Regulation of Ethylene Biosynthesis in Gravistimulated Kniphofia (Hybrid) Flower Stalks

Abstract

Summary Gravistimulation of cut flowering stems of Kniphofia (hybrid) causes rapid upward bending due to a decreased growth rate at the upper half and an increased growth rate at the lower half of the flower stalk. Within a few hours of gravistimulation, the level of 1-aminocyclopropane-1-carboxylic acid (ACC) and the ethylene production in the lower half of the stem increased, apparently due to a rapid increase in ACC-synthase activity. Later, the level of N-malonyl-ACC also increased in the lower half of the stalk. Ethylene, ACC and MACC levels in the upper half of the gravistimulated stem did not change during the experimental period. The activity of the ethylene-forming enzyme was similar in all stem sections. The asymmetric production of ethylene in gravistimulated stems resulted in seven times higher internal ethylene levels in the lower half of the stem. Treatment of the stems with ethylene or inhibitors of ethylene synthesis (aminooxy-acetic acid) and of ethylene action (silver thiosulphate, CO 2 , 2,5 norbornadiene) inhibited elongation growth in vertical controls but had no appreciable effect on the response to gravity. The results therefore indicate that endogenous ethylene plays no pivotal role in flower stalk gravitropism.