Dormant Condition Research Articles

Temperature and Soil Water Effects on Dormancy and Mortality of Subterranean Clover Seed

AbstractGermination tests were conducted to investigate possible causes for a reestablishment failure of subterranean clover (Trifolium subterraneum L.). ‘Mount Barker’ subterranean clover seeds were germinated on blotters and on the soil surface or at 1 cm depth in nonfumigated and fumigated soil at four constant temperatures for 14 d, followed by constant 15°C for 8 d. Fumigation had no effect on germination. Germination on blotters was reduced to 11.1% at 25 and 30°C, compared with 94.5% at 15°C. Emergence of seedlings was reduced to 37.9% at 30°C, compared with 92.5% at 15°C. Emergence of seedlings at 30°C from soil was greater after 14 d than germination on blotters. In a second experiment, seeds buried 1 cm were germinated at soil water levels ranging from 0.0 to 0.816 kg kg−1. Temperatures were 15 or 30°C for 7 d, then 15°C for 7 d more. Seeds failed to germinate at either temperature in dry or saturated soil. Emergence after 7 d was reduced at 30°C compared with 15°C at soil moisture levels from 0.204 to 0.544 kg kg−1. After 7 more d at 15°C, emergence was similar between temperatures at soil moisture levels from 0.0 to 0.544 kg kg−1. Under saturated soil conditions, 28.5 and 80.8% of the seed rotted at 15 and 30°C, respectively. Our results suggest that subterranean clover seeds can survive in pasture soil for 14 d in an embryo dormant condition during the summer, unless the soil is saturated, in which case soft seeds tend to decay.

Myocardial hibernation in terms of the flow-function relationship.

In the northern part of the United States, hibernation is a very real phenomenon. It refers, of course, to the dormant condition in which some types of animals pass through the trying conditions of winter. In fact, the Latin word from which the word derives is hibernus which refers to wintry conditions. In contrast to various woodland creatures who can sleep through the winter largely oblivious to its rigors, the human inhabitants of the North have to stay awake through winter no matter how much they would like to hibernate for several months. With our usual penchant for giving simple, catchy nicknames to very complicated concepts, the cardiovascular research community has adopted the word hibernation to describe the myocardium’s response to coronary inflow restriction that is not severe enough to compromise viability. Faced with the “wintry” circumstances posed by inappropriately low oxygen availability, the idea is that the myocardium “hibernates” to protect itself against the consequences of prolonged supply/demand imbalance.

Growth and reproduction of an estuarine population of the colonial hydroidCordylophora caspia (Pallas) in the northern Baltic Sea

Growth and reproduction of the colonial hydroidCordylophora caspia were monitored during the breeding season in natural conditions. In 1987, a life history study was carried out on the upright stems of the main stolon. Mean size of uprights varied cyclically. The first peak coincided with the peak number of sexual hydranths, after which the mean upright length decreased, possibly indicating somatic costs of sexual reproduction. Extrinsic factors like flooding may also have contributed to cyclical changes in upright size. In 1988 and 1989, colonies were reared on experimental plates in the estuary. In 1988, colonies grew until mid July, after which they regressed to a dormant condition and then started growing again in mid August. Predation and space competition are discussed as possible causes for this dormancy in the middle of the growing season. In 1989, colonies grew continually, with the exception of a decline in colony biomass and number of feeding hydranths at the end of July, just following the peak of sexual reproduction. Sexual reproduction started in the early stages of colonial development for all years. During early summer,C. caspia allocated resources simultaneously in colonial growth and sexual reproduction. However, sexual reproduction had a clear peak in mid summer, and thereafter sexual reproduction ceased while colonial growth continued.

Morphology and Taxonomic Significance of Dormant Branch Primordia, Dormant Buds, and Vegetative Reproductive Organs in the Suborders Leucodontineae and Neckerineae (Musci, Isobryales)

The manner of branch development and shape of vegetative reproductive organs were examined for 19families, 101 genera, and 227 species in the suborders Leucodontineae and Neck- erineae (Musci). Two types were recognized in the manner of branch development. They are distin- guished from each other by the nature of dormant condition: One with swollen primordia (type A) and the other with buds (type S). Filamentous pseudoparaphyllia always accompanied type A primordia, whilefoliose pseudoparaphyllia were always with type S. The presence ofscale-like leaves overarching buds was a good marker for recognizing the type S with ease. Each family and genus, with few exceptions, proved to be stable in the manner ofbranch development and shape of vegetative reproductive organs. Therefore, the two-character combination can be used as a new clue for the taxonomy of higher categories. Five genera, which are not closely related, have paraphyllia. The presence ofparaphyllia is correlated with the type S of branch development, and has no taxonomic significance. The familial affinities of two genera are considered; Henicodium is a monotypic genus and classified in the Pterobryaceae, and Penzigiella in the Neckeraceae. Several families of the Leucodontineae have long

Endogenous inhibitors and seasonal changes in abscisic acid in Dioscorea floribunda Mart. & Gal.

In the tubers of medicinal yam (Dioscorea floribunda Mart. & Gal.) abscisic acid (ABA) content was high in all the parts during the dormant condition in the winter, but it decreased to a very low level in the actively growing plants. ABA content of the entire tuber was negatively correlated with temperature and photoperiod. Growth inhibitors including batatasin-I and phthalic acid were identified in the dormant tuber.

Dormancy and spring development of lateral buds in mulberry (Morus alba)

Patterns of spring development of lateral buds of mulberry (Morus alba L. cv. Shin‐ichinose) coppice shoots on 11‐year‐old low‐pruned stumps varied in response to girdling, pruning and arching. The erect controls showed a weak acrotonic (apex‐favoring) growth habit, in which the majority of the buds, including the basal ones, sprouted and elongated in mid‐ and late April, and hence there was a prolonged imposition of dominance on the upper laterals in mid‐ and late May. In contrast, early spring girdling or pruning enhanced the activity of the upper buds of the proximal (lower) halves of the girdled stems or of the pruned stems, resulting in considerable dominance of the laterals from such buds in late April. Arching markedly inhibited buds on the under side of the arched stems, leading to poor shoots. By late April, the buds on the adaxial (upper) side readily grew into new vertical shoots, which dominated over the lateral ones.When studied by a multiple‐node‐cutting test, increased length of segments of post‐dormant mulberry stems was accompanied by decreased bud activity of the segments and by decreased breaking ability of the lower buds within the segments, suggesting the importance of roots in the weak acrotonic habit of the erect stem in spring. By contrast, the acropetal influences of the attached stems can in part affect dominance relationships, perhaps mediated through competition for factors translocated from the roots. Continuous basal applications of abscisic acid inhibited bud break and shoot growth of the postdormant stem segments, but these inhibitory effects could be reversed by applied gibberellic acid A3 (GA3).Two phases of lateral bud dormancy in erect mulberry coppice shoots were identified. The first was characterized by a smaller breaking capacity in the upper buds than in the lower ones and hence by a basitonic (base‐favoring) gradient in bud growth potential. The second phase corresponded to a restoration of these capabilities in the upper buds and to a change towards a linear gradient in bud growth potential, with disappearance of the dormant condition, in February and March. This gradient change during dormancy release may represent the physiological basis for the weak acrotonic habit of erect mulberry stems in spring.

SEED DORMANCY IN DORMOATS: WINTER SURVIVAL AND SPRING EMERGENCE

Dormoats are derivatives of hybrids between Avena sativa L. and A. fatua L. designed to be sown in autumn to germinate the following spring. Information was needed on the fate of field-planted dormoats throughout the seasons, in order to gain insight into the mechanism(s) contributing to spring emergence. Seeds from three dormoats (PGR8658, PGR16727 and PGR16728) showing variability in depth of dormancy were each sown in fiberglass mesh bags, in the field in late summer. Germination behavior, in field emergence and laboratory tests, after burial of the seeds outdoors for various periods showed that different survival mechanisms were present in dormoats and that dormancy types and levels could fluctuate. Seeds entered, left and re-entered the dormant condition throughout the seasons. These germination behaviors are typical of weeds and the spring emergence levels achieved by dormoats are similar to those of wild oat. It seems that this facet of the expression of the wild oat dormancy trait has not been modified despite the numerous breeding strategies used for dormoats. New approaches have to be sought to achieve good spring emergence of this experimental crop.Key words: Dormancy, dormoats, emergence

An Evaluation of Dormant Oil Phytotoxicity on Six Species of Woody Ornamentals

Conflicting reports concerning possible phytotoxicity of horticultural oils applied to woody plants in dormant condition prompted an evaluation of superior oil Sunspray 6E on six species of ornamentals. Young dormant saplings of pear, sugar maple, Japanese maple, European hornbeam, Scots pine and red pine were unaffected by oil concentrations of up to 8%. Bud break was neither reduced nor significantly delayed and no damage to bark or bud scales was observed at any concentration. Leaves developed normally when dormancy was broken with no twig dieback observed. Results show no phytotoxicity for this product even when applied at rates 4X the usually recommended concentration.

"Missed pill" conception: fact or fiction?

A study of 19 healthy nulliparous women 20-30 years who were using the low dose combined oral contraceptive (OC) demonstrated ovarian folliculogenesis during the 7-day withdrawal in 28 day cycles. This makes the genuine occurrence of conceptions seem less mythical. All of the women had normal menstrual histories before OC use. They had been on treatment for at least 3 months and had regular monthly withdrawal bleeds. Ultrasonographic examination of the ovaries was performed on the last day of 1 pack (day 21) on the last pill day (day 28) and on the 7th day of the next pack (day 7). An Elscint Dynex sector scanner with a 3.5 MHz probe was used which is capable of measuring down to 1.5 mm. All subjects showed some ovarian follicular activity by the last day of the pill-free phase and half developed multiple follicles with a dominant follicular diameter of 7 mm or greater the diameter seen on day 7 of the normal cycle. Continuation of the gonadotrophin stimulation of these dominant follicles would have led to ovulation. By the 7th day of the new pack the follicular appearance had returned to the dormant condition shown by the 1st scan in all but 1 subject and she showed reduction in follicular diameter. No pills were missed by any subject during the study cycles. In 2 subjects small cysts were detected at the 1st scan and at the 2nd and 3rd examinations unaffected by the development and regression of the other follicles. 1 subject inadvertently missed a on day 5 of a cycle after completing the study. She was examined 24 hours later and a 10 mm follicle was seen. She was unable to attend for further examination. With the current 21 day pack it is strongly recommended that alternative contraception be used when a is missed during the first 7 days of a pack even if the woman has been using OC for some time. This is most likely not necessary when a is missed later in the course. Women using OCs should also be warned of the danger of delaying restarting treatment after the 7 free days.

Occurrence of a Resting Stage in Cyclopoid and Harpacticoid Copepods in Nearshore Lake Michigan

Temporal and spatial differences in the abundance of dormant harpacticoid and cyclopoid copepods in a nearshore area of southeastern Lake Michigan are described. Core samples were taken at three depths (11, 17, and 23 m) at monthly intervals from May to November 1976–79. All dormant harpacticoids were Canthocamptus robertcokeri or Canthocamptus staphylinoides, and all dormant cyclopoids were stage IV copepodids, likely Diacyclops thomasi. The percentage of Canthocamptus and copepodids IVfound in the resting state declined dramatically with increased sampling depth. Dormant Canthocamptus were most abundant in late summer/fall in each of the four sampling years. During this period, usually over 50% of all Canthocamptus were found in the dormant condition. Dormant cyclopoids were most abundant between June and September, but exact seasonal patterns varied from year to year. Factors initiating the dormant condition are not clear, but water temperatures and day length may be important environmental cues. Some of the spatial and year-to-year differences in the proportion of dormant individuals appeared related to variations in the amount of surface detritus. This is the first report of a resting stage in the life cycle of cyclopoids in the Great Lakes.

Seed germination in goose grass (Eleusine indica)

Low germination of freshly harvested Eleusine indica caryopses indicated some form of dormancy. Water uptake studies indicated that the covering structures of the propagules are permeable to water. As scarification breaks the dormant condition a mechanical effect for the covering structures is indicated. With ageing, dormancy becomes progressively less and the seeds become more sensitive to gibberellic acid applications which increase germination significantly.

The influence of photoperiod on drought induction of dormancy in Lotus scoparius.

Many species of plants in Mediterranean climate regions have evolved deciduousness, causing reduced leaf area during the long summer drought characteristic of Mediterranean climates. This summer deciduous growth form has been considered a plant adaptation in Mediterranean regions allowing survival during periods of extreme water stress. Many studies have suggested the ecological importance of this growth form but few studies have examined the physiological stimulus for deciduousness.Previous data indicate that abscission in Lotus scoparius (a mediterranean California deciduous species) is influenced by both photoperiod and water stress in a complex manner. Here the physiological basis of long day enhanced leaf fall during water stress is investigated.Examination of water potential components indicate an osmotic adjustment with incresing water stress which enables the maintenance of turgor at lower water potentials. Osmotic adjustment in plants grown under long photoperiods was greater than that in short photoperiods. Therfore, long day enhanced abscission during water stress was not due to a greater susceptability to turgor loss during long days. Rather, long day treatment caused these plants to initiate dormancy (as indicated by soluble protein concentrations) during the onset of water stress. The dormant condition could not be released by subsequent release from water stress. Apparently, Lotus scoparius has evolved a photoperiodic control (presumably through growth regulators) over the initiation of dormancy during water stress. The adaptive significance of this photoperiodic control over the leaf abscission response to water stress relates to the variable climate of Mediterranean regions.

Metabolism and ultrastructure of dormant podocysts of Chrysaora quinquecirrha (scyphozoa)

AbstractOxygen uptake by the podocyst of the scyphozoan, Chrysaora quinquecirrha, is about one‐fourth that of the scyphistoma, based on total protein, but is nearly equal to that of the scyphistoma when calculated on the basis of total DNA. Opening the podocyst cuticle causes a two to threefold increase in oxygen consumption within the first hour.Podocysts held for 11–13 months at 25°C retain viability, even though more than half of the DNA, one‐third of the protein, and one‐fifth of the lipid are lost. Ultrastructural observations indicate that the cyst contains a population of active cells, with numbers of mitochondria and microvilli, and a mass of internal yolkfilled cells, some of which are lysed and/or phagocytized during dormancy. The active cells acquire many phagocytic vacuoles containing large particles. This may represent a unique mechanism for prolonged survival in the dormant condition.

Ultrastructure of Cells in the Overwintering Dormant Shoot Apex of Rhododendron maximum L.

Tissue arrangement and cell structure of terminal leaf buds of Rhododendron maximum were observed while in the dormant overwintering condition. The apical anatomy was typical of angiosperms with a two-cell-layer tunica superior to a corpus which gives rise to a poorly defined rib meristem-pith region below. The tunica-corpus cells had thin cell walls with many plasmodesmata; cells of the rib meristem pith, cortex, and procambium had thick primary cell walls with manifold pit fields. The cells of all these regions contained large ovoid or lobate nuclei, small proplastids with lipid droplets and phytoferritin, abundant dictyosomes, lipid bodies, and small vacuoles which appeared to arise from abundant myeloid figures. Tannins produced in the myeloid vacuolar complexes accumulated in the central vacuoles of cells of the rib meristem, pith, and cortex.

Reliability in the dormant condition

Reliability in the dormant condition

カトレヤの組織培養に関する研究(第3報)

Concerning the browing of liquid media which occasionally takes place in vitro culture of Cattleya shoot tips, the relationship between survival rate of explants and seasonal variation of the amount of browning substrates exuded from the chops of young Cattleya tissues was studied. In addition, effects of rutin supplementation on the survival rate of explants were investigated in this experiment.1. Browning substrates were exuded in large amounts from the chops of young shoot tips in the period from June to September when the growth of shoots was vigorous and the browning of explants, lateral buds, was also remarkable. The survival rate of explants was consequently reduced to about 30%. On the other hand, a survival rate of more than 70% was attained in the period from November to February when stock plants remained in dormant condition and thus browning of explants and exudation of browning substrates both were restrained markedly.2. Survival rate of explants was increased up to 60 or more when rutin was added to the liquid culture medium at a concentration of 50ppm during the period from the summer to the fall when many explants usually fail to survive in vitro culture. Optimum concentrations of rutin added to the culture medium were 50 to 100ppm for the tissue culture of Cattleya plants.

りん片除去, 石灰窒素, GA<sub>3</sub>, 及びエセホンがブドウ‘マスカット•オブ•アレキサンドリア’の芽の休眠打破に及ぼす影響

Experiments were conducted to determine the effects of bud scale removal and application of supernatant of calcium cyanamide (CaCN2) at 20%, gibberellic acid (GA3) at 100ppm, and ethephon at 500 and 1, 000ppm on the termination of bud rest in single eye cuttings of ‘Muscat of Alexandria’ grape (Vitis vinifera L.). Bud scale removal greatly reduced the rest of cutting buds during the collection period from August 30, 1977, to February 28, 1978. In buds treated with CaCN2, termination of rest was hastened during the period from August 30 to November 1, and then delayed gradually until December 27. The bud rest was broken naturally around January 30. Bud rest was markedly prolonged by GA3 application during the collection period. Ethephon applied on November 30, when buds remained in a profound dormant condition, delayed termination of bud rest. These treatments were given to mature grapevines grown in a glasshouse. Appreciable increase in emergence rate was observed in the spring in both scale-removed and CaCN2-applied buds.

Roles of endogenous and exogenous growth regulators in dormancy of Utricularia vulgaris

The roles of endogenous and exogenous growth regulators on dormancy control of Utricularia vulgaris were investigated by extraction and bioassay of endogenous levels of four classes at various developmental stages and by measuring the effects of synthetic regulators on these stages. The bioassays used were oat coleoptile for auxins, abscisic acid and other inhibitors; lettuce hypocotyl for gibberellins; and soybean callus for cytokinins. Two weeks before turion formation and during innate dormancy abscisic acidlike and bound gibberellinlike levels were high while free gibberellinlike and auxinlike levels were low. Abscisic acid exogenously applied to actively growing plants rapidly induced turion formation even under noninductive environmental conditions. Kinetin rapidly and completely caused sprouting in innately dormant turions but would not promote continued vegetative growth. These plants formed new turions within 2 weeks of sprouting. During imposed dormancy, when turions rapidly sprouted, there was a low level of abscisic acidlike inhibitor and high levels of gibberellinlike and auxinlike compounds. Turions collected during this state could be maintained in a dormant condition by incubation with abscisic acid even at high temperatures which normally induce sprouting. During sprouting the endogenous growth regulator pattern was similar to that described for imposed dormancy. A model of the environmental and growth regulator factors which control dormancy is presented.

A TEST FOR JUVENILITY AS AN INDEX OF ROOTABILITY IN CLONAL APPLE ROOTSTOCKS

The occurrence of less phloem fibre and less ring continuity in the tissue of the Ottawa rootstocks at Saskatoon, Saskatchewan compared to tissue supplied from two sources at the Agriculture Canada Research Station, Sidney, British Columbia appears to explain the ease of rooting from softwood cuttings at Saskatoon. A test using phloroglucinol-HCL on cross sections of the mid-internodal region of the basal internode (first fully elongated internode adjacent to bud scars) of 1-yr-old wood in the dormant condition, to determine the amount of fibre in the phloem and the occurrence of gaps in the ring, is suggested as a means to assess the potential ability to root from softwood cuttings. It is further suggested that stools must be pruned severely annually to preserve the rooting potential and pruned to ground level to attain the most juvenile tissue for new propagation blocks. The clone should be distributed as rooted cuttings rather than budsticks.

タマネギの花芽形成に関する研究

Some experiments were carried out to elucidate the effects of bulb size, removal of scaly leaves and foliage leaves and dormant condition on low temperature induction of flower buds in onion bulbs.The results were summarized as follows:1. As the index of bulb size, bulb weight was used effectively in the following experiments.It was found that the larger the bulb size, the shorter the period of low temperature (9°C) exposure required for flower bud formation.There was recognized, however, the presence of the critical bulb size at which the period of low temperature required was minimized.Thus, in “Senshuki” the critical bulb size appeared to be about 100-150g in weight and the minimum period of low temperature exposure to be about 40 days, while in “Sapporoki” they appeared to be about 30-50g and 30 days respectively; the latter being recognized to be more sensitive to low temperature exposure.2. Bulbs, when their scaly leaves were romoved in various degrees before planting, required longer periods of low temperature exposure according to the severity of the treatment. The periods required were shorter, however, as compared with the intact bulbs of the same size corresponding to that of the treated bulbs.The removal of foliage leaves after planting also increased the period of low temperature required.3. The removal of scaly leaves and/or of foliage leaves resulted in remarkable decrease of carbohydrate contents of bulbs, which appeared to be related to the increase of low temperature requirement in treated bulbs.The results mentioned above may be explained well by assuming the accumulation of the precursor in the bulbs, which changed into the so-called florigen at low temperature exposure. This precursor appears to accumulate in higher density in inner scales and its concentration seems to change in parallel with carbohydrate contents.4. When bulbs immediately after, or 30 days after, harvest were exposed to low temperature without water supply, they almost did not respond to, or required much longer period of, low temperature exposure for flower bud formation.