Promotes plant cell differentiation, organogenesis and somatic embryogenesis as well as cell proliferation (By similarity). May be involved in the low quiescent center cell proliferation. Expressed in stems, roots, mature leaves and flowers. Most abundant in vascular bundles. Up-regulated by ERF115, by brassinosteroid treatment, wounding and fungal infection. Sulfation is important for activity and for the binding to a putative membrane receptor. PSK-beta is an enzymatic derivative of PSK-alpha. Belongs to the phytosulfokine family.