Growth of maize coleoptiles in the presence of natural and synthetic growth regulators. Growth correlations

Abstract

The effect of natural (IAA, FC, ABA) and synthetic (2,4-D) growth substances on the increase of the fresh weight of maize coleoptile segments and change of the pH of the incubation medium, accepted here as criteria of maize coleoptile growth, was studied. The growth of maize coleoptiles depended on the concentration of the growth substances, as well as, on the composition of the incubation medium. The highest stimulation of coleoptile growth was seen with FC at a concentration of 10<sup>-4</sup>M, whereas ABA at 10<sup>-3</sup> M gave the highest inhibition of maize coleoptile fresh weight increase and caused alkalization of the medium. The presence of K<sup>+</sup> ions in the incubation medium enhanced the stimulatory effect of IAA and FC on the increase of the coleoptile fresh weight, whereas the presence of these ions and phosphate buffer abolished the growth-promoting effect of IAA and FC. The best correlation of the "fresh weight" and "pH" effects was found in the case of the growth of maize coleoptiles in the presence of FC (r<sub>xy</sub> = 0.67). The inhibition of maize coleoptile growth in the presence of high concentrations of IAA can be explained by the destructive effect of natural auxin at these concentrations on the integrity of mitochondrial membranes, and therefore on the normal functioning of mitochondria.