摘除雌花对甜瓜成熟叶片中糖及相关酶活性的影响

甜瓜有果株的成熟叶片中蔗糖、葡萄糖、果糖含量与无果株的无显著差异,水苏糖与棉子糖含量略低于无果株,肌醇半乳糖苷(合成水苏糖的前体)含量显著低于无果株,蔗糖磷酸合成酶(SPS)和肌醇半乳糖苷合成酶活性与无果株的无显著差异,水苏糖合成酶活性显著高于无果株。     

Important roles of drought- and cold-inducible genes for galactinol synthase in stress tolerance in Arabidopsis thaliana

Raffinose family oligosaccharides (RFO) accumulating during seed development are thought to play a role in the desiccation tolerance of seeds. However, the functions of RFO in desiccation tolerance have not been elucidated. Here we examine the functions of RFO in Arabidopsis thaliana plants under drought- and cold-stress conditions, based on the analyses of function and expression of genes involved in RFO biosynthesis. Sugar analysis showed that drought-, high salinity- and cold-treated Arabidopsis plants accumulate a large amount of raffinose and galactinol, but not stachyose. Raffinose and galactinol were not detected in unstressed plants. This suggests that raffinose and galactinol are involved in tolerance to drought, high salinity and cold stresses. Galactinol synthase (GolS) catalyses the first step in the biosynthesis of RFO from UDP-galactose. We identified three stress-responsive GolS genes (AtGolS1, 2 and 3) among seven Arabidopsis GolS genes. AtGolS1 and 2 were induced by drought and high-salinity stresses, but not by cold stress. By contrast, AtGolS3 was induced by cold stress but not by drought or salt stress. All the GST fusion proteins of GST-AtGolS1, 2 and 3 expressed in Escherichia coli had galactinol synthase activities. Overexpression of AtGolS2 in transgenic Arabidopsis caused an increase in endogenous galactinol and raffinose, and showed reduced transpiration from leaves to improve drought tolerance. These results show that stress-inducible galactinol synthase plays a key role in the accumulation of galactinol and raffinose under abiotic stress conditions, and that galactinol and raffinose may function as osmoprotectants in drought-stress tolerance of plants.     

Phytohormones Accumulation and Distribution in Shoots and Roots of Haploid,Diploid and Tetraploid Barley Seedlings Derived from Microspore Culture

Phytohormones play important roles in plant growth and development, and polyploids are thought to be an important method for plant breeding. However, the relationship between ploidy and phytohormone is still unclear. In this study, barley at three ploidy levels were produced by microspore culture. Therefore, we further analyzed the phytohormone content in the shoots and roots of the three kinds of barley materials to study the effect of ploidy on phytohormones accumulation and distribution. The results showed that Abscisic acid (ABA), gibberellin (GA), jasmonic acid (JA), auxin (IAA), salicylic acid (SA) and cytokinin (CTK) were successfully determined in shoots and roots using LC-MS (liquid chromatography mass spectrometry). By comparing the shoots of the haploid and diploid plants, it was found that the distribution trend of the six phytohormones was consistent, and another consistent trend was found in the roots of the diploid and tetraploid plants. In addition, we further analyzed the shoot/root ratio of the different phytohormones to identify the potential differences for haploid, diploid and tetraploid. Here, the relationship between ploidy and phytohormone we provided would provide new insights into understanding the new phenotypes that occur in polyploid species.     

Metabolic reprogramming in nodules,roots, and leaves of symbiotic soybean in response to iron deficiency

To elucidate the mechanism of adaptation of leguminous plants to iron (Fe)‐deficient environment, comprehensive analyses of soybean (Glycine max) plants (sampled at anthesis) were conducted under Fe‐sufficient control and Fe‐deficient treatment using metabolomic and physiological approach. Our results show that soybeans grown under Fe‐deficient conditions showed lower nitrogen (N) fixation efficiency; however, ureides increased in different tissues, indicating potential N‐feedback inhibition. N assimilation was inhibited as observed in the repressed amino acids biosynthesis and reduced proteins in roots and nodules. In Fe‐deficient leaves, many amino acids increased, accompanied by the reduction of malate, fumarate, succinate, and α‐ketoglutarate, which implies the N reprogramming was stimulated by the anaplerotic pathway. Accordingly, many organic acids increased in roots and nodules; however, enzymes involved in the related metabolic pathway (e.g., Krebs cycle) showed opposite activity between roots and nodules, indicative of different mechanisms. Sugars increased or maintained at constant level in different tissues under Fe deficiency, which probably relates to oxidative stress, cell wall damage, and feedback regulation. Increased ascorbate, nicotinate, raffinose, galactinol, and proline in different tissues possibly helped resist the oxidative stress induced by Fe deficiency. Overall, Fe deficiency induced the coordinated metabolic reprogramming in different tissues of symbiotic soybean plants.     

Raffinose in seedlings of winter vetch (<Emphasis Type="Italic">Vicia villosa</Emphasis> Roth.) under osmotic stress and followed by recovery

During germination of winter vetch (Vicia villosa Roth.) seeds, the degradation of raffinose family oligosaccharides and galactosyl pinitols occurred faster in axis than in cotyledons. After 7 days of germination, all α-d-galactosides disappeared and the soluble carbohydrates in seedling tissues consisted of d-pinitol, sucrose, fructose, glucose and myo-inositol. Osmotic stress caused by incubation of seedlings in PEG 8000 solution (−0.5, −1.0, and −1.5 MPa) for 48 h induced the activity of crucial enzymes of the RFOs pathway, i.e. galactinol synthase and raffinose synthase, in both the root and epicotyl but not in cotyledons. The root and epicotyl accumulated elevated amounts of galactinol and raffinose as the osmotic potential was lowered. This process was transient because when PEG solution was replaced with water, galactinol and raffinose were degraded, thus confirming their direct involvement in the response of tissues to osmotic stress. Among other soluble carbohydrates, only sucrose accumulated in response to stress. The results did not show potential role of d-pinitol in the adjustment of winter vetch seedlings to osmotic stress.     

Galactinol synthase activity and soluble sugars in developing seeds of four soybean genotypes

Galactinol synthase (UDP-galactose:inositol galactosyltransferase) is the first unique enzyme in the biosynthetic pathway of raffinose saccharides. Its role as a regulator of carbon partitioning between sucrose and raffinose saccharides in developing soybean (Glycine max L. Merrill) seeds was examined. Galactinol synthase activity and concentrations of sucrose, stachyose, and raffinose were compared during seed development between two genotypes that were high and two genotypes that were low in mature seed raffinose saccharide concentration. In all genotypes, sucrose concentration increased as seed development progressed, but in both low raffinose saccharide genotypes, greater increases in sucrose concentration were observed late in seed development. Sucrose to stachyose ratios in mature seeds were 2.3-fold greater in low raffinose saccharide genotypes than in the high raffinose saccharide genotypes. During seed development, higher levels of galactinol synthase activity were observed in the high raffinose saccharide genotypes than in the low raffinose saccharide genotypes. A common linear relationship for all four soybean genotypes was shown to exist between galactinol formed estimated from galactinol synthase activity data and the concentration of galactose present in raffinose saccharides. Results of this study implied that galactinol synthase is an important regulator of carbon partitioning between sucrose and raffinose saccharides in developing soybean seeds.     

复苏植物旋蒴苣苔棉子糖合酶基因的克隆和表达

复苏植物是研究植物耐脱水机制的特殊模式植物和宝贵的耐旱基因资源植物。以复苏植物旋蒴苣苔(Boea hygrometrica) 为材料研究其在脱水和复水过程中棉子糖系列寡糖含量的变化, 并克隆了旋蒴苣苔棉子糖合酶基因BhRFS。荧光定量PCR检测表明, BhRFS受干旱、低温(4°C)、高盐(200 mmol·L^–1NaCl)和ABA(100 μmol·L^–1)诱导表达上调, 而高温(37°C)抑制其表达, H₂O₂(200 μmol·L^–1)处理对其没有影响。研究结果表明, BhRFS可能参与了多种非生物逆境胁迫抗性反应, 并受到ABA依赖的信号通路调控。     

Azospirillum brasilense ameliorates the response of Arabidopsis thaliana to drought mainly via enhancement of ABA levels

Production of phytohormones is one of the main mechanisms to explain the beneficial effects of plant growth‐promoting rhizobacteria (PGPR) such as Azospirillum sp. The PGPRs induce plant growth and development, and reduce stress susceptibility. However, little is known regarding the stress‐related phytohormone abscisic acid (ABA) produced by bacteria. We investigated the effects of Azospirillum brasilense Sp 245 strain on Arabidopsis thaliana Col‐0 and aba2‐1 mutant plants, evaluating the morphophysiological and biochemical responses when watered and in drought. We used an in vitro‐grown system to study changes in the root volume and architecture after inoculation with Azospirillum in Arabidopsis wild‐type Col‐0 and on the mutant aba2‐1, during early growth. To examine Arabidopsis development and reproductive success as affected by the bacteria, ABA and drought, a pot experiment using Arabidopsis Col‐0 plants was also carried out. Azospirillum brasilense augmented plant biomass, altered root architecture by increasing lateral roots number, stimulated photosynthetic and photoprotective pigments and retarded water loss in correlation with incremented ABA levels. As well, inoculation improved plants seed yield, plants survival, proline levels and relative leaf water content; it also decreased stomatal conductance, malondialdehyde and relative soil water content in plants submitted to drought. Arabidopsis inoculation with A. brasilense improved plants performance, especially in drought.     

Recent Advances in the Study of Mechanisms of Action of Phytohormones

This review highlights recent advances in studies of mechanisms underlying the effects of five phytohormone groups: auxin, cytokinin, gibberellin, abscisic acid, and ethylene. The review summarizes data on receptors of all these phytohormones and the hormone signal transduction systems, which include second messengers, hormone-dependent trans-factors, and the genes controlled by these factors. The effects of phytohormones involve not only induction of novel protein synthesis via activation of their gene expression, but also degradation of repressor proteins through the ubiquitin system. The review contains examples of successful use of data on genes encoding enzymes of phytohormone synthesis and their receptors for development of transgenic plants with particular hormonal characteristics that provide practically valuable traits.     

SNF1-Related Protein Kinase (SnRK) 1 Involved in the Regulation of Raffinose Family Oligosaccharide Metabolism in Cucumber (Cucumis sativus L.) Calli

SNF1-related protein kinase (SnRK) 1 is an important factor that helps plants to overcome starvation stress. It has been shown that SnRK1 can regulate the activities of some enzymes involved in sucrose and starch metabolism. To uncover whether SnRK1 also plays a role in raffinose family oligosaccharide (RFO) metabolism, the enzymes in RFO metabolism were assessed in cucumber (Cucumis sativus L.) in vitro. Under starvation stress, SnRK1 was activated, which could regulate the expression of three alkaline α-galactosidase genes: CsAGA1, CsAGA2, and CsAGA3. CsAGA1 was down-regulated, whereas CsAGA2 and CsAGA3 were up-regulated, which indicated that they have different physiological functions under starvation stress. In addition, the expression level of one galactinol synthase gene, CsGosl 4, decreased significantly; however, this change did not relate to SnRK1. When cucumber calli were re-supplied with sucrose, stachyose, or raffinose, the activities of SnRK1 and the expression level of CsKIN1 were suppressed. Simultaneously, the expression levels of three acid α-galactosidase genes: CsGAL1, CsGAL2, and CsGAL3, and three alkaline α-galactosidase genes: CsAGA1, CsAGA2, and CsAGA3, were up-regulated by stachyose or raffinose. These six up-regulated genes were involved in the catabolism of RFOs. The galactinol synthase genes, except for up-regulated CsGosl4, were not significantly affected.

     

Physiological aspects of raffinose family oligosaccharides in plants: protection against abiotic stress

Abiotic stresses resulting from water deficit, high salinity or periods of drought adversely affect plant growth and development and represent major selective forces during plant evolution. The raffinose family oligosaccharides (RFOs) are synthesised from sucrose by the subsequent addition of activated galactinol moieties donated by galactinol. RFOs are characterised as compatible solutes involved in stress tolerance defence mechanisms, although evidence also suggests that they act as antioxidants, are part of carbon partitioning strategies and may serve as signals in response to stress. The key enzyme and regulatory point in RFO biosynthesis is galactinol synthase (GolS), and an increase of GolS in expression and activity is often associated with abiotic stress. It has also been shown that different GolS isoforms are expressed in response to different types of abiotic stress, suggesting that the timing and accumulation of RFOs are controlled for each abiotic stress. However, the accumulation of RFOs in response to stress is not universal and other functional roles have been suggested for RFOs, such as being part of a carbon storage mechanism. Transgenic Arabidopsis plants with increased galactinol and raffinose concentrations had better ROS scavenging capacity, while many sugars have been shown in vitro to have antioxidant activity, suggesting that RFOs may also act as antioxidants. The RFO pathway also interacts with other carbohydrate pathways, such as that of O‐methyl inositol (OMI), which shows that the functional relevance of RFOs must not be seen in isolation to overall carbon re‐allocation during stress responses.