Inhibited Bud Formation Research Articles

Organ Regeneration on Excised Roots of Chondrilla Juncea and Its Chemical Regulation

The effects of endogenous factors (plant age, section length, and section location) and environmental factors (temperature and mineral nutrition) upon organ regeneration on isolated root sections of Ohondrilla juncea L. were used to develop a standard assay system for the study of the chemical regulation of regeneration. Bud and root formation and its polarity in the presence of a variety of regulators alone and in combinations were observed quantitatively. Bud numbers were increased by auxin (low concentrations), cytokinin, and gibberellin treatments. High concentra� tions of auxin inhibited bud formation and this effect was reversed by antiauxin, cytokinin, or gibberellin. Adenine did not counteract auxin� induced bud inhibition but adenine and N�6�benzyladenine did counteract inhibition induced by the purine antagonist 2,6�diaminopurine. Numbers of regenerated roots were increased by auxin treatment and reduced by cytokinin and gibberellin treatment. On control and auxin� treated sections, bud formation was strongly polar and proximal and cytokinin and gibberellin treatments lessened the polarity. Growth retardants inhibited regeneration. Of a number of synthetic auxins tested, 2,4.dichlorophenoxy. acet.O.methylhydroxamic acid and 4�amino.3,5,6.trichloropicolinic acid were the most effective inhibitors of bud formation.

Flower Formation in Excised Tobacco Stem Segments; I. Methodology and Effects of Plant Hormones

The formation of flowers has been studied in stem tissue excised from flowering plants of Nicotiana tabacum variety Wisconsin No. 38, and cultured in vitro on Murashige and Skoog nutrient medium. A procedure for quantitative evaluation of factors influencing floral expression has been developed and effects of the growth substances, indole-3-acetic acid (IAA), kinetin and gibberellic acid (GA(3)), on the process are reported.Although a low (1 mum) level of IAA was required for the development of normal flowers on stem segments, higher concentrations tended to inhibit flowering. The decrease in floral buds was rapid in the 3 to 15 mum range. IAA concentrations up to 75 mum increased vegetative bud formation so as to effect a transition from floral to vegetative buds rather than merely an inhibition of bud formation. Higher IAA concentrations inhibited both vegetative and floral bud formation.Kinetin in high concentrations greatly increased the number of vegetative buds but had no significant effect on the number of floral buds per segment. High kinetin concentrations also permitted branching of floral shoots so that flower clusters were formed.GA(3) applied in the medium from the start, strongly inhibited bud formation on the stem segments, but when applied to young floral buds after they had formed, it promoted their further development ("bolting").Flower formation occurred in complete darkness, but light of moderate intensity was required for the development of normal flowers.

Effects of chronic irradiation upon a self-incompatible clone ofLycopersicum peruvianum

Flovering plants from a self-incompatible clone ofLycopersicum peruvianum were exposed during 90 days to different dose-rates of gamma-rays ranging from 2 to 17 rad perhour. Irradiation was continuous, except for a daily interruption of 7 hours.Whereas irradiation at dose-rates higher than 7.50 rad per hour seriously inhibited bud formation and floral development, chronic exposure at dose-rates ranging from 3 to 7 rad/hour increased the number of seeds per plant. This stimulation is not due to a higher number of seeds per fruit but to a very significant rise in the number of fruits per plant. As irradiation treatment did not significantly increase the number of flowers per plant and did not appear to stimulate pollen tube germination in the styles, it is concluded that the recorded increase in fruit-setting essentially resulted from a radio-induced inhibition of the processes which control floral abscission in the absence of cross-pollination.Three plants with reduced self-incompatibility and one completely parthenocarpic individual were observed in theM 2 progeny but no evidence was obtained that irradiation could induce a permanent type of self-compatibility inL. peruvianum.

The induction of flowering in vitro in stem segments of Plumbago indica L.

Internode segments excised from vegetative stems of Plumbago indica, an absolute short-day plant, can be induced to form in vitro a callus, or roots, or vegetative shoots, or inflorescences and flowers. Callus formation was polarized when indolyl-3-acetic acid, L-tryptophane, naphthylacetamide, or 2,3-dichlorophenylacetic acid were incorporated into the medium, but not with isatin, phenylacetic acid or 2,4-dichlorophenoxyacetic acid (2,4-D). Roots without buds developed on cultures receiving 2,3-dichlorophenylacetic acid or 2,4-D in the presence of a cytokinin and adenine.Bud formation occurred generally when no auxin was present in the medium, although low concentrations of IAA encouraged bud formation (in the presence of a cytokinin and adenine). Various cytokinins strongly promoted bud formation, but adenine had to be present in the medium in addition. Adenine could not be replaced by adenosine, guanine, guanosine, cytosine, thymine or uracil. The presence of sugar (supplied in the form of various disaccharides) was necessary for bud formation, the concentration in the medium being critical. Long days inhibited bud formation, and so did three different gibberellins applied under short days. Several amino acids, glutamine, asparagine and riboflavine also tended to reduce budding.