Malondialdehyde (MDA) is a byproduct of lipid peroxidation
and can be used to measure damage resulting from oxidative
stress during tissue senescence [21, 24]. MDA levels in red
MicroTom fruit increased late in ripening. In purple tomatoes,
however, MDA levels did not increase significantly up to
4 weeks after breaker (Figure 4A). Lower oxidative damage in
purple tomato was associated closely with increased total antioxidant
capacity during overripening, which resulted principally
from the accumulation of anthocyanins (Figure 4B). Higher hydrophilic antioxidant capacity/lower ROS levels were associated
with suppression of ripening-related enzyme activities
such as polygalacturonase and b-galactosidase, an effect likely
to be of importance in extending shelf life, since downregulation
of some of the corresponding genes by antisense has been
shown to result in fruit that are firmer for longer than controls
[3, 5] and their combined suppression may extend shelf life
yet further. One explanation for the induced expression of these
genes, late in ripening, is that it is the result of increased ROS
signaling. Our data suggest that ROS signaling is an important
determinant of the rate of ripening, late in fruit development.
High hydrophilic antioxidant capacity can suppress both ROS