Soluble sugar content of white spruce (Picea glauca) seeds during and after germination

In white spruce ( Picea glauca [Moench.] Voss.) seeds, the raffinose family oligosaccharides (RFOs) provide carbon reserves for the early stages of germination prior to radicle protrusion. Some seedlots contain seeds that are dormant, failing to complete germination under optimal conditions. Since dormancy may be imposed through a metabolic block in reserve mobilization, the goal of this project was to identify any impediment to RFO mobilization in dormant relative to nondormant seeds. Desiccated seeds contain primarily, and in order of abundance on a molar basis, sucrose and the first 3 members of the RFOs, raffinose, stachyose and verbascose. Upon radicle protrusion at 25°C, the contents of RFOs decreased to low amounts in all seed parts, regardless of prior dormancy status and sucrose was metabolized to glucose and fructose, which increased in seed parts. During moist chilling at 4°C, RFO content initially decreased before stabilizing and then increasing. In seeds that did not complete germination, the synthesis of RFOs at 4°C favored verbascose, so that at the end of 14 (nondormant) or 35 (dormant) weeks, verbascose contents in megagametophytes exceeded the amount initially present in the desiccated seed. This was also true in the embryos of the dormant seedlot. In seed parts from both seedlots after months of moist chilling, stachyose amounts exceeded raffinose amounts. Upon radicle protrusion at 4°C, RFO contents decreased to amounts most similar to those present in seeds that completed germination at 25°C. Hence, the RFOs are utilized as a source of energy, regardless of the temperature at which white spruce seeds complete germination. Based on the similarity of sugar contents in seed parts between dormant and nondormant seeds that did not complete germination, differences in sugar metabolism are probably not the basis of dormancy in white spruce seeds.     

Cold-induced accumulation of raffinose family oligosaccharides in somatic embryos of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>)

Summary Exposure of mature cotyledonary somatic embryos of Picea abies to low temperature (4°C) resulted in the accumulation of raffinose family oligosaccharides (RFOs)—raffinose and stachyose. The RFO content represented approximately 20% of the total soluble saccharides with the RFO: sucrose ratio being almost 1∶3 (molar basis) after 3 wk of cold exposure. This treatment, like desiccation, brings the endogenous saccharide spectrum nearer to that of mature zygotic embryos of the same species (zygotic embryos, RFO: sucrose ratio 1∶1.5 on a molar basis). Based on indications that RFOs are at least partly responsible for the positive effects of desiccation, we propose cold treatment as an alternative to slow desiccation for conifer somatic embryogenesis protocols.     

Anatomical and Histochemical Changes of Norway Spruce Buds Induced by Simulated Acid Rain

The study was focused on changes of anatomical and histochemical parameters of buds of 4-year-old Norway spruce (Picea abies L. Karst) trees subjected to simulated acid rain (SAR). Solutions of pH 2.9 and 3.9 were applied by spraying on shoot and/or by watering for two years. No macroscopic changes of buds or needles were observed in connection with SAR application and the only induced change was 2-week earlier onset of bud break in all treated variants compared to the control. Two-year treatment caused decrease in number of leaf primordia and increase in number of living bud scales in treated dormant buds while these parameters remained unchanged in the control buds. Treatments with solution of pH 2.9 caused decrease of flatness of bud apical meristem during the vegetative season. Increased activity of non-specific esterase in treated buds occurred during dormancy and bud break and the enhanced accumulation of phenolic compounds was detected at the beginning of shoot growth. Changes in histochemical parameters of bud tissues were induced mainly by spraying of shoots and can thus be qualified as primary damage.     

砧木对梨叶芽休眠的影响及其与多胺代谢的关系

以分别嫁接在杜梨和豆梨上的砂梨品种‘丰水’为试材,研究了2008和2009年11～12月气温变化和不同砧木对‘丰水’梨叶芽休眠进程的影响,分析叶芽中游离态和束缚态内源多胺种类和含量的变化,结果表明：嫁接在豆梨上的‘丰水’叶芽自然休眠结束的时间要比嫁接在杜梨上的‘丰水’叶芽早10d左右,且游离态和束缚态腐胺（Put）、戊二胺（Cad）、己二胺（Hex）、亚精胺（Spd）和精胺（Spm）5种内源多胺含量开始升高的时间与供试材料叶芽自然休眠结束的时间一致,表明梨叶芽的休眠进程与砧木种类和多胺代谢有密切关系,尤其是与束缚态多胺含量变化的关系更为密切。     

植物中棉子糖系列寡糖代谢及其调控关键酶研究进展

棉子糖系列寡糖代谢与植物生长发育、逆境胁迫、种子耐贮性及脱水耐性等关系密切.棉子糖系列寡糖的合成从棉子糖的合成开始,由半乳糖苷肌醇上的半乳糖基的转移依次生成棉子糖、水苏糖、毛蕊花糖等.寡糖代谢是一个复杂的调控体系,其中肌醇-1-磷酸合成酶、肌醇半乳糖苷合成酶、蔗糖合成酶、棉子糖合成酶、水苏糖合成酶和毛蕊花糖合成酶等参与了棉子糖系列寡糖的生物合成过程.本文对植物中棉子糖系列寡糖的代谢及其重要调控酶的特性、功能及分子生物学研究进展进行综述.     

Low night temperatures inhibit galactinol synthase gene expression and phloem loading in melon leaves during fruit development

Low night temperatures seriously affect plant growth and fruit quality. To investigate the effect of low night temperatures on the expression of galactinol synthase genes (GOLS) and phloem loading of raffinose family oligosaccharides, particular stachyose and raffinose (RFO represents stachyose and raffinose in this paper) and to gain a better understanding of the relationship between the phloem loading of RFO and fruit development, melon (Cucumis melo L.) plants at the fruit development stage were treated with temperatures of 28/12°C or 28/9°C (day/night) with 28/15°C as the control. Both the CmGOLS1 and CmGOLS2 gene expression and the activity of galactinol synthase were clearly repressed after treatments with 9 and 12°C at night, and the effect of 9°C was more obvious. Furthermore, low night temperatures inhibited photosynthesis and caused the lower amounts of sucrose to supply the RFO synthesis. However, the total soluble sugar, RFO, and sucrose contents were increased in leaves subjected to low night temperatures. It is supposed that low night temperature blocked symplastic phloem loading, which led to the accumulation of RFO in the leaf cells. With increasing content of RFO in the leaves, the expression of GOLS genes was inhibited according to the principle of feedback, and therefore the decreased expression of GOLS limited RFO synthesis and was indirectly harmful to phloem loading, thereby affecting fruit development.     

Fruit Regulates Bud Sprouting and Vegetative Growth in Field-Grown Loquat Trees (Eriobotrya japonica Lindl.): Nutritional and Hormonal Changes

The effects of fruit on bud sprouting and vegetative growth were compared on fruiting and defruited loquat trees from fruit set onward. Carbohydrate and nitrogen content in leaves and bark tissues and hormone concentrations were studied during the fruit development and vegetative growth periods. On defruited trees, a significant proportion of buds sprouted in winter, whereas buds from fruiting trees sprouted only in the spring when fruit reached its final size. Furthermore, when panicles were completely removed in autumn, the buds also sprouted. In addition, fruit directly affected vegetative growth by reducing shoot length. An effect of sink removal (flower or fruit) promoting bud sprouting, regardless of the season, was then demonstrated. Neither soluble sugar concentration nor nitrogen fraction concentration in leaves or bark tissues was related to bud sprouting, but a certain nutritional imbalance was observed during the most active period of fruit development. Moreover, fruit sink activity significantly modified hormone content by increasing indole-3-acetic acid (IAA) and reducing zeatin concentrations, resulting in a higher IAA/zeatin ratio parallel to the lower bud sprouting intensity. Therefore, these changes caused by fruit removal are all related to vegetative growth, but there is no evidence that they are responsible for bud burst.     

Increases in cytokinin levels in Scots pine in relation to chilling and bud burst

Levels of isopentenyladenosine and zeatin riboside were monitored in buds and needles of Scots pine ( Pinus sylvestris L.) seedlings grown under controlled climatic conditions and in field-grown trees. Extracts were purified by immunoaffinity chromatography and high-performance liquid chromatography. Cytokinin levels were quantified with an enzyme-linked immunosorbent assay. The cytokinin content was low in buds and needles of dormant seedlings but increased during dormancy release, reaching peak values in buds just before resumption of shoot growth. Samples collected in the field also showed a marked increase in the levels of cytokinins just prior to bud burst. Further, the biological activity of applied cytokinins in activating the dormant buds of Scots pine is shown. The results indicate a probable role of cytokinins in seedlings during dormancy release.     

Frost tolerance in excised leaves of the common bugle (Ajuga reptans L.) correlates positively with the concentrations of raffinose family oligosaccharides (RFOs)

Mass increases in raffinose family oligosaccharides (RFOs, α 1,6-galactosyl extensions of sucrose) are well documented in the generative tissues of many plants upon cold acclimation, and they (i.e. mainly the two shortest RFO members, raffinose and stachyose) have been suggested as frost stress protectants. Our focus here was on the longer RFO members as they commonly occur in the frost-hardy evergreen labiate Ajuga reptans in its natural habitat, and accumulate to their highest concentrations in winter when the plant is faced with sub-zero temperatures. We examined the effects of RFO concentration and chain length on frost tolerance using excised leaves which accumulate long-chain RFOs under both cold and warm conditions, thereby uncoupling the acclimation temperature from RFO production. We demonstrated that frost tolerance in excised A. reptans leaves correlates positively with long-chain RFO accumulation under both acclimation temperatures. After 24 d post-excision in the warm, the leaves had increased their RFO concentrations (mainly long-chain RFOs) 22-fold to 78 mg g⁻¹ fresh weight, and decreased their EL₅₀ values (temperature at which 50% leakage occurred) from −10.5 to −24.5 °C, suggesting a protective role for these oligosaccharides in the natural frost tolerance of A. reptans .     

Quantitative trait loci analysis reveals a correlation between the ratio of sucrose/raffinose family oligosaccharides and seed vigour in Medicago truncatula

Seed vigour is important for successful establishment and high yield, especially under suboptimal environmental conditions. In legumes, raffinose oligosaccharide family (RFO) sugars have been proposed as an easily available energy reserve for seedling establishment. In this study, we investigated whether the composition or amount of soluble sugars (sucrose and RFO) is part of the genetic determinants of seed vigour of Medicago truncatula using two recombinant inbred line (RIL) populations. Quantitative trait loci (QTL) mapping for germination rate, hypocotyl and radicle growth under water deficit and nutritional stress, seed weight and soluble sugar content was performed using RIL populations LR1 and LR4. Seven of the 12 chromosomal regions containing QTL for germination rate or post-germinative radicle growth under optimal or stress conditions co-located with Suc/RFO QTL. A significant negative correlation was also found between seed vigour traits and Suc/RFO. In addition, one QTL that explained 80% of the variation in the ratio stachyose/verbascose co-located with a stachyose synthase gene whose expression profile in the parental lines could explain the variation in oligosaccharide composition. The correlation and co-location of Suc/RFO ratio with germination and radicle growth QTL suggest that an increased Suc/RFO ratio in seeds of M. truncatula might negatively affect seed vigour.     

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.     

“Lateral Control”: Phytohormone Relations in the Conifer Treetop and the Short- and Long-Term Effects of Bud Excision in Abies nordmanniana

In a conifer tree, such as Nordmann fir, Abies nordmanniana Spach, the leader bud and its immediate surroundings play a decisive role in crown architecture. As subapical branch buds are segregated from the leader meristem, resource allocation between ortho- and plagiotropic growth is determined. The relationship between treetop buds in young trees was studied in the natural state and after surgical removal in early July of either the leader bud (decapitation) or the subapical whorl branch buds (destipitation). The two bud types showed consistent cytokinin profile differences but similar seasonal dynamics in cytokinins and auxin (IAA). After bud excision, ZRP increased dramatically in the subapical stem within 1 h, followed by ZR within 1 week. Supernormal levels of ZR were maintained through autumn and persisted in spring in the destipitated trees, but had returned to normal in the decapitated trees. The treetop buds remaining after bud excision experienced an immediate decrease in most cytokinins, followed, however, by a large surplus later in the season. The following spring this high level persisted in the leader bud of destipitated trees, but not in whorl buds of decapitated trees. Conspicuous growth pattern changes followed from destipitation, but few from decapitation. Growth reactions suggest that resource allocation to main branch buds inhibits leader growth in normal trees, a kind of “lateral control.” Auxin and ABA content in buds and stems was largely unaffected by treatments. Data suggest that subapical leader tissues beneath the apical bud group are a primary source of cytokinin regulation.     

Contrasting bud bank dynamics of two co-occurring grasses in tallgrass prairie: implications for grassland dynamics

Because most shoot recruitment in perennial grasses occurs from belowground axillary buds, bud dynamics determine plant population dynamics and meristem limitation to population growth. Therefore, grassland vegetation responses to environmental change or disturbance may be influenced by interspecific differences in bud banks and the patterns and environmental controls of bud development and demography. We examined bud bank dynamics in Andropogon gerardii and Dichanthelium oligosanthes in tallgrass prairie by enumerating and classifying buds throughout 15?months to determine whether grass buds live for multiple years and accumulate; whether bud natality, dormancy and outgrowth are synchronous or variable; and whether bud bank dynamics differ between these co-occurring species. Andropogon gerardii (a C₄ species) maintained a larger dormant bud bank, showed synchrony in bud development and transition to tiller, and its buds lived for multiple years. Thus, multiple previous years?? bud cohorts contributed to recruitment. By contrast, D. oligosanthes (a C₃ species) maintained a smaller dormant bud bank, had asynchronous bud development with active buds present year-round, and its buds lived for 1?year. Buds played different roles in the dynamics of each species, allowing A. gerardii to over-winter and recruit new spring tillers and D. oligosanthes to survive and recruit new tillers following summer dormancy. These differences in bud bank age structure, phenology, and dynamics between these species suggest greater demographic buffering and time-lag effects in A. gerardii populations. Interspecific differences in bud bank structure and dynamics may explain and help predict grassland responses to environmental change.     

Genetic analysis of the raffinose oligosaccharide pathway in lentil seeds

Two lentil (Lens culinaris) cultivars, Syrian Local Large (SLL) and PANT-L-406 (PL), have been used to study the genetics of the raffinose family of oligosaccharides (RFO) and a related compound, ciceritol, which is a galactosyl cyclitol. The RFO and ciceritol are the major soluble -galactosides in lentil seeds. Crosses were made between the two lentil lines and the patterns of inheritance for the total -galactoside content and for individual RFO compounds (raffinose, stachyose, verbascose) and ciceritol were determined in the embryos and seed coats from single seeds of the reciprocal F1s, the F2s and ten F3 families. The inheritance patterns for each of the -galactosides were complex and much of this complexity was attributed to an interaction between the embryo and its surrounding testa. A clear-cut segregation pattern was observed for verbascose. This was the result of PL embryos having very low, or no, verbascose. The F2 embryos had a segregation ratio of 3 high to 1 low level for this compound, suggesting that within this cross a low verbascose content was determined by a single recessive gene. There was good evidence from the F2 and F3 generations of a negative correlation between low levels of verbascose and high levels of ciceritol, which suggests a metabolic link between the RFO pathway and the pathway leading to ciceritol. The data are discussed in terms of defining strategies for genetically manipulating the-galactoside composition in lentil seeds, such that their negative effects on nutrition may be overcome without reducing significantly their positive role in abiotic stress resistance.     

Periodicity of response to abscisic acid in lateral buds of willow (Salix viminalis L.)

Aseptically cultured lateral buds of Salix viminalis L. collected from field-grown trees exhibited a clear periodicity in their ability to respond to exogenous abscisic acid (ABA). Buds were kept unopened by ABA only when the plants were dormant or entering dormancy. Short days alone did not induce bud dormancy in potted plants but ABA treatment following exposure to an 8-h photoperiod prevented bud opening although ABA treatment of buds from long-day plants did not. Naturally dormant buds taken from shoots of field-grown trees and cultured in the presence of ABA opened following a chilling treatment. In no cases were the induction and breaking of dormancy and response to ABA correlated with endogenous ABA levels in the buds.Abbreviations ABA abscisic acid - GA₃ gibberellic acid - HPLC high-performance liquid chromatography - LD long day - MeABA methyl ABA - PAR photosynthetically active radiation - SD short day     

Histochemical detection and image analysis of non-specific esterase activity and the amount of polyphenols during annual bud development in Norway spruce

The study focused on Norway spruce trees during their annual development and, specifically, on the histochemical analysis of the activity of the non-specific esterase and the amount of polyphenols in the vegetative buds. Azo-coupling reaction with naphthol-AS-acetate as a substrate and Fast Blue B Salt as a coupling reagent was applied to the longitudinal median cryo-sections of the formalin-fixed buds. A method of image analysis was developed to evaluate the intensity of the histochemical reaction quantitatively. High activity of non-specific esterase was detected in the cells of the collenchymatic plate, the youngest bud scales, the leaf primordia, in the zone of differentiation of vascular tissues and procambium of the dormant bud. The activity of non-specific esterase decreased in all tissues during bud break. During the growth of a new shoot enzyme activity was detected only in the vascular bundles of the shoot. Enzyme activity re-occurred at the beginning of the autumn in the cells of the collenchymatic plate of the newly establishing buds. Three different types of polyphenols at different intracellular localizations (as verified by scanning electron microscopy) were observed: granular, vacuolar and drop-like polyphenols. The amount and localization of those polyphenols changed during the bud growing cycle. The positive reaction of all three types of polyphenols are tannin in nature. These findings are discussed from the viewpoint of frost tolerance and tissue differentiation.