PHYSIOLOGY OF MORPHACTINS - EFFECT ON GRAVI- AND PHOTO-RESPONSE

Plant roots and shoots respond to gravity and light source in a definite way. Thus, there are typical geotropic and phototropic responses for roots and shoots. When seedlings were grown in presence of morphactins, IT 3233 [n-butyl-9-hydroxyfluorene-(9)-carboxylate] or IT 3456 [methyl-2-chloro-9hydroxylfluorene-(9)-carboxylate], on a vertical or a horizontal plane, the roots and shoots lost the capacity to respond to gravity or to unilateral light source. This was true for both monocots and dicots. This suggests that basic mechanism(s) of the 2 tropic responses are the same in the roots and shoots of the 2 plant groups. The site(s) of action of morphactins in unknown. The reaction(s) controlling geotropism and phototropism may be closely related as morphactins affected both geotropic and phototropic response of the same organ. Indoleacetic acid and gibberellic acid per se did not modify the effect of morphactins on geotropism. Growth retardation effect of morphactins appears to be controlled by another mechanism.