Variation in total and specific RNA during inwintering of two contrasting populations of Picea abies

Seedlings of a southern (Romanian) and a northern (Swedish) population of Picea abies (L.) Karst. were cultivated in a phytotron under continuous lighl and 20°C for 10 weeks. Subsequently they were exposed to a regime of long nights (16 h). initially at 20°C but with stepwise lowering to 10°C over 12 weeks. Samples of needles were taken for total RNA extraction and studies of gene expression at intervals from just before the change of regime and onwards. At the same time samples were taken for abseisic acid (ABA) determination. Extension growth, degree of budrest and frosl tolerance were also recorded. The main results were as follows. (1) Extractable total RNA per g fresh weight of needles increased by 150–250% through the period of long nights. (2) The capacity of the total RNA to direct protein synthesis in a cell-free system declined in response to long nights to a minimum value of 5% (northern population) and 23% (southern population) of the reference values under continuous light. (3) In vitro translatability was highly correlated with the size of the polyadenylated fraction of the total RNA, which declined also when normalized to needle fresh weight rather than total RNA. (4) A peak of abscisic acid content in the southern population at 3 days into the long night treatment coincided with a trough in the in vitro translatability of the total RNA. (5) The steady state levels of rbc S-mRNA as a fraction of total RNA declined rapidly to a final value of about 15% of the reference value in both populations, the decline being more rapid for the northern population. (6) In contrast. ubiquitin-mRNA showed an initial increase, particularly in the northern population, and at the end of the long night treatment was only 40% under the reference value. (7) Rapid changes in the molecular characters occurred during the first 3–4 weeks when the morphological and physiological changes were most rapid.     

Effect of frost nights and day and night temperature during dormancy induction on frost hardiness, tolerance to cold storage and bud burst in seedlings of Norway spruce

For trees, the ability to obtain and maintain sufficient levels of frost hardiness in late autumn, winter and spring is crucial. We report that temperatures during dormancy induction influence bud set, frost hardiness, tolerance to cold storage, timing of bud burst and spring frost hardiness in seedlings of Norway spruce (Picea abies (L.) Karst.). Bud set occurred later in 12°C than in 21°C, and later in cool nights (7°C) than in constant temperature. One weekly frost night (−2.5°C) improved frost hardiness. Cool nights reduced frost hardiness early, but improved hardiness later during cold acclimation. Buds and stems were slightly hardier in 21°C than in 12°C, while needles were clearly hardier in 12°C. Cold daytime temperature, cool nights and one weekly frost night improved cold storability (0.7°C). Seedlings receiving high daytime temperatures burst buds later, and were less injured by light frost some days after bud burst.     

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.     

A proposed role for the anaerobic pathway during low-temperature sweetening in tubers of Solanum tuberosum

Survival and growth of temperate zone woody plants under changing seasonal conditions is dependent on proper timing of cold acclimation and development of vegetative dormancy, shortening photoperiod being an important primary signal to induce these adaptive responses. To elucidate the physiological basis for climatic adaptation in trees, we have characterized photoperiodic responses in the latitudinal ecotypes of silver birch ( Betula pendula Roth) exposed to gradually shortening photoperiod under controlled conditions. In all ecotypes, shortening photoperiod triggered growth cessation, cold acclimation and dormancy development, that was accompanied by increases in endogenous abscisic acid (ABA) and decreases in indole-3-acetic acid (IAA). There were distinct differences between the ecotypes in the rates and degrees of these responses. The critical photoperiod and the photoperiodic sensitivity for growth cessation varied with latitudinal origin of the ecotype. The northern ecotype had a longer critical photoperiod and a greater photoperiodic sensitivity than the southern ecotype. Compared with the southern ecotypes, the northern ecotype was more responsive to shortening photoperiod, resulting in earlier cold acclimation, dormancy development, increase in ABA content and decrease in IAA content. However, at the termination of the experiment, all the ecotypes had reached approximately the same level of cold hardiness (−12 to −14°C), ABA content (2.1–2.3 µg g⁻¹ FW) and IAA content (17.2–20.3 ng g⁻¹ FW). In all ecotypes, increase in ABA levels preceded development of bud dormancy and maximum cold hardiness. IAA levels decreased more or less parallel with increasing cold hardiness and dormancy, suggesting a role of IAA in the photoperiodic control of growth, cold acclimation and dormancy development in birch.     

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.     

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.     

Effect of exogenous abscisic acid on cold acclimation in two Magnolia species

In northern China, freezing injury is observed frequently in the rare species Magnolia wufengensis but not in the more common species Magnolia denudata. To investigate the role of the phytohormone abscisic acid (ABA) on frost tolerance in these two species, exogenous ABA was applied to the seedlings and then physiological and biochemical responses were measured during cold acclimation. Shoot growth cessation was stimulated by ABA in M. wufengensis but not in M. denudata. Abscisic acid inhibited shoot growth in M. wufengensis but not in M. denudata. Treatment with ABA stimulated leaf senescence in both species, and this effect was greater in M. denudata. For both species, ABA-treated plants exhibited bud dormancy sooner and had an increased tolerance to freezing, decreased water content and increased accumulation of proline, glucose, and fructose in shoots. These effects were generally greater for M. denudata. Freezing tolerance was significantly correlated with content of water, proline, glucose, and fructose for both species, but freezing tolerance was significantly correlated with raffinose content only in M. wufengensis. We conclude that exogenous ABA could increase cold acclimation and improve cold hardiness of both Magnolia species, although M. denudata was more responsive to ABA than M. wufengensis, which might result from a greater dehydration and accumulation of proline and certain soluble sugars.     

Modifications of abscisic acid level in winter oilseed rape leaves during acclimation of plants to freezing temperatures

An almost twofold increase in abscisic acid (ABA) content was observed in the leaves of winter oilseed rape plants (Brassica napus L., var. oleifera L., cv. Jantar) grown in the cold (>0°C). This ABA increase took place during the first three days of cold treatment. After 6 days of plant growth in the cold, the level of ABA started to decline or remained constant, depending on the calculation basis: dry weight or disc area units, respectively. The exposure of cold-acclimated plants to night frost (–5°C for 18 h) induced a further increase (65%) in the ABA level, which begun during the first few hours after thawing. The comparison of time courses of frost resistance increments and ABA content changes showed that modifications of ABA level in the cold-treated leaves preceded those of frost resistance, whereas in the frost-pretreated tissues the ABA increase occurred later than that of frost tolerance. Possible interrelations between ABA content, frost tolerance and tissue water potential modifications in the low temperature-affected tissues are discussed.     

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.     

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     

Seasonal Fluctuations of Ascorbate-Related Enzymes: Acute and Delayed Effects of Late Frost in Spring on Antioxidative Systems in Needles of Norway Spruce (Picea abies L.)

Seasonal changes of ascorbate peroxidase and monodehydroascorbateradical reductase activities were studied in foliar tissuesof Norway spruce (Picea abies L.). In mature needles, APX activitiesdid not show seasonal fluctuations and were similar to thosefound in resting buds. Monodehydroascorbate radical reductaseactivity was higher in needles than in buds and higher in winterthan in summer. Maximum activities of both enzymes were foundbefore bud break and minimum activities in newly formed needles.When spruce seedlings were exposed to an artifical frost eventof –5°C for one night in spring, ascorbate peroxidaseactivity declined in young needles before the onset of visibleinjury but corresponding to a sudden upsurge in lipid peroxidation.After one week, some shoots showed severe symptoms of injury,some were slightly injured and others did not show any visibleinjury. In lethally injured needles, antioxidative protection(ascorbate peroxidase, monodehydroascorbate radical reductase,glutathione reductase, glutathione, ascorbate, superoxide dismutase)had collapsed. Surviving needles showed a coordinated increasein all components of the antioxidative system suggesting anefficient induction of defense systems. However, enhanced protectionwas observed only transiently. In fall, needles that had beenexposed to frost in spring contained significantly less antioxidantsthan unstressed needles indicating that unseasonal frost causedmemory effects. (Received September 16, 1995; Accepted May 28, 1996)     

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.     

Carotenoid composition and down regulation of photosystem II in three conifer species during the winter

Seedlings and coppice shoots of Betula pubescens Ehrh. were grown under controlled conditions designed to simulate the annual growth cycle, and a water stress was introduced during the short day (SD). Alleviation of hud dormancy after increasing periods at chilling temperatures was tested under long day (LD) conditions. Abscisic acid (ABA) was analysed in leaf and bud samples by gas chromatography-mass spectrometry using [²H₄]ABA as the internal standard. Elongation growth of coppice shoots was faster than that of seedlings under both LD and SD conditions, while the final growth cessation occurred in a similar manner and was not affected by water stress, which significantly reduced growth rate in both plant types. Bud dormancy gradually decreased with increasing length of chilling, starting from the basal parts of the plant axis. Water stress did not retard hudhurst. but rather improved it in the chilled coppice shoots and in the non-chilled and partially chilled seedlings. Water content of buds was higher in coppice shoots than in seedlings, but after exposure to SD. it gradually decreased to 45% in both plant types and was not affected by water stress or chilling. The ABA level in both leaves and buds increased during SD treatment and was" enhanced by water stress. No clear differences in bud ABA level were found between the seedlings and coppice shoots under SD conditions, although coppice shoots had less ABA during the preceding LD conditions. There was, in general, no clear effect of chilling on bud ABA level. Budbursl in chilled, single-node cuttings was inhibited by external ABA treatment, which raised the internal ABA levels 10 to 150 times above normal. The observed correlation between ABA level and water content in buds during induction of dormancy under SD and water stress conditions indicates a possible role for ABA in the regulation of dormancy.     

Changes of Respiration Rate, Ethylene Evolution, and Abscisic Acid Content in Developing Inflorescence and Young Fruit of Olive (Olea europaea L. cv. Konservolia)

Simultaneous measurements of respiration, ethylene production, and abscisic acid (ABA) concentrations, as well as the growth parameters length, fresh weight (FW), and dry weight (DW) of olive (Olea europaea L. cv. Konservolia) inflorescence were carried out at short intervals (3–7 days) during the period from bud burst until the 3rd week after full bloom (AFB), when young fruit reached 8 mm in length. The axis of inflorescence elongated remarkably during the 3rd week after bud burst (ABB), massive bract shedding occurred during the 4th week ABB, full bloom (FB) was observed 7 weeks ABB, and massive floral organ abscission 1 week AFB. The results showed a continuous increase in inflorescence FW and DW from bud burst until 4 days before FB. Respiration rate, ethylene production, and levels of ABA were relatively high during the first 3 weeks ABB. After this period, respiration and ethylene followed a similar pattern of changes, inversely to that of ABA concentration. An accumulation of inflorescence ABA 6 and 4 days before FB was associated with the minimum values of respiration and ethylene production on the same dates. The sharp decrease in the ABA concentration during FB and 3 days later was followed by a high rise in ethylene and an increase in respiration rate, which both rose further 1 week AFB. The results suggest a possible correlation of ABA with the early stage of floral abscission, whereas ethylene production seems to be correlated with the terminal separatory activity in olive inflorescence abscission processes. Received May 28, 1998; accepted November 17, 1998     

Abscisic Acid Analysis in Vitis vinifera in the Period of Endogenous Bud Dormancy by High Pressure Liquid Chromatography

In buds and nodes of Vitis vinifera L. cv. Riesling, the content of abscisic acid (ABA) was measured by high pressure liquid chromatography and related to bud dormancy. In the period of endogenous bud dormancy (rate of bud break is low or zero under favourable climatic conditions) the ABA content increased twelvefold. This indicates a causal relationship between endogenous bud dormancy and ABA.     

The effect of LAB 173711 and ethephon on time of flowering and cold hardiness of peach flower buds

Peach flowers are often killed during bloom by spring frosts. LAB 173711, a compound with abscisic (ABA)-like activity, and ethephon delayed flowering in peach trees. In greenhouse experiments, LAB 173711, at concentrations of 10^?3–10^?2 M, was most effective in delaying bloom when applied after a 5°C cold storage period, rather than before the dormancy breaking treatment. In contrast, ethephon delayed bloom most effectively when applied before 5°C cold storage; ethephon caused flower bud abscission when treatments were made after the chilling requirement had been satisfied. In field experiments, ethephon delayed flowering by 6–7 days, which reduced bud injury after a spring frost during bloom. No flower bud injury was found on ethephon-treated trees after temperatures of ?4.3°C; whereas without ethephon 25% of the flower buds were frost damaged. LAB 173711 delayed the time to 50% bloom by 2–3 days. However, this was not long enough to avoid low-temperature injury to the flower buds.     

Cold acclimation in silver birch (Betula pendula). Development of freezing tolerance in different tissues and climatic ecotypes

A number of environmental cues including short day photoperiod (SD) and low temperature (LT) are known to interact in triggering growth cessation, cold acclimation and other adaptive responses in temperate-zone tree species. Proper timing of these responses is particularly important for survival of trees in the boreal and subarctic regions. Therefore, we used a northern tree species, silver birch ( Betula pendula Roth) as an experimental model to investigate the effect of SD and LT on development of freezing tolerance and on levels of endogenous abscisic acid (ABA) in short-term experiments under controlled conditions. We characterized differences in SD and LT-induced cold acclimation between three different climatic ecotypes from southern, central and northern habitats. The results demonstrated that cold acclimation was rapidly triggered by exposing the plants to SD or LT, and that a combination of the different treatments had an additive effect on freezing tolerance. Freezing tolerance induction was not uniform in the different tissues, the buds and leaves developed freezing tolerance more rapidly than the stem, and the young leaves had a higher freezing tolerance than the old leaves. The ability of the leaves to respond to SD and LT and similarity of the bud and leaf responses indicate that birch leaves provide a rapid and convenient system for studies on molecular mechanisms of cold acclimation. Development of freezing tolerance was dependent on the climatic ecotype, the northern ecotype was clearly more responsive to both SD and LT than the two more southern ecotypes. Development of freezing tolerance induced by SD and LT was accompanied by transient changes in ABA levels. These alterations in ABA levels were ecotype-dependent, the northern ecotype reacting more strongly to the environmental cues.     

Abscinazole-F1, a conformationally restricted analogue of the plant growth retardant uniconazole and an inhibitor of ABA 8′-hydroxylase CYP707A with no growth-retardant effect

To develop a specific inhibitor of abscisic acid (ABA) 8′-hydroxylase, a key enzyme in the catabolism of ABA, a plant hormone involved in stress tolerance, seed dormancy, and other various physiological events, we designed and synthesized conformationally restricted analogues of uniconazole (UNI), a well-known plant growth retardant, which inhibits a biosynthetic enzyme (ent-kaurene oxidase) of gibberellin as well as ABA 8′-hydroxylase. Although most of these analogues were less effective than UNI in inhibition of ABA 8′-hydroxylase and rice seedling growth, we found that a lactol-bridged analogue with an imidazole is a potent inhibitor of ABA 8′-hydroxylase but not of plant growth. This compound, abscinazole-F1, induced drought tolerance in apple seedlings upon spray treatment with a 10 μM solution.     

Abscisic Acid induces anaerobiosis tolerance in corn

Flooding is a frequently occurring environmental stress that can severely affect plant growth. This study shows that treatment of corn (Zea mays L.) seedlings with abscisic acid (ABA) increases their tolerance to anoxia 10-fold over untreated seedlings and twofold over seedlings treated with water. Corn seedlings stressed anoxically for 1 day showed only 8% survival when planted in vermiculite. Pretreatment of root tips with 100 micromolar ABA or water for 24 hours before the 1 day anoxic stress increased the anoxic survivability of seedlings to 87% and 47%, respectively. Cycloheximide (5 milligrams per liter), added together with ABA, reduced the seedling survival rate, indicating that the induction of anoxic tolerance in corn by ABA was partly a result of the synthesis of new proteins. ABA treatment induced a threefold increase in alcohol dehydrogenase enzyme activity in corn roots. However, after 24 h of anoxia, alcohol dehydrogenase enzyme activity between the ABA-pretreated and non-pretreated corn roots was not significantly different. The results indicated that ABA played an important role in inducing anoxic tolerance in corn and that the induced tolerance was probably mediated by an increase in alcohol dehydrogenase enzyme activity before the anoxic stress.     

脱落酸在植物花发育过程中的作用

植物激素脱落酸(ABA)对植物的生长发育具有多方面的调节作用,比如种子休眠、萌发,营养生长,环境胁迫反应等。大量研究显示,ABA也参与了植物的成花调控。影响植物成花调控的环境因子,包括光周期变化、春化作用、干旱等均会导致植物体内ABA代谢的变化。本文从调控植物开花的4条主要途径与植物体内ABA代谢变化之间的相互关系,花芽分化时期ABA在植物叶芽和花芽中的动态分布以及离体培养条件下ABA对花芽分化的影响等方面总结了ABA与植物花发育这一领域的最新研究进展。对ABA在植物成花诱导和花发育中的作用进行了综合分析。