Leaf periderm supports longevity and functionality of crown leaves in Agathis species (Araucariaceae)

Abstract

Periderm of the leaves of two Agathis species was studied. Agathis leaves are long-lived and remain alive for more than 25 years. Periderm occurs regularly and can be initiated in the epidermis, mesophyll, phloem parenchyma of the leaf veins and in the ground tissue of the petiole. Periderm lies on the surface, is located in the mesophyll or splits it. Periderm structure is either typical, consisting of phellogen, multilayered phellem and phelloderm or disordered. Agathis leaves are able to form true wound periderm, which has been shown experimentally. We believe that at least some of the factors inducing periderm initiation are identical both in leaves and in stems. Mechanical tension in the tissues and cell deformation plays an essential role in the periderm initiation. Leaf tissues isolated due to the suberinization process may function as a storage site for the substances not involved in the plant metabolism or excluded from it. Periderm gives an opportunity to keep such substances away from functional tissues, which is important for evergreen plants with long-lived leaves.