Dormancy and Impotency of Cocklebur Seeds: VII. Inability of Dormant Cotyledons to Form Chlorophyll

Dormant seeds of cocklebur (Xanthium pennsylvanicum Wallr.) were characterized by the lack of ability to form chlorophyll. Such an inability of cotyledons of the dormant seeds was improved by the application of various factors and reagents which were capable of breaking the dormancy and of increasing cotyledon enlargement. Of these, ethylene, benzyladenine, and high temperature treatments were particularly effective, and, in turn, oxygen enrichment, gibberellic acid, thiourea, carbon doxide, and potassium nitrate were also promotive to the greening of the dormant cotyledons. The effects of benzyladenine, oxygen enrichment, and high temperature were reduced in the presence of absorbents for endogenously evolve carbon dioxide and ethylene. δ-Aminolevulinic acid could not restore their greening ability.     

Dormancy and Impotency of Cocklebur Seeds VIII. Lack of Germination Responsiveness in Primarily Dormant Seeds to Cyanide, Azide, Anoxia and Chilling

Germination responsiveness to KCN, NaN₃, chilling or anoxiaand respiration activity was compared between non-after-ripenedand after-ripened upper cocklebur (Xanthium pennsylvanicum Wallr.)seeds. The latter, coat-imposed dormant seeds, could germinatein response to the above chemicals and conditions, whereas theformer, primarily dormant seeds, could not respond. There waslittle difference in the respiratory properties of both typesof seeds. (Received June 22, 1981; Accepted October 30, 1981)     

Dormancy and Impotency of Cocklebur Seeds. IX. Changes in ACC-Ethylene Conversion Activity and ACC Content of Dormant and Nondormant Seeds during Soaking

Differences in ethylene production between dormant (D) and nondormant(ND) lower seeds of cocklebur (Xanthium pennsylvanicum Wallr.)were studied with respect to changes in the activity of conversionof 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene andin the contents of ACC and malonyl-ACC in their axial-tissuesduring soaking. Superior ethylene production in ND seeds ascompared to D seeds became evident during a soaking period rangingfrom 12–24 h, when the radicle protrusion in ND seedshad not yet occurred. Ethylene production in ND seeds increasedabruptly after the radicle protrusion. The inhibitors of ethyleneproduction, aminoethoxyvinyglycine, cobaltous ion and -aminoisobutyricacid, inhibited the germination of ND seeds, whereas ACC enabledD seeds to germinate. Activity of ACC-ethylene conversion was absent in dry axialtissues and developed with soaking. After 24 h, this activityin ND axes was superior to that in D axes. Under hypoxia, however,the difference in the ACC-conversion activity appeared before24 h. On the other hand, the contents of ACC in both D and NDaxes remained almost unchanged until 24 h of soaking. It isthus suggested that the inferior ethylene production in D seedsis associated mainly with their low activity of ACC-ethyleneconversion, though partly with their low activity of ACC supply. Activity of ACC-ethylene conversion in the axes of ND seedsincreased sharply after radicle protrusion which occurred after24 h of soaking. Correspondingly, the contents of both ACC andmalonyl-ACC increased in the axes of germinated ND seeds. Theseimply that the high ethylene production in the ND seeds in thepost-germination period comes from the increasing activitiesof ACC supply as well as ACC-ethylene conversion in their axes. Key words: Cocklebur seeds, Dormancy, Ethylene production, 1-aminocyclopropane-1-carboxylic acid, Germination, Xanthium     

Dormancy in Seeds of Charlock (Sinapis arvensis L.): Early Effects of Gibberellic Acid on the Synthesis of Amino Acids and Proteins

Charlock (Sinapis arvensis L.) seeds were imbibed with 10 mm GA(3) for 24 hours at 0 C. After equilibration at 25 C, a 5-fold increase in radioactivity in the amino acids labeled from 2-(14)C-acetate was observed within 2 hours. The total amount of amino acids was reduced to half, and the specific radioactivity increased approximately 10-fold, indicating a diversion of metabolites for amino acid and protein synthesis in GA(3)-treated seeds. The rate of incorporation of l-(14) C-leucine into protein was doubled. Autoradiographs showed that enhancement of protein synthesis was localized in the shoot and root meristems, the developing vascular tissues, and in the endosperm cells inside the testa.     

The Influence of Gibberellic Acid and Temperature on the Growth Rate of Avena sativa Stem Segments

A micro-growth measuring technique was used to determine the growth response of stem segments of Avena sativa cv. Avon to a variety of gibberellic acid (GA₃) concentrations over a range of incubation temperatures. Growth rate varied with GA₃ concentration, the temperature at which the rate was measured, and the growth temperature of the plants prior to excision of the segments. The curves relating segment extension rates to temperature were affected by GA₃ such that the linear portion of the curve was shifted to higher rates as GA₃ concentration was increased. The results seem to be analogous to the GA₃-induced shifts of thermally induced phase transitions in glucose leakage from liposomes, observed earlier (Wood, Paleg 1974 Aust J Plant Physiol 1: 31-40).     

Effects of Gibberellic Acid, Benzyladenine and 2-Chloroethylphosphonic acid (CEPA) on Growth and Fruit Abscission in the Cowpea (Vigna unguiculata L.)

Cowpea cultivars, Adzuki, Ife Brown and New Era, were raisedin a pot-soil experiment, under greenhouse conditions. Whenapplied as a foliar spray, none of the three growth regulators,gibberellic acid (GA), benzyladenine (BA) and 2-chloroethylphosphonicacid (CEPA), had any significant effects on the vegetative growthof either Adzuki or Ife Brown, CEPA, however, suppressed stemelongation and root dry weight, and also caused defoliation,in New Era. GA had no significant effect on fertility (defined as the proportionof the number of floral buds to those developing into mature,functional, seed-bearing pods). GA also had no significant effecton harvest index (expressed as the percentage of whole plantdry weight represented by seed dry weight) in the three cultivars.BA suppressed fertility in both Ife Brown and New Era, but hadno influence on Adzuki. CEPA was effective in controlling abscission in cowpea by reducingthe number of floral buds initiated, but enhancing the numberof functional pods set, in New Era. CEPA also enhanced harvestindex in this cultivar by increasing the absolute seed weightwithout affecting total plant dry weight. The implications ofthese observations on the physiology of the cultivars are discussedin relation to the problem of fruit abscission in the cowpeaplant. Vigna unguiculata L., cowpea, abscission, gibberellic acid, benzyladenine, 2-chloroethylphosphonic acid     

Ethylene Production, 1-Aminocyclopropane-l-Carboxylic Acid Content and Its Conversion to Ethylene in Axial Segments of Dormant and Nondormant Cocklebur Seeds

During the imbibition of water, the change in the ethylene productionof axial segments of nondormant (ND) cocklebur (Xanthium pennsylvanicumWallr.) seeds paralleled the change in the content of free 1-aminocyclopropane-l-carboxylicacid (ACC), but not the change in conjugated hydrolysable ACCin the axes. Aminoethoxyvinylglycine, anoxia and a-aminoisobutyricacid inhibited ethylene production, the lattertwo compoundscausing the accumulation of free ACC. Administration of ACCgreatly enhanced ethylene production in the axes. Thus, freeACC seems to be a direct precursor of ethylene production inthe axial tissue of cocklebur seeds. Imbibed dormant (D) axes characterized by inferior ethyleneproduction had less ability to convert exogenously applied ACCto ethylene as compared to ND axes. But, there was little differencebetween the D and ND axes in the endogenous contents of freeand conjugated ACC. This suggests that the inferior ethyleneproduction found in detached D axes is associated with the lowactivity of an ACC-ethylene converting system. (Received December 17, 1982; Accepted April 30, 1983)     

The Influence of Atrazine, Benzyladenine, and the Embryonic Axis on Chlorophyll Synthesis in Cucumber and Squash Cotyledons

Excision of the embryonic axis prior to 3 1/2 days of germination in the dark followed by 8-h of light decreased the total chlorophyll content of cucumber cotyledons but not squash cotyledons. Benzyladenine stimulated the accumulation of chlorophyll in the cotyledons of intact embryos and excised cotyledons in both cucumber and squash. Gibberellic acid had no effect. Atrazine inhibited chlorophyll formation in excised squash cotyledons. Benzyladenine also increased the carotenoid and xanthophyll content in the cotyledons from intact squash seedlings. The results suggest that pigment synthesis in cotyledons may be controlled by a number of substances produced in the embryonic axis and that cytokinin-like benzyladenine can simulate the action of one of them.     

The Effects of Gibberellic Acid and Scarification on the Seed Dormancy and Germination in Luzula spicata

Luzula spicata L. seeds are completely dormant at maturity. A germination inhibitor is present at the micropylar end. Normally, the only effective means of eliciting germination is a precise scarification of the micropylar end which inactivates the inhibitor. Exogenous application of gibberellic acid, kinetin, KNO₃, and thiourea have no affect on the dormancy of unscarified seeds. Scarification of the hilar end of the seed does not elicit germination, but when gibberellic acid is applied to the hilar scarified seeds moderate germination results. Presumably, these seeds are dormant due to a deficit of endogenous gibberellin; a condition which can be overcome by the application of gibberellic acid to seeds scarified at a site in itself ineffective in producing germination. Apparently the gibberellic acid serves to initiate amylase activity in the endosperm, overcoming the inhibitor block. Luzula spicata seed dormancy is apparently unique in that a germination inhibitor is operative in conjunction with the commonly recognized gibberellin-amylase mechanism.     

Diamine Oxidase Activity During the Germinative and Post-Germinative Growth of the Embryonic Axis in Chickpea Seeds

Diamine oxidase (DAO, EC 1.4.3.6.), which participates in oxidative catabolism of polyamines (PAs), was not detected in the dry viable chickpea (Cicer arietinum L.) seeds. From the time when the embryonic axis acquired an aerobic metabolism, DAO increased concomitantly with the growth of the embryonic axis and at the same time with the deterioration of the cotyledons, although in these organs the values were clearly lower than in the axis. The highest DAO activity in the embryonic axis of seedlings grown for 72 and 96 h was found in the elongation, differentiation and hypocotyl zones, while the lowest was in the apex and plumule. The absence of cotyledons promoted the early appearance of DAO in the embryonic axis. When germination occurred at supraoptimal temperatures (30 – 35 °C), DAO activity was sharply inhibited both in the cotyledons and in the embryonic axis. This inhibition was accentuated further in the presence of cyclohexylamine, an inhibitor of spermidine synthase activity, to such a degree that DAO was undetectable in the cotyledons. DAO inhibition by EGTA and the pronounced reversal induced by Ca²⁺ implies that calcium may be related to DAO activity. The presence of putrescine, spermidine and spermine in the germination medium stimulated DAO activity, although this activity was inhibited when the exogenous PA was cadaverine.     

An Analysis of the Effects of Gibberellic Acid on Tomato Leaf Growth

The effects of four consecutive daily sprays of gibberellicacid (GA₃) on the growth of leaves of young tomato plants cv.Potentate were studied. Total leaf weight and area were increasedby GA₃. The percentage changes were larger in the younger leavesthan in the older but the absolute increases of the middlleleaves accounted for most of the total response. Chlorophyllcontent, both total and per unit weight, was reduced by GA inthe older leaves and increased in the younger; on an area basisit was reduced in all but the youngest leaves. Palisade cell length and palisade cell number per unit sectionlength were reduced by GA₃ in the oldest leaves and increasedin the youngest. There were larger intercellular spaces in bothmesophyll layers and a larger transectional area of the mid-ribsof the oldest and two youngest leaves in GA₃ plants. The ‘surfaceareas’ of epidermal cells were also increased by GA₃ treatment.Leaf fresh weight per unit area was only a true index of laminathickness in the two oldest leaves.     

Effects of Gibberellic Acid on Growth and Parthenocarpy in the Dwarf Telephone Pea

Growth in height and production of seedless pods wore studied in Dwarf Telephone pea seedlings treated with relatively large amounts of the potassium salt of gibberellic acid applied in solution to leaflets. Such treatment produced a saturation in growth in height with 2 mg or more per plant when the plants were allowed to grow to maturity. Larger amounts caused no inhibitory effects on growth. Maximum growth with 1 mg per plant was attained only if the treated leaflets were left on the plant for about 14 days, at least, but increasing numbers of weekly 10-mg applications produced no additional growth affects beyond two applications. Increasing age of plants from 10 to 59 days of age at the time of single 10-mg applications per plant resulted in decreasing final heights. Gibberellic acid caused the formation of seedless pods a number of weeks after application, and deformed flower petals, elongated peduncles, and conspicuously inflated pods were associated with seedlessness. GA was most effective in inducing parthenocarpy when applied to the first true leaves of young seedlings and became progressively less effective with age. A complete absence of seeds in pods formed on the main plant axis was produced by one application of 10 mg GA per plant, while six applications were required for the suppression of seed formation on side branches.     

Effects of 2-Chloroethylphosphonic Acid and Gibberellic Acid on Sex Expression and Growth of Pumpkins

Treatment of pumpkin plants with 2-chloroethylphosphonic acid (CEPHA) induced a greater production of female flowers, shorter internodes and earlier fruit set while treatment with gibberellic acid (GA) induced a greater production of male flowers, longer internodes and later fruit set. Although CEPHA induced the production of a greater number of female flowers, the bulk of the flowers aborted and only a slight increase in the number of fruits per pumpkin plant occurred. The addition of equal concentrations of CEPHA and GA resulted in pumpkin plants with longer internodes and a greater number of female flowers than the untreated plants, although GA partially overcame the effect of CEPHA. The mode of action of CEPHA and GA on sex expression is discussed.     

Growth Regulators and the Phytochrome-Mediated Dormancy of Celery Seeds

Seeds of five celery (Apium graveolens L.) cultivars germinated at 15°C in the light or dark but at 22°C only in the light. This light requirement was overcome by treatment with a mixture of the gibberellins GA₄ and GA₇ (GA_4/7) but interactions of cytokinins, daminozide, ethephon, EDTA and N-phenyl-N′-4-pyridylurea (NC5392) with GA_4/7 were observed. Varietal differences in response to GA_4/7 concentration and the requirement for cytokinins were related to the upper temperature limits for germination of the different cultivars. Seeds of cultivars responding to low concentrations of GA_4/7 appeared to contain less natural inhibitor than those requiring either high concentrations of GA_4/7 or cytokinin in addition to low GA_4/7. The cytokinin requirement for germination was partially removed by leaching the seeds with water. Interaction studies with applied hormones indicated that in seeds incubated in the light inhibition by abscisic acid was partially alleviated by N⁶-benzyladenine but not by GA_4/7 application. The implications of these results are discussed in relation to the involvement of natural plant hormones in the dormancy mechanism of celery seeds.     

The Effects of Gibberellic Acid on Organelle Biogenesis in the Endosperm of Germinating Castor Bean Seeds

Mature seeds of castor bean (Ricinus communis L.) were imbibedin tap water or 0.3 mM GA₃, planted in vermiculite moistenedwith tap water or 0.3 mM GA₃, and incubated at 32 ?C. Duringthe course of germination, GA₃ promoted marked increases inthe activities of the glyoxysomal marker enzyme isocitrate lyaseand certain mitochondrial marker enzymes, but did not affectthe ER marker enzyme choline phosphotransferase. Glyoxysomaland ER protein and phospholipid were not increased in amountby GA₃, whereas mitochondrial protein and phospholipid were.SDS-polyacrylamide gels of the glyoxysomal matrix polypeptidesfrom GA₃-treated beans exhibited two polypeptides additionalto those found to be common to both GA₃-treated and controltissue. Incorporation of CDP-(methyl ¹⁴C)-choline into intactendosperm tissue and the distribution amongst the glyoxysomes,mitochondria, and ER of newly synthesized phosphatidyl-(methyl¹⁴C)-choline was unchanged by GA₃.     

The Effects of Boric Acid and Gibberellic Acid on the Growth of Fiber of Phragmites cormmuhis Trin

Water-cultured young plants of Phragmites communis Trin. were used in this experiment. They were treated with boric acid and gibberellic acid, separately or in combination, by method of foliage spraying. The results are summarized as follows: 1. In comparation with the controls, the length of the fibre cells was remarkably increased following the treatment with boric acid at concentrations ranging from 1 to 200 μmol/l. The optimum concentration of boric acid was found to be 100 μmol/l. Gibberellic acid alone at the concentration of 50 μmol/l also enhanced the length of the fibre cells. However, the best result was obtained in the group treated with a combination of boric acid and gibmberellic acid at a ratio of 200:50 μmol/l. A maximum increasement of fibre length and a greater ratio of length to width were observed in this experimental group. 2. Microscopic study indicates that the increase in both the number of the fibre cells and ,the thickness of the fibre layer are apparent in histological preparation. 3. In addition, The authors have also found that the incorporation of H3-glucose into the fibre cell wall was greatly enhanced by such combination treatment. 4. In conclusion, it has been demonstrated clearly that the boric acid and the gibberellic acid, when used in combination, produces an augmentative effect on both the growth and the development of the fibre cells of Phragmites communis Trin.