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The Effect of Sucrose on the Differentiation of Excised Fern Leaf Tissue into Either Gametophytes of Sporophytes ¹

^a Department of Botany, University of California, Berkeley, California 94720

Excised juvenile leaves of Microgramma vacciniifolia (Polypodiaceae) develop sporophytic regenerants when grown on mineral agar with sucrose. The ratio of sporophytes to gametophytes produced from the leaf tissue increases with higher percentages of sucrose such that at 4% sucrose, the induction of aposporous gametophytes is a rare occurrence. Experiments varying the osmotic potential with sorbitol and those holding the osmotic potential of the culture medium constant while varying the sucrose level indicate that the effect of sucrose on the differentiation of fern leaf tissue into either gametophyte or sporophyte is nutritional rather than osmotic. A significant effect of sucrose in altering the differentiation of fern leaf tissue is the increased rate of senescence promoted by high sucrose concentrations.

¹ This work was supported in part by a University of California Chancellor's Patent Fund grant and by a Grant-in-Aid from Sigma Xi, the Scientific Research Society of North America. Submitted in partial fulfillment of the Ph.D. degree, to the Department of Botany, University of California, Berkeley.