高等植物蔗糖转运的分子调控

在高等植物中,蔗糖的合成、运输与分配是一个复杂的过程。蔗糖由源到库的运输不仅与植物的生长发育相关,还受到植物体内的激素水平以及外界环境条件变化等因素的影响。蔗糖转运蛋白介导了蔗糖在植物韧皮部的装载、运输和卸载,在某些库中的蔗糖转运和库组织分配的分子调控中起有重要的生理作用。此外,简要介绍了笔者实验室在橡胶树蔗糖转运蛋白基因研究方面的最新进展。     

植物体内糖分子的长距离运输及其分子机制

植物器官(如叶、叶鞘、绿色的茎等)可以通过光合作用将CO₂合成为碳水化合物, 并经过长距离运输到达库组织(如新生组织、花粉、果实等)中进行贮存或利用。蔗糖是高等植物长距离运输碳水化合物的主要形式。蔗糖分子从源到库的运输包括源组织韧皮部的装载、维管束的运输和库组织韧皮部的卸载3个步骤。遗传学和分子生物学研究证明, 蔗糖转运蛋白、转化酶和单糖转运蛋白在糖分子的装载和卸载过程中发挥重要作用。该文综述了目前对光合产物运输过程及其调控分子机制的最新研究进展。     

植物蔗糖转运蛋白表达的调控因素与分子机制

植物光合作用的产物主要以蔗糖的形式在植物体内进行从源到库的运输.蔗糖转运蛋白是此过程的重要参与者,其表达和调控与植物中光合作用产物的分配紧密关联,从而调控着植物的生长发育、结果结实、抗逆抗病等性状.蔗糖转运蛋白的表达受到植物发育时期、外界环境条件及激素的影响.蔗糖转运蛋白的调控机制有转录因子的调节、基因内部序列调控、蛋...     

植物体内蔗糖转运蛋白的功能和调控

蔗糖转运蛋白（sucrose transporter,SUT）负责蔗糖的跨膜运输,在韧皮部介导的源-库蔗糖运输和为库组织供应蔗糖的生理活动中起关键作用。本文介绍植物体内蔗糖转运蛋白基因家族、细胞定位与功能调节以及高等植物的蔗糖感受机制的研究进展。     

水稻蔗糖转运及其与产量形成的关系

蔗糖是植物体内主要的光合产物和运输形式,在叶片中合成并经过维管组织向库器官转运,在库组织中水解并用于合成淀粉、蛋白质和纤维素等有机物。水稻蔗糖转运对调控作物生长发育和产量形成,特别是在逆境条件下的产量稳定,都具有十分重要的作用。本文重点综述了水稻蔗糖韧皮部装载、运输和卸载机制以及关键酶的活性和基因表达调控,并讨论了其与水稻产量形成的关系。     

蔗糖膜运输系统与植物整体碳分配相关（综述）

蔗糖是光合作用的主要产物,作为碳同化的产物在植物体内进行分配。蔗糖的转运机制和效率通过减弱产物抑制来影响光合产率,通过控制源／库关系和生物量分配来调控植物活性。蔗糖在细胞质合成,或通过胞间连丝进行细胞问转运,或跨膜区域化,或外输入质外体被相邻细胞吸收。作为相对大极性的化合物,蔗糖的有效膜转运需要转运蛋白协助。跨液泡膜运输机制可能通过异化扩散、质子对向运输和同向运输;而跨质膜的运输则可能通过质子同向运输和异化扩散类似机制。近几十年仅在分子水平对质子同向运输进行了较为详尽的研究。这篇综述旨在综合介绍最近和过去关于蔗糖跨膜转运与植物整体碳分布机制。     

植物蔗糖转运蛋白的基因与功能

蔗糖是植物体内碳水化合物长距离转运的主要( 甚至唯一) 形式, 为植物生长发育提供碳架与能量。蔗糖转运蛋白(sucrose transporter, SUT)负责蔗糖的跨膜运输, 在韧皮部介导的源-库蔗糖运输, 以及库组织的蔗糖供给中起关键作用。自从菠菜中克隆到第一个SUT基因以来, 已先后有多个SUT基因的cDNA得到克隆与功能分析, 涉及34种双子叶与单子叶植物。每种植物都有一个中等规模 的SUT基因家族, 其不同成员之间具有较高的氨基酸序列同源性, 但在蔗糖吸收的动力学特性、转运底物的特异性和表达谱等方面存在差异。本文系统介绍国内外(主要是国外)在植物SUT基因的克隆、分类与进化、细胞定位与功能, 以及研究方法等方面的研究进展, 并简要介绍我们在橡胶树SUT基因研究上的初步结果。     

植物蔗糖转运蛋白的基因与功能

蔗糖是植物体内碳水化合物长距离转运的主要（甚至唯一）形式，为植物生长发育提供碳架与能量。蔗糖转运蛋白（sucrose transporter，SUT）负责蔗糖的跨膜运输，在韧皮部介导的源-库蔗糖运输，以及库组织的蔗糖供给中起关键作用。自从菠菜中克隆到第一个SUT基因以来，已先后有多个SUT基因的cDNA得到克隆与功能分析，涉及34种双子叶与单子叶植物。每种植物都有一个中等规模的SUT基因家族，其不同成员之间具有较高的氨基酸序列同源性，但在蔗糖吸收的动力学特性、转运底物的特异性和表达谱等方面存在差异。本文系统介绍国内外（主要是国外）在植物SUT基因的克隆、分类与进化、细胞定位与功能，以及研究方法等方面的研究进展，并简要介绍我们在橡胶树SUT基因研究上的初步结果。     

植物非结构性碳水化合物代谢及体内转运研究进展

非结构性碳水化合物(NSC)是参与植物能量代谢的主要能量物质,是维持植物自身发育及响应环境调控的重要因子,主要包括单糖、二糖、糖醇、低聚糖和淀粉等。不同NSC成员之间存在相互转化,其代谢和转化由激素和不同环境因子共同调控,其中激素是主导因子。目前NSC的测定方法主要有滴定法、比色法、酶解法、色谱法等,其中色谱法精度高,可同时进行定性和定量分析,目前应用最为广泛。NSC的转运需要糖转运蛋白参与,主要包括单糖转运蛋白(MST)、蔗糖转运蛋白(SUT)和糖外排转运蛋白(SWEET)三类,其中MST和SUT分别负责对各类单糖和蔗糖进行转运,而SWEET既可以对多种单糖进行转运,也参与了蔗糖的运输过程。本文对NSC相关的代谢、定性定量分析及转运调控等基本规律及最新研究进行了总结,以为更好地明确NSC在植物生长发育及环境调控方面的作用和调节机理提供参考。     

植物蔗糖转运蛋白及其生理功能的研究进展

高等植物通过光合作用产生蔗糖,并以蔗糖形式将同化碳源分配到植物各组织器官中,蔗糖的跨膜转运需要蔗糖转运蛋白的参与。目前,已有研究表明蔗糖转运蛋白广泛存在于高等植物体内,主要在种子、花器、叶肉细胞、韧皮部和根等器官中发挥作用,而通过亚细胞定位可以发现,蔗糖转运蛋白主要定位在细胞的液泡膜及细胞质膜上。综述了国内外对蔗糖转运蛋白的发现、结构、分类、生理功能、功能验证及定位等方面的研究内容,分析了研究蔗糖转运蛋白的意义及目前存在的一些问题,旨为更好地理解蔗糖转运蛋白在植物体内的作用机制做铺垫。     

Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures

Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4. Treatment with these compounds did not affect the formation of free radicals or the inhibition of oxidative phosphorylation resulting from malonate exposure alone. Our data suggest that DA plays an important role in the neurotoxicity produced by malonate. These findings provide direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular DA levels and indicate that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through a mechanism involving DA.     

Scurvy in capybaras bred in captivity in Argentine

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

SSTR5 ablation in islet results in alterations in glucose homeostasis in mice

Somatostatin (SST) peptide is a potent inhibitor of insulin secretion and its effect is mediated via somatostatin receptor 5 (SSTR5) in the endocrine pancreas. To investigate the consequences of gene ablation of SSTR5 in the mouse pancreas, we have generated a mouse model in which the SSTR5 gene was specifically knocked down in the pancreatic beta cells (betaSSTR5Kd) using the Cre-lox system. Immunohistochemistry analysis showed that SSTR5 gene expression was absent in beta cells at three months of age. At the time of gene ablation, betaSSTR5Kd mice demonstrated glucose intolerance with lack of insulin response and significantly reduced serum insulin levels. Insulin tolerance test demonstrated a significant increase of insulin clearance in vivo at the same age. In vitro studies demonstrated an absence of response to SST-28 stimulation in the betaSSTR5Kd mouse islet, which was associated with a significantly reduced SST expression level in betaSSTR5Kd mice pancreata. In addition, betaSSTR5Kd mice had significantly reduced serum glucose levels and increased serum insulin levels at 12 months of age. Glucose tolerance test at an older age also indicated a persistently higher insulin level in betaSSTR5Kd mice. Further studies of betaSSTR5Kd mice had revealed elevated serum C-peptide levels at both 3 and 12 months of age, suggesting that these mice are capable of producing and releasing insulin to the periphery. These results support the hypothesis that SSTR5 plays a pivotal role in the regulation of insulin secretion in the mouse pancreas.