Hydroxyl radical‐induced cell‐wall loosening in vitro and in vivo: implications for the control of elongation growth

Abstract

SummaryHydroxyl radicals (OH) are capable of unspeci®cally cleaving cell-wall polysaccharides in a site-speci®c reaction. I investigated the hypothesis that cell-wall loosening underlying the elongation growth of plant organs is controlled by apoplastically produced OH attacking load-bearing cell-wall matrix polymers. Isolated cell walls (operationally, frozen/thawed, abraded segments from coleoptiles or hypocotyls, respectively) from maize, cucumber, soybean, sun¯ower or Scots pine seedlings were pre-loaded with catalytic Cu or Fe ions and then incubated in a mixture of ascorbate + H 2 O 2 for generating OH in the walls. This treatment induced irreversible wall extension (creep) in walls stretched in an extensiometer. The reaction could be promoted by acid pH and inhibited by several OH scavengers. Generation of OH by the same reaction in living coleoptile or hypocotyl segments caused elongation growth. Auxininduced elongation growth of maize coleoptiles could be inhibited by OH scavengers. Auxin promoted the production of superoxide radicals (O 2 ± ), an OH precursor, in the growth-controlling outer epidermis of maize coleoptiles. It is concluded that OH ful®ls basic criteria for a wall-loosening factor acting in auxin-mediated elongation growth of plant species with widely differing cell-wall polysaccharide compositions.

A comparison of the effects of 1,4-naphthoquinone and 2-hydroxy-1,4-naphthoquinone (lawsone) on indole-3-acetic acid (IAA)-induced growth of maize coleoptile cells

“…1, 4). One explanation for the discrepancy between both of these parameters that is found in the presence of NQ and NQ-2-OH probably results from the fact that ROS, similar to protons, cause cell wall loosening, as was postulated by Schopfer's group in experiments performed, among others, with maize coleoptile segments (Frahry and Schopfer 2001;Schopfer 2001;Schopfer et al 2002). Those authors proposed the hypothesis in which · OH is causally involved in the chemorheological wall-loosening reaction that is responsible for the auxin-controlled growth of maize coleoptiles.…”

Biochemistry of fruit softening: an overview

“…The hydroxyl radical ( . OH), the most reactive known compound, if present in the apoplast, OH would cleave polysaccharides and might therefore bring about lead to wall-loosening (Schopfer, 2001;Schweikert et al 2002) (Halliwell and Gutteridge 1999). Reactions (i) to (iii) proceed readily under apoplastically relevant conditions of temperature and pH in vitro.…”

Genome-Wide Identification of Genes Expressed in Arabidopsis Pistils Specifically along the Path of Pollen Tube Growth

“…For example, cell walllocalized peroxidases can cause an increase in wall extensibility by generating hydroxyl radicals that degrade cell wall polysaccharides (Schopfer, 2001) or they can increase wall rigidity by mediating rapid cross-linking (insolubilization) of the structural cell wall Pro-rich extensins, as occurs upon physical damage, treatment with fungal elicitors, and pathogen infection (Bradley et al, 1992;Brownleader et al, 2000;Jackson et al, 2001). The presence of stigma surface peroxidases has been used as an indication of stigma receptivity for pollination in several species (e.g.…”