An immunoaffinity purified plant natriuretic peptide analogue modulates cGMP levels in the Zea mays root stele

Natriuretic peptides (NPs) are a family of peptide hormones strongly implicated in the regulation of salt and water homeostasis in vertebrates. Recently, evidence has been presented for the presence of a NP hormone system in plants. Atrial natriuretic peptide (ANP) bound specifically to isolated leaf membranes and promoted stomatal opening in a concentration and conformation dependent manner. We have immunoaffinity purified biologically active plant NP analogues from Hedera helix (ivy). Here we report that one of these immunoreactive plant NP fractions rapidly and specifically increases cyclic guanosine-3',5'-monophosphate (cGMP) levels in stele tissue isolated from maize roots within 30 s. ANP and kinetin do not affect cGMP levels in maize root stele tissue. Moreover LY 83583 an inhibitor of guanylate cyclase does not affect any of these responses. Since LY 83583 does not always inhibit particulate guanylate cyclase, these results support the existence of a membrane bound PNP receptor containing intrinsic guanylate cyclase activity analogous to animal NP receptors. We postulate the presence of biologically active PNP system in the stele and speculate that it modulates solute movements in and out of this tissue.