套袋对梨果实发育过程中糖组分及其相关酶活性的影响

以翠冠和黄金梨为试材,测定套袋和未套袋(对照)梨果实发育时期果实中蔗糖、葡萄糖、果糖和山梨醇含量以及蔗糖代谢相关酶酸性转化酶(AI)、中性转化酶(NI)、蔗糖合成酶(SS)和蔗糖磷酸合成酶(SPS)的活性,并对果实中糖组分积累与酶活性的关系进行了分析.结果表明:(1)两梨品种套袋果实在发育过程中蔗糖、葡萄糖、果糖、山梨醇和糖代谢相关酶活性变化趋势与对照基本一致,套袋果实糖含量均低于对照但差异不显著,而各相关酶活性在两类果实间差异表现各异.(2)在梨果实发育早期,果实中以分解酶类为主,糖分积累低;发育后期以合成酶类为主,糖分积累多.(3)两品种套袋和对照果实AI活性与葡萄糖含量均呈显著或极显著正相关,SS合成方向活性与蔗糖含量均为极显著正相关,且翠冠对照果SPS活性与蔗糖含量呈极显著正相关.可见,套袋通过提高果实发育早期转化酶(Inv)活性,降低果实后期蔗糖磷酸合成酶(SPS)、蔗糖合成酶(SS)的活性来影响糖分积累,从而影响梨果品质.     

Carbohydrate availability affects growth and metabolism in peach fruit

Along with sucrose, sorbitol represents the main photosynthetic product and form of translocated carbon in peach. This study aimed at determining whether peach fruit carbohydrate metabolism is affected by changes in source–sink balance , and specifically whether sorbitol or sucrose availability regulates fruit enzyme activities and growth. In various trials, different levels of assimilate availability to growing fruits were induced in vivo by varying crop load of entire trees, leaf : fruit ratio (L:F) of fruiting shoots, or by interrupting the phloem stream (girdling) to individual fruits. In vitro, fruit tissue was incubated in presence/absence of sorbitol and sucrose. Relative growth rate (RGR), enzyme activities and carbohydrates were measured at different fruit growth stages of various peach cultivars in different years. At stage III, high crop load induced higher acid invertase (AI, EC 3.2.1.26) activities and hexose : sucrose ratios. Both sorbitol and sucrose contents were proportional to L:F, while sorbitol dehydrogenase (SDH, EC 1.1.1.14) activity was the only enzyme activity directly related to L:F in both fruit growth stages. Girdling reduced fruit RGR and all major carbohydrates after 4 days and SDH activity already after 48 h, but it did not affect sucrose synthase (SS, EC 2.4.1.13), AI and neutral invertase (NI, EC 3.2.1.27). Fruit incubation in sorbitol for 24 h induced higher SDH activities than in buffer alone. In general, assimilate availability affected both sorbitol and sucrose metabolism in peach fruit, and sorbitol may function as a signal for modulating SDH activity. Under highly competitive conditions, AI activity may be enhanced by assimilate depletion, providing a mechanism to increase fruit sink strength by increasing hexose concentrations.     

套袋梨贮藏过程中糖代谢及相关酶活性变化特征

以‘翠冠’梨为材料,研究了套双层遮光纸袋梨果实贮藏过程中蔗糖、果糖、葡萄糖、山梨醇及糖代谢中酶活性的变化规律。结果表明,贮藏套袋梨果实中果糖、葡萄糖、山梨醇和蔗糖含量都低于未套袋对照;套袋梨果实中山梨醇脱氢酶活性在贮藏的前5d都低于对照,贮藏10d后活性均高于对照,且与山梨醇含量呈现极显著正相关;贮藏套袋梨果实中蔗糖磷酸合酶(SPS)及蔗糖合酶(SS)分解和合成方向活性都是前期低于对照,贮藏后期都高于对照,且蔗糖含量与蔗糖磷酸合酶和蔗糖合酶(分解方向)活性都呈显著正相关;贮藏的套袋梨果实和对照中的山梨醇含量与果糖含量均呈极显著负相关,蔗糖含量与葡萄糖含量呈极显著负相关,即在贮藏过程中山梨醇可能转化为果糖,而蔗糖则转化成葡萄糖。     

枇杷果实发育过程中糖积累及相关酶活性变化研究

以'青种'、'霸红'和'鸡蛋白'3个枇杷品种为材料,测定不同果实发育时期果实中蔗糖、葡萄糖和果糖含量以及蔗糖代谢相关酶即酸性转化酶(AI)、中性转化酶(NI)、蔗糖合成酶(SS)和蔗糖磷酸合成酶(SPS)的活性,并对果实中糖积累与酶活性的关系进行了分析.结果表明:在果实膨大期(5月3日)之前,3种枇杷果实的蔗糖、葡萄糖和果糖积累缓慢,之后则迅速积累,存在着明显的转折点;果实成熟(5月23日)之后糖分积累速度趋于平稳.3种枇杷果实在发育过程中转化酶、蔗糖合成酶和蔗糖磷酸合成酶的活性变化与3种糖积累的动态变化趋势相一致.NI和AI活性在果实膨大期之前都较低且没有明显的变化,之后均快速上升;SS和SPS的活性在果实膨大期之前都很低且几乎无变化,随后'鸡蛋白'的活性迅速上升至果实成熟之后便缓慢上升,而'青种'和'霸红'随果实成熟度的增加而升高,但均低于'鸡蛋白'.可见,枇杷果实膨大期是糖分积累代谢活跃期,其糖积累受蔗糖代谢相关酶综合调控.     

Changes in carbohydrate and enzyme levels during development of leaves of Prunus persica, a sorbitol synthesizing species

Carbohydrate levels and activities of enzymes associated with starch, sucrose and sorbitol metabolism were assayed in leaves of peach [ Prunus persica (L.) Batsch cv. Redhaven] of different ages, in order to examine developmental changes in leaf carbohydrate metabolism. Dry matter, soluble protein, chlorophyll and the activities of key enzymes of the reductive pentose phosphate pathway increased during leaf development. The levels of leaf carbohydrates, especially sorbitol and starch, also increased. Changes of starch levels were related to increases in the activities of enzymes associated to starch metabolism, such as ADPglucose-pyrophosphorylase (E.C. 2.7.7.27) and amylase (E.C. 3.2.1.1. plus E.C. 3.2.1.2). The activities of enzymes involved in sucrose and sorbitol degradation decreased during leaf development, whereas the activities of aldose-6-phosphate reductase (E.C. 1.1.1.200) and cytosolic fructase-1,6-bisphosphatase (E.C. 3.1.3.11) increased. In contrast, the activity of sucrose-phosphate synthase (E.C. 2.4.1.14) did not vary in a significant manner. The results suggest that the ability to synthesize and utilize both sucrose and sorbitol changes as peach leaves mature, and also that there are differences in metabolism of these two transport sugars during leaf development.     

网纹甜瓜发育果实糖分积累与蔗糖代谢参与酶的关系

随着网纹甜瓜果实的发育,果实中葡萄糖和果糖的含量增加,蔗糖的快速积累发生在果实发育的中后期,高蔗糖积累型果实中蔗糖积累速率明显快于低蔗糖积累型.蔗糖磷酸合成酶活性在果实发育的前期短暂下降, 而后稳步上升,在果实发育的中后期高蔗糖积累型果实中该酶的活性显著高于低蔗糖积累型果实;随着果实发育,蔗糖合成酶的分解活性降低而合成活性升高.酸性和中性转化酶在未成熟果实中活性较高,而在成熟果实中很低; 高蔗糖积累型果实中酸性转化酶活性显著低于同期低蔗糖积累型果实.合成蔗糖的酶活性小于分解蔗糖的酶活性时蔗糖几乎没有积累.根据这些结果推测,转化酶活性的下降、蔗糖磷酸合成酶活性的增加以及蔗糖合成酶分解活性的下降和合成活性的增加,是引起果实蔗糖积累的主要内在因子.     

Drought stress revealed physiological,biochemical and gene-expressional variations in ‘Yoshihime’ peach (Prunus Persica L) cultivar

It is indispensable to comprehend the mechanism that regulates plant responses to drought conditions to intensify the water use efficiency of stone fruits. The physiological, biochemical and molecular responses of drought-treated peach leaves were investigated. Results revealed that drought-treated plants manifested a significant attenuation in water potential as compared to control plants. Furthermore, sorbitol and proline contents were accumulated contrary to glucose, fructose, and sucrose that were dwindled significantly throughout the drought period. Similarly, the activities of antioxidant enzymes and expression pattern of related genes were hoisted to counter the lipid peroxidation in drought-treated plants. Moreover, reduced stomatal conductance has repressed the photosynthesis process and linked genes during drought stress. The expression level of regulatory genes (dehydration-responsive element-bindings and WRKYs) exhibited up-regulation in the drought-treated group. Overall, this study asserts that ‘Yoshihime’ peach cultivar possesses unique physiological, biochemical, and molecular responses under different spells of drought stress.     

果实中糖的运输、代谢与积累及其调控

叶片光合产物向果实运输的主要形态是蔗糖,但在木本蔷薇科果树中,光合产物的主要运输形态为山梨醇.糖从质外体空间跨膜运入共质体的过程由糖运输蛋白介导,而糖运输蛋白的基因表达伴随着果实糖的积累而增强.蔗糖代谢酶参与了细胞内外4个与糖运输有关的无效循环.己糖代谢抑制是果实糖快速积累的前提.在木本蔷薇科果实中,蔗糖代谢酶活力仍非常活跃,表明蔗糖可能与山梨醇在果实生长发育中都起重要的作用.糖作为信号分子,调节了承担糖运输与代谢的基因的表达.自然环境因子和栽培措施能有效调控糖运输、代谢与积累.反义抑制Ivr基因表达能提高番茄果实含糖量的实验结果表明遗传工程调控糖积累的潜力.阐明糖信号与其它信号互作对糖运输与代谢的调控机制是今后研究的重点.     

杨梅果实发育进程中的碳水化合物代谢

以‘乌紫’和‘荸荠’两个杨梅品种为试材,测定了干鲜重、糖含量、可滴定酸含量、蔗糖和己糖代谢相关酶活性的动态变化。结果表明,杨梅果实的干鲜重、含糖量的快速增长和可滴定酸含量的快速下降均发生在果实发育后期。成熟‘乌紫’杨梅果实的蔗糖含量约占总糖的2／3以上,而‘荸荠’杨梅仅为总糖的49％。‘荸荠’杨梅的转化酶和蔗糖合酶分解活性随着果实发育呈上升趋势,‘乌紫’杨梅的则变化不大。两个品种的蔗糖磷酸合酶活性随着果实发育呈上升趋势,但蔗糖合酶合成活性到果实发育中期后下降。两个品种的己糖激酶活性变化相似,但果糖激酶活性的变化趋势不同。     

Sucrose Synthase in Wild Tomato, Lycopersicon chmielewskii, and Tomato Fruit Sink Strength

Here it is reported that sucrose synthase can be readily measured in growing wild tomato fruits (Lycopersicon chmielewskii) when suitable methods are adopted during fruit extraction. The enzyme also was present in fruit pericarp tissues, in seeds, and in flowers. To check for novel characteristics, the wild tomato fruit sucrose synthase was purified, by (NH₄)₂SO₄ fraction and chromatography with DE-32, Sephadex G-200, and PBA-60, to one major band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The following characteristics were obtained: native protein relative molecular weight 380,000; subunit relative molecular weight 89,000; K_m values with: sucrose 53 millimolar, UDP 18.9 micromolar, UDP-glucose 88 micromolar, fructose 8.4 millimolar; pH optima between 6.2 to 7.3 for sucrose breakdown and 7 to 9 for synthesis; and temperature optima near 50°C. The enzyme exhibited a high affinity and a preference for uridylates. The enzyme showed more sensitivity to divalent cations in the synthesis of sucrose than in its breakdown. Sink strength in tomato fruits also was investigated in regard to sucrose breakdown enzyme activities versus fruit weight gain. Sucrose synthase activity was consistently related to increases in fruit weight (sink strength) in both wild and commercial tomatoes. Acid and neutral invertases were not, because the published invertase activity values were too variable for quantitative analyses regarding the roles of invertases in tomato fruit development. In rapidly growing fruits of both wild and commercially developed tomato plants, the activity of sucrose synthase per growing fruit, i.e. sucrose synthase peak activity X fruit size, was linearly related to final fruit size; and the activity exceeded fruit growth and carbon import rates by at least 10-fold. In mature, nongrowing fruits, sucrose synthase activities approached nil values. Therefore, sucrose synthase can serve as an indicator of sink strength in growing tomato fruits.     

Sugar metabolism in germinating soybean seeds: evidence for the sorbitol pathway in soybean axes

Characterization of sugar content and enzyme activity in germinating soybean (Glycine max L. Merrell) seeds led to the discovery of sorbitol accumulating in the axes during germination. The identity of sorbitol was confirmed by relative retention times on high-performance liquid chromatography and gas liquid chromatography and by mass spectra identical with authentic sorbitol. Accumulation of sorbitol in the axes started on day 1 of germination as sucrose decreased and glucose and fructose increased. Sucrose also decreased in the cotyledons, but there was no accumulation of sorbitol, glucose, or fructose. Accumulation of sorbitol and hexoses was highly correlated with increased invertase activity in the axes, but not with sucrose synthase and sucrose phosphate synthase activities. Sucrose synthase activity was relatively high in the axes, whereas the activity of sucrose phosphate synthase was relatively high in the cotyledons. Ketose reductase and aldose reductase were detected in germinating soybean axes, but not in cotyledons. Fructokinase and glucokinase were present in both axes and cotyledons. The data suggest a sorbitol pathway functioning in germinating soybean axes, which allows for the interconversion of glucose and fructose with sorbitol as an intermediate.     

Sucrose phosphate synthase and other sucrose metabolizing enzymes in fruits of various species

Recent reports have suggested that sucrose phosphate synthase (EC 2.4.1.14), a key enzyme in sucrose biosynthesis in photosynthetic “source” tissues, may also be important in some sucrose accumulating “sink” tissues. These experiments were conducted to determine if sucrose phosphate synthase is involved in sucrose accumulation in fruits of several species. Peach (Prunus persica NCT 516) and strawberry (Fragaria x ananassa cv. Chandler) fruits were harvested directly from the plant at various stages of fruit development. Kiwi (Actinidia chinensis), papaya (Carica papaya), pineapple (Ananas comosus) and mango (Mangifera indica) were sampled in postharvest storage over a period of several days. Carbohydrate concentrations and activities of sucrose phosphate synthase, sucrose synthase (EC 2.4.1.13), and acid and neutral invertases (EC 3.2.1.26) were measured. All fruits contained significant activities of sucrose phosphate synthase. Moreover, in fruits from all species except pineapple and papaya, there was an increase in sucrose phosphate synthase activity associated with the accumulation of sucrose in situ. The increase in sucrose concentration in peaches was also associated with an increase in sucrose synthase activity and, in strawberries, with increased activity of both sucrose synthase and neutral invertase. The hexose pools in all fruits were comprised of equimolar concentrations of fructose and glucose, except in the mango. In mango, the fructose to glucose ratio increased from 2 to 41 during ripening as sucrose concentration more than doubled. The results of this study indicate that activities of the sucrose metabolizing enzymes, including sucrose phosphate synthase, within the fruit itself, are important in determining the soluble sugar content of fruits of many species. This appears to be true for fruits which sweeten from a starch reserve and in fruits from sorbitol translocating species, raffinose saccharide translocating species, and sucrose translocating species.     

Sucrose accumulation in developing peach fruit

Uptake of ¹⁴C-sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring ¹⁴C-sucrose and ¹⁴C-glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 m M ¹⁴C-sucrose and ¹⁴C-glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.
At 10 m M , glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanide m -chlorophenylhydrazone (CCCP) at 25 μ M. These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.
Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate pool directly.     

Primary and secondary metabolism in the sun‐exposed peel and the shaded peel of apple fruit

The metabolism of carbohydrates, organic acids, amino acids and phenolics was compared between the sun‐exposed peel and the shaded peel of apple fruit. Contents of sorbitol and glucose were higher in the sun‐exposed peel, whereas those of sucrose and fructose were almost the same in the two peel types. This was related to lower sorbitol dehydrogenase activity and higher activities of sorbitol oxidase, neutral invertase and acid invertase in the sun‐exposed peel. The lower starch content in the sun‐exposed peel was related to lower sucrose synthase activity early in fruit development. Dark respiratory metabolism in the sun‐exposed peel was enhanced by the high peel temperature due to high light exposure. Activities of most enzymes in respiratory metabolism were higher in the sun‐exposed peel, but the concentrations of most organic acids were relatively stable, except pyruvate and oxaloacetate. Due to the different availability of carbon skeletons from dark respiration in the two peel types, amino acids with higher C/N ratios are accumulated in the sun‐exposed peel whereas those with lower C/N ratios are accumulated in the shaded peel. Contents of anthocyanins and flavonols and activities of phenylalanine ammonia‐lyase, UDP‐galactose:flavonoid 3‐O‐glucosyltransferase and several other enzymes were higher in the sun‐exposed peel than in the shaded peel, indicating the entire phenylpropanoid pathway is upregulated in the sun‐exposed peel. Comprehensive analyses of the metabolites and activities of enzymes involved in primary metabolism and secondary metabolism have allowed us to gain a full picture of the metabolic network in the two peel types under natural light exposure.     

Growth, sucrose synthase, and invertase activities of developing Phaseolus vulgaris L. fruits

Activities of the sucrose-cleaving enzymes, acid and neutral invertase and sucrose synthase, were measured in pods and seeds of developing snap bean (Phaseolus vulgaris L.) fruits, and compared with ¹⁴C-import, elongation and dry weight accumulation. During the first 10 d post-anthesis, pods elongated rapidly with pod dry weight increase lagging behind by several days. The temporal patterns of acid invertase activity and import coincided closely during the first part of pod development, consonant with a central role for this enzyme in converting imported sucrose during pod elongation and early dry weight accumulation. Later, sucrose synthase became the predominant enzyme of dry weight accumulation and was possibly associated with the development of phloem in pod walls. Sucrose synthase activity in seeds showed two peaks, corresponding to two phases of rapid import and dry weight accumulation; hence, sucrose synthase was associated with seed sink growth. Acid invertase activities in seeds were low and did not show a noticeable relationship with import or growth. All neutral invertase activities, during pod and seed development, were too low for it to have a dominant role in sucrose cleavage. Changes in activities of certain sucrose-cleaving enzymes appear to be correlated with certain sink functions, including import, storage of reserves, and biosynthetic activities. The data supports the association of specific sucrose-cleaving enzymes with the specific processes that occur in the developing pods and seeds of snap bean fruits; for example, acid invertase with pod elongation and sucrose synthase with fruit dry matter accumulation.     

Transgenic tomato plants with decreased sucrose synthase are unaltered in starch and sugar accumulation in the fruit

Sucrose is the photoassimilate transported from the leaves to the fruit of tomato yet the fruit accumulates predominantly glucose and fructose. Hydrolysis of sucrose entering the fruit can be accomplished by invertase or sucrose synthase. Early in tomato fruit development there is a transient increase in sucrose synthase activity and starch which is correlated with fruit growth and sink strength suggesting a regulatory role for sucrose synthase in sugar import. Using an antisense sucrose synthase cDNA under the control of a fruit-specific promoter we show that sucrose synthase activity can be reduced by up to 99% in young fruit without affecting starch or sugar accumulation. This result calls into question the importance of sucrose synthase in regulating sink strength in tomato fruit.     

苹果中磷酸蔗糖合酶家族基因的表达特性及其与蔗糖含量的关系

磷酸蔗糖合酶(sucrose phosphate synthase,SPS)是植物中蔗糖合成的主要限速酶,影响植物的生长发育和果实中蔗糖的含量。为探明苹果中SPS基因家族特性及其在蔗糖合成中的作用,该研究从苹果基因组中分离了MdSPS家族基因,分析了它们的进化关系以及mRNA表达特性与酶活性和蔗糖含量的关系。结果显示:(1)在苹果基因组中有8个SPS家族基因表达,它们分别属于双子叶植物的3个SPS亚家族。(2)荧光定量PCR分析显示,苹果C类的MdSPS6基因和A类的MdSPS1a/b基因是苹果中表达丰度最高的SPS基因成员,其中MdSPS6在苹果成熟果中表达丰度最高,其次是成熟叶片,而MdSPS1a/b在不积累蔗糖的幼果中表达丰度最高。(3)在果实发育过程中,除MdSPS1a/b之外,其它5个苹果MdSPS家族基因均随果实的生长表达丰度增加,与SPS活性和蔗糖含量明显呈正相关关系。研究表明,C类家族MdSPS6是苹果果实发育后期和叶片中蔗糖合成的主要SPS基因。