In previous studies with tomato (Lycopersicon esculentum
L.) exposed to a low level (3.7 kJ m –2) of UV-C
(λ: 254 nm) radiation, which is defined as a beneficial level, we
report a delay in fruit ripening by at least 1 week for treated fruit. In the
present study, we investigate the changes in the activities of different
enzymes involved in defense mechanisms, such as guaiacol peroxidase, ascorbate
peroxidase, catalase, superoxide dismutase, ascorbate oxidase, lipoxygenase
and phenylalanine ammonia lyase in tomato fruit in response to a beneficial
level of UV-C. The irradiation leads to an increase in the guaiacol peroxidase
and ascorbate peroxidase activities, whereas catalase activity remains similar
to the control. The activities of superoxide dismutase and ascorbate oxidase
were significantly reduced after UV-C exposure. In UV-C-treated fruit, an
increase of lipoxygenase and phenylalanine ammonia lyase activities occurred
within the first 5 d, followed by a second period in which these activities
were below those of the control. Our study suggests that the level of UV-C
used induced a rapid but moderate accumulation of photooxidation products, to
which plants react by stimulating their defence mechanisms against oxidation.
This activation may explain the delay observed in ripening and senescence of
irradiated tomato fruit.
Cold-induced Antioxidant Enzymes Changes in Leucanthemum maximum`Silver Princess'