冬性植物春化过程中玉米赤霉烯酮的内源生成及马拉硫磷对它的抑制

Stob等(1962)首先从玉米赤霉菌(Gibberella zeae,其无性世代为禾谷玫瑰镰刀菌[Fusarium roseum ’graminearum’])中分离出玉米赤霉烯酮。此后,Mirocha等(1967),Nelson等(1968)及Caldwell等(1970)先后证明玉米赤霉烯酮是某些真菌     

Factors controlling Flowering in the Chrysanthemum: IV. THE SITE OF VERNALIZATION AND TRANSLOCATION OF THE STIMULUS

By confining low-temperature treatment to the growing tip ofthe Chrysanthemum plant, the apex has been shown to be the seatof perception of vernalization, a result which is in full accordwith earlier experiments on other plants requiring vernalization.Experiments on the translocation of the stimulus through maturetissues involving stock/scion and ‘approach’ graftswith or without defoliation gave negative results. By decapitatingin turn the main axis and the resulting laterals produced, ithas been shown that the stimulus is passed on from existingapices to laterals of up to the seventh order at least, lateralapices which were formed well after the time of chilling. Theseresults are discussed in relation to prior work on the existenceof a specific vernalization substance as well as a floweringhormone and their translocation.     

The VERNALIZATION 2 gene mediates the epigenetic regulation of vernalization in Arabidopsis.

The acceleration of flowering by a long period of low temperature, vernalization, is an adaptation that ensures plants overwinter before flowering. Vernalization induces a developmental state that is mitotically stable, suggesting that it may have an epigenetic basis. The VERNALIZATION2 (VRN2) gene mediates vernalization and encodes a nuclear-localized zinc finger protein with similarity to Polycomb group (PcG) proteins of plants and animals. In wild-type Arabidopsis, vernalization results in the stable reduction of the levels of the floral repressor FLC. In vrn2 mutants, FLC expression is downregulated normally in response to vernalization, but instead of remaining low, FLC mRNA levels increase when plants are returned to normal temperatures. VRN2 function therefore stably maintains FLC repression after a cold treatment, serving as a mechanism for the cellular memory of vernalization.     

The quantitative response of wheat vernalization to environmental variables indicates that vernalization is not a response to cold temperature

The initiation of flowering is a crucial trait that allows temperate plants to flower in the favourable conditions of spring. The timing of flowering initiation is governed by two main mechanisms: vernalization that defines a plant's requirement for a prolonged exposure to cold temperatures; and photoperiod sensitivity defining the need for long days to initiate floral transition. Genetic variability in both vernalization and photoperiod sensitivity largely explains the adaptability of cultivated crop plants such as bread wheat (Triticum aestivum L.) to a wide range of climatic conditions. The major genes controlling wheat vernalization (VRN1, VRN2, and VRN3) and photoperiod sensitivity (PPD1) have been identified, and knowledge of their interactions at the molecular level is growing. However, the quantitative effects of temperature and photoperiod on these genes remain poorly understood. Here it is shown that the distinction between the temperature effects on organ appearance rate and on vernalization sensu stricto is crucial for understanding the quantitative effects of the environmental signal on wheat flowering. By submitting near isogenic lines of wheat differing in their allelic composition at the VRN1 locus to various temperature and photoperiod treatments, it is shown that, at the whole-plant level, the vernalization process has a positive response to temperature with complex interactions with photoperiod. In addition, the phenotypic variation associated with the presence of different spring homoeoalleles of VRN1 is not induced by a residual vernalization requirement. The results demonstrate that a precise definition of vernalization is necessary to understand and model temperature and photoperiod effects on wheat flowering. It is suggested that this definition should be used as the basis for gene expression studies and assessment of functioning of the wheat flowering gene network, including an explicit account of the quantitative effect of environmental variables.     

植物春化特性及春化作用机理

春化作用是某些高等植物成花转变的重要环节,被认为是植物在低温诱导下促使其相关基因的表达,从而导致生理状态转变的一种受遗传控制的生理过程。本文对植物春化反应特性、春化作用的生理生化特性及春化作用的分子生物学等方面的研究进展进行了概述,并对春化研究中的问题进行了分析和展望。     

The gibberellic acid biosynthesis mutant ga1-3 of Arabidopsis thaliana is responsive to vernalization.

The Arabidopsis mutant ga1-3 contains a deletion in an enzyme that catalyzes an early step in the synthesis of gibberellic acid. It has been shown that ga1-3 mutant plants cannot flower under 8-h short-day (SD) conditions, even after vernalization. In this article, we present data demonstrating that the ga1-3 mutation does not block the response to vernalization in intermediate photoperiods or in long-day conditions in a late-flowering, vernalization-responsive background. Thus, GA may not have a direct role in the vernalization response in Arabidopsis, but it may be required for an alternate pathway that promotes flowering in noninductive photoperiods.     

冬小麦春化作用相关cDNA克隆Vrc79的分子克隆

在低温需求型植物的发育过程中,春化作用是诱导植物成花的必要因子。在冬小麦春化进程中存在着一个核酸代谢的关键期,为了探讨春化作用的分子机理,以不春化及脱春化的冬小麦京冬1号（Ｔｒｉｔｉｃｕｍ　ａｅｓｔｉｖｕｍＬ．ｃｖ．Ｊｉｎｄｏｎｇ　Ｎｏ．１）胚芽的ｍＲＮＡ为对照,通过减法杂交构建了富集冬小麦春化相关基因的ｃＤＮＡ文库,经过差异筛选分离到了一个仅在春化２１ｄ这一关键期表达,而在不春化、春化４ｄ、脱春化不表达的春化相关。ｃＤＮＡ克隆Ｖｒｃ７９。Ｎｏｒｔｈｅｍ杂交及同源性分析表明它是一个在植物中新发现的不同于低温胁迫诱导基因的春化特异克隆,其对春化需求型植物的成花诱导可能起重要的调控作用。     

Growth Hormone Changes in Chrysanthemum morifolium: Effects of Environmental Factors Controlling Flowering

Simultaneous quantitative analyses have been made of the endogenouslevels of auxin- and gibberellin like substances, growth inhibitors,and auxin-oxidizing enzyme activity in the cold-requiring Chrysanthemummorifolium cv. Sunbeam subjected to different daylength, lightintensity and temperature regimes known to affect flowering.While little hormone or enzyme activity was found in extractsfrom unvernalized plants, a striking rise in auxin-oxidizingenzyme activity occurred rapidly after the end of cold treatment.Increased auxin activity was also recorded shortly after vernalization.At 28 °C both enzyme and auxin activity declined over aperiod of 3–4 weeks; at 20 °C this response was delayed.Gibberellin activity at 28 °C rose steeply about 2 weeksfrom vernalization and declined several weeks later; at 20 °Ca similar response was less marked. Low light intensity treatment,which may have increased endogenous auxin levels, or exogenousauxin application reduced gibberellin-like substance levelsand cause d devernalization.Phosphon D treatment also loweredgibberellin levels and prevented flowering. An extract fromvernalized plants containing gibberellin-like substances intensifiedthe flowering of partially vernalized test plants. Persistenceof high auxin activity in vernalized plants on long days wasassociated with failure to form normal flower buds. Stem elongationrates correlated in general with levels of endogenous auxin-and gibberellin-like substances. Significant amounts of an abscisin-likeinhibitor were found in extracts of flower buds. The mechanismof natural devernalization is discussed in relation to theseobservations.     

Aa TFL1 confers an age-dependent response to vernalization in perennial Arabis alpina

Flowering of many plants is induced by environmental signals, but these responses can depend on the age of the plant. Exposure of Arabidopsis thaliana to vernalization (winter temperatures) at germination induces flowering, whereas a close perennial relative Arabis alpina only responds if exposed when at least 5 weeks old. We show that vernalization of these older A. alpina plants reduces expression of the floral repressor PEP1 and activates the orthologs of the Arabidopsis flowering genes SOC1 (Aa SOC1) and LFY (Aa LFY). By contrast, when younger plants are vernalized, PEP1 and Aa SOC1 mRNA levels change as in older plants, but Aa LFY is not expressed. We demonstrate that A. alpina TFL1 (Aa TFL1) blocks flowering and prevents Aa LFY expression when young plants are exposed to vernalization. In addition, in older plants, Aa TFL1 increases the duration of vernalization required for Aa LFY expression and flowering. Aa TFL1 has similar functions in axillary shoots, thus ensuring that following a flowering episode vegetative branches are maintained to continue the perennial life cycle. We propose that Aa TFL1 blocks flowering of young plants exposed to vernalization by setting a threshold for a flowering pathway that is increased in activity as the shoot ages, thus contributing to several perennial traits.     

Molecular Cloning of a Vernalization related cDNA Clone (Vrc) of Vrc79 in Winter Wheat (Triticum aestivum L.)

Vernalization is an essential factor in the flowering development of cold-required plants. There is a key stage of nucleic acid metabolism in the process of vernalization in winter wheat. To probe into the molecular determinants of vernalization, a cDNA library presumably enriching vernalization-related genes was prepared by specially expressed mRNAs from winter wheat ( Triticum aestivum L. cv. Jingdong No. 1) plumules at the key stage of 21 d vernalization being recovered as cDNAs after subtraction with mRNAs from nonvernalized and devernalized plumules. One vernalization-related cDNA clone (Vrc), Vrc79, which was only expressed at the key stage of 21 d vernalization, but not at other stages of nonvernalization, 4 d vernalization and devemalization, was isolated by differential screening of the library, and shown to be a vernalization-specific clone by Northern blot. Result of homology search suggested that Vrc79 was a novel gene identified in higher plant which was different from the cold-stress-induced genes and might play an important role in the floral induction in vernalization-requiring plants.     

Thermoinductive Regulation of Gibberellin Metabolism in Thlaspi arvense L. (II. Cold Induction of Enzymes in Gibberellin Biosynthesis)

Vernalization of Thlaspi arvense L. results in the alteration of gibberellin (GA) metabolism such that the metabolism and turnover of the GA precursor ent-kaur-16-en-19-oic acid (kaurenoic acid) is dramatically increased. This cold-induced change in GA metabolism is restricted to the shoot tip, the site of perception of cold in this species (J.P. Hazebroek, J.D. Metzger [1990] Plant Physiol 94: 157-165). In the present report additional biochemical information about the nature of this low-temperature-regulated process is provided. The endogenous levels of kaurenoic acid in leaves and shoot tips of plants were estimated by combined gas chromatography-chemical ionization mass spectrometry at various times after 4 weeks of vernalization at 6[deg]C. The endogenous levels in shoot tips declined 10-fold by 2 d after the plants were returned to 21[deg]C; this decline continued such that there was nearly 50-fold less kaurenoic acid by 10 d after the end of vernalization. No effect of vernalization on the endogenous levels of kaurenoic acid in leaves was observed. An in vitro enzyme assay was developed to monitor changes in the ability of tissues to convert kaurenoic acid to ent-7[alpha]-hydroxykaur-16-en-19-oic acid (7-OH kaurenoic acid). The activity of this enzyme rapidly increased in microsomal extracts from shoot tips following the end of vernalization. No thermoinduced increase in activity was observed in leaves. The enzymic oxidation of ent-kaurene to ent-kaurenol was also induced in shoot tips by vernalization. However, this reaction does not appear to be rate limiting for GA biosynthesis, because substantial amounts of kaurenoic acid accumulated in noninduced shoot tips. These results corroborate our hypothesis that the conversion of kaurenoic acid to 7-OH kaurenoic acid is the primary step in GA metabolism regulated by vernalization in Thlaspi shoot tips.     

Vernalization sensitivity in Arabidopsis thaliana (Brassicaceae): the effects of latitude and FLC variation

Latitudinal variation in climate is predicted to select for latitudinal differentiation in sensitivity to the environmental cues that signal plants to flower at the appropriate time for a given climate. In Arabidopsis thaliana, flowering is promoted by exposure to cold temperatures (vernalization), and several vernalization pathway loci are known. To test whether natural variation in vernalization sensitivity could account for a previously observed latitudinal cline in flowering time in A. thaliana, we exposed 21 European accessions to 0, 10, 20, or 30 d of vernalization and observed leaf number at flowering under short days in a growth chamber. We observed a significant latitudinal cline in vernalization sensitivity: southern accessions were more sensitive to vernalization than northern accessions. In addition, accessions that were late flowering in the absence of vernalization were more sensitive to vernalization cues. Allelic variation at the flowering time regulatory gene FLC was not associated with mean vernalization sensitivity, but one allele class exhibited greater variance in vernalization sensitivity.     

Factors controlling Flowering in the Chrysanthemum: III. FAVOURABLE EFFECTS OF LIMITED PERIODS OF LONG DAY ON INFLORESCENCE INITIATION

Experiments are described which indicate that Chrysanthemumcuttings derived from unvernalized long-day stock plants flowersooner and with lower leaf numbers after vernalization thansimilarly treated cuttings from short-day stock. Long-day treatmentof young cuttings also hastens inflorescence initiation providedthe period of such treatment is limited and given before orimmediately after vernalization. The effect of long day appearsto be maximal when vernalization is complete. Long-day treatmentcannot substitute for vernalization.     

Ecological genetics of vernalization response in Bromus tectorum L. (Poaceae)

BACKGROUND AND AIMS: Bromus tectorum (cheatgrass or downy brome) is an exotic annual grass that is dominant over large areas of former shrubland in western North America. To flower in time for seed production in early summer, B. tectorum plants generally require vernalization at winter temperatures, either as imbibed seeds or as established seedlings. METHODS: Variation in response to increasing periods of vernalization as seeds or seedlings for progeny of ten full-sib families from each of four B. tectorum populations from contrasting habitats was studied. KEY RESULTS: As vernalization was increased from 0 to 10 weeks, the proportion of plants flowering within 20 weeks increased, weeks to initiation of flowering decreased, and seed yield per plant increased, regardless of whether plants were vernalized as seeds or seedlings. Most of the variation was accounted for by differences among populations. Plants of the warm desert population flowered promptly even without vernalization, while those of the cold desert, foothill and montane populations showed incremental changes in response variables as a function of vernalization period. Populations differed in among-family variance, with the warm desert population generally showing the least variance and the cold desert population the most. Variation among populations and among families within populations decreased as vernalization period increased, whereas the non-genetic component of variance showed no such pattern. CONCLUSIONS: Variation in vernalization response was found to be adaptively significant and apparently represents the result of contrasting selection regimes on a range of founder genotypes.     

A cluster of Arabidopsis genes with a coordinate response to an environmental stimulus

Vernalization, the promotion of flowering after prolonged exposure to low temperatures, is an adaptive response of plants ensuring that flowering occurs at a propitious time in the annual seasonal cycle. In Arabidopsis, FLOWERING LOCUS C (FLC), which encodes a repressor of flowering, is a key gene in the vernalization response; plants with high-FLC expression respond to vernalization by downregulating FLC and thereby flowering at an earlier time. Vernalization has the hallmarks of an epigenetically regulated process. The downregulation of FLC by low temperatures is maintained throughout vegetative development but is reset at each generation. During our study of vernalization, we have found that a small gene cluster, including FLC and its two flanking genes, is coordinately regulated in response to genetic modifiers, to the environmental stimulus of vernalization, and in plants with low levels of DNA methylation. Genes encoded on foreign DNA inserted into the cluster also acquire the low-temperature response. At other chromosomal locations, FLC maintains its response to vernalization and imposes a parallel response on a flanking gene. This suggests that FLC contains sequences that confer changes in gene expression extending beyond FLC itself, perhaps through chromatin modification.     

Effect of Vernalization,Photoperiod, and Light Quality on the Flowering Phenotype of Arabidopsis Plants Containing the FRIGIDA Gene

We have compared the flowering response to vernalization, photoperiod, and far-red (FR) light of the Columbia (Col) and Landsberg erecta (Ler) ecotypes of Arabidopsis into which the flowering-time locus FRIGIDA (FRI) has been introgressed with that of the wild types Col, Ler, and San Feliu-2 (Sf-2). In the early-flowering parental ecotypes, Col and Ler, a large decrease in flowering time in response to vernalization was observed only under short-day conditions. However, Sf-2 and the Ler and Col genotypes containing FRI showed a strong response to vernalization when grown in either long days or short days. Although vernalization reduced the responsiveness to photoperiod, plants vernalized for more than 80 d still showed a slight photoperiod response. The effect of FRI on flowering was eliminated by 30 to 40 d of vernalization; subsequently, the response to vernalization in both long days and short days was the same in Col and Ler with or without FRI. FR-light enrichment accelerated flowering in all ecotypes and introgressed lines. However, the FR-light effect was most conspicuous in the FRI-containing plants. Saturation of the vernalization effect eliminated the effect of FR light on flowering, although vernalization did not eliminate the increase of petiole length in FR light.     

Genetic and physiological analysis of biennialism in Hyoscyamus niger

A genetic and physiological study of biennialism in the diploid selfer Hyoscyamus niger (black henbane), an obligate long-day plant, is described. Three annual and two biennial accessions that were homozygous for their respective growth habits were selected. The early-flowering trait of two annual accessions was dominant over the late-flowering trait of the third annual accession. The late-flowering annual accession, but not the early-flowering ones, responded to vernalization. Two biennial accessions remained vegetative after more than 1 year in soil and thus had an obligate vernalization requirement. Crosses between annual and biennial accessions showed that biennialism was conferred through a single dominant gene. However, plants containing only one copy of this dominant gene were transformed from biennials into very late-flowering winter-annual plants that responded more rapidly to vernalization than biennials. Taken together, these results indicated that there were allelic differences in photoperiod-specific flowering time genes and that biennialism was a dose-dependent trait with incomplete dominance. Models for flowering time regulation in henbane involving photoperiod-, vernalization-, and most likely gibberellin-specific pathways are discussed.     

The molecular basis of vernalization-induced flowering in cereals

Genetic analyses have identified three genes that control the vernalization requirement in wheat and barley; VRN1, VRN2 and FT (VRN3). These genes have now been isolated and shown to regulate not only the vernalization response but also the promotion of flowering by long days. VRN1 is induced by vernalization and accelerates the transition to reproductive development at the shoot apex. FT is induced by long days and further accelerates reproductive apex development. VRN2, a floral repressor, integrates vernalization and day-length responses by repressing FT until plants are vernalized. A comparison of flowering time pathways in cereals and Arabidopsis shows that the vernalization response is controlled by different MADS box genes, but integration of vernalization and long-day responses occurs through similar mechanisms.