Auxin enhancement ethylene

Auxin enhances ethylene production in roots (Chadwick and Burg 1967,... 

Brassinosteroids are reported to stimulate overall plant growth and development, especially under stress conditions, to enhance auxin-induced growth as well as auxin-induced ethylene production (5, 6). Brassinosteroids interact with most of the phytohormones, such as cytokinins and gibberellins, and in particular with auxin. 

The most common effects of cytokinin, ethylene, and abscisic acid on stem and coleoptile cell elongation are inhibitory. They inhibit both auxin-enhanced... 

Ethylene as a stimulator of growth and development. The most observed actions of ethylene on growing plants involves growth inhibition, or acceleration of senescence. These actions are especially evident in the antagonism or opposition of ethylene to auxins, gibberellins and cytokinins (27), as already outlined above. Actually ethylene stimulates growth in many types of cells, especially in water plants (Table II). When ethylene acts to stimulate cell elongation, as in water plants, auxins and CC>2 enhance the ethylene effect (38,39). This interaction is the reverse of that observed on land plants wherein ethylene opposes the effects of auxin, GA3 and cytokinins. 

Auxins (67), gibberellins (68), cytokinins (69), and abscisic acid (67) can enhance the production of ethylene if added in concentrations that are generally considered stronger than tissue levels. Paradoxically, ethylene was one of the first chemicals identified as a potent defoliant (70), and now it has been shown to be a natural product of plant tissues that seems to regulate abscission (68, 71) as well as an influence on a host of other physiological reactions (7). 

Chloro-3-methyl-4-nitro-lH-pyrazole (Release) has no auxin-, gib-berellin-, or cytokinin-like activity, yet it is an ejffective abscission agent. At the present, there is no evidence to indicate that Release retards auxin, gibberellin, or cytokinin activity. It does stimulate and enhance the tissue production of ethylene (105). Release is fairly stable, and there is no indication that it is degraded by the tissue to ethylene per se (106). 

ABA enhances both the uptake and metabolism of GA in barley half-seeds (Nadeau et al. 1972) with the enhancement of metabolism apparently resulting from enhanced uptake (Stolp et al. 1973). In leaves of potato Solarium andi-gena) ABA causes as much as a 100-fold increase in GA activity (Railton and Wareing 1973 a), while in Solarium tuberosum, sprouts from ethylene-treated tubers contain high levels of GA (Dimalla and Van Staden 1977). In maize shoots ABA causes a reduction in GA (Wareing etal. 1968) while )ff-inhibitor preparations exert a similar effect in apices of birch (Thomas et al. 1965). Auxin causes an increase in the GA content of Chenopodium rubrum (Teltscherova 1970), an effect which may be related to flowering. 

Kinetin promotes the formation of ethylene in the elongation zone of eorn roots. Although enhancement of ethylene production by kinetin is greater than by auxin, Svensson (1972) concluded on the basis of other data that ethylene does not mediate the inhibitory effect of kinetin on root elongation. A similar conclusion was reached by Dubucq (1976). 

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