| RNase I activity showed a gradual increase in resistant and susceptible
plants and also in healthy and inoculated plants from 10th day to 20th day
stage. There was almost 2 to 3 fold increase in activity in respective categories.
RNase I specific activity was generally high in inoculated plants as compared
to healthy plants at different leaf stages (Fig. 1b).
ROHRlNGER et al. (1961) observed similar increase in wheat leaves
infected with rust. CHAKRAVORTY & SCOTT (1979) reported changes in catalytic
properties and substrate preference of the enzyme in barley leaves inoculated
with E. graminis f.sp. hordei. Two fold increase in activity
was observed at the 15th day stage in inoculated plants over healthy plants.
Specific activity was found to be low in case of susceptible genotypes as
compared to resistant genotypes at three different leaf stages. However,
FRIC (1975) observed an increase in activity in susceptible lines of barley
upon infection by E. graminis as compared to resistant lines. In
the present study, probably the resistance mechanism exhibited by the host
may be due to a high amount of ribonuclease activity as observed in the
case of peroxidase (SEEVERS et al. 1971). The specific activity of RNase II + Nu I in inoculated plants showed a gradual increase from the 10th day to the 20th day stage which was almost two fold. In healthy resistant plants also there was 2 fold increase in activity except for susceptible genotypes where there was no substantial increase (Fig. 1c). The activity was more in inoculated plants compared to healthy plants at different stages. The activity was high and almost 2 times for resistant genotypes in both healthy and inoculated plants as compared to susceptible genotypes. The combined RNase II + Nu I specific activity was more as compared to RNase I at different stages of seed germination. SODEK & WRIGHT (1969) observed more of RNase II + Nu I activity in wheat leaves following detachment. Acknowledgement Financial assistance received from the University is gratefully acknowledged. References ARYA, H.C. 1962. Studies on the physiologic specialization and varietal reaction of wheat to powdery mildew in India. Indian Phytopath. 15: 127-132. BRADFORD, M.M. 1976. A rapid and sensitive method for the quantitation of microgram quantities of proteins utilizing the principle of protein dye binding. Anal Biochem. 7: 1837-1849. CHAKRAVORTY, A.K. and K.J. SCOTT. 1979. Changes in two barley leaf ribonuclease fractions during infection by the powdery mildew fungus. Physiol. Plant Pathol. 14: 85-98. DE WITT, P.T.G. and J. BAKKER. 1980. Differential changes in insoluble tomato leaf proteins after inoculation with virulent and avirulent races of Cladosporium fulvum. Physiol. Plant Pathol. 17: 121-130. FRIC, V.F. 1975. Influence of powdery mildew (Erysiphe graminis f.sp. hordei Marchal) on activity of the non specific phosphatase and ribonuclease in the tissues of susceptible and resistant varieties of barley. Phytopath. 2, 82: 266-277. GIANINAZZI, S., P. AHL, A. CORNU, R. SCALLA and R. CASSINI. 1980. First report in 'b' protein appearance in response to fungal infection in Tobacco. Physiol. Plant Pathol. 16: 337-342. JOHNSON, L.B., B.L. BRANNAMAN and F.P. Jr. ZSCHELLE. 1968. Protein changes in wheat leaves following: infection with Puccinia recondita. Phytopathol. 58: 578-583. RANDLES, J.W. 1968. Ribonuclease isoenzymes in Chinese Cabbage systematically infected with turnip yellow mosaic virus. Virology 36: 556-563. ROHRINGER, R., D.J. SAMBORSKI and C.O. PETERSON. 1961. Ribonuclease activity in rusted wheat leaves. Can. J. Bot. 39: 263-267. SEEVERS, P.M., J.M. DALY and F.F. CATEDRAL. 1971. The role of peroxidase isozymes in resistance to wheat stem rust disease. Plant Physiol. 48: 353-360. SODEK, L. and S.T.C. WRIGHT. 1969. The effects of kinetin on ribonuclease, acid phosphatase, lipase and esterase levels in detached wheat leaves. Phytochem. 8: 1629-1640. SUTTON, C.S.B. and M. SHAW. 1982. Changes in two ribonuclease I isozyme during rust infection of flax cytoledons. Plant Physiol. 69: 205-209. WILSON, C.M. 1975. Plant nucleases. Ann. Rev. Plant Physiol. 26: 287-209. |
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