Involved in cytokinin-mediated development (PubMed:20011053, PubMed:29467189). Together with SOFL2, triggers the endogenous content of specific bioactive cytokinins derived from the biosynthetic intermediates trans-zeatin riboside monophosphate (tZRMP) and N(6)-(Delta(2)-isopentenyl)adenosine monophosphate (iPRMP) such as N-glucosides trans-zeatin 7-glucoside (tZ7G), cis-zeatin 7-glucoside (cZ7G) and N(6)-(Delta(2)-isopentenyl)adenine 7-glucoside (iP7G) (PubMed:20011053). Predominantly expressed in the vascular tissues of seedlings, developing leaves, flowers and siliques, but barely detectable in roots and stems. In seedlings, strong levels in the hydathode region of cotyledons as well as in the upper part of hypocotyls and weak content in the vascular tissue of cotyledons (PubMed:20011053). In developing leaves, strongly expressed in the midrib of leaf veins, but weak levels in the hydathode regions (PubMed:20011053). In developing flower buds, accumulates in pistil tips and the vascular tissue of stamens and sepals (PubMed:20011053). In mature flowers, detected in the vascular bundles between the two anther locules, the central vascular cylinders of the filaments, vascular tissues of tips of the pistils, and sepal vascular tissue (PubMed:20011053). Also present in tips and bases of developing siliques, and progressively restricted to the vascular tissues at the silique tips (PubMed:20011053). Domains SOFL-A and SOFL-B are required for function in cytokinin-mediated development. No obvious developmental defects (PubMed:20011053). Plants missing both SOLF1 and SOLF2 have reduced endogenous cytokinin levels and accumulate lower levels of trans-zeatin riboside monophosphate (tZRMP) and N(6)-(Delta(2)-isopentenyl)adenosine monophosphate (iPRMP), biosynthetic intermediates of bioactive cytokinins as well as decreased response to exogenous cytokinin in both callus-formation and inhibition-of-hypocotyl-elongation assays (PubMed:20011053). Belongs to the SOFL plant protein family.