Hg. Lu et Vj. Higgins, The effect of hydrogen peroxide on the viability of tomato cells and of the fungal pathogen Cladosporium fulvum, PHYSL MOL P, 54(5-6), 1999, pp. 131-143
An oxidative burst was previously demonstrated to be induced in tomato plan
ts by race specific elicitors of the fungal pathogen Cladosporium fulvum. T
he in planta levels of H2O2 estimated to occur during elicitor treatment, w
ere compared with the levels required to show toxicity to host cells and to
the fungal pathogen. Injection of Cf-9 tomato leaves with 100 mM H2O2 caus
ed an insignificant degree of necrosis and 1 M H2O2 was required to cause c
omplete leaf necrosis comparable to that induced by the AVR9 elicitor. Assa
ys with Cf-5 tomato cell suspensions confirmed the low toxicity of H2O2 to
tomato cells but, as expected, the addition of Fe2+ with H2O2 (or with inte
rcellular fluids containing AVR5 elicitor) enhanced cell death as determine
d by the Evans Blue assay. Germination and germ tube growth of conidia of C
. fulvum were significantly retarded by 4-5 mM H2O2, and at higher concentr
ations, death of germ tubes was observed (ED50 = 22 mM), as determined by t
he fluorescein diacetate assay. The addition of Fe2+ with H2O2 had little e
ffect on fungal growth or viability in vitro. These results suggest that th
e amount of H2O2 accumulating during an elicitor-induced response in leaves
may be sufficient to affect fungal colonization but not to affect viabilit
y of host cells unless the Fe2+ status in the apoplast is in some way alter
ed by the elicitor to facilitate OH. production via the Fenton reaction. (C
) 1999 Academic Press.