THE HYPERSENSITIVE REACTION OF COTTON PLANTS TO XANTHOMONAS CAMPESTRIS pv. MALVACEARUM: EARLY EVENTS INVOLVED
C MARTINEZ1, E BRESSON1, K ASSGBETSE1, JF DANIEL1, D FERNANDEZ1, JL MONTILLET1, JP GEIGER1 and M NICOLE1
1ORSTOM, Department of Plant Pathology, BP 5045, 34032, Montpellier, France; 2CEA, Department of Plant Physiology, 13018, St Paul Lez Durance, France
Background and objectives
Results and conclusions
Assessment of PoxA by biochemistry (IEF, spectrophotometry, tissue printing) and histochemistry following infection indicated that activity of anionic Pox isozymes dramatically increased at HR sites from 6 h.p.i. A systemic increase in these PoxA was also seen in non-infected leaves, 24 h.p.i. of cotyledons. Northern blot analysis using a Pox clone demonstrated transcription of Pox genes during the HR with detection of accumulation of two peaks of mRNA, 3 and 12 h.p.i.
Salicylic acid (SA) was shown to be produced between 3 and 6 h.p.i. in cells that had undergone the HR. Infiltration of H2O2 in cotyledon tissues induced the accumulation of SA. Infiltration of SA triggered anionic PoxA locally at infiltration sites, and systemically in leaves. These experiments suggest that H2O2 is likely at the onset of SA accumulation in infected cotton cells and activation of local (LR) and systemic (SR) resistances.
Histochemistry revealed a strong accumulation of flavonoids (9 h.p.i)  and sesquiterpenes (48-72 h.p.i.)  in Xanthomonas-infiltrated tissues during the incompatible interaction as compared to susceptible infected plants.