Gibberellin-Auxin Interaction in Pea Stem Elongation

Abstract

Summlary. Joint application of gibberellic acid and indole-3-acetic acid to excised stem sections, terminal cuttings, and decapitated plants of a green dwarf pea results in a markedly synergistic growth response to these hormones. Synergism in green tall pea stem sections is comparatively small, although growth is kinetically indistinguishable from similarly treated dwarf sections.Gibberellin-induced growth does not appear to be mediated throtugh its effect on auxin synthesis, since gibberellin pretreatment of dwarf cuttings fails to elicit an enhanced tryptophan-induced growth response of sections, whereas auxin-induced growth is strongly enhanced. Also, tryptophan-gibberellin synergism is not significant in sections and cuttings of green dwarf peas, while auxin-gibberellin synergism is.Administration of gibberellic acid prior to indole-3-acetic acid results in greatly increased growth. In reversed order, the application fails to produce any synergistic interaction. This indicates that gibberellin action must precede aulxin action in growth regulation.Both gibberellins and auxins contribute to growth in length of excised etiolated Alaska pea epicotyl sections (4, 7, 16) and green pea stem sections (1,3) although gibberellin is less effective in green sections. \Vhen gibberellin and auxin are applied together to etiolated Alaska sections, growth is either equal to or less than the sum of the separate responses (17). This has led to the conclusion that gibberellin and auxin make independent contributions to stem growth throtugh different biochemical pathways. In contrast to these results, a small degree of atuxin-gibberellin synergism has been demonstrated in sections from Progress No. 9 pea seedlings grown in weak red light (21).Joint application of the 2 hormones to green pea tissuies, such as Alaska stem sections (3) and Meteor stem sections (1) results in a marked synergistic interaction between auxin and gibberellin, being more pronounced in the latter (dwarf) cultivar. These results, together with those derived from the petiole of single-node cuttings of sweet potato (11) indicate that gibberellin-induced growth is dependent on auxin. It thus appears that auxingibberellin synergism is a phenomenon characteristic of sections from dwarf peas, and is more

Blockage by Gibberellic Acid of Phytochrome Effects on Growth, Auxin Responses, and Flavonoid Synthesis in Etiolated Pea Internodes

“…It is also evident that the magnitude of the red light inhibition is very small in the absence of exogenous IAA ' (Fig. 2), increases to a maximum at concentrations (5 X 10-" M) substantially less than optimal for conitrol growth ( 16).…”

Genetic Dissection of the Relative Roles of Auxin and Gibberellin in the Regulation of Stem Elongation in Intact Light-Grown Peas

“…However, with the addition of exogenous IAA, applied GA manifested a specific growth response in these segments beyond the large response inducible by IAA alone; pretreatment with GA further enhanced the growth response of these segments to a subsequent treatment with IAA (Brian and Hemming, 1958;Ockerse and Galston, 1967;Ockerse, 1970;Reid and Davies, 1992). Clearly, these responses also occur in intact plants but are limited to IAA-deficient lkb dwarfs (Fig.…”

Functions of Hormones at the Cellular Level of Organization

“…synergos = working together) refers to the special case of interdependent interaction in which the effect of two promotive factors is more than the additive effect of each given separately. Examples of apparent synergistic promotive interaction between hormones include (1) the interaction of ethylene and ABA in the promotion or rice mesocotyl elongation (TAKAHASHI 1973), (2) kinetin enhancement of auxin-induced ethylene production in mung bean hypocotyls (LAL: et al 1977 a) and (3) GA3 enhancement of auxin-promoted elongation in cucumber hypocotyl and pea stem segments (OKERSE and GALSTON 1967). These are examples in which two factors cooperate to enhance a particular response and hence the term synergistic promotive interaction is appropriate.…”