Action of some phytohormones on the respiration and on the absorption of phosphate by aging potato tuber discs.Discs of potato tuber incubated in aerated medium show an increase of the rates of respiration and phosphate absorption with aging time; the rates increase by two and nine respectively during the time period between 5 and 24 h of aging. Adenine or some N-6 substituted adenines I benzylaminopurine (BAP), furfurylaminopurine (FAP), methylaminopurine (MAP)], which present variable degrees of cytokinin activity, partially inhibit the increase of the rate of phosphate absorption and, to a lesser extent, the increase of the rate of respiration. Also abscisic acid (ABA), Indole 3-acetic acid (lAA), and gibbereilic acid (GA,) produce inhibition of the increase of the rate of phosphate absorption with varied effects on the respiration. With regard to phosphate uptake, the effects of ABA, lAA and GAj were additive to those of BAP. The effects on respiration were different from the effects on phosphate uptake, so that there is no direct relationship between inhibition of respiration and inhibition of phosphate uptake.