Regulation of sucrose synthase activity and sugar yield by nitrogen in sugar beet

The content of sugar is influenced by sucrose synthase (SS) activity in roots. The effects of nitrogen level in the amino- nitrate ratio on SS activity of leaves and roots, roots yield and sugar content in sugar beet were studied in the field experiment by nutrient solution culture. The results showed that SS activity in leaves was lower than that in roots. With nitrogen level increasing, SS decomposition activity enhanced, and synthesis activity reduced. SS activity was regulated by different nitrogen forms and the ratio of NO3– and NH4 . SS synthesis activity was enhanced as NH4 increasing when NO3–: NH4 ≥1, and it decreased as increasing NH4 when NO3–: NH4 ≤1, and it was the highest when NO3–: NH4 =1. SS decomposition activity was enhanced as NO3– increasing. Sucrose content in root was lowed as nitrogen level increasing, but it was enhanced as NH4 increasing in the same nitrogen level. Root and sugar yield were the highest in the medium nitrogen level and NO3–: NH4 =1. The result in field experiment corresponded with that in the nutrient fluid culture. It provides a basis for using reasonably nitrogen fertilizer in sugar beet production.     

The Effect of Different Nitrogen Form on Key Enzyme Activity of Sugarbeet（Vulgaris L.） Carbon and Nitrogen Metabolism

This article analyses the effect of the proportion of the different nitrogen forms on key enzyme activity of carbon and nitrogen metabolism under the condition of nutritional water while Tian Yan-7 was used as experimental material.The result showed that nitrate reductase(NR) activity in the leaves gradually enhanced with the increase of NO3^-,No matter in root or leaves,glutamina synthetase(GS) activity first enhanced with increasing NH4^ when NH4^ was lower than that of NO3^-,and GS activity was the highest when NH4^ and NO3^- was equal,then GS activity declined with NH4^ increasing further,In the anaphase of growth,synthetic activity in root of sucrose synthetase(SS) in the mixed NH4^ and NO3^- was obviously highr than or NO3^- alone,Both of the root and sugar yields were the highest when the proportion of NH4^ and NO3^- was 1:1.     

Effect of Chlorimuron-Ethyl on Biochemical Mechanism in Tolerant Sugar Beet

Effect of chlorimuron-ethyl on biochemical mechanism in tolerant sugar beet was investigated to provide basic data on using the tolerant genotype properly. Tolerant sugar beet was used to analyze its biochemical mechanism under chlorimuron- ethyl stress with frame culture in field and water culture. Glutathione S-transferase （GST） activity of leaves in tolerant sugar beet was remarkably increased as chlorimuron-ethyl was preemergence applicated at 0.5 and 1.5 g a.i. hw1, at the same time glutathione （GSH） content increased 50.0-490.1 p.g g-~. GST activity of sensitive sugar beet decreased 122.6 U mg-~ min-1 compared with tolerant sugar beet and GSH content only increased to 7.4 p.g g-~ at chlorimuron-ethyl 0.5 g a.i. ha-~ in sensitive sugar beet. The higher GST activity and GSH content conjugated chlorimuron-ethyl absorbed in tolerant sugar beet and made it lost activity. Acetolactate synthases （ALS） activity of the tolerant sugar beet increased to 62.5 and 70.6%, respectively in seedling and leaf growth period, at the same time ALS activity of the sensitive variety was decreased to 36.8 and 64.8%, respectively. The rapidly increased GST activity, GSH content, and ALS, the target enzyme activity were the important pathways for enduring chlorimuron-ethyl in tolerant sugar beet.     

Studies on Glutamine Synthetase Activity in Sugar Beet（Beta vulgaris L.） under Different Levels of Nitrogen

It was shown from the experiment that glutamine synthetase activity (GSA) in both leaf blades and roots under different nitrogen levels rose rapidly to reach its peak from seeding stage to foliage rapid growth stage and declined to its lowest level at the latter stage of root rapid growth,and then increased slightly,GSA in leaf blades had positive correlation with nitrogen level during the whole period of growth,GSA in roots showed the same tendency as it in leaf blades at the early middle stage of growth,but at the latter stage of growth,no positive correlation was established.GSA in leaf blades was the strongest compared with crowns,petioles and roots,and could represent the highest enzyme activity of the whole pant,GSA had quadratic curvilinear correlation with root yield and sugar production.GSA in leaf blades had significant positive correlation with α-NH2-N at the foliage rapid growth stage.     

Studies on some characteristics of nitrate reductase from sugar beet （Beta vulgaris L.）leaves

Some characteristics of nitrate reductase from sugar beet leaves shown in this paper were as follows:The nitrate reductase from sugar beet leaves required NADH as an electron donor.Accordingly,the nitrate reductase was classified as NADH-dependent(E.C.1.6.61).The Km value of the nitrate reductase for NADH and NO3^- were 0.86m mol and 0.18μ mol respectively.The optimum pH in reaction mixture solution for nitrate reduction activity was 7.5.The effect of variable concentrations of inorganic phosphorus in the reaction buffer on nitrate reductase activity was investigated.When the inorganic phosphorus concentration was below 35m mol,the nitrate reductase activity was increased with increase of inorganic phosphorus concentration.Conversely,when the inorganic phosphorus concentration was over 35m mol,the nitrate reductase activity was inhibited.The nitrate reductase activity assayed in vitro was 3.2 and 5.6times of that assayed in vivo under the condition of exogenous and endogenous ground substance respectively.     

Research on Glutamate Dehydrogenase Activity in Sugar Beet（Beta vulgais L）under Different Nitrogen Levels

The experiment of Glutamate Dehydrogenase(GDH) activity in various plant parts under dif-ferent nitrogen levels in frame culture during the whole period of growth was carried out on campus of Northeast Agricltural University in 1993.The result showed that GDH activity in leafblades un-der four nitrogen applied levels rose rapidly to the acme from the seedling to foliage rapid growth stage,then diminished rapidly to the lower level at the latter stage of foliage rapid growth.This level was kept to harvest.GDH activity in roots at each growth stage under all nitrogen levels exhibited little disparity and did not show ostensible regularity of changes.GDH activity in leat blades was stimulated with nitrogen,however,it reduced with nitrogen fertilizer applying further.GDH activity in leaf blades was the biggest compared with crowns,petioles and roots ,which suggested that it could represent the highest enzyme activityof the whole plant.     

Changes of Nitrate Reductase Activity in Cucumber Seedlings in Response to Nitrate Stress

In China, nitrogen fertilizer application rates in intensive agricultural systems have increased dramatically in recent years, especially in protected vegetable production systems. This excessive use of nitrogen fertilizer has resulted in soil secondary salinization, which has become a significant environmental stress for crops such as cucumber, in the protected farmland of China. So it is necessary to illuminate how crops respond to nitrate stress. The objective of this work was to examine the effects of increased nitrate concentration [14 （CK） and 140 mmol L^-1 （T）] on NO3- concentration, and in vitro and in vivo nitrate reductase activities in the roots and leaves of cucumber （Cucumis sativus L. cv. Xintaimici） seedlings with hydroponic culture. The results showed that the NO3- concentration in the roots and leaves of T seedlings significantly increased over treatment course, and at 12 d increased by 1.08 and 1.72 times with respect to CK seedlings, respectively; in vitro nitrate reductase activity of T was increased dramatically to 1.74 times of CK in the roots at 2 d and 1.56 times of CK in the leaves at 6 d, and then decreased. At 12 d, in vitro activity was still 24.3% higher in the roots and only 9.9% lower in the leaves than CK. Compared with in vitro nitrate reductase activity, in vivo activity responded differently to the increase of treatment time. At the beginning, in vivo nitrate reductase activity in the roots and leaves of T had no significant difference from CK, whereas with the increase of treatment duration, the activity decreased. At 12 d, in vivo activity in the roots and leaves of T lowered by 20.1 and 52.8% with respect to CK, respectively. This evidence suggests that posttranslational activation of nitrate reductase in cucumber seedlings may be seriously inhibited by nitrate stress.     

Relationships Between C4 Enzyme Activities and Yield in Soybeans （Glycine max （L.） Merr.）

To study the relationships between C4 enzyme activities and yield, C4 enzyme activities (phosphoenolpyruvate carboxylase (PEPCase), NADP-malate dehydrogenase (NADP-MDH), NADP-malic enzyme (NADP-ME), and pyruvate phosphate dikinase (PPDK)) in different organs of ten soybean cultivars with different yields were measured at different growth stages in China. The result showed that four enzyme activities in C4 pathway were obviously different among cultivars, especially PPDK activity was not detected in the leaves of Dongnong 1567 and Dongnong 1068 and the young leaves of Gongjiao 9107-1 and Dongnong 97-172, but there were weak activities in pod coats. The order of C4 enzyme activities is young leaves < old leaves < pod coats. The correlation coefficients between PEPCase activity and yield and between NADP-MDH activity at blooming stage and yield were 0.6979 and 0.6565, respectively, and both reached the significant level (5%), and PEPCase activity kept significant positive correlation with plant photosynthetic rate. There was a negative correlation between NADP-ME activity and yield, and no correlation was found between PPDK activity and yield.     

^15N Isotope Techniques for Estimating Effects of Urea-N Fertilizer Application Rate on Yields and Nutrient Contents of Pakchoi Cabbage and Asparagus Lettuce and Nitrogen Utilization Efficiency

A pot experiment combined with^15N isotope techniques was conducted to evaluate effects of the varying rates of urea-N fertilizer application on yields,quality,and nitrogen use efficiency （NUE） of pakchoi cabbage （Brassica chinensis L.） and asparagus lettuce （Lactuca saiva L.）.^15N-labbled urea （5.3515N atom %） was added to pots with 6.5 kg soil of 0.14,0.18,0.21,0.25,and 0.29 g N/kg soil,and applied in two splits：60 percent as basal dressing in the mixture and 40 percent as topdressing.The fresh yields of two vegetable species increased with the increasing input of urea-N,but there was a significant quadratic relationship between the dose of urea-N fertilizer application and the fresh yields.When the dosage of urea-N fertilizer reached a certain value,nitrate readily accumulated in the two kinds of plants due to the decrease in NR activity; furthermore,there was a linear negative correlation between nitrate content and NR activity.With the increasing input of urea-N,ascorbic acid and soluble sugar initially increased,declined after a while,and crude fiber rapidly decreased too.Total absorbed N （TAN）,N derived from fertilizer （Ndff）,and N derived from soil （Ndfs） increased,and the ratio of Ndff and TAN also increased,but the ratio of Ndfs and TAN as well as NUE of urea-N fertilizer decreased with the increasing input of urea-N.These results suggested that the increasing application of labeled N fertilizer led to the increase in unlabeled N （namely,Ndfs） presumably due to ＂added nitrogen interaction＂ （ANI）,the decease in NUE of urea-N fertilizer may be due to excess fertilization beyond the levels of plant requirements and the ANI,and the decrease in the two vegetable yields with the increasing addition of urea-N possibly because the excess accumulation of nitrate reached a toxic level.     

同一氮素水平不同NO_3~-/NH_4~+对NRA和GSA的影响

为确定硝态氮和氨态氮的最佳配方,以达到氮肥的最佳调控,试验研究了不同的NO3-/NH4+对甜菜同化关键酶的影响。结果表明,在整个生育期间,同一氮素水平、不同比例的NO3-/NH4+的NRA变化趋势与单一施硝态氮、氨态氮的NRA变化趋势一致,在生育前期较高,而后下降。但不同比例的NO3-/NH4+的NR活力不同,以NO3-/NH4+为3∶1的NR活力最高,而以NO3-/NH4+为0∶4的NR活力最低。在根和叶片中,不同比例的NO3-/NH4+的GS活力变化不同,在叶片中GS活力随NO3-比例增加而增加,但在根中,GS活力则随NH4+的比例增加而增加。     

甜菜氮代谢关键酶与其产质量的关系

不同氮肥处理的 NR和 GS与 α-氨基态氮呈线性相关 ,但不同生育期间 ,NR及叶部的 GS与 α-氨基态氮相关不显著 ,而根部的 GS与 α-氨基态氮则呈显著正相关。NR和 GS与产量及产糖量则呈二次型抛物线关系 ,即在一定范围内 ,随 NR和 GS活性增强 ,产量和产糖量增加 ,但超过 NR和 GS的最适值时 ,二者呈下降趋势。在硝态氮作用下 ,NR与各测试指标相关性较大 ,而 GS与各指标在铵态氮处理下相关性较大 ,说明硝态氮对 NR有促进作用 ,而铵态氮对 GS有较强的促进作用。     

Effect of Salt Stress on Nitrogen Assimilation of Functional Leaves and Root System of Rice in Cold Region

The aims were to investigate the effect of salt stress on key enzyme activity of nitrogen metabolism and the concentration of nitrate nitrogen and ammonium nitrogen response to salt stress.Two rice cultivars,Mudanjiang 30 (sensitive cultivar) and Longdao 5 (salt-tolerant cultivar),were treated with different salt concentrations (CK 0%,S1 0.075%,S2 0.15%,S3 0.225% and S4 0.3%).The results showed that the activities of nitrate reductase (NR),glutamine synthase (GS),glutamate synthase (GOGAT) and glutamate dehydrogenase (GDH) in the functional leaves and roots of rice in cold region presented a single peak curve change and the peak occurred in the heading stage;compared with those of the CK,the activities of NR,GS and GOGAT of rice in cold region decreased,but the activity of GDH increased in the heading stage under salt stress.The variation for key enzyme activity of nitrogen metabolism was the highest under S4 treatment.The activities of NR,GS and GOGAT in the functional leaves significantly decreased compared with those in roots;the concentrations of nitrate nitrogen and ammonium nitrogen in the functional leaves and roots of rice in cold region presented a single peak curve change and the peak occurred in the heading stage;compared with that of the CK,the concentration of nitrate nitrogen decreased in leaves and roots,the concentration of ammonium nitrogen decreased and the concentration of ammonium nitrogen in roots increased under salt stress.The variations for the activities of NR,GS and GOGAT in the functional leaves and roots of Longdao 5 were less than those of Mudanjiang 30 under the same concentration of salt stress.     

甜菜氮糖代谢酶活力与蔗糖代谢的关系

初步探讨了甜菜生育期间叶片和根体中氮糖代谢关键酶 NR、GS、Ru SPase、SS活力的协调关系以及蔗糖的积累转化。结果表明 (1)氮糖代谢酶活力及其相关性主要在叶丛形成期和块根增长期达到显著 ,这两个时期是通过氮素协调氮代谢酶活力 ,实现以正常氮代谢促进蔗糖积累和转化的关键时期。 (2 )在叶丛形成期 ,随施氮量增加 ,NR、 GS、 Ru BPase和 SS分解方向活力提高 ,蔗糖和单糖含量下降 ;生育中后期 ,随施氮量增加 ,NR和 SS分解方向活力增强 ,GS和 SS合成方向活力减弱 ,蔗糖含量下降 ,单糖含量上升 ,总糖量降低。 (3)氮素对糖分含量的影响是通过氮素对氮糖代谢谢酶之间的协调作用的结果。根体中 GS与 SS活力的矛盾贯穿整个生育期 ,GS对 SS催化方向的改变可能起很关键的作用。     

几种豆科植物茶园问作的氮素协调性研究

以白三叶的铺地、考拉和紫花苜蓿的金达品种为材料,采用硝、铵氮素比为1：1的水培液测定其喜氮类型,并测定不同生育时期的硝酸还原酶（NR）和谷氨酰胺合成酶（GS）活性。结果表明,三种豆科植物均有较强的喜硝特性,与喜铵的茶树间作具有氮素种类上的协调性。其中,以金达的总NR活性最高,GS活性最低,GS／NR值和吸氮量最小,最适宜茶园间作。     

不同氮吸收效率水稻品种蔗糖代谢酶的活性比较

[目的]阐明氮素代谢效率的高低与蔗糖代谢强度的关系。[方法]以不同浓度的NH4NO3(0.1、0.5、2.5、12.5 mm/mol)对2个水稻品种桂单4号(GD)和南光(NG)进行水培处理,并对不同供氮水平下不同水稻品种的蔗糖代谢酶的活性进行了比较。[结果]GD叶片蔗糖磷酸合酶以及叶片和根中酸性转化酶活性高于NG,蔗糖含量和低氮水平下谷氨酰胺合成酶(GS)活性高于NG,而中性转化酶的活性在不同供氮水平下的两品种间差异不显著。在所有供氮水平下NG叶片和根中的硝酸还原酶(NR)活性均高于GD。[结论]GD的氮素代谢水平高与低氮水平下GS的活性、蔗糖的合成与分解活性较高有关,而与NR活性无关。     

甜菜氮素同化与蔗糖代谢的关键酶及相关性研究

试验以甜菜高糖品种甜研7号为试材,采用框栽方法,进行各生育时期氮素同化酶与蔗糖代谢关键酶的测定。研究表明,在甜菜幼苗期和叶丛形成期,叶片硝酸还原酶(NR)活性分别与根中蔗糖磷酸合成酶(SPS)活性和蔗糖合成酶(SS)分解方向活性呈显著和极显著关系,叶片NR活性与根中SS合成方向活性关系虽呈正相关但未达到显著水平;在甜菜块根增长初期,根中谷氨酰胺合成酶(GS)活性与根中SPS活性呈正相关但未达显著水平、分别与根中SS合成与分解方向活性呈显著和极显著关系。可见根中氮素同化和蔗糖代谢存在既相互联系又相互制约的关系。     

不同氮源对甜菜蔗糖合成酶的影响

不同氮素形态对蔗糖合成酶（SS）活性影响不同，硝态氮促进SS分解活性，氨态氮则促进SS合成活性。生育前期SS分解活性大于SS合成活性，有利于器官的形态建成，而在生育后期SS合成活性大于SS分解活性，则有利于根中蔗糖的形成。生育前期根中的SS分解活性较强，说明根中有蔗糖合成后的再分解过程。     

氮磷钾对甜菜氨同化关键酶的影响

以甜菜品种KWS0143为材料,采用“3414”设计方案,探讨肥料对酶活性的影响及酶活性与甜菜产量的关系.结果表明,在甜菜生育期间,随着施氮水平的升高,谷氨酰胺合成酶和谷氨酸合成酶活性增强,磷肥与酶活性在生育前期呈显著或极显著正相关关系;在8月初(块根增长初期)可以通过增施相应肥料来调节氨同化途径的强度;谷氨酰胺合成酶...     

防落素对大棚无籽西瓜叶片氮代谢及果实品质与产量的影响

通过对叶片氮代谢及氮含量与代谢相关酶活性之间相关性的分析,以及果实品质与产量的测定,探讨防落素(PCPA)在大棚栽培无籽西瓜生产上的适用浓度,为其在无籽西瓜上的应用提供一定理论依据。在始花期、盛花期和幼果期喷施PCPA溶液（质量浓度分别为0、10、20、40 mg/L）,分别测定不同处理的无籽西瓜叶片可溶性蛋白、总氮含量和代谢相关酶(GS、NR、GDH)活性、果实品质和产量等指标。结果表明：（1）随着PCPA溶液浓度的提高,叶片总氮、可溶性蛋白含量以及GS、NR和GDH活性的变化趋势均为先升后降。PCPA浓度为20 mg/L时促进效果最明显,叶片可溶性蛋白、总氮含量以及GS、NR和GDH活性等指标值均为最高,且均极显著高于CK;PCPA浓度为40 mg/L时,叶片可溶性蛋白、总氮含量以及GS、NR和GDH活性均急速降低,各项指标值均极显著低于10、20 mg/L处理。各项指标的相关性分析表明,无籽西瓜叶片总氮含量与GS、NR和GDH活性之间均呈显著或极显著正相关关系。（2）在所有处理中,20 mg/L处理的果实产量和可溶性固形物含量最高,均极显著高于CK。PCPA在大棚栽培无籽西瓜生产上的适用浓度为20 mg/L。