Figure 1.

Modulation of peroxide efflux by Nod factor and oligouronide elicitor. Generation of H₂O₂ in plant root segments was measured by the conversion of nonfluorescent substrate to fluorescent product in the presence of endogenous plant peroxidases. A, Accumulated fluorescence measured at 5-min intervals for untreated (n = 101 plants pooled from 16 experiments), 1 nm Nod factor-treated (n = 97), and 75 nm PGA-treated (n = 91) plant segments presented as mean fluorescence. Error bars = three sds of the mean. B, Nod factor, applied at four different concentrations, shows a retardation response beginning at 20 to 30 min at 100 pm and higher concentrations. Note initial elevation of activity at 10 nm. C, PGA heptamers, applied at four different concentrations, elicit activity at concentrations above 7.5 nm (n > 11 plants from two separate experiments for all experiments in B and C; error bars omitted for clarity).