Polygalacturonases of a latent and wound postharvest fungal pathogen of muskmelon fruit
B. D. Bruton, W. S. Conway, K. C. Gross, J. X. Zhang, C. L. Biles and C. E. Sams
Postharvest Biology and Technology Vol: 13 Issue: 3 Pages: 205-214.
1998
บทคัดย่อ
Partially purified endo- and exo-polygalacturonases (PG) from two fungal pathogens (Phomopsis cucurbitae and Rhizopus stolonifer) were compared in relation to their ability to macerate netted muskmelon tissue at different stages of fruit development. PG extracts from P. cucurbitae, a latent infection pathogen, produced little maceration until fruit were 50 days post-anthesis (10 days postharvest). In contrast, PGs from R. stolonifer, a wound pathogen, produced high levels of maceration at all stages of fruit development from 20 to 50 days post-anthesis. Both pathogens demonstrated highest levels of total PG activity in mesocarp and lowest levels in exocarp (peel) tissues. Isoelectrofocusing¯polyacrylamide gel electrophoresis indicated two prominent PG isozymes in R. stolonifer and nine isozymes in P. cucurbitae. Cell wall carbohydrate analysis showed an approximately 6-fold decrease in galactosyl residue content between 10 and 50 days post-anthesis in uninfected fruit. Infected fruit showed approximately 7- and 8-fold decreases in galacturonic acid content when infected with P. cucurbitae and R. stolonifer, respectively. Significant decreases in cell wall rhamnosyl and arabinosyl residues occurred during infection of fruit with both pathogens. These results support a role for cell wall pectin degradation during the decay process of muskmelon by these pathogens. The ability to macerate fruit tissue, as related to the latent infection phenomenon, may be due to substrate specificity or inhibitors present in muskmelon fruit tissue.