Studies on the effect of the applications of synthetic growth substances, on the natural hormone content of plants

The possible effects of growth regulating substances on the level of beta-indolylacetic acid in plants have not been fully studied in the past. This has been mainly due to the lack of sensitive methods for the separation and estimation of natural auxins in extracts of plant tissues. For this reason, seedlings of peas, beans and sunflowers have been treated with 2,4-Dichlorophenoxyacetic acid (2,4-D.); with the supposed anti-auxin 2,3-J-tri-iodobenzoic acid (TIBA); and with maleic hydrazide (MH), a growth regulating substance.These substances have been applied at nontoxic levels, but in sufficient quantities to cause well narked growth responses. Alcoholic extracts of both treated and noxmal plants have been analysed by a method of paper partition chromatography, and estimations of the quantities of active growth substances determined by a direct:sensitive bioassay of the developed chromatogram. indolylacetic acid,and a second inhibitory aciaic compound have been recorded in all tissue exti*acts. At least three other active growth substances have been detected in certain tissues. Only the effects of treatments on the IAA levels have been followed in detail. 2,4-B. treatment of plants has no detectable effect on the level of IAA in the extracts of eitlier roots or shoots. It is concluded therefore that 2,4-D. exerts its effects on growth directly and not via a disturbance of IAA metabolism. There are indications that growth of pea seedlings in maleic hydrazide may slightly increase the level of IAA in their roots,but further work Is necessary. Growth of pea seedlings in TIBA solutions,however, causes a marked reduction in the IAA content of the roots. The implications of this result is discussed in relation to the physiological and morphological responses of plants to TIBA treatment.