Dormancy Cycle Research Articles

Influência das variacões estacionais e profundidade de sementes no solo na dormência e germinação em Rumex crispus L.

Sementes de Rumex cripus L. foram enterradas às profundidades de 1 e 10 cm no solo e coletadas a intervalos regulares durante dois anos. As sementes coletadas foram testadas a 10 e 20oC no escuro; a 5/25oC (16/8 horas) com 10mM de nitrato de potássio e luz; e num regime de temperatura alternadas correspondendo às mínimas e máximas médias do solo (MMTS), a profundidade de 1 cm durante 6 dias anteriores a cada coleta. Os tratamentos MMTS foram executados no escuro com 1 mM de nitrato de potássio ou uma mistura de estimulantes de germinação consistindo de nitrato de potássio, tiuréia, etefon, azida de sódio e peróxido de hidrogênio. A perda de viabilidade das sementes no solo durante o período estudado foi praticamente desprezível. As sementes mostraram ciclos de dormência ao longo do ano, quando as baixas temperaturas do solo superaram a dormência primária e paralelamente induziram dormência secundária, a qual por sua vez era superada pela elevação da temperatura. A dormência decresceu no segundo ano. O ambiente a 10 cm favoreceu a perda de dormência, entretanto o decréscimo de sementes devido à germinação in situ foi mais acentuado a 1cm de profundidade. A mistura química foi mais eficiente quando a dormência era mínima e as temperaturas do solo eram mais promotivas, o que correspondeu ao período quente do ano (da primavera ao outono). Discutem-se as implicações destes resultados na interpretação do comportamento ecológico da espécie e na adoção de práticas de manejo de bancos de sementes da invasora no solo.

Expression of a Ribosomal Protein Gene in Axillary Buds of Pea Seedlings

Axillary buds of intact pea seedlings (Pisum sativum L. cv Alaska) do not grow and are said to be dormant. Decapitation of the terminal bud promotes the growth of these axillary buds, which then develop in the same manner as terminal buds. We previously showed that unique sets of proteins are expressed in dormant and growing buds. Here we describe the cloning, sequencing, and expression of a cDNA clone (pGB8) that is homologous to ribosomal protein L27 from rat. RNA corresponding to this clone increases 13-fold 3 h after decapitation, reaches a maximum enhancement of about 35-fold after 12 h, and persists at slightly reduced levels at later times. Terminal buds, root apices, and elongating internodes also contain pGB8 mRNA but fully expanded leaflets and fully elongated internodes do not. In situ hybridization analysis demonstrates that pGB8 mRNA increases in all parts of the bud within 1 h of decapitation. Under appropriate conditions, growing buds can be made to stop growing and become dormant; these buds subsequently can grow again. Therefore, buds have the capacity to undergo multiple cycles of growth and dormancy. RNA gel blots show that pGB8 expression is reduced to dormancy levels as soon as buds stop growing. However, in situ hybridization experiments show that pGB8 expression continues at growing-bud levels in the apical meristem for 2 d after it is reduced in the rest of the bud. When cultured stems containing buds are treated with indoleacetic acid at concentrations >/=10 mum, bud growth and expression of pGB8 in the buds are inhibited.

Effects of Fall Fertilizer Applications on Mitotic Index and Bud Dormancy of Loblolly Pine Seedlings

Abstract A series of studies examined the effects of fall fertilization with diammonium phosphate (DAP) on mitotic index and bud dormancy [as measured by mean days to budbreak (DBB)] of two half-sib seed sources of loblolly pine. The first study tested different rates of DAP (0, 67, and 202 kg N/ha), the second study compared DAP with ammonium nitrate, and the third study examined the effect of different application dates (September 28, October 19, and November 9). An increase in mitotic index of unfertilized seedlings was observed during October and was due to developmental activity which follows initial budset. Differences in mitotic index were observed between families in all three studies. Overall, the Georgia family has a higher mitotic index, but in one study, the Virginia family had higher values in the spring. Both families tended to reach a minimum level of mitotic index at the same time (mid- to late December). However, the Virginia family reached maximum rest (as measured by days to budbreak) about 1 to 2 weeks prior to the Georgia family. Fertilization with DAP in the fall (after budset in September) did not delay the progression of the bud dormancy cycle as measured by days to budbreak in a greenhouse. The overall effect of fall fertilization on increasing the mitotic index was temporary and only lasted for about three weeks after fertilization. These findings indicated that a direct relationship may not exist between the bud dormancy cycle and mitotic index. For. Sci. 38(2):336-349.

Slash pine bud dormancy as affected by lifting date and root wrenching in the nursery.

Bud dormancy of root wrenched and unwrenched slash pine (Pinus elliottii Engelm.) seedlings growing in a forest nursery was measured on five lifting dates. Determination of bud dormancy was based on days to budbreak (DBB) under optimal growing conditions, mitotic activity in the apical meristem, chilling hours accumulated, and bud morphology. Based on DBB, seedlings were most dormant at Lift 2 on November 24 after exposure to 189 hours below 10 degrees C and 93 hours below 6.7 degrees C. Mitotic activity in the apical meristem was at its lowest 23 days later at Lift 3, possibly indicating the period when seedlings are most resistant to transplanting stresses. Multiple wrenching resulted in a slight shift in the dormancy cycle as wrenched seedlings set bud sooner in the nursery and broke bud sooner at the planting site in the spring than control seedlings. This implies that wrenched seedlings can be successfully lifted from the nursery earlier and will initiate spring shoot growth earlier than control seedlings.

The role of light and alternating temperatures on germination of Polygonum aviculare seeds exhumed on various dates

Summary:The annual dormancy cycle was investigated in buried seeds of Polygonum aviculare L. exposed to natural temperature changes in Lexington, Kentucky, U.S.A. Seeds were exhumed monthly from December 1984 to February 1987 and tested in light (14‐h daily photoperiod) and continuous darkness at 12/12‐h daily alternating temperature regimes of 15/6, 20/10, 25/15, 30/15 and 35/20°C. During autumn and winter, seeds became non‐dormant, and in March 1985 they germinated to 95‐100% at all thermoperiods in light and to 7‐61% in darkness. Seeds remained non‐dormant during spring but became more specific in their germination requirements in early summer. During July and August 1985, seeds germinated to 17‐53% in light at 30/15 and 35/20°C but to 0‐10% at all other test conditions. By September, about 65% of the seeds were dormant, but the others were able to germinate under the higher alternating temperatures in light. A similar seasonal cycle was recorded in the following year through to the spring of 1987. The results confirm the seasonal pattern of dormancy in this species (Courtney, 1968) but indicate that alternating temperatures combined with light are important in determining germination potential in P. aviculare.

Nuclear size and shape changes in fusiform cambial cells of Abies balsamea during the annual cycle of activity and dormancy

Interphase, prophase, and telophase nuclei were measured at different times during the year in fusiform cambial cells located at the base of the main stem of 6-year-old trees and in 1-year-old shoots from the top of 21-year-old trees. In both materials, the size and shape of nuclei exhibited seasonal changes that were independent of the cell cycle. Nuclear length was greater, whereas nuclear width and depth were smaller, when the cambium was dormant than when it was active. Nuclear volume gradually declined during the growing period and increased during the rest stage of dormancy. Nuclei had the highest surface to volume ratio in the quiescence stage of dormancy. During cambial activity, the projected area of prophase nuclei decreased, whereas it did not change for telophase nuclei. Nuclear volumes from the present investigation were combined with nuclear DNA contents previously recorded to estimate seasonal changes in nuclear DNA concentration which appear to be associated with the annual cycle of cambial activity and dormancy. Key words: balsam fir, periodicity, nucleus, xylogenesis, rest.

Distribution of Indole-3-Acetic Acid and the Occurrence of Its Alkali-Labile Conjugates in the Extraxylary Region of Pinus sylvestris Stems

Free and conjugated indole-3-acetic acid (IAA) were measured by quantitative gas chromatography-selected ion monitoringmass spectrometry in the extraxylary region of the stem of large Pinus sylvestris (L.) trees during the annual cycle of cambial activity and dormancy. The extraxylary region at the stem top and bottom was divided into 3 and 4 fractions, respectively, for the free IAA measurements, while the entire extraxylary region was extracted when the IAA-conjugates were analyzed. The effect on the distribution pattern of expressing IAA level as a concentration (per gram fresh weight or dry weight) and as total amount (per square centimeter) was examined. The IAA level was much higher in the cambial region than in the fractions that contained the nonfunctional phloem and the periderm. The largest IAA concentration occurred in the fraction that included the cambium, whereas the total amount of IAA was greatest in the phloemcontaining fraction. The significance of the nonuniform radial distribution of IAA for estimating the IAA concentration in the cambial region is discussed in relation to how the cambial region is sampled. A slight Iongitudinal gradient in IAA concentration, decreasing from the top to the bottom of the stem, was observed in the cambial region when the cambium was in the grand period of activity, but not at the end of the cambial growing period. In all fractions, the total amount of IAA was highest when the cambium was active. However, the IAA concentration in the cambial region did not follow the same pattern, actually being lowest during the tracheid production period at the stem bottom. IAA conjugates were detected on all sampling dates except June 23, but their concentrations were always less than 14% of that of free IAA, and their occurrence did not obviously vary during the year. In general, there was a higher concentration of ester conjugates than of amide conjugates, and the ester conjugates were more abundant at the top of the stem than at the bottom.

Role of temperature in regulating timing of germination in soil seed reserves of Thlaspi arvense L.

Summary. Most freshly‐matured seeds of Thlaspi arvense L. (Brassicaceae) were dormant at maturity in May. Seeds sown on soil germinated in autumn and spring, but mostly in autumn. Buried seeds exhumed at monthly intervals and tested in light and darkness over a range of thermoperiods exhibited annual dormancy/non‐dormancy cycles. However, the dormant period was short, usually only in April, but sometimes May, and in some years 1–6% of the seeds remained conditionally dormant. After‐ripening occurred during summer, and seeds were non‐dormant during autumn. Seeds entered conditional dormancy in winter and dormancy in late winter or early spring. When buried dormant seeds were kept at 25/15, 30/15 or 35/20°C for 12 weeks, they gained the ability to germinate to 95–100% at 15/6, 20/10, 25/15, 30/15 and 35/20°C. After burial for 12 weeks at 15/6 and 20/10°C, seeds germinated to 80–100% at 15/6, 20/10 and 25/15°C. but to only 11–64% at 30/15 and 35/20°C. After 4 weeks at 5°C, initially‐dormant seeds germinated to 100% at all thermoperiods except 35/20°C, where only 15% of them germinated. However, after 18 weeks at 5°C, only 0–1% of the seeds germinated at all thermoperiods. Most non‐dormant seeds exposed to 1, 5 and 15/6°C for 16 weeks were induced into dormancy; 1–15% entered conditional dormancy and thus germinated only at 15/6, 20/10 and 25/15°C. This study indicates that seeds of winter annual plants of T. arvense are non‐dormant in autumn and enter dormancy in winter, while those from summer annuals are dormant in autumn and become non‐dormant during winter.

Germination responses of buried seeds of Capsella bursa‐pastoris exposed to seasonal temperature changes

SummaryBuried seeds of Capsella bursa‐pastoris exhibit an annual conditional dormancy/non‐dormancy cycle. Seeds after‐ripen during summer and remain non‐dormant during autumn and winter. Seeds enter conditional dormancy in early spring, first showing marked decreases in ability to germinate at high (35/20°C) and then at lower (30/15, 25/15°C) temperatures. Seeds do not lose the ability to germinate to high percentages at March (15/6°C) and April (20/10°C) temperatures in March and April. Thus, C. bursa‐pastoris is a facultative winter annual, germinating in both autumn and spring if seeds are exposed to light. However, because some seeds retain the ability to germinate at 30/15 and 25/15°C, they could do so throughout the growing season in regions with cool, moist summers. Conditional dormancy developed in all seeds given 12 weeks at 5°C and subsequently kept for 4 weeks each at March (15/6°C), April (20/10°C) and May (25/15°C) temperatures. Thus, seeds of C. bursa‐pastoris enter conditional dormancy as temperatures increase in spring.

The Role of Temperature on the Dormancy Cycle of Seeds of Rumex obtusifolius L.

Seeds of Rumex obtusifolius L. were buried at different depths in bare soil, under a grass turf and under shrubs. The temperature was measured daily at seed level. During 3 years, monthly samples were exhumed and the germination was tested at different temperature regimes. The dormancy levels follow a seasonal pattern. Additional germination experiments were set up in order to explain the underlying principles of a season-sensing mechanism of buried seeds. In this respect, the importance of a sudden shift to higher temperatures for induction of germination is demonstrated. Key-words: Dormancy, Rumex, germination, temperature, seeds

Detection of tomato ringspot virus in white ash and adjacent vegetation in central New York

Tissue samples from 15 woody and herbaceous plant species, including white ash (Fraxinusamericana L.), were collected monthly during the spring and summer of 1985 and indexed by ELISA for tomato ringspot virus. The virus was detected in 12 of 23 white ash indexed, most frequently in the roots. Of 88 white ash seedlings inoculated with purified tomato ringspot virus, the virus was detected by ELISA in 7 seedlings after two cycles of growth and dormancy, and in only 1 seedling after one cycle of growth and dormancy postinoculation. The virus was also detected in Fragariavirginiana Mill., Prunusvirginiana L., Rubusoccidentalis L., R. strigosus Michx., Solidagocanadensis L., Trifoliumpratense L., T. repens L., and Daucuscarota L. growing within 50 m of infected ash.

Field emergence of Lamium amplexicaule L. and L. purpureum L. in relation to the annual seed dormancy cycle

Summary: Résumé: ZusammenfassungSeedling emergence of Lamium amplexicaule L. and L. purpureum L. was monitored in field plots tilled at various times during the growing season, and the number of viable seeds in the soil was determined. In plots tilled in early spring, only seeds of L. amplexicaule, germinated, but seeds of both species germinated in the same plots in autumn without further disturbance. Additional seeds of L. amplexicaule, but not of L. purpureum, germinated the following spring. In plots tilled in late spring and summer, seeds of L. amplexicaule germinated in autumn and the following spring, whereas seeds of L. purpureum germinated only in autumn. The number of viable seeds in the top 13 mm layer of soil ranged from 189 to 1216 m−2 for L. amplexicaule and from 131 to 854 for L. purpureum. These field results support those obtained in previous glasshouse‐laboratory physiological studies on the annual dormancy cycle in the two Lamium species. Levée au champ de Lamium amplexicaule L. et L. purpureum L. par rapport au cycle annuel de la dormance des grainesLa levée de jeunes plants de Lamium amplexicaule L. et L. purpureum L. a été observée sur des parcelles cultivées à différentes époques de la saison de végétation et le nombre de graines viables au sol a été déterminé. Sur les parcelles cultivées en début de printemps, seules les graines de L. amplexicaule ont germé, mais des graines des deux espèces ont germé en automne sur les mêmes parcelles, sans cultivation ultérieure. Au printemps suivant, une nouvelle germination a été constatée chez L. amplexicaule mais pas chez L. purpureum. Sur les parcelles cultivées en fin de printemps et en été, des graines de L. amplexicaule ont germé en automne et aussi au printemps suivant, tandis que les graines de L. purpureum n'ont germé qu'en automne. Le nombre de graines viables dans les premiers 13 mm de la surface du sol allait de 189 à 1216 m−2 pour L. amplexicaule et de 131 à 854 pour L. purpureum. Ces résultats sur le terrain confirment ceux obtenus dans des études physiologiques sur le cycle annuel de dormance chez les deux espèces de Lamium, menées préalablement en serre et au laboratoire. Ueber dus Auflaufen von Lamium amplexicaule L. und L. purpureum L. in Bezug auf den Jährlichen Zyklus der Samenruhe unter FeldbedingungenIn Parzellen, die zu verschiedenen Zeitpunkten während der Vegetationsperiode einer Boden‐bearbeitung unterworfen worden waren, wurde sowohl das Auflaufen der Keimlinge von Lamium amplexicaule L. und L. purpureum L. registriert, als auch die Anzahl lebenfähiger Samen festgestellt. Nach Bodenbearbeitung im frühen Frühling keimten nur Samen von L. amplexicaule; im Herbst keimten in denselben Parzellen jedoch Samen beider Arten, sofern der Boden nicht mehr bewegt worden war. Weitere Samen von L. amplexicaule, nicht aber von L. purpureum, keimten im folgenden Frühling. In Parzellen, die im späten Frühling und im Sommer bearbeitet worden waren, keimte L. amplexicaule im Herbst und im folgenden Frühling. Während L. purpureum nur im Herbst keimte. Die Anzahl lebensfähiger Samen m−2 in den obersten 13 mm des Bodens bewegte sich zwischen 189 und 1216 für L. amplexicaule und zwischen 131 und 854 für L. purpureum. Diese Feldresultate bestätigen Ergebnisse von Gewüchshausstudien über den jährlichen Zyklus der Samenruhe der beiden Lamium‐Arten.

The Annual Dormancy Cycle in Buried Weed Seeds: A Continuum

Weed seeds in the soil go through annual dormancy-nondormancy cycles, exhibiting a continuum of changes in physiological responses. These gradual transitions may be related to changes in membrane properties. Seeds of winter and summer annuals respond in opposite ways to seasonal temperature changes; in both groups the responses are important life cycle adaptations to the habitat.

Role of temperature in regulating timing of germination in soil seed reserves of Lamium purpureum L.

SummaryFresh seeds of Lamium purpureum L. were dormant at maturity, and when buried and exposed to natural seasonal temperature changes they exhibited an annual dormancy/non‐dormancy cycle. During burial in summer, fresh seeds and those that had been buried for 1 year afterripened and thus were non‐dormant by September and October; light was required for germination. During autumn and winter seeds re‐entered dormancy, and during the following summer they became non‐dormant again. Dormant seeds afterripened when buried and stored over a range of temperatures, becoming conditionally dormant at low (5, 15/6°C) and non‐dormant at high (20/10, 25/15, 30/15 and 35/20°C) temperatures. Conditionally dormant seeds germinated to high percentages at 5, 15/6 and 20/10°C, while non‐dormant seeds germinated to high percentages additionally at 25/15, 30/15 and 35/20°C. Low temperatures caused non‐dormant seeds to re‐enter dormancy, while high temperatures caused a sharp decline in germination only at 30/15 and 5°C. The temperature responses of L. purpureum seeds are compared to those of L. amplexicaule L.

Physiological studies in birch

SynopsisAspects of whole-plant physiology of birch are reviewed, and previously unpublished research is presented. Seasonal cycles of shoot growth and bud dormancy are discussed, with environmental and hormonal factors affecting the rate and duration of shoot extension and leaf production. Also covered are variability in branching patterns, aspects of cambial activity, onset of the reproductive phase, factors affecting flowering and sex ratio, and seed viability and dormancy. Finally, the regenerative capacity of birch is described, and its future roles are mentioned.

Control of cambial activity and dormancy in Picea sitchensis by indol-3-ylacetic and abscisic acids

The combined gas chromatography – mass spectrometry (GCMS) technique of single-ion current monitoring was used to measure indol-3-ylacetic acid (IAA) and abscisic acid (ABA) levels in diffusible, acidic, and conjugated fractions obtained from the cambial region of Sitka spruce (1) during the annual cycle of cambial activity and dormancy in trees reared under natural and controlled environmental conditions, and (2) after debudding, girdling, defoliating, applying exogenous IAA, droughting, or changing the photoperiod. Seasonal changes occurred in the level of IAA and ABA in each fraction, but not obviously and consistently in conjunction with specific changes in cambial activity and dormancy. Debudding and girdling halted tracheid production, decreased the radial enlargement of the last-formed tracheids, and abruptly reduced the content of IAA and ABA in the diffusible and acidic fractions without affecting the ABA level in the conjugated fraction. Applying exogenous IAA to debudded shoots maintained tracheid production and differentiation, and largely prevented the decrease in IAA and ABA content. Elevating the internal water stress inhibited apical and cambial growth, increased the contents of diffusible, acidic, and conjugated ABA, and decreased diffusible and acidic IAA levels; the foliar concentrations of acidic IAA, acidic ABA, and conjugated ABA were similarly altered. Short-day photoperiod induced apical and cambial dormancy and reduced the levels of diffusible and acidic IAA and diffusible, acidic, and conjugated ABA; the decline in hormone content occurred mainly after the cambium ceased activity. Exogenous IAA could not prevent the cambium from ceasing activity under natural field conditions or short-day photoperiod. It is concluded that (1) there is an intrinsic seasonal pattern of change in IAA and ABA levels in the cambial region, governed primarily by seasonal changes in foliar hormone production; (2) this pattern is readily and variously perturbed by changes in the environment, particularly by factors affecting the internal water stress; (3) the evidence accumulated to date casts doubt on a role for ABA in controlling cambial dormancy; (4) cambial activity and the completion of the springtime transition from quiescence to activity depend on a continuous supply of basipetally transported IAA; (5) the changeover from activity to rest at the end of the cambial growing period is due to the development of an inability to respond to IAA, not to a deficiency in IAA supply; and (6) the transition from rest to quiescence during the cambial dormant period involves regaining the ability to respond to IAA.

The Banjhi (Dormancy) Cycle in Tea (camellia sinensis)

SUMMARYThe ‘banjhi’ or dormancy cycle in free-growing tea trees appears to be the result of an endogenous rhythm. However, in harvested tea apical dominance causes dormant shoots to be produced under conditions favourable to growth, and the synchronized flushing cycle causes periods of apical shoot (active terminal bud) and secondary shoot (dormant terminal bud) production.

Seasonal variation of abscisic acid in the dormant shoots of Douglas-fir

The occurrence of abscisic acid (ABA) in the dormant shoots of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) was confirmed by bioassay, thin-layer chromatography, gas–liquid chromatography, and gas–liquid chromatography – mass spectrometry. Seasonal variation of ABA in the buds, leaves, and stems was then determined using 2-trans-ABA as an internal standard. Concentrations of ABA were highest in the autumn for buds (2.1 μg/g) and needles (0.79 μg/g) and highest in January for stems (0.34 μg/g). The lowest concentrations for all tissues were in February and March, before bud burst. Close correlation of levels of ABA with previously measured physiological evidence of growth and metabolic activity suggests a possible role in the dormancy cycle of Douglas-fir.

Growth and Dormancy Cycles in Citrus Bud Cultures and Their Hormonal Control

AbstractAn in vitro bud culture method was devised in order to better understand the control mechanism of Citrus bud development. This technique offers a new approach to the study of hormonal control of growth, dormancy and flowering cycles in perennial plants.Buds were excised from orchard trees throughout the year, cultured on defined media for prolonged periods, and their vegetative growth responses to various growth hormones were determined. The buds proceeded with their vegetative development in vitro and achieved sprouting on a basal medium. The various growth regulators affected both the time required for sprouting (TRS) and the type of growth. In summer buds, IAA delayed sprouting, while GA enhanced it and caused shoot elongation. Cytokinins specifically induced the formation of numerous adventitious buds, whereas ABA completely inhibited sprouting; this inhibition, however, was reversible. A marked decrease in total protein and in the rate of its synthesis was evident during the first 20 days of sprouting induction and early bud growth.The annual growth rhythm was determined in spring buds sampled and cultured throughout the year, and an innate dormancy of citrus buds was revealed. Both the dormancy and the sprouting periods of buds in vitro corresponded to the natural periods occurring under field conditions. The effect of exogenous IAA, GA and cytokinins on the TRS varied at different periods along the season, suggesting the concept of “critical levels” in the endogenous balance of hormones.

Phytochrome Controlled Changes in Dormancy and Germination of Buried Weed Seeds

Seeds of six weed species were buried in the field at depths of 2.5, 7.6, and 15.2 cm. Seed germination after various light and temperature treatments was determined before burial and after recoveries in darkness at 3-month intervals over 12 and 20-month periods. In one experiment the five species studied were ungerminable before burial. After 6 months burial, most species responded to light but became ungerminable again after this time. These results suggest cycles of dormancy where seeds pass from total dormancy at maturation to a phytochrome-controlled dormancy after burial and then return to total dormancy. During the phytochrome-controlled dormancy period, some species were highly light sensitive. In another experiment the response of yellow rocket(Barbarea vulgarisR. Br.) seeds to thirteen light and temperature treatments was determined before and after burial. Without light treatment, germination of the recovered seeds at various temperatures was low. Germination was usually high after brief exposures to red light, particularly in seeds recovered from 15.2 cm. Very large increases in germination were induced by light exposures of 3 × 10−9Einsteins cm−2incident in the 600 to 680-nm region (1 sec). The evidence suggests changes in total phytochrome (Ptot) are responsible for a seasonal change in light sensitivity and a previously undescribed type of dormancy.