Auxin-Gibberellin Interaction in Rice Coleoptile Elongation

Abstract

\Vhile, oIn present evidence, it is generally agreed that both auxin and gibberellin contribute to the con-trol of plant cell enlargement, the nature of their con-tributions is not known (1). Four hypotheses on their contributions, the first tlhree of which postulate that gibberellin's contribution is auxin-dependent while the fourth postulates independent contributions by auxin and gibberellin to cell enlargement, are as follows: 0 I. Galston (5, 6) suggested that gibberellin in-creased the concentration of a phenolic inhibitor (4) of the indoleacetic acid (IAA) oxidase system, there-by producing greater auxin concentrations in tissues. -II. From their comparison of the growth of in-tact and isolated pea internodles treated with gibberel-lin and auxin, Brian and Hemlming (2) postulated that gibberellin inhibits an endogenous inhibitor of auxin in(luced growth. R III. In an attempt to rationalize the interaction of the known classes of growth regulator in the con-trol of mlany growth processes, Kefford and Goldacre (8) proposed a scheme in wlhich auxin and gibberellin influenced sequential processes leading to cell en-largement, sucli that gibberellin was dependent upon auxin for its action and its contribution to enlarge-ment was proportional to the contribution by auxin. -IV. Purves and Hillman (14) proposed that auxin an(l gibberellin ma(le indlependent contributions