Te. Kraus et Ra. Fletcher, PACLOBUTRAZOL PROTECTS WHEAT SEEDLINGS FROM HEAT AND PARAQUAT INJURY - IS DETOXIFICATION OF ACTIVE OXYGEN INVOLVED, Plant and Cell Physiology, 35(1), 1994, pp. 45-52
Paclobutrazol (PBZ), a member of the triazole family, protected wheat
(Triticum aestivum L.) seedlings from injury due to heat (50-degrees-C
for 2.5 h) and paraquat (2 mM). Both stresses induced photoinhibition
, loss of fresh weight and membrane integrity, suggesting the possible
involvement of toxic oxygen species. This study tested the hypothesis
that PBZ-induced protection from stress is in part mediated by enhanc
ed detoxification of active oxygen. The results support this hypothesi
s since PBZ stimulated a 16, 32 and 21% increase in the activities of
superoxide dismutase, ascorbate peroxidase (AP), and glutathione reduc
tase (GR), on a fresh weight basis. The increased activities of AP and
GR were maintained to a higher degree than their corresponding contro
ls after exposure to both heat and paraquat stress. Ascorbate and glut
athione pools were 14 and 8% higher respectively in the PBZ-treated wh
eat than in the controls. Within the cytoplasm, PBZ increased the acti
vities of catalase (45%) and guaiacol peroxidase (29%) on a fresh weig
ht basis and these higher activities, over the controls, were conserve
d after stress. It is suggested that the damage caused by two differen
t stresses, heat and paraquat, is in part due to increased generation
of active oxygen and that PBZ protects plants by maintaining increased
antioxidant enzyme activity.