植物休眠的分子调控

本文介绍植物季节性休眠尤其是冬季休眠的诱导、建立、维持、解除以及重建的分子机制研究进展。     

木本植物季节性休眠的分子机制

季节性休眠是多年生木本植物在生态和进化上的一种"权衡"机制,也是植物界多样性生存策略的组成部分.木本植物的休眠反应首先是Ca2+作为信号物质诱导CO/FT基因的表达,进而引起与休眠相关的DAM基因的表达;而低温可以诱导休眠的发生,冷诱导表达的基因CBF和COR在休眠期间也有表达;而与逆境相关的蛋白如脱水蛋白、抗冻蛋白、热激蛋白和热稳定蛋白等也与休眠反应有密切的关系.本文就与木本植物季节性休眠相关的分子机制进行了综述.     

木本植物叶片衰老研究进展

者红色是典型的叶片衰老现象,该过程受到各种复杂外源环境信号(如光周期和温度)和内源植物激素(如脱落酸和乙烯)等因素的影响和有序的时空调控,是叶片发育的最后一个生物学过程.本文对木本植物季节性叶片衰老与营养/生殖生长的关系、植物激素在调控木本植物叶片衰老过程中的作用机制以及叶片衰老与季节性休眠之间的关系进行了阐述和总结,并且提出了木本植物叶片衰老的研究方向与研究方法.     

赤霉素对几种树木幼苗的效应

赤霉素对树木生长的作用,及其实用的可能性,最近在国内外的报导逐渐增多。从报导来看,都肯定了赤霉素有打破休眠,促进生长和发育的作用等。赤霉素可以打破檫树种子的休眠,以及解除桃树的休眠,促进萌发。赤霉素处理桉树属(Eucalyptus)七     

种子物理休眠研究进展

种子物理休眠是由种皮不透水层引起的一种休眠类型,是植物在长期系统发育进程中获得的一种适应环境变化的特性。该文简述了种子物理休眠的定义与概念;从不透水层、种皮的特殊水孔器结构以及胚的形态特异性等方面,综述了物理休眠种子的形态特征、物理休眠与综合休眠的解除方法以及物理休眠的可能解除机制;利用Angiosperm Phylogeny Group Ⅲ(APG Ⅲ)系统分析了种子物理休眠的植物在系统发育中的位置;最后提出了今后种子物理休眠有待研究的主要问题。     

低温诱导大百合鳞茎休眠解除与酚类代谢关系

大百合(Cardiocrinum giganteum)为多年生球根药食同源植物,其鳞茎具有典型的生理休眠特性,而低温是百合鳞茎解除休眠的重要环境因子。为揭示大百合鳞茎休眠解除的分子机制,该研究对4℃低温处理0、30和60d的鳞茎分别进行代谢组和转录组分析。结果表明,鳞茎休眠的解除与酚类物质的代谢相关,酚类物质的降解有利于解除休眠,其中苯丙氨酸解氨酶基因(PALs)在此过程中可能起主要作用。同时,bHLH、bZIP、MYB和MADS等转录因子家族成员均与酚类代谢物显著相关,且参与解除休眠。共表达分析证实PAL、CAD和POD是酚类代谢重要的调控基因,MYB4、MYB114和ICE1参与了酚类代谢调控网络,其中ICE1可能是连接温度信号和酚类代谢的关键因素。这些转录因子与酚类物质的共同作用可能对鳞茎打破休眠具有重要作用。     

赤霉素代谢与信号转导及其调控种子萌发与休眠的分子机制

种子的萌发能力由胚周围组织(种皮和胚乳)强加的物理限制与胚的生长潜能之间的平衡所决定.覆盖胚根尖端的珠孔端胚乳细胞的弱化被植物激素赤霉素(gibberellin, GA)促进但被脱落酸抑制,是胚根伸出的重要前提.GA是一种调控植物许多关键生理过程,如种子萌发、根和茎的伸长、开花、座果和种子发育的重要激素. GA在种子萌发与休眠解除中的作用主要受其生物合成与分解代谢和信号转导途径的调控.本文主要综述了GA的生物合成与代谢、GA的信号转导以及它们对种子萌发和休眠解除调控的研究进展.此外,本文也提出了本领域需要进一步研究的科学问题,试图为解释GA调控种子萌发与休眠的分子机理提供新的研究信息.     

脱落酸和赤霉素调控种子休眠与萌发研究进展

种子的休眠与萌发是高等植物生长发育进程中非常重要的环节,是维系物种繁衍的重要过程。而激素在这一过程中扮演着非常重要的角色。而在这个过程中脱落酸(abscisic acid,ABA)和赤霉素(gibberellin GA)发挥着尤其重要的作用。本文综述了当前对复杂分子网络的理解,这些分子网络涉及脱落酸和赤霉素在调节种子休眠和萌发中的关键作用,其中含AP2结构域的转录因子起着关键作用。     

低温在木本植物种子发芽促进中的应用

木本植物种子中除能直播的以外 ,还有许多种子存在着各种类型的休眠 ,而使发芽迟滞 ,妨碍直播作业。在生产中 ,此类种子播前都需要进行发芽促进处理 ,以解除其休眠 ,使其顺利萌发生长。低温处理即是种子各种处理方法中常用的一种 ,具体操作是指低温过程或低温层积阶段。在“木本植物种子综合特征与发芽促进类型相关性的研究”课题中 ,我们根据几十年工作的经验积累 ,同时查阅了大量国内外有关资料 ,并做了大量的种子萌发试验 ,验证了低温在木本植物种子萌发中的作用和具体应用。低温后熟解除种子休眠 ,通常是指 0～ 1 0℃的温度效应 ,其中以…     

珍稀植物青檀种子休眠与萌发的研究

为了探讨和研究青檀种子休眠和萌发特性,采用石蜡切片法、生物鉴定(白菜籽发芽实验)法、赤霉素溶液浸种、以及赤霉素与低温层积相结合等方法,寻找引起青檀种子休眠的原因和解除休眠的最佳措施。结果表明:青檀种子本身含有发芽抑制物和存在生理后熟是引起休眠的2个主要原因,用质量浓度为300mg/L的赤霉素溶液浸种24h或低温层积后用赤霉素处理均能在一定程度上解除休眠促进萌发,其中以低温层积25d后用500mg/L的赤霉素浸种36h效果最好。发芽率和发芽势分别达到83.5%和65%。     

Poplar woody root proteome during the transition dormancy-active growth

Woody plants living in temperate climates finely regulate their growth and development in relation to seasonal changes; their transition from vegetative to dormancy phase represents an adaptation to their environment. Events occurring in the shoot during onset/release from dormancy have been largely investigated, whereas in woody roots they remain completely unknown. In recent years, we have been interested in understanding the molecular and physiological events occurring in poplar woody root during release from dormancy. Here, we propose the results of a comparative analysis of the proteome of poplar woody root sampled at different time points: T₀ (dormancy condition), T₁ (release from dormancy), and T₂ (full vegetative condition). This study identified proteins that may be involved in the long-term survival of a dormant root or landmarking a specific time point.     

Expression of beta-tubulin during dormancy induction and release in apical and axillary buds of five woody species

Cell cycle activity was studied in apical and axillary buds of Norway maple ( Acer platanoides L.), apple ( Malus ' M9 ') , pedunculate oak ( Quercus robur L.), Scots pine ( Pinus sylvestris L.) and rose ( Rosa corymbifera 'Laxa') during dormancy induction and release. Flow cytometric analyses revealed that in dormant buds, cells mainly were quiescent at the G₀/G₁ phase, while in non-dormant buds, a significantly higher frequency of G₂ cells was found in all species. In western blots accumulation of 55 kDa beta -tubulin was found in active growing plant material, whereas in dormant buds the accumulation was much lower or below detection level. It was observed for all species that during dormancy induction the amount of beta -tubulin decreased, while during dormancy release a fast accumulation of beta -tubulin occurred. The dynamics of the beta -tubulin accumulation reflected the dormancy status of tree buds of the five species studied suggesting that the beta -tubulin level might be useful as a marker for the dormancy status in buds of temperate woody species.     

Molecular control of cold acclimation in trees

Frost tolerance is an acquired characteristic of plants that is induced in response to environmental cues preceding the onset of freezing temperatures and activation of a cold acclimation program. In addition to transient acclimation to low non-freezing temperatures and enhancing survival to short frost episodes during the growth season, perennial woody plants need additionally to survive the cold winter months. Trees have evolved a complex dynamic process controlling the development of dormancy and freezing tolerance that secures accurate initiation and termination of the overwintering process. Although the phenology of overwintering has been known for decades, only recently has there been progress in elucidating the molecular mechanisms of dormancy and freezing tolerance development in perennial plants. Current molecular and genomic studies indicate that herbaceous annual and woody perennial plants share similar cold acclimation mechanisms. Both the signal processes controlling cold acclimation and the cold-regulated target genes appear to be shared by herbaceous and woody plants. However, the dormancy development during overwintering brings new players in the molecular control of seasonal cold acclimation of woody perennials.     

Photoperiodic control of dormancy in Sedum telephium and some other herbaceous perennial plants

The environmental control of dormancy and flowering of the herbaceous perennial Sedum telephium was studied in controlled environments. Short photoperiods induced growth cessation and the formation of resting buds in both seedlings and mature plants, whereas long photoperiods resulted in immediate growth activation of dormant buds. No chilling was required for dormancy release, even in plants induced to dormancy and maintained at high temperature (21°C) for more than 3 months. The critical photoperiod for dormancy release was about 15 h, a minimum of four long-day (LD) cycles (24 h) being required. The true photoperiodic nature of this response was ascertained by night interruption experiments. Flowering of S. telephium was found to have an obligatory LD requirement, with no requirement for vernalization. The critical photoperiod and minimum number of inductive cycles for floral induction were the same as for dormancy release. Dormancy release by long days was also obtained in preliminary experiments with three other herbaceous perennials. The eco-physiological significance of photoperiodic control of dormancy is discussed, and it is concluded that the mechanism ensures stability of winter dormancy, even under conditions of climatic warming.     

Ecotype-dependent control of growth,dormancy and freezing tolerance under seasonal changes in <Emphasis Type="Italic">Betula pendula</Emphasis> Roth

Woody plants in the temperate and boreal zone undergo annual cycle of growth and dormancy under seasonal changes. Growth cessation and dormancy induction in autumn are prerequisites for the development of substantial cold hardiness in winter. During evolution, woody plants have developed different ecotypes that are closely adapted to the local climatic conditions. In this study, we employed distinct photoperiodic ecotypes of silver birch (Betula pendula Roth) to elucidate differences in these adaptive responses under seasonal changes. In all ecotypes, short day photoperiod (SD) initiated growth cessation and dormancy development, and induced cold acclimation. Subsequent low temperature (LT) exposure significantly enhanced freezing tolerance but removed bud dormancy. Our results suggested that dormancy and freezing tolerance might partially overlap under SD, but these two processes were regulated by different mechanisms and pathways under LT. Endogenous abscisic acid (ABA) levels were also altered under seasonal changes; the ABA level was low during the growing season, then increased in autumn, and decreased in winter. Compared with the southern ecotype, the northern ecotype was more responsive to seasonal changes, resulting in earlier growth cessation, cold acclimation and dormancy development in autumn, higher freezing tolerance and faster dormancy release in winter, and earlier bud flush and growth initiation in spring. In addition, although there was no significant ecotypic difference in ABA level during growing season, the rates and degrees of ABA alterations were different between the ecotypes in autumn and winter, and could be related to ecotypic differences in dormancy and freezing tolerance.     

Photoperiodic induction of dormancy and freezing tolerance in Betula pubescens. Involvement of ABA and dehydrins

In many woody plants photoperiod signals the initiation of dormancy and cold acclimation. The photoperiod-specific physiological and molecular mechanisms have remained uncharacterised. The role of abscisic acid (ABA) and dehydrins in photope-riod-induced dormancy and freezing tolerance was investigated in birch, Betula pubescens Ehrh. The experiments were designed to investigate if development of dormancy and freezing tolerance under long-day (LD) and short-day (SD) conditions could be affected by manipulation of the endogenous ABA content, and if accumulation of dehydrin-like proteins was correlated with SD and/or the water content of the buds. Experimentally, the internal ABA content was increased by ABA application and by water stress treatment under LD, and decreased by blocking the synthesis of ABA with fluridone under SD. Additionally, high humidity (95% RH) was applied to establish if accidental water stress was involved in SD. ABA content was monitored by gas chromatography-mass spectrometry with selective ion monitoring (SIM). Short days induced a transient increase in ABA content, which was absent in 95% RH, whereas fluridone treatment decreased ABA. Short days induced a typical pattern of bud desiccation and growth cessation regardless of the treatment, and improved freezing tolerance except in the fluridone treatment. ABA content of the buds was significantly increased after spraying ABA on leaves and after water stress, treatments that did not induce cessation of growth and dormancy, but improved freezing tolerance. In addition to several constitutively produced dehydrins, two SD-specific proteins of molecular masses 34 and 36 kDa were found. Photoperiod- and experimentally-induced alterations in ABA contents affected freezing tolerance but not cessation of growth and dormancy. Therefore, involvement of ABA in the photoperiodic control of cold acclimation is more direct than in growth cessation and dormancy. As the typical desiccation pattern of the buds was found in all SD plants, and was not directly related to ABA content or to freezing tolerance, this pattern characterises the onset of photo-period-induced growth cessation and dormancy. The results provide evidence for the existence of various constitutively and two photoperiod-induced dehydrins in buds of birch, and reveal characteristics of dormancy and freezing tolerance that may facilitate further investigations of photoperiodic control of growth in trees.     

Temperature-driven plasticity in growth cessation and dormancy development in deciduous woody plants: a working hypothesis suggesting how molecular and cellular function is affected by temperature during dormancy induction

The role of temperature during dormancy development is being reconsidered as more research emerges demonstrating that temperature can significantly influence growth cessation and dormancy development in woody plants. However, there are seemingly contradictory responses to warm and low temperature in the literature. This research/review paper aims to address this contradiction. The impact of temperature was examined in four poplar clones and two dogwood ecotypes with contrasting dormancy induction patterns. Under short day (SD) conditions, warm night temperature (WT) strongly accelerated timing of growth cessation leading to greater dormancy development and cold hardiness in poplar hybrids. In contrast, under long day (LD) conditions, low night temperature (LT) can completely bypass the short photoperiod requirement in northern but not southern dogwood ecotypes. These findings are in fact consistent with the literature in which both coniferous and deciduous woody plant species’ growth cessation, bud set or dormancy induction are accelerated by temperature. The contradictions are addressed when photoperiod and ecotypes are taken into account in which the combination of either SD/WT (northern and southern ecotypes) or LD/LT (northern ecotypes only) are separated. Photoperiod insensitive types are driven to growth cessation by LT. Also consistent is the importance of night temperature in regulating these warm and cool temperature responses. However, the physiological basis for these temperature effects remain unclear. Changes in water content, binding and mobility are factors known to be associated with dormancy induction in woody plants. These were measured using non-destructive magnetic resonance micro-imaging (MRMI) in specific regions within lateral buds of poplar under SD/WT dormancing inducing conditions. Under SD/WT, dormancy was associated with restrictions in inter- or intracellular water movement between plant cells that reduces water mobility during dormancy development. Northern ecotypes of dogwood may be more tolerant to photoinhibition under the dormancy inducing LD/LT conditions compared to southern ecotypes. In this paper, we propose the existence of two separate, but temporally connected processes that contribute to dormancy development in some deciduous woody plant: one driven by photoperiod and influenced by moderate temperatures; the other driven by abiotic stresses, such as low temperature in combination with long photoperiods. The molecular changes corresponding to these two related but distinct responses to temperature during dormancy development in woody plants remains an investigative challenge.