Shoot Inversion Inhibition of Stem Elongation in Pharbitis nil

Abstract

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 ethyleneinduced hydroxyproline-rich glycoprotein and lignin may be responsible for the later stages of cessation of elongation in the inverted Pharbitis shoot.Shoot inversion-induced release of apical dominance in Pharbitis nil is preceeded by inhibition of elongation of the inverted stem (6,21). This inhibition is apparently due largely to gravity stress-induced ethylene production in the terminal 10 cm of the inverted shoot (20; Fig. 1). There is evidence to suggest that ethylene inhibits elongation by altering cell wall mechanical properties via modification of the orientation of cellular microfibrils, cell wall pectic fraction, or of cell-wall cross-linking ( 12).There have been a number of studies relating accumulation of Hp2 in the cell wall to cessation of elongation (5,24,25 (NPK,20:20:20)

Changes in Isozyme Profiles of Catalase, Peroxidase, and Glutathione Reductase during Acclimation to Chilling in Mesocotyls of Maize Seedlings

“…To determine which POX isozymes were localized in the cell wall and therefore potentially involved in lignification, protoplast and ionically bound cell-wall proteins from Ac and AcCh mesocotyls were extracted according to the method of Prasad and Cline (1987). The cell-wall fraction was desalted and concentrated on a Centricon microconcentrator (Amicon, Danvers, MA) with a 10,000 molecular weight exclusion limit, according to the manufacturer's instructions.…”

Localization and Characterization of Peroxidases in the Mitochondria of Chilling-Acclimated Maize Seedlings

“…Total cell wall proteins were extracted in 1 M NaCl for 1 h at 4°C from cell walls prepared from mesocotyl tissues, as previously described (Prasad and Cline, 1987). Total protein content was determined by the method of Lowry et al (1951) using BSA as a standard.…”

Isolation and sequencing of cDNA clones encoding ethylene-induced putative peroxidases from cucumber cotyledons

“…However, the physiological functions of both endogenous and hormonally regulated peroxidases are not fully understood. Evidence has accumulated which shows that peroxidase plays an important role in cell wall lignification [ 17,23]. Evidence both for [2] and against [8,24] the concept that peroxidase is used in the defense of plants against microbes has also been presented.…”