Figure 5.

Cytosolic Ca²⁺ Elevation Is Induced and Is Required for PSK-Induced Tomato Immunity against B. cinerea.

(A) and (B) PSK-induced cytosolic Ca²⁺ elevation in leaves of aequorin-expressing tomato plants as affected by Ca²⁺ channel inhibitors (A) or PSKR1 or PSKR2 gene silencing (B). Tomato leaf discs were preincubated for 30 min with RR or Ver at 20 μM, and 10 μM PSK ligand was then added at time 0. The signals shown at 0.5-min intervals are mean values ± sd (n = 10 to 12 leaf discs). In (A), 50 total leaf discs obtained from at least five plants were used for experiment and each treatment had 10 leaf discs. In (B), 12 leaf discs obtained from five independent plants served as one treatment.

(C) to (F) Effects of Ca²⁺ channel inhibitors on innate immunity against B. cinerea in tomato. Four-week-old tomato plants were treated with 10 µM PSK, 20 μM each Ca²⁺ channel inhibitor, or water 12 h before B. cinerea inoculation.

(C) Representative chlorophyll fluorescence imaging of ΦPSII at 2 dpi. Bar = 1 cm.

(D) Representative images of trypan blue staining for cell death in tomato leaves at 2 dpi. Bar = 250 µm.

(E) Quantification of ΦPSII at 2 dpi.

(F) Relative B. cinerea actin transcript abundance in infected leaves at 1 dpi. The results in (E) and (F) are presented as mean values ± sd; n = 3 leaves from different plants. Different letters indicate significant differences between treatments (P < 0.05, Tukey’s test).

The above experiments were repeated three times with similar results.