Growth Regulators and Flowering. II. The Cobaltous Ion.

It was shown previously that cobaltous ion inhibits flowering of the short-day plant cocklebur if it is applied to plants at concentrations of about 3 X 10-4 to 6 X 10-2 moles per liter just before a single inductive dark period (10). Although development of the floral bud is inhibited by extremely high concentrations of cobaltous ion applied at any time, lower concentrations are only effective in floral inhibition providing they are applied before the end of the critical night (the minimum period of darkness required to produce flowers). Cobaltous ion increases the duration of the critical night-that is, the biological timing mechanism in the leaf of the cocklebur appears to be slowed down by cobaltous ion (fig. 1, discussed below, illustrates this phenomenon). The literature contains more than 60 references relating to the effect of the cobaltous ion upon plants. Most of these are concerned with nutrition, although some do attempt to ascertain the mechanism of action in the response under consideration. Some five mechanisms have been suggested, and'the first four of these were investigated in the present study, in regards to the action of cobaltous ion in the flowering process: 1) An inhibition of peroxigenesis. Galston and Siegel (3) reported that cobaltous ion inhibited the formation of organic peroxides in pea stem sections and thus spared the destruction of indole acetic acid by indole acetic acid oxidase. They further reported that manganous ion would act in an opposite or even antagonistic manner in this tissue. 2) Oxidation of phenol type compounds. Gillette et al (4) reported that Mn++, Co++, Ni++, Ca+ + and Fe+ + catalyze the oxidation of certain phenolic type compounds. They are effective in the order shown. 3) A promotion of metabolism. Thimann (12) demonstrated that the promotion by cobaltous ion of elongation of Avena coleoptile sections or etiolated pea sections could be reversed by dinitrophenol. He concluded that cobaltous ion might channel respiratory energy into growth. 4) Relation of cobaltous ion to endogenous sulfhydryl compounds. Nickerson and van Rij (8) re-