K. Kpemoua et al., CYTOCHEMISTRY OF DEFENSE RESPONSES IN CASSAVA INFECTED BY XANTHOMONAS-CAMPESTRIS PV MANIHOTIS, Canadian journal of microbiology, 42(11), 1996, pp. 1131-1143
Stems of susceptible and resistant cassava plants have been cytologica
lly investigated for their defense reactions to an aggressive strain o
f Xanthomonas campestris pv. manihotis. Histochemistry, in conjunction
with gold cytochemistry, revealed that in susceptible and resistant p
lants, phloem and xylem parenchyma cells displayed a wide range of res
ponses that limited the bacterial growth within the infected plants. L
ignification and suberization associated with callose deposition were
effective mechanisms that reinforced host barriers in the phloem. In t
he infected xylem, vessels were plugged by a material of pectic and (o
r) lignin-like origin. Flavonoids have been seen to be incorporated in
secondary cell wall coatings. These reactions occurred at a higher in
tensity in the resistant plants. The number of phoem and xylem cells p
roducing autofluorescent compounds was higher in infected resistant pl
ants than in susceptible plants. Reactions have been observed in the r
esistant variety only, such as secretion of phenol-like molecules by t
yloses and hyperplasic activity of phloem cells that compartmentalized
bacterial lysis pockets, which are potent secondary inoculum sources.