Diffusible and Extractable Gibberellins in Bean Cotyledons in Relation to Dwarfisni

Dwarfism in bean plants (Phaseolus vulgaris L.) is investigated in relation to the diffusible and extractable gibberel-lins in cotyledonary tissues. These gibberellins were partitioned into four parts prior to thin layer chromatograplty: non-acidic and acidic ethyl acetate fractions, and non-acidic and acidic butanol fractions. Cotyledonary segments from a tall plant (cv. Kentucky Wonder) seem to diffuse, preferentially acropetally, more gibberellins in each fraction than those from a dwarf plant (cv. Masterpiece). The diffusion increases with the length of the segments and decreases with period after sowing. From experiments on extraetable gibberellins, however, it is concluded that these phenomena actually result from differences in the gibbereliin contents of the tall and the dwarf plants, from differences in the gibberellin contents of the distal and proximal parts of cotyledons, and from the gibberellin contents before and after imbibition. Ten kinds of gibberellin-Iike substances are detectable in the diffusates, exudates and extracts from the cotyledons of both the plants; two in the non-acidic ethyl acetate, three in the acidic ethyl acetate (GA₁, GA₆ and another), two in the non-acidic butanol, and three in the acidic butanol frac—tion. They are almost identical in quality in the dwarf and tall plants, but in the latter they are more abundant in the cotyledons, particularly in their distal part. With respect to the change in content during the period after sowing, the gibberellin-Iike substances are classified in three groups; unchanging, decreasing (GA₁, GA₆, others) and increasing (butanol soluble glucosyl esters and glucosides of gibberellins)-. The increase of glucose-bound gibberellins and the decrease of free gibberellins during the sowing period suggest the occurrence of conversion. This is obvious only in the tall plants. The gibberellin content in cotyledons is higher in the tall plant than in the dwarf plant. Thus, the marked hypocotyl growth in the tall plants may be dependent on the higher content of gibberellins in their cotyledons and on the higner rate of conversion from free to bound forms.     

Light Actions in the Germination of Cocklebur Seeds: V. EFFECTS OF ETHYLENE, CARBON DIOXIDE AND OXYGEN ON GERMINATION IN RELATION TO LIGHT

Esashi, Y., Hase, S. and Kojima, K. 1987. Light actions in thegermination of cocklebur seeds. V. Effects of ethylene, carbondioxide and oxygen on germination in relation to light.–J.exp. Bot. 38: 702–710. Effects of ethylene, CO² and O² on the germination of after-ripenedupper cocklebur (Xanthium pennsylvanicum Wallr.) seeds wereexamined in relation to pre-irradiation by red (R) or far-red(FR) light In order to remove the pre-existing Pfr, seeds weresoaked in the dark for various periods prior to light irradiationand gas treatments. Regardless of light, 0.3 Pa C₂H₄ promotedgermination at 23 ?C, but it strongly inhibited germinationwhen applied at 33 ?C, the optimal temperature for the germinationof this seed. However, delayed application of C₂H₄ during 33?C incubation stimulated germination independently of lightin a similar manner to that seen at 23 ?C. It is, therefore,suggested that the germination-regulating action of C2H4 iscompletely independent of phytochrome. In contrast, the germination-promoting effect of 3–0 kPaCO₂ was pronounced only when the seeds were previously irradiatedby R, regardless of temperature, suggesting that CO₂ actionto promote germination depends upon Pfr. A synergism betweenCO₂ and C₂H₄ at 23 ?C was observed only in the germination ofseeds pre-irradiated by R, while at 33 ?C an antagonism occurredindependently of light. The stimulation of C₂H₄ production byCO₂ was most striking in the cotyledonary tissue pre-irradiatedby R. However, the R-dependent enhancement of CO₂-stimulatedC₂H₄ production was negated by the subsequent FR and it wasnot found in the presence of 1-aminocyclopropane-1-carboxylicacid (ACC). Moreover, the R dependency of the germination-promotingCO₂ effect disappeared in the presence of C₂H₄. The R-dependentC₂H₄ production enhanced by CO₂ may thus be involved, at leastpartially, in some step of conversion from methionine to ACC. The germination-promoting effect of C₂H₄, but not CO₂, was enhancedby O₂ enrichment regardless of light. However, the germination-promotingeffect of pure O₂ itself appeared to depend upon pre-irradiationwith R Key words: Carbon dioxide, cocklebur seed, ethylene, far-red light, germination, oxygen, red light, Xanthium pennsyloanicum     

No contribution of the pentose phosphate pathway in dormancy-breaking of cocklebur seeds

The role of the oxidative pentose phosphate (PP) pathway in the dormancy-breaking of cocklebur (Xanthium pennsylvanicum Wallr.) seeds was investigated. D-[1-¹⁴C]-glucose or D-[6-¹⁴C]-glucose was fed to dormant and non-dormant lower seeds or to their axial or cotyledonary segments which were imbibed for different durations, and C₆/C₁ ratios of respired ¹⁴CO₂ as an index of the PP pathway activity were calculated. Contrary to expectation, there was no significant difference in the C₆/C₁ ratios between the dormant and non-dormant seeds or segments during a water imbition period of 24 h, although the PP pathway actually operated already in an early stage of water imbibition. Also concerning the activities of G6PDH and 6PGDH, the key enzymes of this pathway, no difference between the dormant and non-dormant seeds was found. It was thus concluded that, unlike other seeds, there is no contribution of the PP pathway to the regulation of dormancy of the cocklebur seed.     

Protein Synthesis in Dormant and Non-Dormant Cocklebur Seed Segments

Using the axial and cotyledonary segments of lower cocklebur (Xanthium pensylvanicum Wallr.) seeds, protein synthesis as shown by incorporation of radioactive leucine was examined in relation to their dormant status. During the first 9 h of water imbibition, the protein synthesis was higher in the dormant axes than in the non-dormant, after- ripened ones. When imbibed for more than 12 h non-dormant axes had a higher activity than dormant ones. This was also the case with the cotyledonary segments. Cyctoheximide, an inhibitor of protein synthesis, blocked protein synthesis in the axial tissue regardless of its dormant status, and thereby inhibited germination of the non-dormant seeds. In the dormant seeds, however, cycloheximide at 3 mM slightly stimulated germination without stimulating the C₂H₄ production. Based on these results, it is suggested that in cocklebur seeds there may be some proteinaceous system which is involved in the maintenance of dormancy.     

STUDIES ON THE FORMATION AND SPROUTING OF AERIAL TUBERS IN BEGONIA EVANSIANA ANDR. X. TUBERIZATION UNDER LONG-DAYS AND IN DARKNESS

1. Aerial tuber formation of Begonia evansiana Andr. known totake place usually in response to short-day conditions occurredalso under long-day conditions, provided a part of the photoperiodswas maintained at a lower temperature (chillng). Such a changeof the critical daylength was marked in degree when the chillingtemperature was from 9° to 13°. The effectiveness ofthe chilling was more pronounced when it was given during thelater part of photoperiods, namely, just before nyctoperiods,than when given during the early part. No promotion of the chillingeffect by sugar application was found. 2. If the plant was previously subjected to chilling under illumination,aerial tuber formation occurred in continuous darkness. Themagnitude of this dark tuberization increased with decreasingthe temperature and with prolonging the duration of the chilling. 3. If the plant was previously exposed to chilling, aerial tuberformation occurred in response to a single photoperiodic cycle,whose critical dark length was shorter than that in the standardcondition. The magnitude of the tuberization was increased withthe prolongation of the chilling period. The effectiveness ofthis previous chilling survived over one day even under illuminationand a temperature of 30°. In a plant unexposed to the chilling,tuber formation required at least two cycles of short-days. 4. The aged plant which is known to tuberize in darkness wasunable to respond to a single short-day. 5. Upon a modification of Gregory's scheme of the process ofshort-day response, the above findings were inclusively explained. (Received August 2, 1963; )     

STUDIES ON THE FORMATION AND SPROUTING OF AERIAL TUBERS IN BEGONIA EVANSIANA ANDR. IX. EFFECTS OF TEMPERATURE ON TUBER INITIATION

The effects of temperature on the aerial tuber initiation ofBegonia evansiana Andr. in response to short-day condition wereinvestigated. Tuberization was inhibited by relatively low and high temperaturesduring the dark periods. The optimal nycto-temperature was 23°and hardly changed by not only photo-temperature but also daylength.There were two temperature-sensitive phases in the dark period;one came at its beginning, and the other later one came at varioustimes depending on the length of the light period. Low temperatureswere effective at both of these sensitive phases, but high temperatureshad an influence only at the later one. Photo-temperatures exerted little influence on tuberizationunder the sub-optimal daylength, but the lower temperatureswere promotive under longer daylengths. (Received August 2, 1963; )     

Stimulation by Ethylene of Axis and Hypocotyl Growth in Bean and Cocklebur Seedlings

Effects of ethylene on the elongation of bean (Phaseolus vulgaris) embryonic axes and hypocotyls, and of cocklebur (Xanthium pennsylvanicum) hypocotyls were studied. In the bean axes, exogenous ethylene was promotive in stimulating longitudinal growth during the early germination period, but thereafter it turned inhibitive. This transition of the ethylene action is likely involved in the appearance of newly differentiated tissues in the hypocotyl, which are negatively sensitive to the gas. The ethylene stimulated elongation of the axes was hardly affected by light or by the presence of the cotyledons. In the bean hypocotyl segment unit, elongation was stimulated by ethylene in its limited zone, when the concentration of ethylene and the exposure times to ethylene were adequate (0.3 to 30 μl/l, 6 to 8 h): Elongation in the much younger region near to the elbow was inhibited by ethylene treatment, whereas the treatment of the upper region of the shank with ethylene finally resulted in significantly increased growth as compared to the untreated controls. In the continuing presence of ethylene over 3 days, the elongation of every region was retarded markedly and radial growth was induced in most regions of the shank from just below the elbow. These ethylene responses occurred independently of red light irradiation, but the ethylene promotion of elongation was lost by shortening the segment height, by removing the hook portion from the segment unit, or with its natural disappearance as a result of ageing. Fundamentally, similar effects of ethylene was observed in cocklebur hypocotyls.     

A bimodal germination response to temperature in cocklebur seeds. I. Cyanide-sensitive and cyanide-resistant respirations

Abstract. Pre-imbibed cocklebur ( Xanthium penn-sylvanicum Wallr.) seeds displayed bimodal germination-temperature responses with two optima at 8 and 33° C. Such germination responses occurred subsequent to bimodal respiration-temperature upsurges at lower and higher temperature regions. At lower temperatures, cocklebur seeds respired predominantly through a cyanide-sensitive cytochrome pathway. A rise in temperature resulted in a marked increase in flux via an alternative pathway, a propyl gallate- (PG) or benzohydroxamic-acid- (BHAM) sensitive pathway, thus resulting in an increase in the ratio of this pathway relative to the cytochrome pathway. Both an increased capacity for the alternative pathway and an increase in the ratio of this pathway to the cytochrome pathway were obtained when pre-imbibed seeds were exposed to either 8 or 33°C for a short period. The effects of low temperature were reduced as the exposure time was prolonged beyond 3d, resulting in a reduction in germination. Neither PG nor BHAM had an inhibitory effect on the chilling-induced germination, but the germination-stimulating effect of high temperatures was less pronounced in the presence of PG or BHAM. At high temperatures, on the other hand, KCN and NaN₃ were ineffective or, rather, slightly inhibited germination. It was thus concluded that low and high temperatures exert their germination-stimulating effects by an essentially similar manner which increases fluxes both via the cytochrome pathway and, especially, via the alternative pathway and, as a result, raises the ratio of the latter to the former.     

Reversal of ethylene action on cocklebur seed germination in relation to duration of pre-treatment soaking and temperature

Abstract At 23°C, both C₂H₄ and CO₂ stimulated the germination of freshly imbibed upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds, but C₂H₄, unlike CO₂, changed to an inhibitor of germination under some soaking conditions. However, when seeds were pre-soaked for more than several hours at 23 °C prior to treatment, C₂H₄ strongly inhibited their germination at 33 °C, the degree of inhibition increasing with the duration of pre-soaking. Maximum inhibition occurred at 1–3 cm³ m^?3 C₂H₄ when seeds were pre-soaked for 1 week; further increases of C₂H₄ concentration and pre-soaking period decreased the inhibitory effect. C₂H₄ was synergistic with CO₂ when C₂H₄ promoted germination, whereas it was antagonistic when inhibitory. Such a transition of the C₂H₄ action occurred at ca. 27 °C. Also 1-andnocyclopropane-1-carboxylic acid, a C₂H₄ precursor, inhibited the germination of pre-soaked seeds at 33 °C, although it promoted the germination at 23 °C. When pre-soaked seeds were prepared for germination by chilling at 8 °C for 3 d, the inhibitory effect of C₂H₄ on the subsequent germination was manifested even at 23 °C. The reversal of the C₂H₄ action from promotion to inhibition in cocklebur seed germination is discussed in relation to the engagement of two respiratory pathways in the imbibed seeds.     

Calcium Deposition in Idioblasts of Mulberry Leaves

Large, rounded idioblasts were observed in adaxial leaves ofmulberry plants; they were clearly distinguishable from epidermal,trichome and parenchyma cells. The size and density of idioblastsvaried according to leaf age. Cytological features of idioblastswere as follows: the outermost region (‘cap’) ofidioblasts was situated on the adaxial surface as a dome-likeprotrusion; a cylindrical protuberance extended from the capregion to the inner part of the idioblast; in idioblasts frommature leaves a crystal mass was suspended from the lower tipof the cylindrical protuberance. Elemental analysis of idioblastsdemonstrated that silicon (Si) was localized in both the capregion and the cylindrical protuberance but calcium (Ca) waspresent in the large crystal, indicating site-specific cellularlocalization of Ca and Si within an idioblast. Histochemicalassays showed that a distinct Ca crystal filled the vacuolesof idioblasts in mature leaves, while immature leaves had manyidioblasts without Ca deposition. The increase in the Ca contentof leaves was directly proportional to the increase in leafage and appeared to be closely related to the Ca sink capacityof the developing idioblast vacuoles. The maximum sink capacitywas quantified to be approximately 40 ng per idioblast whenmulberry plants were grown hydroponically with excess Ca.Copyright1999 Annals of Botany Company Morus alba, idioblast, Ca deposition, Ca sink capacity, silicon, X-ray microanalysis, histochemistry, scanning electron microscopy.