Exudation from Aphid Stylets during the Period from Dormancy to Bud break in Tilia americana (L.)

Aphid stylet exudation during the period from dormancy to budbreak was studied in Tilia americana by means of detached branchesbrought from the woods into conditions of warmth and extendedphotoperiod. During physiological dormancy little exudationwas obtained. Thereafter until mid-March exudation was morevariable, but its onset accelerated progressively until mid-March,after which persistent exudation could be obtained from allbranches within 2 days. When the buds were removed from onebranch at this time, exudation persisted for only 5 days comparedwith 14 to 21 days for branches with buds. To account for theseresults it is suggested that a hormonal factor is produced bythe buds which results in sieve-tube activation, that the factoris virtually absent during physiological dormancy, and thereafterrequires a few weeks to become fully active. Determinations of sugar concentration, level of exudation, andbud dry weight indicated that exudation was most intense beforethe bud sinks were active and then rapidly falls off. It issuggested that the stylet acts as a sink competing with thenatural sinks for solutes from a limited region of the stem.Other interpretations are also considered.     

Nuclear Replication Activity During Seed Development, Dormancy Breakage and Germination in Three Tree Species: Norway Maple (Acer platanoidesL.), Sycamore (Acer pseudoplatanusL.) and Cherry (Prunus aviumL.)

Flow cytometric analyses of nuclear DNA levels were carriedout during development, stratification and germination of dormantseeds from three tree species with contrasting characteristics.Norway maple (Acer platanoides) and sycamore (Acer pseudoplatanus)have orthodox (desiccation-tolerant) and recalcitrant (desiccation-sensitive)storage behaviours, respectively, and require only a periodof cold to break dormancy, whereas, orthodox cherry (Prunusavium) seeds require an initial warm period before cold stratificationto fully stimulate germination. Whole embryos and radicle tipsof both Norway maple and sycamore were found to have stablehigh levels of 4C DNA during the latter stages of developmentand both contained nuclei arrested at the 2C and 4C levels atmaturity. Mature cherry embryos had nuclei predominantly arrestedat the 2C level. This suggests that the acquisition of desiccationtolerance is not correlated with the arrest of the cell cycleat any particular nuclear DNA level. Neither DNA replicationin radicle cells nor germination occurred when seeds were maintainedmoist at a constant 20 °C. However, in the late stages ofcold treatment during stratification, nuclear DNA levels inradicle cells changed in advance of radicle emergence in theorthodox Norway maple and cherry, whereas in the recalcitrantsycamore, change was not recorded until after radicle emergence.These results show that DNA replication has potential use asan indicator of the progress of tree seeds through stratificationtreatments used to break some types of dormancy. The ways inwhich this indicator could be exploited for seed quality andperformance testing are discussed.Copyright 1998 Annals of BotanyCompany Norway maple,Acer platanoidesL., sycamore,Acer pseudoplatanusL., cherry,Prunus aviumL., DNA replication, flow cytometry, seed dormancy, stratification     

我国东部温带植物群落的季相及其时空变化特征

 植物群落季相阶段的划分,对于诊断地方、区域和全球尺度上生态系统对气候变化的快速响应和进行遥感植被生长季节的地面检验,具有重要 的科学意义。该文利用物候累积频率拟合法对我国东部温带地区7个站点1982～1996年的植物群落季相阶段进行划分,并分析了植物群落季相的 空间差异和年际变化及其与气候因子的关系。结果表明：1）各站点多年平均变绿期和旺盛光合期初日随纬度的升高而推迟,凋落期和休眠期初 日随纬度的升高而提前;多年平均变绿期、旺盛光合期和凋落期长度随纬度的变化不甚明显,而休眠期则随纬度的升高明显延长;2）在研究期 间内,站点平均变绿期初日以0.6 d&;#8226;a^－1的平均速率显著提前,且长度以0.7 d&;#8226;a^－1的平均速率显著延长;旺盛光合期初日呈不显著推迟,长 度呈不显著缩短;凋落期初日呈微弱提前,长度呈微弱延长;休眠期初日呈微弱提前,但长度却以0.9 d&;#8226;a^－1的平均速率显著缩短;3）站点平 均变绿期初日与当月平均气温的负相关显著,平均气温每升高1 ℃,初日提前约4.3 d;站点平均旺盛光合期初日与初日前第二个月到初日当月 平均气温的负相关显著,平均气温每升高1 ℃,初日提前约4.4 d;站点平均凋落期和休眠期初日与气温的相关均不显著。     

Seed Dormancy in Acer: The Role of Testa-imposed and Embryo Dormancy in Acer velutinum

The embryo dormancy shown in freshly harvested samples of Acervelutinum seeds is weakly established and very short-lived.Loss of this embryo dormancy occurred during post-harvest fruitstorage at either 5 or 17 C. In contrast, the dormancy of intactfruits and seeds was overcome only during storage at the lowertemperature. Removal of the cotyledons from embryos of freshlyharvested fruits allowed more rapid germination of the embryonicaxes, indicating that the cotyledons exert an inhibitory effect,although the axes still retained a measure of innate dormancy.The inhibitory effect of the cotyledons became less marked withincreasing duration of fruit storage, this loss of inhibitoryeffect occurring at both storage temperatures. Applied ABA stronglysuppressed germinative capacity in intact embryos and isolatedembryonic axes from freshly harvested fruits, but when ABA wasapplied to embryos of fruits that had been stored for variousperiods at 5 or 17 C, the inhibitory effect was first weakenedand then lost with increased storage. Although dormancy in the seeds of A. velutinum may be describedas intermediate between testa-imposed dormancy and true dormancy,it is perhaps more properly included in the former category. Acer velutinum Boiss. var. vanvolxemii, abscisic acid, embryo dormancy, germination, seed storage, testa-imposed dormancy, tissue sensitivity     

Radicle emergence with increased temperatures following summer dispersal in Trillium camschatcense: A species with deep simple double morphophysiological dormancy in seeds

Seeds with deep simple double morphophysiological dormancy (MPD) need cold stratification during the first winter after dispersal for radicle emergence, followed by the summer for root and bud development and finally a second winter for shoot emergence. In a previous study, we demonstrated that Trillium camschatcense seeds have this type of dormancy with radicles emerging from most seeds after the first winter. However, radicles also emerged from a few seeds in autumn during the same year as dispersal. We thought that temperatures after seed dispersal played a role in radicle emergence before the first winter. To confirm our idea, we investigated germination phenology outdoors, relationships between temperatures after seed dispersal and radicle emergence in the first year outdoors, radicle emergence in the first winter under varied temperatures using incubators, and shoot emergence from seeds with an emerged radicle in the first year outdoors. Our phenology study confirmed that T. camschatcense seeds have deep simple double MPD. Over 7 years, 0.2–7.5% of radicles emerged in the first year before winter and these percentages were moderately positively correlated with temperatures, especially minimum temperatures. Increasing August and September temperatures increased radicle emergence in the laboratory. Shoots emerged from seeds with an emerged radicle in the first year after the first winter. With increased autumn temperatures in warmer regions or with global warming, we predict that germination phenology may shift: increased radicle emergence in the first year and shoot emergence following the first (and not second) winter.     

The Effects of Temperature and Photoperiod on the Onset of Summer Dormancy in Poa bulbosa L.

Poa bulbosa L. plants became dormant in long days (16 h), whilein short days (8 h) they remained non-dormant for extended periods.Morphologically, the onset of dormancy was expressed by theformation of a true bulb at the base of every tiller, by thecessation of tillering and leaf emergence and, finally, by thedrying-up of the leaves. Low temperature delayed the onset ofdormancy but did not prevent it. This effect of temperaturemay explain the delayed onset of dormancy observed in naturalpopulations under a cool climate at a hilly habitat, comparedto plants growing under a warmer climate, at a lower, coastal-plainhabitat. Dormancy could be induced under short days by pre-exposureof the plants to a limited number of long days. The responsewas proportional to the number of long days given. The adaptivesignificance of the results for plant survival in a Mediterraneanclimate is discussed. Poa bulbosa L., summer dormancy, photoperiod, temperature, leaf emergence, bulbs, tillers     

Mechanisms regulating seedling emergence of orchardgrass (Dactylis glomerata L.) and western wheatgrass (Pascopyrum smithii [Rydb.] L.): Dormancy change,seed fate and seeding date

Seed germination and seedling emergence of ‘Arctic’ and ‘Lineta’ orchardgrass (Dactylis glomerata L.) and ‘Walsh’ and ‘LC9078a’ western wheatgrass (Pascopyrum smithii [Rydb.] L.) were studied both in the field and laboratory. Four seeding dates were conducted each year over 2 years and seedling emergence and seed fate in the soil were monitored. The effects of alternating temperature and light on germination were quantified and correlated with seedling emergence from soil and in the field. Orchardgrass seeds were less dormant than western wheatgrass as indicated by the disparity in germination percentage between constant and alternating temperatures. Seed germination percentage was usually higher than seedling emergence in the field for orchardgrass but lower for western wheatgrass, and temperature was not responsible for the difference. Exposing orchardgrass seeds to light during germination check helped break dormancy in orchardgrass when temperature was unfavorable (low and/or constant temperatures), while favorable temperatures (optimal, alternating temperatures) conditions overcame the inhibiting effect of light in western wheatgrass. The final seedling emergence of orchardgrass was either similar among the four seeding dates or decreased slightly from early May to early June. For western wheatgrass, however, final seedling emergence increased with seeding dates from early to late May and decreased in early June. Soil temperatures of the first 2 weeks after seeding increased from the early May to late May and then decreased. These temperatures were below or near the optimal temperatures for western wheatgrass seeds to release dormancy and germinate. Germination of the previously buried seeds indicated that orchardgrass and western wheatgrass had the potential for a high germination percentage under field conditions for all seeding dates. While soil temperatures close to the optimal temperature for dormancy breaking and germination promoted germination of orchardgrass, the same conditions could cause deterioration of seeds if they failed to germinate. For western wheatgrass, deeper dormancy reduced seed mortality.     

The Annual Rhythm of Activity of the Lateral Meristems (Cambium and Phellogen) in Cupressus sempervirens L

The annual rhythm of cambial activity in Cupressus sempervirensseems to be endogenous and fits well the Mediterranean climaticrhythm. Under outdoor conditions the cambium begins its activitytowards the autumn when temperatures drop and water is lesslimiting. The cambium continues to be active during the mildMediterranean winter and enters dormancy towards the beginningof the dry summer. A constant supply of water is not enoughto avoid cambial dormancy but may result in earlier onset anda prolonged period of activity. Relationships between xylemand phloem production, between shoot and root, and between cambialand phellogen activity are discussed. Cupressus sempervirens L., cypress, cambium, phellogen, annual rhythm, wood production     

Changes in Dormancy and Sensitivity to Vernalization in Axillary Buds of Satsuma Mandarin Examined in vitro During the Annual Cycle

Effect of season and the presence of fruit on bud-endodormancyand the flowering response to low temperature treatments weredetermined using bud cultures of Owari satsuma mandarin (Citrusunshiu Marc). Bud dormancy was deeper in fruiting as comparedto defruited trees. In fruiting trees, the intensity of buddormancy was highest in spring, decreased to a low value byearly Jul. and then increased until early winter. This increasein dormancy during summer and early autumn did not occur innon-fruiting trees. No flowers formed in buds cultured betweenMay and Sep. Both in fruiting and defruited trees, buds becamecompetent to show a vernalization response to chilling by theend of Oct., at the time they also became capable of sproutingin vitro at low temperature (15/10 °C). There was a directeffect of fruit on the buds which persisted long after fruitremoval and resulted in a reduction of the flowering responseto chilling.Copyright 1995, 1999 Academic Press Citrus flowering, Citrus unshiu Marc., dormancy, flower induction, flowering, in vitro flowering, satsuma mandarin, vernalization     

Breaking of Seed Dormancy by Nitrate as a Gap Detection Mechanism

Germination of Planlago lanceolata seeds buried in a chalk grasslandwas higher in bare soil than in vegetated soil, and measurementof soil nitrate concentrations showed that they were high enoughto account for this stimulation. When seeds of P. lanceolatawere sown in pots of soil with or without plants, and wateredwith nutrient solution containing either no nitrate, or 14 mMnitrate (sufficiently high that not all nitrate was absorbedby the plants), the presence of plants inhibited germinationonly when the nutrient solution contained no nitrate. It wasconcluded that breaking of seed dormancy by nitrate can functionas a gap detection mechanism if nitrate concentrations in baresoil are high enough to break seed dormancy, but are too lowto break dormancy when vegetation is present Plantago lanceolata, seed, dormancy, germination, nitrate, gap detection     

Variation in dormancy and germination in three co-occurring perennial forest herbs

Mesic deciduous forest herbs often disperse seed with morphophysiological dormancy (MPD) that prevents germination during unfavorable periods for seedling survival. However, for seeds of some species with MPD, seasonal separation of root and shoot emergence and variation in dormancy levels can complicate interpretation of seedling emergence timing in the field. We tested whether dormancy-break and germination requirements differed among co-occurring perennial forest herbs, Actaea racemosa, Hydrastis canadensis, and Sanguinaria canadensis, which are wild-harvested for their medicinal properties and known to have MPD. Seeds of all species exhibited a summer → autumn → winter requirement for seedling emergence in spring. However, species differed in seed-bank persistence due to variation in primary dormancy levels and stratification requirement of seeds. A. racemosa and H. canadensis can form short-term persistent seed bank, whereas S. canadensis can form a long-term persistent seed-bank, regardless of whether elaiosomes were removed from seeds prior to burial. A. racemosa seeds are dispersed in autumn with weak physiological dormancy, as seeds germinated to high rates at 15/6°C after 8 weeks. In contrast, most seeds of the summer dispersed species, H. canadensis and S. canadensis, require summer temperatures to overcome physiological dormancy. Consequently, seedling emergence is reduced and delayed by 1 year if seeds are not sown immediately following the period of natural dispersal. Seedling emergence was much lower in the field than in controlled conditions for all species, especially in the small-seeded A. racemosa. Interspecific variation in dormancy levels and germination traits must be considered when establishing populations for conservation purposes and in understanding recruitment limitation in perennial forest herbs.     

Root Growth of Bulbous Species during Winter

Bulbs of Allium moly, Scilla siberica, Triteleia uniflora, Tulipakaufmanniana and Narcissus lobularis were planted in a rhizotronand root growth was monitored weekly for an 18 week period.All the genera produced roots until the soil temperature droppedto 3 °C. Root outgrowth from the bulbs and growth of emergedroots then ceased or was strongly inhibited in N. lobularis,S. siberica and T. uniflora but not in the other genera. Mostbulbs resumed root elongation when the soil temperature hadwarmed to 4 °C. Root emergence and continued growth occurredfor a longer period during the winter than has generally beenassumed. Allium moly, Scilla siberica, Triteleia uniflora, Tulipa kaufmanniana, Narcissus lobularis, rhizotron, bulb, root growth     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, during Winter: The Effect of Photoperiod and Temperature on the Induction of Dormancy and the Annual Cycle of Development

The effects of daylength and temperature on the induction ofdormancy in shoots of Calluna vulgaris were investigated usingcontrolled environment growth rooms. Short days did not induce dormancy in Calluna but floweringwas inhibited and shoots having a characteristic end-of-seasonmorphology were formed. Short days combined with low temperaturesarrested growth but the depth of dormancy was not as great asthat of plants in the field in late autumn. Long days combinedwith low temperature did not induce dormancy or the end-of-seasonmorphology. Results from the growth room experiments may be interpretedin relation to the annual cycle of development of Calluna underfield conditions. Calluna vulgaris (L.), photoperiod, temperature, dormancy, flowering, annual cycle of development     

The role of the persistent fruit wall in seed water regulation in Raphanus raphanistrum (Brassicaceae)

Background and Aims

Dry fruits remain around the seeds at dispersal in a number of species, especially the Brassicaceae. Explanations for this vary, but usually involve mechanisms of innate dormancy. We speculate that, instead, a persistent fruit may give additional protection through control of dehydration, to species growing in arid or Mediterranean environments where water is sporadic.

Methods

X-rays and weight measurements were used to determine the extent to which Raphanus raphanistrum seeds within mature fruits imbibe water, and germination tests determined the roles of the fruit and seed coat in seed dormancy. Rates of water uptake and desiccation, and seedling emergence were compared with and without the fruit. Finally, germinability of seeds extracted from fruits was determined after various periods of moist conditions followed by a range of dry conditions.

Key Results

Most seeds rapidly take up water within the fruit, but they do not fully imbibe when compared with naked seeds. The seed coat is more important than the dry fruit wall in maintaining seed dormancy. The presence of a dry fruit slows emergence from the soil by up to 6–8 weeks. The fruit slows the rate of desiccation of the seed to a limited extent. The presence of the fruit for a few days during imbibition somehow primes more seeds to germinate than if the fruit is absent; longer moist periods within the pod appear to induce dormancy.

Conclusions

The fruit certainly modifies the seed environment as external conditions change between wet and dry, but not to a great extent. The major role seems to be: (a) the physical restriction of imbibition and germination; and (b) the release and then re-imposition of dormancy within the seed. The ecological significance of the results requires more research under field conditions.     

Interpopulation variability on embryo growth,seed dormancy break,and germination in the endangered Iberian daffodil Narcissus eugeniae (Amaryllidaceae)

The main goal of the study was to assess germination requirements in a threatened daffodil to elaborate a detailed protocol for plant production from seeds, a key tool for conservation. Experiments were carried out both in the laboratory and outdoor conditions. In Pseudonarcissi section, endemic Iberian species of Narcissus studied heretofore have different levels of morphophysiological dormancy (MPD). Embryo length, radicle emergence, and shoot emergence were analyzed to determine the level of MPD. Both interpopulational variability and seed storage duration were also studied. Mean embryo length in fresh seeds was 1.32 mm and the embryo had to grow until it reached at least 2.00 mm to germinate. Embryo growth occurs during warm stratification, after which the radicle emerges when temperatures go down. Seed dormancy was broken in the laboratory at 28/14°C in darkness followed by 15/4°C, but the germination percentage varies depending on the population. In outdoor conditions, seed dispersal occurs in June, the embryo grows during the summer and then the radicle emerges in autumn. The radicle system continues to grow during the winter months, but the shoot does not emerge until the beginning of the spring because it is physiologically dormant and requires a cold period to break dormancy. Early cold temperatures interrupt embryo growth and induce dormancy in seeds with an advanced embryo development. Seeds of N. eugeniae have deep simple epicotyl MPD. In addition, we found that embryo growth and germination were improved by seed storage duration.     

Advantageous and Detrimental Effects of Osmotic Pre-Sowing Treatment on the Germination Performance of Agrostemma githago Seeds

Dormant and after-ripened seeds of Agrostemma githago (corn-cockle)were pretreated in polyethylene glycol 400 (PEG) solutions attemperatures which would have allowed germination if the seedshad been imbibed in water, viz. 4?C or 20?C for after-ripenedseeds, and 4?C for dormant seeds. Pretreated seeds germinatedfaster than untreated seeds. The maximum decrease of the T₅₀(time to 50% germination) was 66%. Furthermore, pretreated seedswere capable of germination at supra-optimal temperatures whichotherwise had inhibited germination completely (20?C for dormantseeds and 30?C for after-ripened seeds). The percentage germinationat a supra-optimal temperature was considerably higher whenthe seeds had been primed at a temperature at which they developedmore extension power. The advantageous effects of the osmotic pretreatment were lessthan might be expected when the osmoticum had inhibited onlycell elongation. This was largely, if not fully, due to a generaldetrimental effect of osmotic stress and not to a selectiveinhibition of the processes which occur during the pregerminativephase in preparation for growth. Thus, during priming seedscomplete all or almost all processes which occur in water-imbibedseeds prior to radicle emergence. Key words: Agroatemma githago, dormancy, germination, germination performance, osmotic stress, priming     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, During Winter: Classification of Dormancy

Experiments are described in which plants of Calluna vulgariswere transferred from a high altitudinal blanket bog to controlledenvironment rooms under a range of conditions, to determinethe type of dormancy mechanism which occurs in this speciesduring the winter months. It was found that in autumn, Callunaexhibits semi-dormancy, bud break not occurring under shortphotoperiods. From December onwards, bud break will occur under short photoperiodsif warm temperatures are applied; at this time the plants arein a state of post-dormancy. Calluna lacks a period of truedormancy since it can always be forced to resume growth by longphotoperiods. Although in autumn, plants will not break dormancy under shortdays, after experiencing the natural outdoor conditions of winter,they will break dormancy equally readily under long and shortdays when brought into warm controlled environment rooms inthe spring. Calluna vulgaris (L.) Hull., heather, dormancy, pre-dormancy, post-dormancy, semi-dormancy     

Failure of Chlorophyll Formation in the Cotyledons from Secondarily Dormant Cocklebur Seeds

The cotyledons of secondarily dormant cocklebur (Xanthium pennsylvankumWallr.) seeds lacked not only growing potential but also chlorophyll-formingability. These properties developed as the seeds establishedsecondary dormancy during a soaking period. The inability toform chlorophyll in cotyledonary segments was not improved inthe presence of S-amino levulinic acid. But this ability wasgreatly restored by benzyladenine or ethylene treatment, whichis effective in increasing cotyledonary growth. Similarly, theapplication of ethylene together with enriched oxygen and carbondioxide, or subsequent to a KCN treatment, which were the mosteffective means for breaking secondary dormancy, completelyrestored both chlorophyll formation and growing ability of thecotyledons. The depression of the greening-ability in cotyledonsmay be involved in development of secondary dormancy of cockleburseeds in concert with the decline of their growth pontential. (Received September 24, 1982; Accepted December 27, 1982)     

Hormonal independence of courtship behavior in the male garter snake

Garter snakes exhibit a dissociated reproductive tactic in which gonadal activity is minimal at the time of mating, increasing only after the breeding season has ended. Experiments are presented demonstrating that neither short-term nor longterm castration affects courtship behavior in adult male red-sided garter snakes (Thamnophis sirtalis parietalis). So long as males have passed through a low-temperature dormancy period (hibernation), castration either shortly after emergence in the spring, or before entering winter dormancy in the fall, does not prevent the display of intense courtship behavior on emergence. Similarly, males castrated during mating activity the previous spring prior to the annual testicular growth phase actively courted females on emergence from hibernation. Males adrenalectomized and castrated during low-temperature dormancy also courted females on emergence. Hypophysectomy during or before low-temperature dormancy did not prevent males from displaying high-intensity courtship behavior on emergence from hibernation. Treatment with sex steroid hormones, as well as hypothalamic and pituitary hormones, and a variety of neural and metabolic affectors also fails to elicit courtship behavior in noncourting males during the summer. It was concluded that causal mechanisms controlling courtship behavior in the red-sided garter snake are fundamentally different, at least at the physiological level, from those mechanisms described for many laboratory and domesticated species.     

Change in Size and Cell Number during the Development of Lateral Root Primordia in Zea mays L.

Increase in cell number, anlage volume and length have beeninvestigated during the overall period of lateral root primordiumdevelopment in excised primaries and in attached roots of Zeamays L. Each of these aspects of anlage growth was found toincrease more or less exponentially during the interval betweenprimordium initiation and subsequent emergence as a lateralin both batches of roots. Values were then determined for celldoubling time (Td), the size of the proliferative fraction (Pf),and for anlage volume (Tv) and length (Tt) doubling times duringthe overall period of primordium development and at intervalsduring this period in both the excised and attached roots. Thepattern of change which took place in Td, Tv, Tl and Pf duringlateral primordium development was found to be similar in bothbatches of roots. However, the overall period of anlage developmentwas shorter in the excised roots than in the attached ones.Moreover, when laterals grew out of the excised roots they didso with fewer cells than comparable laterals emerging from theattached roots. Zea mays L., maize, root primordia, lateral emergence, cell doubling time