ROOT-SHOOT SIGNALING IN SUNFLOWER PLANTS WITH CONFINED ROOT SYSTEMS

Sunflower plants were grown hydroponically under controlled conditions with the root systems confined in small containers. Root confinement inhibited the growth of sunflower plants as indicated by reduction in both leaf and cotyledon area and root and shoot fresh weight. This eff ect was more pronounced in shoots. Root confinement favored the accumu lation of potassium in the roots and shoots, and the exudation of pota ssium and water in excised roots. Xylem sap from root confined plants inhibited cotyledon expansion as revealed by bioassay with decapited s unflower seedlings. In addition decapited control plants incubated in ABA solution also showed cotyledon growth reduction. Xylem sap ABA ana lysis indicated a 7-times higher concentration in root confined than c ontrol plants. Our results suggest the synthesis of a chemical signal in the roots of plants subjected to mechanical stress which can be res ponsible for the inhibition of plant growth.