Seasonal Changes in the Levels of Free and Bound Abscisic Acid in Blackcurrant (Ribes nigrum) Buds and Beech (Fagus sylvatica) Buds

Free and bound abscisic acid (ABA) levels in blackcurrant andbeech buds have been determined by an extraction procedure involvingseveral thin-layer chromatography purification stages and finalbioassay in the wheat coleoptile straight-growth test. In bothspecies the highest level of free ABA occurs in the autumn atabout the time of onset of winter dormancy. The free ABA contentthen declines throughout the winter months reaching its lowestvalue just before bud burst. These results strengthen the viewthat free ABA plays an important role in the induction and maintenanceof winter dormancy. The bound ABA level increases in both species throughout theautumn and winter until halfway through the bud swelling phaseand then declines. It is proposed that the bound ABA accumulatesin the buds because it cannot be translocated or further metabolizedduring the winter months. The ratios of free to bound ABA were plotted and the resultingcurves show a distinctive annual cycle with the highest freeABA/ bound ABA ratio (F/B) occurring in the autumn and the highestbound ABA/ free ABA ratio (B/F) coinciding with bud burst. Agradual increase in the B/F ratio during bud swelling may indicatea feed-back reaction between free and bound ABA which maintainsthe free ABA at a sufficiently high level to put a gentle brakeon growth. At bud burst the B/F ratio falls very sharply anda period of very rapid growth ensues.     

剥鳞和激素处理对大樱桃花芽休眠解除及内源激素变化的影响

采用高效液相色谱法(HPLC)分析了剥鳞与激素处理对大樱桃花芽休眠解除及内源生长素(IAA)、赤霉素(GAD、玉米素(ZT)和脱落酸(ABA)变化的影响。结果表明,花芽中的ABA主要分布于鳞片内,鳞片中的GA3和ZT含量远低于去鳞芽,也低于完整芽。剥鳞能明显增加休眠花芽中内源GA2和ZT的含量,降低ABA的含量,对IAA含量的影响不大。剥鳞降低了ABA／GA3、ABA／ZT的比值,使花芽向促进生长、抑制休眠的方向转化。同时,休眠前、后期剥鳞均能明显提高萌芽率,中期剥鳞效果不明显。剥鳞后施用外源激素随休眠时期不同而有不同的破眠效果,早期剥鳞GA3的效果最好,6-BA次之,IAA最差;中期破眠效果不如早期,GA。和6-BA没有明显差别;后期以6-BA效果最好,其次是GA3和IAA;3次处理中ABA均明显抑制花芽萌发。     

Opposite patterns in the annual distribution and time-course of endogenous abscisic acid and indole-3-acetic acid in relation to the periodicity of cambial activity in Eucommia ulmoides Oliv

The seasonal change of free abscisic acid (ABA) and indole-3-acetic acid (IAA) and their relationship with the cambial activity in Eucommia ulmoides trees were investigated by ABA and IAA immunolocalization using primary polyclonal and rhodamine-red fluorescing secondary antibodies, ABA and IAA quantification using high performance liquid chromatography (HPLC), and systematic monitoring of vascular cell layers production. ABA and IAA clearly displayed opposite annual distribution patterns. In the active period (AP), both immunolocalization and HPLC detected an abrupt decrease of ABA, reaching its lowest level in the summer. During dormancy, ABA started increasing in the first quiescence (Q1) (autumn), peaked in the rest (winter), and gradually decreased from the onset of the second quiescence (Q2) (the end of winter). IAA showed a reverse pattern to that of ABA: it sharply increased in AP, but noticeably decreased from the commencement of Q1. Longitudinally, the ABA distribution increased apico-basally, contrasting with IAA. Laterally, most of the ABA was located in mature vascular tissues, whereas the IAA essentially occurred in the cambial region. The concomitant IAA-ABA distribution and seasonal changes in vascular tissues greatly correlated with xylem and phloem cell production, and late wood differentiation and maturation. Interestingly, the application of exogenous ABA to quiescent E. ulmoides branches, in a water-culture system, inhibited external IAA action on cambial activity reactivation. These results suggest that, in E. ulmoides, ABA and IAA might probably interact in the cambial region. The annual cambial activity could be influenced by an IAA:ABA ratio; and ABA might play a key role in vascular cambium dormancy in higher plants. The relationship between hormonal changes and the (particular) annual life cycle of E. ulmoides is also discussed.     

Spatial and temporal changes in multiple hormone groups during lateral bud release shortly following apex decapitation of chickpea (Cicer arietinum) seedlings

Although the co-ordination of promotive root-sourced cytokinin (CK) and inhibitory shoot apex-sourced auxin (IAA) is central to all current models on lateral bud dormancy release, control by those hormones alone has appeared inadequate in many studies. Thus it was hypothesized that the IAA : CK model is the central control but that it must be considered within the relevant timeframe leading to lateral bud release and against a backdrop of interactions with other hormone groups. Therefore, IAA and a wide survey of cytokinins (CKs), were examined along with abscisic acid (ABA) and polyamines (PAs) in released buds, tissue surrounding buds and xylem sap at 1 and 4 h after apex removal, when lateral buds of chickpea are known to break dormancy. Three potential lateral bud growth inhibitors, IAA, ABA and cis -zeatin 9-riboside (ZR), declined sharply in the released buds and xylem following decapitation. This is in contrast to potential dormancy breaking CKs like trans -ZR and trans -zeantin 9-riboside 5'phosphate (ZRMP), which represented the strongest correlative changes by increasing 3.5-fold in xylem sap and 22-fold in buds. PAs had not changed significantly in buds or other tissues after 4 h, so they were not directly involved in the breaking of bud dormancy. Results from the xylem and surrounding tissues indicated that bud CK increases resulted from a combination synthesis in the bud and selective loading of CK nucleotides into the xylem from the root.     

Abscisic acid, indole-3-acetic acid and cytokinin changes in buds of Pseudotsuga menziesii during bud quiescence release

Bud quiescence release, considered as the ultimate dormancy breaking phase, was achieved in Pseudotsuga menziesii (Mirb.) Franco by a 9-week cold (5°C) treatment, under short daylength (9 h) followed by a transfer to mild temperature (22°C) under long daylength (16 h). Indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin-type (Z) and isopentenyladenine-type (iPA) cytokinin (CK) levels were measured by means of an ELISA technique performed on HPLC-fractionated extracts of terminal and axillary buds. During the cold period, all hormones except IP-type CK levels decreased, whereas the opposite observation was made after transfer to mild temperature and long daylength, when buds started to grow. Some other immunoreactive compounds were also detected and quantified. The ABA-glucosyl ester (ABA-GE) level pattern was similar to that of ABA, but no accumulation occurred at mild temperatures. A putative IAA conjugate, more polar than IAA, was also detected. Its level increased transiently like IAA in terminal buds and, to a lesser extent, in axillary buds during the 10th week of the experiment. In terminal buds, isopentenyladenosine ([9R]-iP) was released by alkaline hydrolysis of a polar immunoreactive compound detected with anti-[9R]iP antibodies. This compound accumulated during the cold period and quickly dropped at 22°C. Relationships between environmental conditions and endogenous hormones are discussed.     

Branch development in Lupinus angustifolius L.#II. Relationship with endogenous ABA, IAA and cytokinins in axillary and main stem buds

The concentrations of indole-3-acetic acid (IAA), cytokinins (CK) and abscisic acid (ABA) were measured in buds of different regions (main stem and lateral branches) of Lupinus angustifolius L. (cv. Merrit) and at different stages in the development of branches. In lupin, branching patterns are the result of discrete regions of axillary branches (upper, middle and basal) which elongate at much different rates. Early in development only the main shoot elongates, followed usually by basal branch growth and then rapid upper branch growth. Branches in the middle of the main stem grow only weakly or fail to develop. Levels of IAA were generally high in the apical buds of slowly growing branches and low in buds from strongly growing branches, whereas CK levels showed the opposite relationship. CK:IAA ratio showed a closer relationship with the rate of growth of a particular branch better than the levels of either CK or IAA alone. During early stages of growth ABA concentration did not follow the rate of branch growth. However, later in development, where growth did not closely match the ratio of CK:IAA, ABA level showed a strong negative relationship with growth. A significant decrease in ABA was associated with continued strong growth of the main stem apex following a decline in CK:IAA ratio. Overall, the best relationship between the level of growth factors in apical buds and branching pattern in lupin was the ratio of CK:IAA, implying that high CK:IAA at a given bud would promote growth. ABA level appeared to play a secondary role, as a growth inhibitor.     

Abscisic acid,abscisic acid-esters and phaseic acid in vegetative terminal buds of Acer pseudoplatanus during emergence from winter dormancy

Levels of free-abscisic acid and boundabscisic acid (alkaline hydrolyzable abscisic acidesters) in replicated samples of terminal vegetative buds of sycamore trees were measured during natural emergence from winter dormancy by gas chromatographic methods together with isotope dilution estimation of recovery rates. Not until after the buds had been released from true dormancy in January by winter chilling did any clear change occur in either abscisic acid (ABA) fraction, or in total ABA, on any basis of comparison. The percentage of total ABA present as the free acid declined at the end of true dormancy to approximately two-thirds of its value in the earlier winter months. It is concluded that glucosylation of ABA is unlikely to play a major part in the mechanism of release from dormancy in vegetative sycamore buds. At the end of true dormancy there was a large transient increase in what appeared to be phaseic acid, but this was not accompanied by any marked decrease in either free- or bound-ABA.Abbreviations ABA abscisic acid - TLC thin layer chromatography - GLC gas chromatography     

Effect of thidiazuron on abscisic acid content in apple bud relative to dormancy

The effect of N -phenyl- N '-1,2,3,-thidiazol-5-ylurea (thidiazuron, Dropp, SN 49537) on abscisic acid (ABA) level in apple ( Malus domestica Borkh. cv. York Imperial) buds associated with bud break and bud development was determined. The data showed that increased ABA content in apple buds was associated with thidiazuron-induced bud break and bud development. ABA stimulated growth of apple buds that had emerged from dormancy by thidiazuron treatment. The ABA in apple buds was confirmed by GC-EIMS and GC-CIMS.     

刺楸种子层积过程中内源植物激素的动态变化及激素在种子休眠中的作用

本文主要以高效液相色谱为主要手段,结合生物测定方法,测定了4种不同层积条件下激素动态变化。结果表明刺楸干种子中存在有两种抑制物质-脱落酸(ABA)和香豆素(C),在种子层积的不同阶段又相继有GA₃,IAA和Z出现,并在层积后熟过程中呈现非常有规律的变化。根据激素的变化,可把种子整个后熟过程分三个阶段;即阶段Ⅰ,以抑制物质(ABA,C)和IAA水平迅速减少为主要特征,阶段Ⅱ主要表现为GA₃和Z合量的上升,阶段Ⅲ各种激素处于相对稳定的状态。种子的休眠与否可能主要取决于阶段Ⅱ的状况。在刺楸种子胚形态后熟期间,胚的生长与分化同ABA和C水平有很高的相关性,但同时也受GA₃和IAA的调节。生理后熟主要与Z有关,同ABA和C无明显相关性。同时本文还对激素相对水平做了初步研究,发现GA₃/ABA+IAA,Z/GA₃+IAA和GA₃/C+IAA^*,在种子后熟期间的变化同胚生长发育存在高度的一致性。认为激素的相对水平对种子休眠起重要的控制作用,还推测激素的作用可能类似于"板机"机制。     

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.     

珍稀濒危植物珙桐种子休眠萌发过程中内源激素的变化

珙桐是我国特有珍稀濒危植物,休眠期长且具二次休眠现象。将处于休眠萌发过程中的珙桐种子依据胚根长度划分为4个阶段,利用高效液相色谱(HPLC)测定各阶段种子及其内果皮中ABA(脱落酸)、GA(赤霉素)、KT(细胞分裂素)、IAA(3-吲哚乙酸)4种内源激素含量,分析其比值动态变化,并与幼苗阶段进行比较。结果显示:未破壳种子的内果皮中内源激素含量以ABA最高,其次是GA、IAA、KT,随着种子破壳后四种激素含量显著降低。除ABA外,种子中GA、IAA和KT含量随着胚根的伸长逐渐升高,但仍低于幼苗阶段。此外,随着胚根伸长,种子中GA/ABA、IAA/ABA、KT/ABA比值逐渐增大,其中以GA/ABA的变化最显著。因此,珙桐种子的休眠和萌发可能主要受ABA和GA的平衡和拮抗来调控。     

Changes in abscisic acid and indole-3-acetic acid in axillary buds of Elytrigia repens released from apical dominance

Growth of axillary buds on the rhizomes of Elytrigia repens (L) Nevski is strongly dominated by the rhizome apex, by mechanisms which may involve endogenous hormones. We determined the distribution of indole-3-acetic acid (IAA) and abscisic acid (ABA) in rhizomes and measured (by gas-chromatography-mass spectrometry) their content in axillary buds after rhizomes were decapitated. The same measurements were also made in buds induced to sprout by removing their subtending scale leaves. The ABA content tended to be higher in the apical bud and in the axillary buds than in the adjacent internodes, and tended to decline basipetally in the internodes and scale leaves. IAA was similary distributed, except that there was less difference between the buds and other rhizome parts. After rhizomes were decapitated, the ABA content of the first axillary bud declined to 20% of that of control values within 24 h, while the IAA content showed no marked tendency to change. The ABA content also declined within 12 h in the first axillary bud after rhizomes were denuded, while the content of IAA tended to increase after 6 h. These changes occurred before the length of the first axillary bud increased 24–48 h after rhizomes were decapitated or denuded. We conclude that the release of axillary buds from apical dominance in E. repens does not require IAA content to be reduced, but is associated with reduced ABA content.     

南方红豆杉种子综合处理过程中内源激素的动态变化

为揭示南方红豆杉种子内源激素与休眠的关系,采用酶联免疫吸附法(ELISA)测定了经过层积处理的种皮和胚乳的脱落酸(ABA)、赤霉素(GA3 )、吲哚乙酸(IAA)、玉米素核苷(ZR)4种内源激素含量的变化情况.结果表明:种子胚乳中内源ABA的含量随着层积时间的延长而逐渐下降,GA含量增加,IAA和ZR的含量先增加后降低...     

Abscisic acid content at defined levels of bud dormancy and frost tolerance in two contrasting populations of Picea abies grown in a phytotron

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies were cultivated under continuous light and 20°C for 10 weeks. To arrest growth, induce terminal bud dormancy and promote frost tolerance the seedlings were then exposed to 16 h nights for 12 weeks, with gradually lower temperature during the last 6 weeks. Samples for estimating the abscisic acid content of the needles were taken just before the onset of the night treatment, at day 3 of the treatment, and then with one, and later 2 week, intervals. From the second week onwards (third week for frost tolerance) bud dormancy and frost tolerance were assessed at the same time as abscisic acid (ABA) determinations. Phosphate-buffered saline extracts were purified on mini-columns (in some cases immunoaffinity colums) and quantified by HPLC. The degree of dormancy was estimated by transferring the seedlings to growth conditions and determining the number of days until growth was resumed. The frost tolerance of the needles exposed to –10°C and –20°C was classified in 6 classes. The frost tolerance of the terminal buds was estimated as the number of seedlings that showed some growth after 6 weeks in growth conditions. The night treatment rapidly induced terminal bud dormancy in both populations, but the release of dormancy occurred earlier in the northern population. The needles and the terminal buds became highly frost tolerant more rapidly in the northern than in the southern population and before the temperature decrease. The degree of dormancy began to decline before full frost tolerance was obtained in the southern population and this decline continued in both populations, while frost tolerance remained at a high level. The southern population showed a transient peak in ABA content at day 3. Although the ABA content of the northern population was lower than in the southern before the 16-h night treatment, it increased in the northern population during the treatment period, in particular after the temperature decrease.     

Changes of Abscisic Acid and Gibberellin Contents during the Release of Dormancy in Winter Buds of Populus tomentosa Carr.

Changes of abscisie acid (ABA) and gibberellin (GA3) contents during the release of dormancy in winter bud of Populus tomentosa Carr. were determinedwith GC. After leaf fall in autumn, content of ABA in the bud was 888.0 μg/kg. fr.wt. Obvious decrease in ABA content was observed during the bud released from dormancy. The bud kept in room temperature opened about two months earlier thanthat under natural condition; and the rate of decrease of ABA content in these budwas also more rapid. The ABA contents of buds with similar outer appearance werecompared, either the bud from outside under natural condition or under room temperature, they were similar, although time of their occurrence was quite different, withalmost a difference of about two months. From this fact it has been assumed that thereis a close relationship between the release of dormancy and the decrease in ABA content. Another fact was noticed before Dec. 6, no GA3 could be detected in the dormantbud. From Jan. 9 and thereafter, GA3 content increased gradually and reached itsmaximum (20 μg/kg. fr.wt) by Mar. 19, the bud was inflated. GA3 decreased again as the bud was opened, it seems to be that the process of releasing dormancy in bud mightbe promoted by GA3.     

Indoleacetic acid, abscisic acid and phenolic substances during development of hazel leaves

The levels of indoleacetic acid (IAA), abscisic acid (ABA) and phenolic substances were measured monthly in leaves of hazel ( Corylus avellana L. cv. Negreta) in different stages of development from April till abscission in November. IAA and ABA were quantified by flame ionization detector gas-chromatography (GLC), and the total phenolic content by a colorimetric technique. During spring, IAA levels were the highest, coinciding with the greatest expansion of the leaves; after which IAA gradually decreased as the leaves became older, although minor increases were observed in July-August and November. The ABA level in hazel leaves was low throughout the period of leaf existence, with a maximum in July and a second increase in November, coinciding with the last month in which hazel bears leaves. The phenols of the neutral fraction showed a minimum in May and a pronounced increase in June, remaining at this level during summer and decreasing in November. The acid and alkaline fractions showed a maximum in August, which could be related to the decrease in the growth rate of leaves. The residual fraction remained at a relatively low level until September, increasing rapidly in October and November.     

Hormone Levels and Apical Dominance in the Aquatic Fern Marsilea drummondii A. Br

Terminal buds and successively subjacent lateral buds of the water fern, Marsilea drummondii, were examined to determine the pattern of hormone distribution in relation to apical dominance. Quantitative levels of indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin and zeatin riboside (Z and ZR), and isopentenyladenosine (iPA) were determined by a solid-phase immunoassay using polycional antihormone antibodies. Enzyme-linked immunosorbent assay was used following a one-step HPLC purification procedure to obtain the free hormones. Active shoot apices contained the most IAA and Z-type cytokinins and inhibited buds the least. No significant differences in ABA levels were found leading to the conclusion that ABA did not play any role in apical dominance. The normal precedence of the most rapid outgrowth of the youngest inhibited bud as observed previously in decapitated plants was well correlated with its very high level of iPA observed in this study. The same phenomenon was observed in the median buds but with a weaker amplitude. The presence of this storage form could indicate that a bud at its entry into quiescence eventually looses the ability to hydroxylate iPA to Z-type cytokinins when it is fully inhibited. IAA and Z + ZR are concluded to be essential for lateral bud growth.     

Response of Amaranthus retroflexus L. seeds to gibberellic acid, ethylene and abscisic acid depending on duration of stratification and burial

Freshly harvested, dormant seeds of Amaranthus retroflexus were unable to germinate at 25 and 35 °C. To release their dormancy at the above temperatures, the seeds were stratified at a constant temperature (4 °C) under laboratory conditions or at fluctuating temperatures in soil or by outdoor burial in soil. Fully dormant, or seeds stratified or buried (2006/2007 and 2007/2008) for various periods were treated with exogenous gibberellic acid (GA₃), ethephon and abscisic acid (ABA). Likewise, the effects of these regulators, applied during stratification, on seed germination were determined. The results indicate that A. retroflexus seed dormancy can be released either by stratification or by autumn–winter burial. The effect of GA₃ and ethylene, liberated from ethephon, applied after various periods of stratification or during stratification, depends on dormancy level. GA₃ did not affect or only slightly stimulated the germination of non-stratified, fully dormant seeds at 25 and 35 °C respectively. Ethylene increased germination at both temperatures. Seed response to GA₃ and ethylene at 25 °C was increased when dormancy was partially removed by stratification at constant or fluctuating temperatures or autumn–winter burial. The response to GA₃ and ethylene increased with increasing time of stratification. The presence of GA₃ and ethephon during stratification may stimulate germination at 35 °C. Thus, both GA₃ and ethylene can partially substitute the requirement for stratification or autumn–winter burial. Both hormones may also stimulate germination of secondary dormant seeds, exhumed in September. The response to ABA decreased in parallel with an increasing time of stratification and burial up to May 2007 or March 2008. Endogenous GA_n, ethylene and ABA may be involved in the control of dormancy state and germination of A. retroflexus. It is possible that releasing dormancy by stratification or partial burial is associated with changes in ABA/GA and ethylene balance and/or sensitivity to these hormones.     

Endogenous hormone concentrations correlate with fructan metabolism throughout the phenological cycle in Chrysolaena obovata

Background and Aims Chrysolaena obovata, an Asteraceae of the Brazilian Cerrado, presents seasonal growth, marked by senescence of aerial organs in winter and subsequent regrowth at the end of this season. The underground reserve organs, the rhizophores, accumulate inulin-type fructans, which are known to confer tolerance to drought and low temperature. Fructans and fructan-metabolizing enzymes show a characteristic spatial and temporal distribution in the rhizophores during the developmental cycle. Previous studies have shown correlations between abscisic acid (ABA) or indole acetic acid (IAA), fructans, dormancy and tolerance to drought and cold, but the signalling mechanism for the beginning of dormancy and sprouting in this species is still unknown.Methods Adult plants were sampled from the field across phenological phases including dormancy, sprouting and vegetative growth. Endogenous concentrations of ABA and IAA were determined by GC-MS-SIM (gas chromatography–mass spectrometry–selected ion monitoring), and measurements were made of fructan content and composition, and enzyme activities. The relative expression of corresponding genes during dormancy and sprouting were also determined.Key Results Plants showed a high fructan 1-exohydrolase (EC 3.2.1.153) activity and expression during sprouting in proximal segments of the rhizophores, indicating mobilization of fructan reserves, when ABA concentrations were relatively low and precipitation and temperature were at their minimum values. Concomitantly, higher IAA concentrations were consistent with the role of this regulator in promoting cell elongation and plant growth. With high rates of precipitation and high temperatures in summer, the fructan-synthesizing enzyme sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) showed higher activity and expression in distal segments of the rhizophores, which decreased over the course of the vegetative stage when ABA concentrations were higher, possibly signalling the entry into dormancy.Conclusions The results show that fructan metabolism correlates well with endogenous hormone concentrations and environmental changes, suggesting that the co-ordinated action of carbohydrate metabolism and hormone synthesis enables C. obovata to survive unfavourable field conditions. Endogenous hormone concentrations seem to be related to regulation of fructan metabolism and to the transition between phenophases, signalling for energy storage, reserve mobilization and accumulation of oligosaccharides as osmolytes.