采用田间小区试验研究“推荐配比”(N:P2O5:K2O比率为190:90:100 kg hm-2)、“高氮量配比”(N:P2O5:K2O比率为210:90:100 kg hm-2)、“低氮量配比”(N:P2O5:K2O比率为170:90:100 kg hm-2)以及“常规配比”(N:P2O5:K2O比率为216:112.5:202.5 kg hm-2)4种氮、磷、钾配比施肥对饲用稻威优198蔗糖合成酶(SUS)、腺苷二磷酸焦磷酸化酶(AGPase)、硝酸还原酶(NR)、谷氨酰胺合成酶(GS)以及产量和糙米蛋白质的影响。结果表明:“推荐配比”能提高不同生育时期水稻功能叶(旗叶)和粒籽中碳、氮代谢关键酶的活性,这些关键酶活性的变化显著影响水稻产量和糙米全氮以及蛋白氮的含量。统计(P0.05)结果证实“推荐配比”能提高水稻产量达到8200 kg hm-2,与“常规配比”相比产量提高了24.81%;“推荐配比”糙米全氮和蛋白氮含量分别达到22.70 g kg-1和21.98 g kg-1,与“常规配比”相比差异显著,并且其全氮和蛋白氮含量分别提高17.01%,18.38%。     

Quantification of zinc transport via the phloem to the grain in rice plants (Oryza sativa L.) at early grain-filling by a combination of mathematical modeling and 65Zn tracing

Zinc (Zn) is an essential nutrient for human beings, and most Zn intake occurs through vegetables or cereals such as rice (Oryza sativa L.) grains. Recently, we detected Zn as well as cadmium, which may be partitioned to rice grains, in the phloem saps from the uppermost internodes of rice and in the xylem saps from the cut stems at early grain-filling. To quantify Zn transport to the grains via the phloem and xylem, a mathematical model previously developed for cadmium transport to rice grains was applied. We examined the translocation of zinc into the grains of rice plants at early grain-filling by feeding zinc-65 (⁶⁵Zn) via a root-bathing medium, through culm cuts above and below the flag-leaf nodes, and through the flag leaves. The estimate made using the mathematical model and experimental data for three types of ⁶⁵Zn transport suggests that the grain Zn may be accumulated predominantly via the phloem through two means of transport, phloem transport of stored Zn from the leaves and, more importantly, xylem-to-phloem transfer at the nodes from Zn as it is being absorbed. The Zn transport via the phloem to the grains is more selective than that of cadmium, a non-nutrient element, as also evidenced by the greater transport of cadmium to the glumes via the xylem.