H(2)O(2) and Ca(2+) Signaling Crosstalk Counteracts ABA to Induce Seed Germination

Seed germination is a critical stage and the first step in the plant’s life cycle. H(2)O(2) and Ca(2+) act as important signal molecules in regulating plant growth and development and in providing defense against numerous stresses; however, their crosstalk in modulating seed germination remains largely unaddressed. In the current study, we report that H(2)O(2) and Ca(2+) counteracted abscisic acid (ABA) to induce seed germination in melon and Arabidopsis by modulating ABA and gibberellic acid (GA(3)) balance. H(2)O(2) treatment induced a Ca(2+) influx in melon seeds accompanied by the upregulation of cyclic nucleotide-gated ion channel (CNGC) 20, which encodes a plasma membrane Ca(2+)-permeable channel. However, the inhibition of cytoplasmic free Ca(2+) elevation in the melon seeds and Arabidopsis mutant atcngc20 compromised H(2)O(2)-induced germination under ABA stress. CaCl(2) induced H(2)O(2) accumulation accompanied by the upregulation of respiratory burst oxidase homologue (RBOH) D and RBOHF in melon seeds with ABA pretreatment. However, inhibition of H(2)O(2) accumulation in the melon seeds and Arabidopsis mutant atrbohd and atrbohf abolished CaCl(2)-induced germination under ABA stress. The current study reveals a novel mechanism in which H(2)O(2) and Ca(2+) signaling crosstalk offsets ABA to induce seed germination. H(2)O(2) induces Ca(2+) influx, which in turn increases H(2)O(2) accumulation, thus forming a reciprocal positive-regulatory loop to maintain a balance between ABA and GA(3) and promote seed germination under ABA stress.