Peroxidase isozyme patterns in the skin of maturing tomato fruit

Abstract

The cessation of tomato fruit growth is thought to be induced by an increase in the activity of enzymes which rigidify cell walls in the fruit skin. Peroxidase could catalyse such wall-stiffening reactions, and marked rises in peroxidase activity were recently reported in skin cell walls towards fruit maturity. Peroxidase isoforms in the fruit are here analysed using native gel electrophoresis. New isoforms of apparent M r 44, 48 and 53 kDa are shown to appear in cell walls of the fruit skin at around the time of cessation of growth. It is inferred that these isozymes are present in the cell wall in vivo. Fruit from a range of nonripening mutants were also examined. Some of these do not soften or ripen for many weeks after achieving their final size. The new isozymes were found in skin cell walls of mature fruit in each of these mutants, as in the wild-type and commercial varieties. It is concluded that the lateappearing isozymes are not associated with fruit ripening or softening, and are probably not ethylene-induced. They may act to control fruit growth by cross-linking wall polymers within the fruit skin, thus mechanically stiffening the walls and terminating growth.

Oxidative stress and antioxidant systems in Guava (Psidium guajava L.) fruits during ripening

“…This suggests that POX may not be playing an important role in scavenging H 2 O 2 during fruit ripening (Moller et al, 2007). These observations are further supported by the findings of Andrews et al (2000) where POX has also been reported to catalyze cell wall softening reactions during fruit ripening.…”

Peroxidases have more functions than a Swiss army knife

“…During tomato fruit development as in other cell elongation processes described previously, cell expansion is dependent on cell wall loosening (Andrews et al 2000). Hence the implication of peroxidases in such a process is related to the fine balance between cell wall loosening and stiffening.…”

Responses of bioenergy sorghum cell wall metabolism to agronomic practices

“…Increased soil tillage intensity increased the maximum velocity of the peroxidase reaction without altering the Km value (non- competitive inhibition). Cell wall metabolism: Lignin and cellulose yields: Peroxidases are cell wall-bound enzymes that participate in lignin and suberin biosynthesis [15,17,19]. Changes in their activity altered the lignin and cellulose yields (Table 1) and the cellulose/lignin ratios.…”

“…This further supports the observed increases in the Vmax values. The lowering of the Km values for hydrogen peroxide increased the affinity of peroxidases and their capacity to synthesize lignin and suberin for the stiffening of mechanical supportive and transport tissues [15,17,19]. Crop residue return, nitrogen fertilization rate, corn-sorghum rotation or continuous sorghum cropping, and soil tillage are physically different agronomic practices but they acted in concert on the wall-bound peroxidase isoenzymes, whose maximum velocities changed in response to these practices.…”

“…Peroxidases (EC 1.11.1.7) are a multi-isoenzymatic family of cell wall-bound oxidoreductase enzymes that participate in lignin biosynthesis [15][16][17] and stiffening of the cell wall. Since the lignin of crop residues increases soil organic carbon content because it is slow to degrade [18], agronomic management practices that enhance peroxidase activity might improve both biomass yield and soil carbon sequestration; whereas those that inactivate the enzyme might minimize lignin contents of crop residues, thereby resulting in less carbon sequesteration or possibly even promoting soil organic carbon depletion with time.…”