| Summary: | 碩士 === 國立中興大學 === 植物學系 === 84 === The effects of high O2 on photosynthesis and antioxidant enzymes
wereinvestigated in rice (Oryza sativa L.). Different potted
rice varieties(KK30, TN67, NJBN, TC65, TN1, and Mars) were
short-term treated withdifferent concentrations of oxygen. Rates
of photosysthesis decreasedwith the increasing of oxygen
concentrations in all rice varietiestested, but the degrees of
inhi-bition were different. These six ricevarieties were
classified into two groups according to their sensitivityof
photosynthesis to high oxygen : the sensitive group (KK30, NJBN,
TC65)and the less-sensitive group ( TN67, TN1, Mars). Long-term
treatmentswith mixed air ( 20% O2 plus 350 ppm CO2, 40% O2 plus
700 ppm CO2, or60% O2 plus 1050 ppm CO2 ) the degrees of O2 in-
hibition were differentthan those of short-term O2 treatments
with highest O2 inhibitionoccurred at 60% O2 treatment in Mars
variety. The degree of lipidperoxidation of membrane was also
the highest in Mars among 4 ricevarieties tested. Damaged
membrane structure caused by active oxygenattack would be the
major contribution to the decreased rate ofphotosynthesis under
high O2 stress. Activities of SOD, one of the antioxidant
enzymes, were increasedafter high oxygen treatments in Mars,
while treatments with TN67,NJBN, and TN1 showed no affect on SOD
activities. The activitiesof GR and APX were significantly
increased in the TN67 and NJBN,while the TN1 and Mars were not.
Although SOD was the first committedenzyme in the antioxidant
systems, accumulation of H2O2 , the productof SOD, would cause
oxidative damages to the living tissues. To evaluate the
effects of oxidizing reagents, different con-centrations of H2O2
and MV were applied to the suspension culturesof two rice
varieties, TN67 and NJBN. Growth inhibition of culturedcell was
found in both H2O2 and MV treatments . The growth of
NJBNestimated by packed cell volume was signifi-cantly reduced
by 5 mMH2O2. The growth of TN67 was corre-lated with the
increase of APXactivity, but not with the SOD activity. The
results showed thatconstitutive level of SOD in mature leaves of
rice is high enoughto scavenge the superoxide evolved from high
oxygen treatments.The efficient H2O2 scavenging system under
oxidative stressesvia ascorbate-glutathione cycle may play a
major role in theantioxidant system.
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