GROWTH ORIENTATION OF UNDERGROUND SHOOTS IN PERENNIAL HERBACEOUS PLANTS .4. THE ROLE OF LIGHT AND HORMONES IN THE CONTROL OF DIATROPIC GROWTH ORIENTATION OF STOLONS

Growth orientations and hormonal status of the stolen shoot apices exc ised from the plants of stubwort (Oxalis tuberosa Caldas) and potato ( Solanum cardenasii Zuk. et Buk.) and exposed to light and exogenous ho rmones, were studied. Detached stolons retained their ability for grow th orientations. Stolen shoot apices subjected to darkness or darkness interrupted by far-red light (FR) demonstrated diatropic growth orien tation, i.e., the apices curved downward to the soil. Red light Oil ir radiation changed growth orientation. There were no changes in IAA, GA , or ABA activity in the growing apical zone of stolons after R or FR treatment. Exogenous hormones (IAA + ABA or IAA + GA) applied to the a bove-ground organs of the maternal plant did not affect the pattern of stolen growth orientation. It has been concluded that stolons have an autonomous mechanism of growth orientation control located in the api cal zone. When an underground shoot apex appears on the soil surface, the light signal is percepted by the phytochrome, which controls the a ctivity of growth processes within the transversal axis.