Sprouting promotion by inhibitors of nucleic acid and protein synthesis in the bulbils of some herbaceous plants

The sprouting of immature bulbils of Laportea bulbifera andpartially dormant (in-sufficiently chilled) mature bulbils ofL. bulbifera, Elatostema involucratum and E. umbellatum waspromoted by inhibitors of nucleic acid and protein synthesis(8-azaguanine, 5-fluorouracil, 2-thiouracil, ethionine, canavaninesulfate, p-fluorophenylalanine and cycloheximide in Laporteaand 5-fluorouracil, cycloheximide and chloramphenicol in Elatostema).However, the sprouting of nondormant (chilled) mature bulbilsof L. bulbifera was not promoted, but slightly suppressed whenthese inhibitors (especially, 8-azaguanine, cycloheximide andchloramphenicol) were applied either during or after chillingtreatment These results suggest that the two counteracting systems,dormancy-inducing and -breaking which involve nucleic acid andprotein synthesis participate in the dormancy regulation. (Received December 2, 1977; )     

Dormancy in Dioscorea: Sprouting promotion by inhibitors of protein synthesis in bulbils and rhizomes

The sprouting of immature and half-dormant mature bulbils andrhizomes in some species of Dioscorea was promoted by treatmentwith inhibitors of protein synthesis, although the sproutingof completely awake mature bulbils was inhibited. Gibberellicacid (GA₃) inhibition of the sprouting was relieved by cycloheximideand some base and amino acid analogues. Polyphenol oxidase activity in the bulbils decreased after incubationwith the protein-synthesis inhibitors. Possible involvement of protein synthesis in inducing dormancyof Dioscorea bulbils is discussed. (Received July 11, 1977; )     

Dormancy in bulbils of several herbaceous plants: Effects of photoperiod,light, temperature,oxygen and gibberellic acid

Effects of some environmental conditions (photoperiod, white and colored lights, temperature, partial oxygen pressure) and growth regulators (gibberellic acid, 2-chloroethyltrimethylammonium chloride) on induction and release of dormancy of the bulbils ofDioscorea batalas, Laportea bulbifera, Elatostema involucratum andSedum bulbiferum were investigated. Bulbils were formed under short-day conditions inLaportea andElatostema, under long-day conditions inSedum, and irrespective of photoperiods inDioscorea. In all species exceptSedum, immature bulbils required light, particularly blue or far red, for sprouting (photo-sprouting stage), and mature bulbils required a cold treatment (thermo-sprouting stage). The duration of photo-sprouting and thermo-sprouting stages and the degree of dependency on light or low temperature of sprouting differed from species to species. Sprouting of chilled mature bulbils of these species was promoted by light, especially by red or green light. Both immature and mature bulbils ofSedum sprouted under short-day conditions. Continuous irradiation with blue, far-red and green light markedly inhibited their sprouting. Oxygen at high concentration inhibited the sprouting of immature bulbils inDioscorea; in the other species it promoted sprouting regardless of the maturation of the bulbils. Applications of gibberellic acid caused the sprouting of bulbils the absence of light, chilling or photoperiodic treatment in all species exceptDioscorea, in which gibberellic acid inhibited sprouting. Polyphenol oxidase activity was very high in the homogenates ofDioscorea bulbils, and increased further when the bulbils had been treated with gibberellic acid. In the other species, little or no such activity was observed.     

Gibberellin-induced dormancy in bulbils of Dioscorea

Summary The sprouting of bulbils of some plants in genus Dioscorea was inhibited by gibberellin (GA) treatment and was promoted by treatment with growth retardants. The results suggest that endogenous GAs in some manner induce and maintain the dormant state in these bulbils.     

Dormancy in Dioscorea: Generality of gibberellin-induced dormancy in asexual dormant organs

Effects of GA₃ and CCC application on the sprouting of bulbilsor subterranean dormant organs of 10 species in the genus Dioscoreawere observed. Although the efficiency of both chemicals differedby species, in general GA₃ inhibited and CCC promoted the sproutingof the above dormant organs. In some species, however, dilutedGA₃ (0.003–0.3 µM) has a promotive and diluted CCC(3–30 µM) has an inhibitive effect on sprouting. Effects of GA₃ application on shoot elongation were tested onsprouted bulbils. GA₃ promoted elongation when applied directlyto the shoots and inhibited it when applied to the bulbous parts. These results suggest that GA activates two opposing reactions—sprouting-promotingand sprouting-inhibiting—in these organs. The complicatedrelation between GA₃ or CCC concentrations and sprouting wereexplainable by assuming that the two counteractive reactionswere activated by GA in different degrees. ¹ Present address: Department of Biology, Faculty of Science,Yamagata University, Yamagata 990, Japan. (Received June 21, 1976; )     

Dormancy inDioscorea: Different temperature adaptation of seeds,bulbils and subterranean organs in relation to north-south distribution

Temperature dependencies of sprouting and germination were compared for subterranean perennating organs and seeds of ten closely related species of the genusDioscorea (Dioscoreaceae), a group of monocotyledonous summer perennials which are distributed from the tropics to the subarctic. The species used wereD. nipponica Makino,D. tokoro Makino,D. japonica Thunb.,D. tenuipes Franch. et Savat.,D. septemloba Thunb.,D. quinqueloba Thunb.,D. izuensis Akahori,D. bulbifera L. f.spontanea (Makino) Makino et Nemoto,D. pentaphylla. L. andD. alata L.; they are distributed from cold northern areas to warmer southern areas approximately in this order in and around Japan. Bulbil sprouting was also studied in those forming bulbils. Subterranean organs of the tropical species sprouted faster without any prior temperature treatment, whereas those of species from the more northern areas sprouted after prechilling. Northern species required longer, periods of prechilling for sprouting. On the other hand, with seeds or bulbils, the southern species required longer periods of prior temperature treatment for dormancy breaking. This difference in the length of dormant periods between seeds or bulbils and subterranean organs among the ten species may be related to their size and position of shedding; seeds or bulbils are small and are shed on the ground surface, whereas subterranean organs are large and are located below the surface. It is important to determine in other perennials whether the above relation between dormant features of seeds or bulbils and subterranean organs are common properties or not.     

Comparative Observations on the Polarity of Sprouting of Bulbils of Dioscorea bulbifera L. and Dioscorea alata L.

The sprouting process of aerial bulbils of D. bulbifera andD. alata was compared. In D. alata, sprouts originated normallyfrom the proximal pole, at or near to the point of abscision,and irrespective of moisture, light or orientation of the bulbil.In D. bulbifera, sprouts originated primarily in response tomoisture and were less influenced by polarity. Post-harvesttreatment with gibberellic acid delayed the sprouting of bulbilsof D. alata but not of D. bulbifera; treatment with 2-chloroethanolor ethanol promoted sprouting in both species. Physiologically,sprouting was characterized by a transient increase in respiratoryrate at the onset of, or just prior to, sprout emergence. Thepromotion of sprouting by chloroethanol was accompanied by asurge in respiratory activity. Dioscorea spp., yams, bulbil germination, polarity     

Variation of Abscisic Acid and Batatasin Content in Yam Bulbils--Effects of Stratification and Light Exposure

Batatasin content of yam (Dioscorea batatas Decne.) bulbilsdecreased slowly during 5 month stratification at 4°C, whileit remained virtually unchanged when stored at 23°C. Abscisicacid increased considerably during the 1st month at 23°Cbut only slightly at 4°C and thereafter remained constantup to the end of the 5-month storage period. On transfer to sprouting beds at 23°C the batatasin contentof stratified bulbils decreased sharply but that of non-stratifiedbulbils showed only slight variation. Light exposure duringsprouting tests suppressed the sprouting of the non-stratifiedbulbils but promoted that of the stratified ones. The changesin batatasin contents were found when the bulbils were exposedto light and this is discussed in relation to sprouting responsesto light. A scheme for batatasin economy in bulbil dormancyis proposed.     

Rise in the Ratio Heavy to Light Extractable Ribosomal RNA during Sprouting of Birdcherry Buds

Using the diethyl pyrocarbonate method, nucleic acids have been extracted from buds of European bird-cherry (Prunus padus L.) in different developmental stages and analysed by sucrose gradient centrifugation. The ratio heavy to light ribosomal RNA was about I in extracts from dormant and non-dormant but slowly growing buds. In extracts from sprouting buds the ratio was about 1.7. This increase probably reflects an increased extractability of heavy ribosomal RNA and may depend on a change of ribosomal structure during sprouting.     

The Production of Plantlets from Tissue Cultures of Brussels Sprout (Brassica oleracea L. var gemmifera D.C.)

Shoots were induced on callus derived from sprout sections andpetiole slices of an inbred parent line of Brussels sprout (Brassicaoleracea L. var gemmifera D.C.). The shoots, when excised andtransferred to fresh medium, enlarged and formed roots. Theseplantlets could be transferred to soil or their number increasedby a multiplication process involving the production of newshoots from the dormant lateral buds. Some of the plantletsderived from sprout callus were grown to maturity in the fieldand their morphology and chromosome number compared to seedgrown plants. There were no significant differences in sproutsize and stem diameter but there were significant differencesin plant shape. None of the plants in the field experiment showedpolyploidy. Plants derived from callus possessed an enhanced ability toform callus and redifferentiate when sections from these plantswere placed back on to nutrient medium.     

Adaptive significance of sprouting ofEuptelea polyandra,a deciduous tree growing on steep slopes with shallow soil

We investigated growth characteristics ofEuptelea polyandra Sieb. et Zucc. (Eupteleaceae), a Japanese endemic deciduous tree species growing on unstable ground such as that of very steep slopes with thin soil.Euptelea polyandra began to sprout at the juvenile stage and had a multiple-stemmed tree form. There was a positive correlation between diameter of the maximumsized stem within a stool (DMS) and the number of stems within the stool. Many stools had suffered from disturbances as shown by the fact that uprooting scars were found on 31.4% and 42.4%, respectively, of the stools of the two populations studied. Sprouting played a significance role in repairing damaged stems and stools, and at least 15.5% and 18.2% of the stools of the two populations, respectively, had apparently avoided death by sprouting. Sprouted stems gradually inclined with the increase in their relative sizes within each stool, and this seemed to facilitate the establishment of younger sprouted stems. The small younger sprouted stems had their own roots. There were dormant buds on stems which originated from axillary buds, and secondary dormant buds occurred by branching. The total number of dormant buds in a stool increased with DMS. It is concluded thatE. polyandra accumulates dormant buds for sprouting in order to respond to disturbances quickly.     

Seasonal variation in antioxidant enzymes and the sprouting response of Gmelina arborea Roxb. nodal sectors cultured in vitro

Nodal sector explants of Gmelina arborea Roxb. showed seasonal variation in the sprouting of axillary buds in vitro. Explants from mature trees showed only 20% sprouting in summer, while those from seedlings and young trees showed over 85% sprouting in this season. In winter, there was a significant decrease in the sprouting response of explants from young and mature trees but not in that of seedling explants. We have attempted to correlate the sprouting response of the explants with their antioxidant status. Activities of three enzymes, namely ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase which form a part of the antioxidant defense system of plants, were studied in the excised nodal sectors before and after placing them on culture medium. Prior to culture, higher activities of ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase were observed during winter than during summer. During the culture period, ascorbate peroxidase, superoxide dismutase and guaiacol-dependent peroxidase showed variation depending on the season in which the explants were isolated, and the age of the donor. Axillary bud sprouting in vitro appeared to depend more on the physiological state of the donor, than on the oxidative stress generated during culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

In Vitro Multiplication of Sesame (Sesamum indicum) through Tissue Culture

Tissue cultures were established from different parts of sesame(Sesamum indicum L. cv. PT) seedlings. A callus tissue derivedfrom hypocotyl segments produced embryo like structures. Shoottips with cotyledons excised from 8 to 10-d-old seedlings producedmultiple shoot buds on a cytokinin-enriched medium. Presoakingand germination of seeds in BA or 2iP (8 mg l–1) enhancedthe development of shoot buds. Upon isolation and culture theshoots buds formed rooted plantlets in a charcoal-enriched medium. Sesamum, multiple buds, plantlets     

Basipetal Gradient of Axillary Bud Inhibition Along a Rose (Rosa hybridaL.) Stem: Growth Potential of Primary Buds and their Two Most Basal Secondary Buds as Affected by Position and Age

InRosa hybridaL. cv. Ruidriko ‘Vivaldi’®, theeffect of position on growth and development potentials of axillarybuds was investigated by single internode cuttings excised alongthe floral stem and its bearing shoot. The experiments werecarried out in both glasshouses and in a phytotron. The studyfirstly concerned the development of the primary shoot fromthe onset of bud growth until anthesis. The primary shoot wasthen bent horizontally to promote the growth of the two mostproximal secondary buds, the collateral buds, already differentiatedinside the primary bud. They gave rise to basal shoots. In thebasipetal direction, the axillary buds along the floral stemexhibited both an increase in the lag time before bud growthand a decrease in bud growth percentage, demonstrating the existenceof a physiological basipetal gradient of inhibition intrinsicto the buds or due to short range correlations. The same basipetalgradient of inhibition was observed along the floral stem andits bearing shoot, demonstrating that the age of the bud wasnot a major factor in determining the rate of bud growth. Afterbending the primary shoot, the percentage of collateral budgrowth was also affected by the cutting position. The more proximalthe cutting, the lower the sprouting ability of collateral buds.The growth potential of these buds appeared to be already determinedinside the main bud before cutting excision.Copyright 1998 Annalsof Botany Company Axillary bud; basal shoot; cutting; development; endodormancy; growth; paradormancy; position; primary shoot;Rosa hybridaL.; rose; secondary bud; topophysis.     

Hemicellulosic Polysaccharides from the Xylopodium of Ocimum nudicaule: Changes in Composition in Dormancy and Sprouting

Changes in the yield and composition of hemicelluloses fromthe underground organs (xylopodia) of Ocimum nudicaule wereinvestigated. Hemicelluloses constituted about 12% of the delipidizedpowder in sprouting and about 30 % in dormant phases. Xyloseis the major component of hemicelluloses A and B (and is alsopresent in C), followed by arabinose, galactose, glucose, rhamnoseand mannose. The amounts of hemicellulose B decreased by sixtimes between dormancy and sprouting, whereas the yields ofhemicelluloses A and C remained constant. This, together withthe higher solubility of hemicellulose B and its higher susceptibilityto hemicellulase in sprouting indicates that this fraction constitutesa cell-wall bound storage polysaccharide, which may play a rolein the onset of xylopodia bud sprouting. Ocimum nudicaule, hemicelluloses, cell-wall storage polysaccharide     

Loss of short-day requirement for dormancy breaking of bulbils from gibberellic acid-treated plants in Sedum bulbiferum

Sedum bulbiferum forms bulbils at superterranean nodes under long-day conditions, and the detached bulbils sprout after exposure to short-days [1]. When gibberellic acid was applied to the mother plant at the start of the long-day induction period, the number of bulbils formed increased slightly and these bulbils sprouted on incubation in the dark but not under short days of continuous light. However, when gibberellic acid was applied directly to detached bulbils during incubation, the short-day requirement for sprouting was conserved. Gibberellic acid application to the mother plants enhanced sprouting ability of detached bulbils when incubated under illumination with blue, green or far-red light. However, presence of gibberellic acid during bulbil exposure to light did not induced marked enhancement in sprouting under blue, green of far-red light. Thus, gibberellic acid application to the mother plant modified light and photoperiodic requirements for the sprouting of detached bulbils of S. bulbiferum.     

Analysis of Cycles of Dormancy and Growth in Pea Axillary Buds Based on mRNA Accumulation Patterns of Cell Cycle-Related Genes

Axillary buds of pea (Pisum sativum L. cv. Alaska) do not growon intact plants. Dormant axillary buds can be stimulated togrow rapidly after decapitation. Here, we isolated cDNAs ofPCNA, cyclinB, cyclinD, and cdc2 from pea. The mRNA expressionlevels of these genes were very low in dormant axillary buds,whereas they remarkably increased after decapitation. Basedon the mRNA accumulation patterns of these genes, we found thatmost cells in dormant axillary buds are arrested at the G₁ phasein the cell cycle. There are four buds at the second node onpea seedlings. After decapitation, mRNAs became abundant inthe large and small buds and were kept during the following3 d. After 4 d, mRNAs were still present in the large bud, butnot in the small bud. However, after removal of the large bud,the mRNA levels started to increase again in the small bud.These mRNA accumulation patterns were the same as those afterthe first decapitation. These results suggested that most cellsin axillary buds at the second node are arrested at the G₁]phase again and have the capacity to undergo multiple cyclesof dormancy and growth. Moreover, in situ hybridization analysesdemonstrated that PCNA mRNA increased in all parts of the axillarybuds after decapitation. (Received October 31, 1997; Accepted December 11, 1997)     

Rates of Mitosis in Shoot Apices of Potatoes at the Beginning and End of Dormancy

Rates of mitosis in regions of the shoot apices of potatoeshave been measured by accumulating metaphases under the influenceof colchicine. In sprouting buds excised from dormant tubersthe cell-doubling time is 74 h on the flanks of the meristemand 117 h at the summit. In stolons about to start tuberizationthe reduction in meristematic activity affects the flanks morethan the summit. At all stages the pith zone has the lowestrate of mitosis and the procambium the highest.     

Batatasins: New dormancy-inducing substances of yam bulbils

Summary Three growth inhibitors, for which the names batatasins I, II and III are proposed, occur in dormant yam bulbils. Application of these inhibitors suppresses the sprouting of bulbils, and the inhibition is reversible by low-temperature stratification. Batatasins I and III were isolated as crystals and partially characterized as phenotic compounds not identical with known inhibions.     

Hormonal Regulation of Seed Dormancy in Hazel (Corylus avellana L.) and Beech (Fagus sylvatica L.)

Dormancy in seeds of hazel (Corylus avellana L.) and beech (Fagussylvatica L.) has been studied with special reference to changesin growth-promoting and inhibiting substances during after-ripening.About 12 weeks at low temperature and under moist conditionsis necessary for complete after-ripening. Gibberellic acid,kinetin, and thiourea stimulate germination in dormant seedsbut have no effect on nuts with the pericarp intact. Gibberellin‘D’ is ten times more active than gibberellic acid.Bio-assays, following chromatographic fractionation of seedextracts, have revealed no significant changes in the concentrationsof auxins and inhibitors during after-ripening. Dwarf maize-leafsection assays have revealed low concentrations of gibberellin-likesubstances in purified extracts of chilled, dormant hazel seedbut no gibberellin activity in extracts of dormant seed. Gibberellinsare present in both dormant and germinating beech seeds butthere appear to be differences in the chromatographic patternof activity. The possible role of endogenous gibberellins inthe after-ripening process is discussed.