Effect of ABA on H2O2 accumulation in epidermal cells after infection with B. cinerea. A, Association of DAB accumulation with B. cinerea conidia. In sitiens, H2O2 was located at the site of penetration and in some parts of the anticlinal wall of the penetrated cell, whereas in wild type and in sitiens supplemented with ABA, no H2O2 accumulation was detected. Germinating conidia were classified in two groups based on the presence or absence of associated DAB accumulation in the epidermal cells, whose percentage is shown. B, DAB accumulation in epidermal cell walls. In sitiens, DAB staining was general in the entire outline of the anticlinal cell wall, whereas in wild type and sitiens supplemented with ABA, no H2O2 accumulation was detected at 8 hpi (top). The restriction of sitiens DAB accumulation to the epidermal layer was confirmed on cross sections (bottom). Epidermal cells were classified in two groups based on the presence or absence of DAB accumulation in the anticlinal walls, whose percentage is shown in the anticlinal walls at 8, 16, and 20 hpi. C, Intracellular DAB accumulation in epidermal cells showing an HR-like reaction. At 16 hpi, wild-type and ABA-supplemented sitiens epidermal cells did not accumulate intracellular DAB, whereas in sitiens, groups of HR-like cells with intracellular DAB accumulation were present near the site of fungal penetration. Epidermal cells were classified in two groups based on the presence or absence of intracellular DAB accumulation and the percentage is shown at 12, 16, and 20 hpi. In all graphs, bars represent the means and the sds of data from six inoculation droplets originating from three plants. In each inoculation droplet, at least 50 conidia (A) or 300 epidermal cells (B and C) originating from representative zones within each inoculation droplet were counted. Data from one experiment is presented. The experiment was repeated with similar results. Scale bar = 50 μm.