RESPONSES OF MAIZE MESOCOTYLS TO ATTEMPTED PENETRATION BY FUNGAL PATHOGENS (HELMINTHOSPORIUM MAYDIS NISIK. AND MIY. AND COLLETOTRICHUM GRAMINICOLA (CES.) WILS.): PAPILLA FORMATION, LIGNIFICATION, CHANGES IN PEROXIDASE ACTIVITY AND ISOZYMES (ZEA MAYS L., PHENOLIC COMPOUNDS)
Abstract
The timing of papilla formation in epidermis of the maize mesocotyl was followed after inoculation with Helminthosporium maydis and Colletotrichum graminicola. Histochemical tests showed the presence of phenols and lignin in papillae and the surrounding cell wall material. Peroxidase (E.C. 1.11.1.7) enzyme activity was detected histochemically in the vesicles which give rise to papillae and in the papillae themselves. Soluble and ionically bound peroxidases were extracted from epidermal tissue during the time of papilla formation. The pattern of soluble anionic isozymes in epidermis which had been undergoing papilla formation was different from the pattern of isozymes from uninoculated epidermis or inoculated epidermis which had not yet started to form papillae. The same eight isozymes were present in the soluble peroxidase fraction of uninoculated tissue and tissue inoculated but not yet forming papillae. Two new isozymes were detected in tissue in which papillae had been formed. The identical isozyme pattern was found in two maize cultivars during papilla formation in response to two different fungi, suggesting that the occurrence of isozymes was part of a non-specific host response to attempted fungal penetration. Because of the importance of phenylpropanoids to lignin and lignification, changes in these compounds were studied in extracts from epidermal strips taken from maize mesocotyls (B73(,Ht) and B73(,Htrhm)) 24 h after inoculation with Helminthosporium maydis. There was a significant decrease in the amount of ferulic acid which could be extracted from epidermal cell walls of the inbred B73(,Htrhm). Extractable wall-bound p-coumaric acid was found to increase in both cultivars after inoculation. No consistent pattern of changes of phenylpropanoids was evident in either of the free phenol fractions after inoculation of either cultivar. The results suggest that the changes in extractable base hydrolyzable wall-bound phenols are related to lignification and papilla formation, which occurs in response to attempted penetration by H. maydis.
Degree
Ph.D.
Subject Area
Plant pathology
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