Abstract
Flooded soybean hypocotyls form secondary aerenchyma (SAE). Unlike lysigenous aerenchyma formed by cell death, SAE is spongy tissue with phellogen-derived living cells and rich intercellular spaces. SAE in some flood-tolerant legumes, as well as lysigenous aerenchyma in rice, contributes to gas exchange between aerial tissues and anaerobic roots, however, little is known about the mechanisms of its formation.
When soybean (cv Enrei) seedlings were flooded, SAE was formed in hypocotyl after 3 to 4 days, and then spread radially and longitudinally, yet SAE formation was almost completely inhibited by 1 μM abscisic acid (ABA). ABA and ethylene (ET) function as negative and positive regulators in responses of rice to complete submergence, respectively, thus we aimed to clarify whether ET is involved in SAE formation in soybean. We selected soybean cDNAs for ET biosynthetic enzymes form public databases, and then examined expression of corresponding genes by qPCR. Expression of an ACC synthase gene (GmACSd) was induced 4 days after flooding; in contrast, it was not induced in ABA-treated seedlings. Therefore, GmACSd is thought to be an ACC synthase gene induced during SAE formation.
