GRADIENT OF ETHYLENE FORMATION IN THE GROWING LEAF OF WINTER RYE SEEDLINGS - EFFECT OF ETHEPHON

We studied distribution of the rate of ethylene formation in the growing leaf of winter rye seedlings (Secale cereale L.) in the norm and during inhibition of growth processes by the ethylene producer ethephon. The leaf blade of 5-day seedlings showed a reliable gradient of the ethylene evolution rate, ACCA* (1-aminocyclopropane-1-carboxylic acid) content, and ACCA oxidase activity. The most significant rate of ethylene formation is characteristic of actively elongating tissues. The rate of ethylene biosynthesis in growing leaves was determined both by the content of ACCA and by activity of the ethylene-forming system. In fully grown parts of the leaf, ethylene synthesis was limited by low activity of the ethylene-forming system. Treating 4-day seedlings with 0.01 M ethephon caused increase of ethylene evolution and ACCA oxidase activity and decline of ACCA content, which points to the possibility of intensified formation of endogenous ethylene under the influence of an ethylene producer or to intensified malonylation of ACCA. It is concluded that increase in formation of endogenous ethylene can occur due to stimulation of the ethylene-forming system without strengtening of ACCA synthesis.