The Changing Concept of Auxin

Abstract

Kefford, N. P., and P. L. Goldacre. (Division of Plant Industry, C.S.I.R.O., Canberra, Australia.) The changing concept of auxin. Amer. Jour. Bot. 48(7): 643–650. Illus. 1961.—Recent findings in auxin research are interpreted as follows: The concept of auxin as only a cell‐enlargement regulator can no longer accommodate the variety of growth phenomena controlled by auxin. In isolated tissues, auxin interacts with gibberellin in the control of cell enlargement, and auxin and kinin interact in initiating cell division. Some evidence suggests a single site of auxin action for both processes. It is proposed that auxin is not a determining agent but a predisposing agent, causing the production of something in limiting amount which is required in both processes —in the presence of kinin, cell division is activated; in the presence of gibberellin, cell enlargement is activated. In the presence of limiting amounts of auxin, there could be competition between the 2 processes, the outcome depending on the balance of kinin and gibberellin. The possibility of competition in the presence of supraoptimal auxin concentrations is also suggested. Difficulties arise in the application of this concept to observations on intact plants, where cause and effect relationships are not readily established; the use of excised plant parts shows the relationships more clearly. The role of auxin in cell and organ differentiation is also discussed. The primary auxin reaction is not yet known. The biological assay for auxins is discussed with reference to this and to natural auxins. The function of auxin in the correlation of tissue and organ growth through the auxin transport system is stressed, and it is pointed out that if transport is a necessary requirement of a native auxin, indole‐3‐acetic acid is at present the only substance known to qualify.

Plant Growth in Relation to Endogenous Auxin, With Special Reference to Cereal Seedlings

“…In fact, the generalization was based upon the second dictum rather than on experimental data: if more auxin induces more growth, then ipso facto more growth must signify more auxin. Earlier observations of Laibach and Meyer (1935) and of Fiedler (1936) which apparently demonstrated that growth could occur in the absence of extractable auxin were obviously at variance with the major precept 'without auxin, no growth'. In their important review of auxin physiology Went and Thimann (1937, pp.…”

Auxin-Gibberellin Interaction in Rice Coleoptile Elongation

“…R III. In an attempt to rationalize the interaction of the known classes of growth regulator in the control of mlany growth processes, Kefford and Goldacre (8) proposed a scheme in wlhich auxin and gibberellin influenced sequential processes leading to cell enlargement, sucli that gibberellin was dependent upon auxin for its action and its contribution to enlargement was proportional to the contribution by auxin.…”

The effect of hormones and chemical growth regulators on ear development and grain yield of nonprolific corn (Zea mays L.)

“…Kefford (1962) proposed that the contribution of exogenous GA to elongation of the rice {oryza sativa L.) coleoptile was dependent upon the auxin status of the coleoptile. This proposed scheme of GA action being dependent on auxin was also put forward by Kefford and Goldacre (1961). Phillips (1971a) has attempted to clarify the role of exogenously applied GA3 by showing that it can be a modifying factor in auxin-regulated apical dominance.…”

“…There are conflicting reports on the interaction between the action of gibberellins and auxins in plants (Galston, 1957;Brian and Hemming, 1958;Kato, 1958;Brian, 1959;Galston and McCune, 1961;Kefford and Goldacre, 1961;Kefford, 1962;Kuraishi and Muir, 1962;Sastry and Muir, 1963;Scott et al, 1967;Tanimoto et al, 1967;and Phillips, 1971a).…”