Antioxidant metabolism of grapefruit infected with Xanthomonas axonopodis pv. citri

作者：Kumar Naveen; Ebel Robert C^*; Roberts Pamela D

来源：Environmental and Experimental Botany, 2011, 71(1): 41-49.

DOI：10.1016/j.envexpbot.2010.10.019

• Citrus paradisi
• Ascorbate peroxidase
• Catalase
• Peroxidase
• Reactive oxygen species

Grapefruit is one of the most susceptible citrus genotypes to Asiatic Citrus Canker, caused by Xanthomonas axonopodis pv.citri (Xac), that can cause severe losses in citrus yield and quality. Although much is known about citrus response to Xac, little is known of the role of antioxidant metabolism. Grapefruit leaves were artificially injected with a strain of Xac obtained from a commercial grove in Florida and components of oxidative metabolism were measured. Symptoms observed included water soaking (2 dai; days after inoculation), raised and ruptured epidermis (6-8 dai), formation of necrotic lesions (16 dai), and leaf abscission (21 dai). The Xac population increased to a maximum (approximate to 10(9) CFU/cm(2)) 8 dai and then declined to approximate to 10(7) CFU/cm(2) by 20 dai. Lipid peroxidation was higher in infected leaves than uninoculated controls from 4 to 21 dai indicating greater oxidative stress. H(2)O(2) concentration demonstrated a biphasic pattern with peak concentrations at 4 and 13 dai and minimum concentrations that were lower than the controls at 10 and 20 dai. The H(2)O(2) concentration somewhat corresponded with superoxide dismutase (SOD) activity, which generates H(2)O(2) via dismutase of superoxide ions. Total SOD activity in Xac-infected leaves increased to a maximum at 4 dai, the day of highest H(2)O(2) concentration, and then declined and remained at or below controls. Mn-SOD and Fe-SOD activities both increased to maximum activities at 4 dai. Mn-SOD had four isoforms in Xac-infected leaves but only three in the controls. Fe-SOD had three isoforms in both infected and control plants. Suppression of H(2)O(2) in Xac-infected leaves also corresponded to higher activities of the H(2)O(2) catabolising enzymes catalase (CAT), ascorbate peroxidase (APOD), and peroxidase (POD). Two additional CAT isoforms were detected in infected leaves and not the controls. Three POD isoforms were detected in both control and infected leaves. Previous research has shown that Xac is sensitive to intraplant H(2)O(2) concentration, however, the pattern of Xac in this study did not correspond to H(2)O(2) concentration, which initially increased due to enhanced SOD activity, but was later suppressed apparently with the aid of peroxidases. In conclusion, Xac infection altered H(2)O(2) metabolism in grapefruit leaves by changes in the activities and isoforms of SODs, CATs, PODs and APOD. Published by Elsevier B.V.

• 出版日期2011-4