ABNORMAL STOMATAL DEVELOPMENT IN FOLIAGE LEAVES OF BEGONIA ARIDICAULIS

DEHNEL, GEORGE S. (U. Missouri, Columbia.) Abnormal stomatal development in foliage leaves tf Begonia aridicaulis. Amer. Jour. Bot. 48(2): 129-133. Illus. 1961.-The results of 2 types of aberrant stomatal development in abaxial epidermis of normal laminae of B. aridicaulis are discussed and illustrated. The more common is a so-called persistent stomatal initial that is an essentially circular cell (in face view) with chloroplasts and a wall of uniform thickness. The other type of anomalous development yields a single guard cell, -Ahich possesses chloroplasts, differential wall thickening, rarely a pore, and a form characteristic of a normally paired guard cell. Both types of cells may either be isolated or occur variably in close relationship to normal stomata. IN AN unpublished dissertation (Dehnel, 1957), a report was made of attempts to induce the guard cells of Begonia aridicaulis Zies. to divide and resume growth by artificial application of various chemical growth regulators. Although these attempts were unsuccessful, there was revealed during the course of the study a wide range of developmental stomatal anomalies in abaxial epidermis of normal leaves. It is felt that a description of the extent of structural and morphological variability of the cells resulting from this aberrant development would be of interest. Reports of naturally occurring, or experimentally induced, abnormal stomatal cells have appeared occasionally in the literature. Brat and Weber (1951) observed persistent stomatal initials2 in petals of Nyrnphaea zanzibariensis growing under normal conditions, while Kenda and Weber (1950) discussed their occurrence in green, leaf-like, corolla members of Verbascum blattaria. The writer has seen these chloroplast-filled cells in abaxial epidermis of laminae of Zantedeschia aethiopica. Gertz (1919) discussed and illustrated persistent initials associated with galls of fungal and insect etiology. Reports of induction of persistent stomatal initials by various experimental procedures have been made by Weber (1943), Tonzig and Ott-Candela (1946), and Weissenb5ck (1949), employing colchicine, and by Kropfitsch using ultra-violet light (1951a) and apple (ethylene) gas (1951b). MATERIALS AND METHODS.-The plant used was Begonia aridicaulis Zies. Voucher specimens are on file in the University of California Herbarium, Berkeley. Plants were grown in a general soil potting mixture and kept in a greenhouse at a temperature of approximately 750F. A minimum of 2,200 mm.2 of abaxial epidermis was inspected for presence of abnormal stomatal 1 Received for publication May 7, 1960. This paper represents a portion of a Ph.D. dissertation completed in the Dept. of Botany, Univ. of Calif., Berkeley, under the direction of Prof. A. S. Foster. 2 A persistent stomatal initial is defined as a generally circular epidermal cell filled with chloroplasts. cells. One sample of 25 mm.2 was removed from each of 24 separate leaves, and another of 16 mm.2 from each of 100 leaves. Only newly mature foliage leaves from clones derived from one original plant were used, and the areas of each leaf sampled occupied the same position in the lamina. Accuracy of sampling was ensured by making paradermal hand sections with razor blades. The free-hand sections were stored in vials of 70% ethyl alcohol. Camera lucida drawings were prepared from temporary unstained mounts in 70% alcohol. Care was taken to depict accurately the visible number, size, and shape of chloroplasts, as well as the position and size of nuclei. If no nucleus was observed in a particular cell, it was omitted from the drawing. OBSERVATIONS.-Basically, the results of 2 types of anomalous stomatal development were observed: (1) an essentially circular cell containing chloroplasts and without differential wall thickening; and (2) a single cell characterized mainly by a form, chloroplasts, differential wall thickening, and, only rarely, a pore like that of paired guard cells. In all laminae, by far the more common anomaly was the persistent stomatal initial (fig. 1, 15). These cells occurred most commonly in association with one or more stomata.3 When isolated the form, as observed in face viewv, is a nearly perfect circle (fig. 1). Such persistent initials may develop also in the position normally occupied by one pair of guard cells of paired stomata (fig. 2). Indeed, judging from the arrangement and shape of the 3 cells adjacent to the initial (cf. fig. 1, also), it seems possible that this persistent initial may have developed from a regular stomatal initial after it had formed subsidiary cells-the final division, which would have yielded paired guard cells, being eliminated. In this particular instance, 1 guard cell of the pair is degenerating. Two stomata, and occasionally 3, in close association are common in abaxial epidermis of B. aridicaulis. 3 Stoma (sing.) stomata (pl.) is here defined as, basically, paired guard cells plus the included pore.