Interrelationships between plant growth regulators and fruit tree mineral nutrition.

Information is presented for fruit trees to show the effect of applied growth substances on mineral uptake and tissue mineral levels. The effects of nutrient supply to the roots on hormone synthesis and levels in the plant are also considered. The data are discussed in terms of a direct effect of applied growth substances on the actual nutrient absorption occurring in the roots, and of an indirect influence occurring via growth effects induced by growth substances which weaken or strengthen sink demand and consequently affect mineral nutrition. In a few cases, the evidence for a direct effect on mineral uptake by the root is quite sound, but most experiments are inconclusive with respect to the explanation of the observed phenomena.