isopentenyladenine

Isopentenyladenine (iP) is a plant hormone in the cytokinin family. It is a purine derivative in which an isopentenyl group is attached to the N6 position of adenine. In plants, iP is found both as the free-base molecule and in phosphorylated or sugar-linked forms, such as isopentenyladenosine (the riboside) and the corresponding nucleotides, including isopentenyladenine-5′-monophosphate (iPMP).

Biosynthesis occurs when isopentenyl transferases (IPTs) transfer an isopentenyl moiety from dimethylallyl diphosphate (DMAPP) to adenosine monophosphate, generating iPMP. Subsequent ribosylation yields the riboside (iP riboside), and phosphatases or kinases modify the nucleotide pool to produce the free base, riboside, and other phosphorylated forms that participate in metabolism and signaling.

Isopentenyladenine acts as a cytokinin by binding to surface receptors of the histidine-kinase type (AHKs) and triggering a phosphorelay through histidine phosphotransfers (AHPs) to response regulators (ARRs). This signaling modulates gene expression related to cell division, shoot formation, leaf senescence, and other developmental processes. Cytokinin activity interacts with auxin signaling to influence organogenesis and vascular development.

Within plants, iP is enriched in meristems, young leaves, and roots and participates in delaying senescence. In plant tissue culture and horticulture, iP and its derivatives are used as plant growth regulators to promote shoot proliferation and improve regeneration, often in combination with auxins. Natural and synthetic cytokinins including iP contribute to developmental outcomes depending on concentration, tissue type, and environmental conditions.