Wound regeneration in the lamina of magnoliaceous leaves

Abstract

Reparative tissue was observed around healed natural wounds in leaves of 53 species of 9 of the 12 magnoliaceous genera: Aromadendron, Elmerrillia, Kmeria, Liriodendron, Magnolia, Manglietia, Michelia, Paramichelia, and Talauma. Additional evidence was obtained from wounding experiments carried out on attached leaves of two evergreen species, Magnolia grandiflora and Michelia figo. Regeneration was studied over a 6-week period. Evergreen leaves produced more abundant regenerative tissues than deciduous leaves; a narrow-to-broad periderm forms consistently in all evergreen magnoliaceous leaves around wounds, but wounds in the deciduous species invoke little or no periderm development. The healing process in these leaves consists of three steps: (1) cells die along the wound, and cells immediately adjacent become physiologically altered; (2) a callus forms by randomly oriented cell divisions throughout mesophyll, vein sheath, and (in most species) epidermis; and (3) a periderm eventually forms in the band of callus parallel to the wound. The complete process takes 4 to 6 weeks in the evergreen magnoliaceous plants studied. The differences in healing processes are contrasted between evergreen and deciduous leaves. Of special interest is the observation that guard cells of mature leaves in several taxa dedifferentiate and undergo division in the area of wound repair.