Cytosolic alkalization and cytosolic calcium oscillation in Arabidopsis guard cells Response to ABA and MeJA

Abscisic acid (ABA)- and methyl jasmonate (MeJA)-induced stomatal closure are accompanied by cytosolic alkalization in guard cells. However, it remains to be clarified how the alkalization functions in not only ABA signaling but also MeJA. We investigated cytosolic alkalization in guard cells during ABA-, MeJA- and Ca²⁺-induced stomatal closure of wild type, abi1-1, abi2-1, ost1-2 and coi1 using a pH-sensitive fluorescent dye, BCECF-AM. ABA induced cytosolic alkalization in guard cells of wild-type and coi1 but not in ost1-2 guard cells whereas MeJA elicited cytosolic alkalization in wild-type and ost1-2 guard cells but not in coi1. Neither ABA nor MeJA induced cytosolic alkalization in abi1-1 and abi2-1 guard cells. Exogenous Ca²⁺ induced stomatal closure accompanied by cytosolic alkalization in guard cells of wild-type, abi1-1, abi2-1, ost1-2 and coi1 plants. An agent to acidify cytosol, butyrate, suppressed Ca²⁺-induced cytosolic alkalization and ABA-, MeJA- and Ca²⁺-induced cytosolic Ca²⁺ oscillation in wild-type guard cells to prevent stomatal closure. These results indicate that cytosolic alkalization and cytosolic Ca²⁺ oscillation coordinately function in ABA and MeJA signaling in Arabidopsis guard cells.