Influence of growth retardants on the internode and ethylene production of sunflower plants

Abstract

The growth‐retarding activity of the norbornenodiazetine tetcyclacis and the di‐oxanylalkenyl triazole LAB 150 978 as well as the ethylene‐forming compounds 2‐chloroethyl‐phosphonic acid (ethephon) and 1‐amino‐cyclopropane‐l‐carboxylic acid (ACC) on stem histogenesis and ethylene production of sunflower plants (He‐lianthus annuus L. cv.Spanners Allzweck) has been studied. The shoot growth of plants hydroponically grown and treated was reduced by the compounds. The shortening in the length of the 1st internode caused by tetcyclacis and LAB 150 978 was mainly induced by inhibition of cell division (the internode possessed fewer cortical cells per cell file). In contrast, ethephon and ACC decreased internode elongation mainly by reducing the rate of cell enlargement.The ethylene production of sunflower seedlings cultivated on agar nutrient medium rose with increasing concentrations of ethephon and ACC, the shoot length of the plants being progressively reduced.Tetcyclacis and LAB 150 978 inhibited both the formation of ethylene and shoot growth. It is suggested that in contrast to ethephon and ACC, tetcyclacis and LAB 150 978 do not achieve their growth‐retarding effect by influencing the production of ethylene.