PLANT GROWTH HORMONES

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Abstract
Methods generally used for the determination of plant growth hormones are the amount of curvature produced in the Avena coleoptile by a unilateral application of the active substance, the straight growth method, and the slit stem method. Substances active in these tests are called auxins. Centers of auxin formation include many seeds, the tip of the oat coleoptile, buds, young leaves, and possibly root tips. The transport of auxin from these centers of formation is polar, i.e., from the apex of the organ to the base. Auxins are active in asymmetrical growth, i.e., tropisms, in the formation of swellings (these being in part the result of cell division), possibly in the normal growth of roots, in the formation of lateral roots, in the growth and swelling of ovaries and the production of fruits, in the growth of buds, in the inhibition of the development of lateral buds, and in the development of roots on cuttings. Accessory substances other than auxins have been found to have a growth-promoting effect: yeast extract, vitamin B-1, and various amino acids for isolated tomato and pea roots; biotin, pantothenic acid, lactoflavin, nicotinic acid, vitamin C, oestrogenic substances and vitamin B-l for excised embryos, vitamin C for the shoot, and pro-vitamin A for the formation of roots on cuttings. No saturated substance has shown auxin activity; the introduction of methyl groups reduces the activity greatly. Plasticity of the cell wall is increased by auxin. Certain evidence associates the action of auxin with an oxidation process.

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