Shoot inversion inhibition of stem elongation in Pharbitis nil: a possible role for ethylene-induced glycoprotein and lignin.

Inversion of the upper shoot of Pharbitis nil results in the inhibition of elongation in the inverted stem. The objective of the present study was to determine how shoot inversion-induced gravity stress inhibited elongation and to elucidate the possible role of ethylene-induced glycoprotein and lignin in this process. Determinations of hydroxyproline, peroxidase, phenylalanine ammonia-lyase (PAL), phenol, and lignin content/activity were carried out by appropriate spectrophotometric methods. It was found that inversion and Ethrel treatments of upright shoots caused significant increases in hydroxyproline content, peroxidase, and PAL activity in 12 hours and in phenol and lignin contents in 24 hours. All of these increases except for that of cytoplasmic peroxidase activity were partially reversed by AgNO3, the ethylene action inhibitor. It is concluded that possible cross-linking associated with the accumulation of the ethylene-induced hydroxyproline-rich glycoprotein and lignin may be responsible for the later stages of cessation of elongation in the inverted Pharbitis shoot.