Effect of abscisic acid (ABA) on sugar accumulation in the flesh tissue of peach fruit at the start of the maturation stage

Experiments were conducted on¹⁴C-sorbitol, fructose, and glucose uptakeinto flesh discs, and sorbitol efflux from thediscs, with and without ABA application toexamine the effect of abscisic acid (ABA) onsugar accumulation in peach fruit flesh at thestart of the maturation stage in relation tomembrane transport. Total uptake of¹⁴C-sorbitol, fructose, and glucose intoflesh discs was effectively promoted by ABA ata concentration of 10^–5 M. PCMBS(p-chloromercuribenzensulfonicacid)-sensitive uptake, which was considered ascarrier-mediated uptake, of sorbitol into thediscs was clearly stimulated by ABA at10^–5 M, compared with glucose andfructose uptake. Sorbitol efflux from the discsacross the tonoplast was restricted by ABA at10^–5 M. ABA application todeveloping fruit increased sugar accumulationin the fruit. Estimated ABA concentration inthis fruit was approximately 10^–5 M. These results indicate that sugar accumulationin peach fruit flesh is stimulated by ABA at aconcentration of 10^–5 M both invitro and in vivo. ABA stimulatesuptake of sugars, especially sorbitol, into theflesh by enhancing carrier-mediated transportpossibly across both tonoplast and plasmamembrane.     

Glyoxylate metabolism and fatty acid oxidation in mango fruit during development and ripening

Throughout the development (maturation) of mango fruit the contents of citric and glyoxylic acids increased steadily. As the fruit matured the levels of isocitrate lyase, malate lyase and alanine: glyoxylate aminotransferase increased and reached maximum values prior to the time of harvesting. At and after harvest the levels of malate lyase and alanine : glyoxylate aminotransferase began to decrease but that of isocitrate lyase remained high until after the harvest when it decreased. The level of glyoxylate reductase was highest in the early developmental stage but declined as the fruit matured and ripened. As the fruit ripened, after harvest, the amounts of citric and glyoxylic acids decreased concomitant with a considerable increase in the levels of isocitrate dehydrogenase, malic dehydrogenase, malic enzyme and glyoxylate dehydrogenase.Fatty acid oxidizing capacity of mitochondria isolated from immature (developing) and postclimacteric fruit pulps was much less than that observed with mitochondria from preclimacteric and climacteric fruit. Glyoxylate stimulated the oxidation of caprylic, lauric, myristic and palmitic acids and inhibited the activity of isocitrate dehydrogenase in vitro.     

Thermal responses in the citrus fruit fly,Dacus tsuneonis: evidence for a pupal diapause

Thermal responses controlling pupariation and adult eclosion in a citrus fruit fly,Dacus tsuneonis (Miyake), were studied to understand the winter biology of this species. When mature larvae were exposed to various temperature conditions, the highest percentage of pupariation was obtained at 15 °C, although the variance at this temperature was greater than at 20 °C or 25 °C. Pupariation occurred most rapidly at 20 °C and an alternating temperature with a mean of 15 °C. At constant 15 °C, pupae failed to emerge as adults. Pupae were characterized by a reduced respiration rate, which is typical of a diapausing pupa. When insects were stored at different temperatures for 45 days after pupariation, and then transferred to 25 °C, adult eclosion occurred earlier when the initial temperature was 10 °C than when it was 5 °C or 15 °C. Adult eclosion occurred most synchronously and pupal mortality was lowest when insects were stored at 15 °C for 90 days before incubation at 25 °C. These results strongly suggest thatD. tsuneonis enters a pupal diapause.     

Properties of proton and sugar transport at the tonoplast of tomato (Lycopersicon esculentum) fruit

Tonoplast vesicles were isolated from tomato (Lycopersicon esculentum Mill.) fruit pericarp and purified on a discontinuous sucrose gradient. ATPase activity was inhibited by nitrate and bafilomycin A₁ but was insensitive to vanadate and azide. PPase hydrolytic activity was inhibited by NaF but was insensitive to nitrate, bafilomycin A₁ vanadate and azide. Kimetic studies of PPase activity gave an apparent K_m, for PP₃ of 18 μM. Identical distributions of bafilomycin- and NO₃-sensitive ATPase activities within continuous sucrose density gradients, confirmed that bafilomycin-sensitive ATPase activity is a suitable marker for the tonoplast. By comparing the distribution of bafilomycin-sensitive ATPase activity with that of PPase activity, it was possible to locate the PPase enzyme exclusively at the tonoplast. The apparent density of the tonoplast did not change during fruit development. Measurements of tonoplast PPase and ATPase activities during fruit development over a 35-day period revealed an 80% reduction in PPase specific activity and a small decrease in ATPase specific activity. ATP- and PP₁-dependent ΔpH generation was measured by the quenching of quinacrine fluorescence in tonoplast vesicles prepared on a discontinuous Dextran gradient. No H⁺ efflux was detected on the addition of sucrose to energized vesicles. Therefore a H⁺/sucrose antiport may not be the mechanism of sucrose uptake at the tomato fruit tonoplast. Similar results were obtained with glucose, fructose and sorbitol. The lack of ATP (or PP₁) stimulation of [¹⁴C]-sucrose uptake also suggested that an antiport was not involved. Initial uptake rates of radiolabelled glucose and fructose were almost double that for sucrose. The inhibition of hexose uptake by p-chloromercuribenzene sulphonate (PCMBS) implicated the involvement of a carrier. Therefore storage of hexose in the tomato fruit vacuole and maintenance of a downhill sucrose concentration gradient into sink cells is likely to be regulated by the activity of sucrose metabolizing enzymes, rather than by energy-requiring uptake mechanisms at the tonoplast.     

中华倒刺鲃能量代谢和热耐受特征的体重效应

为了探讨体重对中华倒刺鲃能量代谢和热耐受特征的影响,在25℃条件下分别测定不同体重大小(1、10、25、>50 g组)中华倒刺鲃的静止代谢率(Resting metabolic rate,RMR)、力竭运动后过量耗氧(Excess post-exercise oxygen consumption,EPOC)和热耐受参数。随体重的增加,中华倒刺鲃个体RMR、最大代谢率(Maximum metabolic rate,MMR)、代谢空间(Metabolic scope,MS)和EPOC均显著增加(P<0.05);单位体重RMR、MMR和MS则均显著降低,而单位体重EPOC随体重的增加显著增加(P<0.05)。RMR、MMR、MS和EPOC的代谢尺度指数分别为0.796、0.834、0.849和1.137且显著大于2/3,因此中华倒刺鲃的能量代谢参数均呈异速度增加的关系而变化。这些变化可能与其个体变大游泳运动能力增强导致能量代谢需求增加相关。中华倒刺鲃临界低温(Critical thermal minimum,CT_min)和致死低温(Lethal the...     

大豆柑桔间作系统中磷的分配和迁移规律研究

用微区试验和³²P同位素示踪技术,比较研究了大豆、柑桔间作和单作条件下,P在大豆和柑桔体中的分配、转移及其在土壤中的迁移规律.结果表明,间作大豆的吸P量和各部位累积P量显著地低于单作大豆;³²P肥料浅施,间作大豆吸收的³²P量显著低于单作大豆;³²P肥料深施,间作大豆吸收的³²P量显著高于单作大豆,但间作不影响P和³²P在各部位的转移和分配.间作柑桔吸收的³²P量显著低于单作柑桔.柑桔新吸收的³²P可快速向地上部分输送,并优先供应生长活跃部位.间作不影响³²P在柑桔各部位的转移和分配,但是P肥深施使柑桔吸收的³²P向地上部分和生长活跃部位的转移速率减慢.间作使土壤中P的生物移动性增强,可促进土壤深层P向土壤浅层迁移.试验结果表明,大豆柑桔间作磷肥的施用深度以保持在20cm以内为佳.     

叉头转录因子1基因FOXO1的特征及其在葱蝇夏滞育前期蛹体内糖脂代谢中的作用(英文)

【目的】克隆和鉴定葱蝇Delia antiqua叉头转录因子1基因,探究其在葱蝇夏滞育前期蛹体内糖代谢和脂代谢中的作用。【方法】本研究基于葱蝇转录组数据利用3′RACE法克隆叉头转录因子1基因的全长开放阅读框;利用生物信息学法分析了该基因编码蛋白的序列特征、保守结构域和二级结构,并采用最大似然法对其与其他13种昆虫来源的同源序列进行了聚类分析。通过RNA干扰技术沉默目的基因后,采用实时定量PCR法分析葱蝇夏滞育前期蛹体内目的基因下游脂肪酶brummer基因(DaBmm)和磷酸烯醇式丙酮酸羧化酶基因(DaDepck)的表达规律,并对甘油三脂(TAG)、海藻糖和葡萄糖含量及总脂肪酶的活性变化进行分析。【结果】克隆得到了葱蝇叉头转录因子1基因DaFOXO1 (GenBank登录号: MG813258),其编码蛋白含有619个氨基酸,具有典型的叉头DNA结合域,核定位信号,2个14-3-3结合区和1个富含谷氨酰胺区;DaFOXO1与铜绿蝇Lucilia cuprina FOXO1蛋白的氨基酸序列有87%的一致性,并与其聚为一支。干扰葱蝇夏滞育前期蛹DaFOXO1后,8-20 h间可显著抑制DaBmm基因的表达,12-24 h间可显著影响TAG含量和总脂肪酶的活性,8-20 h(16 h除外)间可显著降低DaPepck的表达,但对葡萄糖和海藻糖的含量没有显著影响。【结论】本研究结果表明海藻糖和葡萄糖的积累在化蛹前已完成;DaFOXO1对DaBmm和DaDepck基因的表达调控可能有利于葱蝇夏滞育前期蛹体内的脂肪积累。同时也表明靶向Bmm依赖性脂类水解过程及其下游因子可为打破昆虫滞育提供一种有效策略。     

Silencing of the tomato Sugar Partitioning Affecting protein (SPA) modifies sink strength through a shift in leaf sugar metabolism

Limitations in our understanding about the mechanisms that underlie source‐sink assimilate partitioning are increasingly becoming a major hurdle for crop yield enhancement via metabolic engineering. By means of a comprehensive approach, this work reports the functional characterization of a DnaJ chaperone related‐protein (named as SPA; sugar partition‐affecting) that is involved in assimilate partitioning in tomato plants. SPA protein was found to be targeted to the chloroplast thylakoid membranes. SPA‐RNAi tomato plants produced more and heavier fruits compared with controls, thus resulting in a considerable increment in harvest index. The transgenic plants also displayed increased pigment levels and reduced sucrose, glucose and fructose contents in leaves. Detailed metabolic and enzymatic activities analyses showed that sugar phosphate intermediates were increased while the activity of phosphoglucomutase, sugar kinases and invertases was reduced in the photosynthetic organs of the silenced plants. These changes would be anticipated to promote carbon export from foliar tissues. The combined results suggested that the tomato SPA protein plays an important role in plastid metabolism and mediates the source‐sink relationships by affecting the rate of carbon translocation to fruits.     

Sucrose metabolism and fruit growth in parthenocarpic vs seeded blueberry (Vaccinium ashei) fruits

Although fruit set and development are induced by applications of gibberellins, final fruit weight of gibberellin-induced parthenocarpic fruit is often less than that of pollinated fruit. We examined changes in the activities of sucrose-metabolizing enzymes and sugar accumulation in developing fruits of cultivated blueberry (Vaccinium ashei Reade) and their correlation with fruit growth upon pollination or exogenous applications of gibberellic acid (GA₃). The objective was to determine if differences in fruit growth could be attributed to differences in enzyme activities and subsequent sugar accumulation in fruits. The fruit development period of GA₃-treated fruits was 15 days longer than that of pollinated fruits. At maturity, GA₃-treated fruit accumulated an average of 180 mg dry weight while pollinated fruit accumulated 390 mg dry weight. Dry weight accumulation in nonpollinated fruits was negligible and these fruits abscised by 45 days after bloom (DAB). The total carbon (C) cost (dry weight C + respiratory C) for fruit development was 109 and 244 mg C fruit^-1 for GA₃-treated and pollinated fruits, respectively. Hexose concentration increased to 100 mg (g fresh weight)^-1 at ripening in both GA₃-treated and pollinated fruits. Nonpollinated fruits reached a maximum hexose concentration at 45 DAB. Sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) activities reached a maximum of ≤5.0 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits. Soluble acid invertase (EC 3.2.1.26) activity increased to about 60 μmol (g fresh weight)^-1 h^-1 in both GA₃-treated and pollinated fruits at ripening, while in nonpollinated fruits, a maximum soluble acid invertase activity of 0.12 μmol (g fresh weight)^-1 h^-1 was measured at 24 DAB. Insoluble acid invertase activity declined during the early stages of fruit growth and remained relatively low throughout fruit development. Neutral invertase activity was low throughout development, increasing to 5 μmol (g fresh weight)^-1 h^-1 at ripening in GA₃-treated and pollinated fruits. Our studies demonstrate that blueberry fruit development does not appear to be limited by sucrose metabolizing enzyme activity and/or the ability to accumulate sugars in either GA₃-treated or pollinated fruits.     

A kinetic model of sugar metabolism in peach fruit reveals a functional hypothesis of a markedly low fructose‐to‐glucose ratio phenotype

The concentrations of sugars in fruit vary with fruit development, environment and genotype. In general, there were weak correlations between the variations in sugar concentrations and the activities of enzymes directly related with the synthesis or degradation of sugars. This finding suggests that the relationships between enzyme activities and metabolites are often non‐linear and are difficult to assess. To simulate the concentrations of sucrose, glucose, fructose and sorbitol during the development of peach fruit, a kinetic model of sugar metabolism was developed by taking advantage of recent profiling data. Cell compartmentation (cytosol and vacuole) was described explicitly, and data‐driven enzyme activities were used to parameterize equations. The model correctly accounts for both annual and genotypic variations, which were observed in 10 genotypes derived from an interspecific cross. They provided important information on the mechanisms underlying the specification of phenotypic differences. In particular, the model supports the hypothesis that a difference in fructokinase affinity could be responsible for a low fructose‐to‐glucose ratio phenotype, which was observed in the studied population.     

饥饿和温度驯化对中华倒刺鲃静止代谢和游泳能力的影响

为了探讨饥饿和温度驯化对中华倒刺鲃(Spinibarbus sinensis)幼鱼维持代谢和游泳运动能力的影响,在不同温度(15、25℃)条件下分别测定了经0(对照)、1、2、4周饥饿后中华倒刺钯的静止代谢率(M_(O_2_(rest))和匀加速最大游泳速度(U_(CAT))。饥饿和低温对M_(o_2_(rest))和U_(CAT)均有负效应。在高温条件下,实验鱼经1周饥饿后其M_(o_2_(rest))和U_(CAT)均显著下降(P0.05);但在低温条件下,仅4周饥饿组的M_(o_2_(rest))和U_(CAT)显著下降(P0.05)。U_(CAT)与M_(o_2_(rest))在不同的饥饿周期具有相似的变化趋势;在低温条件下,前期饥饿阶段M_(o_2_(rest))和U_(CAT)变化较小,后期饥饿阶段变化较大;但在高温条件下则相反。无论是在低温还是在高温条件下,U_(CAT)与M_(o_2_(rest))之间均呈显著线性正相关(P0.05),但低温组回归方程斜率显著高于高温组回归方程斜率(F_(1,4)=11.416,P=0.028)。在不同温度下,中华倒刺钯游泳运动能力对饥饿的反应不尽相同可能与维持代谢、生化反应速率、机体能量储存、代谢酶活性及底物利用类型等的差异相关,这种对策的差异可能是其对栖息地环境温度和食物资源季节性变化的适应。     

Proteins, non-structural carbohydrates and organic acids in the flowers of sweet orange (Citrus sinensis (L.) osbeck)

The concentration of soluble proteins in open flowers of sweet orange (Citrus sinensis (L.) Osbeck) was about 35% of the protein content found in green leaves, while ovary and stigma, with attached style, contained up to 85%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicates that flowers and leaves contained ribulose bisphosphate carboxylase-oxygenase (Rubisco). At least 12 polypeptides, ranging from 22 to 100 kDa, were more distinct in flowers than in leaves. The polypeptide band at about 100 kDa in the flower extract suggests the presence of phosphoenolpyruvate carboxylase (PEPCase) in citrus flowers. Activity of Rubisco and PEPCase, expressed in μmol g tissue fresh weight⁻¹ hr⁻¹, averaged 14.2 and 64.6 for intact open flowers, and 547.9 and 63.3 for the leaves, respectively. Starch and reducing sugars were 1.2- and 8.4-fold higher, respectively, and dark respiration rates were about five-fold greater for open flowers than fully expanded, sun leaves. Quinic and malic acids made up about 96% of the organic acids found in flowers and leaves. Ascorbic, citric, fumaric, and shikimic acids were in small or trace amounts. The large accumulation of starch and soluble sugars, in addition to the presence and activity of Rubisco and PEPCase, indicates that the flowers of sweet orange would have some capability to perform photosynthetic CO₂ assimilation, the metabolites of which might play some important role in flower development and fruit setting.     

荔枝蒂蛀虫(Conopomorpha sinensis Bradley)的饲养及其实验种群生命表

荔枝蒂蛀虫(Conopomorpha sinensis Bradley)是影响荔枝生产及出口的重要害虫。由于其具有钻蛀为害的习性,其生态学研究薄弱。以荔枝果核、龙眼果核为饲料,在室内成功饲养了连续3个世代的荔枝蒂蛀虫。并编制了荔枝蒂蛀虫实验种群的特定时间生命表和特定年龄生命表。特定时间生命表参数为：第一世代R0(I)＝2.0503,rm＝0.0230;第二世代R0 (I)＝7.5067,rm＝0.0538;第三世代R0 (I)＝0.3104,rm＝0.0321。特定年龄生命表参数为：第一世代R0 (I)＝2.0594,rm＝0.0217;第二世代R0 (I)＝7.5261,rm＝0.0559;第三世代R0 (I)＝0.3114,rm＝0.0333。研究了两类生命表参数之间的关系,并进行了相应的换算论证。通过R0≈I的关系,在本例中,两种生命表之间的参数是可以进行换算的。生殖力表不同于特定时间生命表,它丢失了幼期累计存活率而使R0失真。