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 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.     

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 in Laportea bulbils: experiments with buds cultured in vitro

Dormancy in bulbils of Laportea bulbifera was investigated usingbuds cultured in vitro. Buds excised from immature bulbils couldsprout in light, but scarcely in the dark. Regardless of lightconditions, buds isolated from mature bulbils failed to sproutwhile those from chilled mature bulbils could. GA and BA stimulatedthe sprouting of buds excised from dormant mature bulbils. Incontrast, ABA and morphactin inhibited the sprouting of budsexcised from nondormant chilled mature bulbils. These resultssuggest that, in dormant Laportea bulbils, the buds themselvesare in a dormant state which may be controlled by a balanceof activity between growth-inhibiting and -promoting substances. (Received October 29, 1976; )     

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.     

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     

Gibberellin-induced dormancy and batatasin content in yam bulbils

The sprouting of partially stratified yam bulbils was promotedby exogenous benzyladenine, cycocel (CCC) and indole-3-aceticacid and suppressed by gibberellin A₃(GA₃. Light exposure causedslight suppression of sprouting. GA₃ raised the content of batatasinsbut not that of abscisic acid. We suggest that the sprouting-inhibitingactions of GA₃ and light are exerted by raising the batatasinlevel in the bulbils. A possible mechanism of the natural dormancyinduction in yam bulbils was discussed. ¹This paper concerns K. H.'s Ph. D. dissertation presented toTohoku University based on work done at I.P.C.R. ² Present address: Biological Institute, Faculty of Science,Tohoku University, Sendai 980, Japan (Received May 25, 1973; )     

Histochemical Localization of Calcium Oxalate Crystals in Starch Grains of Yams (Dioscorea)

The bulbils and/or tubers of seven species of yams (Dioscorea)were examined for crystal content using light microscopy andhistochemistry. Calcium oxalate crystals in the form of raphide bundles werelocalized in the parenchymatous tissues. Within starch grains,crystals of various shapes and sizes were observed. The variationin shape and sizes of the intra-amylar crystals could be exploitedfor taxonomic purposes. Calcium oxalate crystals appear to serve a storage functionin these starch grains. Yams, Dioscorea, raphides, oxalate crystals, histochemistry     

The Origin, Development and Germination of Bulbils in Two Dioscorea Species

The origin, development and germination of aerial bulbils ofDioscorea alata and D. bulbifera are described and the significanceof the primary nodal complex (PNC) in bulbil ontogeny discussed.Further evidence is provided for the view that the PNC, or itsinitial, is the site of renewed growth in Dioscorea species. Dioscorea species, yams, bulbil germination, primary nodal complex     

Gibberellin-induced dormancy in Begonia aerial tubers. Increase of the growth inhibitor content by gibberellin treatment

Changes in the amount of growth inhibitors by gibberellin (GA)treatment in tubers of Begonia evaniana was studied. Acidic,neutral and basic ethyl acetate-soluble and n-butanol-solublegrowth inhibitors increased with GA treatment and also withthe progress of natural dormancy. These inhibitors suppressedthe sprouting of nondormant aerial tubers. The increase of neutralethyl acetate-soluble inhibitors in the GA-treated tubers wassuppressed by incubation in low-O₂ atmosphere. In early dormantstage tubers, the inhibitor increased remarkably during incubationat 28?C in light. The aerial tubers probably enter a dormantstate when sufficient amounts of inhibitors accumulate in them. (Received February 9, 1973; )     

Regulation of the Stoichiometry of Thylakoid Components in the Photosynthetic System of Cyanophytes: Model Experiments Showing that Control of the Synthesis or Supply of Chl a can Change the Stoichiometric Relationship between the Two Photosystems

Regulation of the assembly of the photosystem I (PS I) complexin response to the light regime in the photosynthetic systemof cyanophytes was studied in Synechocystis PCC 6714. The relationshipbetween the assembly of the PS I complex and synthesis of Chla was examined by model experiments in which synthesis of Chla was controlled by two inhibitors, gabaculine (GAB) and 2,2'-dipyridyl(DP). Both inhibitors caused a change to a lower ratio of PSI to PS II even under light that normally induces a high ratioof PS I to PS II. The change in stoichiometry induced by theseinhibitors was suppressed when protein synthesis was inhibitedby chloram-phenicol, similarly to the change in the stoichiometryinduced by light that excites mainly PS I (PS I light). Comparisonof the levels of PS I, PS II and Cyt b₆-f complexes per cellindicated that a selective suppression of the assembly of thePS I complex was induced by the inhibitors: the stoichiometricrelationship among PS I, PS II and Cyt b₆-f complexes was identicalto that induced by PS I light or white light of high intensity.GAB induced a decrease in size of the phycobilisome also, whileDP did not, similarly to PS I light. The results indicate thatthe ratio of PS I to PS II can be changed by the control ofsynthesis of Chl a. They also suggest that control of the synthesisor supply of Chl a probably exerted at site(s) in or after theprocess of the Mg-protoporphyrin branch, is involved in themechanism of regulation of the assembly of the PS I complexin cyanophytes. (Received September 7, 1989; Accepted November 20, 1989)     

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.     

Involvement of the Accumulation of Glutamine in the Initiation of Adventitious Buds in Stem Segments of Torenia

Active meristematic divisions in stem segments of Torenia culturedin vitro can be induced in the epidermis by application of cytokininor the calcium ionophore A23187 [GenBank] , resulting in the differentiationof adventitious buds. Endogenous free glutamine accumulatedat a high concentration in the epidermal tissues during theearly stages of such cultures. The accumulation of glutaminewas caused by an increase in glutamine synthetase (GS) activity,and the increase of GS activity was suppressed by the applicationof some inhibitors of GS activity, mRNA synthesis, protein synthesis,or calmodulin. Incorporation of these inhibitors into the culturemedium also inhibited initiation of adventitious buds. The inhibitoryeffect of an inhibitor of GS, methionine sulfoximine (MSX),was apparent only at the very begining of the culture, and theeffect could be overcome by the simultaneous addition of glutamine.The inhibitory action of MSX on initiation of buds seemed tobe caused by an accumulation of ammonium ions. Reduction inlevels of NH₄NO₃ in or its elimination from the culture mediumstimulated the initiation of adventitious buds. Therefore, boththe accumulation of glutamine and the reduction in levels ofammonium ions seem to play a role in the initiation of adventitiousbuds in stem., segments of Torenia. ¹Present address: Faculty of Agriculture, University of Saga,Honjo-cho, Saga, Saga, 840 Japan. (Received October 3, 1988; Accepted March 9, 1989)     

Gibberellic acid-induced prolongation of the dormancy in tubers or rhizomes of several species of East Asian Dioscorea

Effects of the application of gibberellic acid on sprouting of tubers or rhizomes were tested in seven species of the genus Dioscorea that are native to the temperate regions of East Asia. The lowest concentrations for significant inhibition of sprouting in these species varied from 0.1–1 µM Application of gibberellic acid at 100 µM inhibited sprouting for more than 500 days at 20 °C. Some responses to the application of gibberellic acid differed between species and between sections of the genus. In D. japonica, the application of gibberellic acid inhibited sprouting of tubers and bulbils while it promoted seed germination.     

The nature of gibberellin-induced dormancy in aerial tubers of Begonia evansiana

Four kinds of GA, GA₁, GA₂, GA₃, and GA₄, all inhibited sproutingin aerial tubers of Begonia evansiana. The sprout-inhibiting action of GA increased with incubationin a high O₂ concentration, and decreased in a low O₂ Concentration. Inhibition of sprouting by GA was reduced by incubation in thepresence of p-nitrophenol, resorcinol, salicylaldoxime, 2, 4-dinitrophenol,sodium azide and cycloheximide. The higher activity of polyphenol oxydase was observed in ahomogenate of GA treated tubers. Existence of counteracting two systems which were activatedby GA was considered. (Received January 13, 1972; )     

S-acylation regulates Kv1.5 channel surface expression

The number of ion channels expressed on the cell surface shapes the complex electrical response of excitable cells. An imbalance in the ratio of inward and outward conducting channels is unfavorable and often detrimental. For example, over- or underexpression of voltage-gated K⁺ (Kv) channels can be cytotoxic and in some cases lead to disease. In this study, we demonstrated a novel role for S-acylation in Kv1.5 cell surface expression. In transfected fibroblasts, biochemical evidence showed that Kv1.5 is posttranslationally modified on both the NH₂ and COOH termini via hydroxylamine-sensitive thioester bonds. Pharmacological inhibition of S-acylation, but not myristoylation, significantly decreased Kv1.5 expression and resulted in accumulation of channel protein in intracellular compartments and targeting for degradation. Channel protein degradation was rescued by treatment with proteasome inhibitors. Time course experiments revealed that S-acylation occurred in the biosynthetic pathway of nascent channel protein and showed that newly synthesized Kv1.5 protein, but not protein expressed on the cell surface, is sensitive to inhibitors of thioacylation. Sensitivity to inhibitors of S-acylation was governed by COOH-terminal, but not NH₂-terminal, cysteines. Surprisingly, although intracellular cysteines were required for S-acylation, mutation of these residues resulted in an increase in Kv1.5 cell surface channel expression, suggesting that screening of free cysteines by fatty acylation is an important regulatory step in the quality control pathway. Together, these results show that S-acylation can regulate steady-state expression of Kv1.5. quality control; potassium; channels; palmitoylation; posttranslational     

The Role of Growth Substances in the Regulation of Onion Bulb Dormancy

The correlation between sprouting and changes in endogenousgrowth substances was investigated in stored onion bulbs (Alliumcepa c.v. Rijnsburger and Lancastrian). In the main experimentsbulbs were removed from store at approximately fortnightly intervals,samples were assessed for percentage sprouting and non-sproutingbulbs were either extracted for hormone assay or treated withgrowth substances in an attempt to induce sprouting. In otherexperiments the hormone content of bulbs at different stagesof sprouting was assessed. Growth-inhibitor and gibberellinactivity decreased before sprouting, but there was an increasein gibberellin and auxin activity as sprouting commenced. Gibberellinactivity was highest in bulbs with well-developed sprouts whereasauxin activity occurred mainly in bulbs in which early sproutdevelopment was visible only on their being cut open. Therewas no conclusive evidence that bulb dormancy could be brokenby application of the gibberellins GA₃ and GA_4/7, or the auxin1-naphthylacetic acid (NAA). Maleic hydrazide (MH) completelyinhibited root and sprout development but the growth retardant(2-chloroethyl)trimethylammonium chloride (CCC) was mainly effectivein reducing root development and sprouting was only slightlyinhibited.     

The Effect of Growth in D2O on the Metabolism of Winter Rye

The metabolism of winter rye seedlings (Secale cereale, L. ev.Winter) cultured in 99.8 per cent D₂O was investigated. Comparedwith water-grown seedlings, the protein content was much lowerin the D₂O-cultured seedlings and the pattern of incorporationof [³H]leucine and [³H]phenylalanine into protein was substantiallydifferent. Seedlings cultured in D₂O incorporated [³H]thymidineinto DNA, but did not take up [³H]uridine. The results suggestthat some of the toxic effects of D₂O culture on higher plantscan be attributed to a partial block of protein synthesis.     

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.     

Alteration of Soybean Seedling Development in Darkness and Light by the Stay-green Mutation cytG and Gd1d2

The stay-green mutations cytG and Gd₁d₂ prevent the normal yellowingduring senescence of soybean (Glycine max) leaves and cotyledons.Because light plays such an important role in regulating morphogenesisand it promotes the formation of chlorophyll (Chl), we determinedthe effect of cytG and Gd₁d₂ (in a cv. Clark background) onthe development and some light responses of seedlings. AlthoughcytG and Gd₁d₂ seeds, particularly the cotyledons, are greenwhen mature, 44 and 71 % respectively of this Chl broke downwhen the seeds were germinated in darkness. Chlorophyllidesand phaeophytins were not present in the seeds in significantamounts. cytG and Gd₁d₂ as well as wild type (cv. Clark) seedlingsdeveloped a full etiolation syndrome (morphology and lack ofChl) in darkness. Light induced rapid Chl accumulation in thedark-grown seedlings with no apparent difference among the threeisolines. A short (8 h) exposure to light induced some Chl inthe cotyledons of dark-grown plants, and 22 h of light producedfour times more. Following return to darkness, the 8-h groupshowed very little breakdown over the next 12 d. After the 22-hgroup was returned to darkness, the wild-type lost Chl steadily,but Gd₁d₂ and eventually also cytG inhibited this breakdown.In the 22-h group, the Chl a/b ratio decreased in wild typeand cytG indicating preferential breakdown of Chl a relativeto Chl b; however, Gd₁d₂ prevented this change. cytG and Gd₁d₂seem to act preferentially on Chl breakdown rather than synthesis.Copyright1995, 1999 Academic Press Glycine max, soybean, chlorophyll, chlorophyll a/b ratio, cotyledons, etiolation, cytG, Gd₁d₂, mutations, senescence