Auxin stimulated growth

Table II. Effects of xyloglucan oligosaccharide subunits on auxin-stimulated growth of pea epicotyl segments in vivo and pea endo-1,4-/ -glucanase activity in vitro. Growth of segments in 1 //M 2,4-D was measured after 18 h. Endo-1,4-/J-gIucanase activity was determined viscometrically after 30 min using tamarind xyloglucan as substrate. Data calculated from refs. 50 and 51...

G. J. McDongall and S. C. Frey, Inhibition of auxin-stimulated growth of pea stem segments by a specific nonasaccharide of xyloglucan, Plania 175 412-416 (1988). 

Other auxin-like herbicides (2,48) include the chlorobenzoic acids, eg, dicamba and chloramben, and miscellaneous compounds such as picloram, a substituted picolinic acid, and naptalam (see Table 1). Naptalam is not halogenated and is reported to function as an antiauxin, competitively blocking lAA action (199). TIBA is an antiauxin used in receptor site and other plant growth studies at the molecular level (201). Diclofop-methyl and diclofop are also potent, rapid inhibitors of auxin-stimulated response in monocots (93,94). Diclofop is reported to act as a proton ionophore, dissipating cell membrane potential and perturbing membrane functions. 

Auxins are synthesized in the apical buds of growing shoots. They stimulate growth of the main shoot, but inhibit... 

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. 

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. 

Auxins are synthesized in apical buds (at the tip) of growing shoots. They stimulate growth of the main shoot and inhibit lateral shoot development. A class of auxin-binding membrane proteins may represent auxin receptors. Auxin action involves pumping protons out of the cell, possibly in conjunction with a membrane ATPase. 

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