Microsporogenesis and ultrastructure of pollen grains in the cocoa plant, Theobroma cacao

Introduction: We know of no studies on the microsporogenesis of the cocoa plant, and little is known about the ultrastructure of its pollen grains. Objective: To describe microsporogenesis and ultrastructure of pollen grains in T cacao. Methods: We processed over 30 flowers for each floral stage and stained with Safranin-Alcian Blue, PAS-Amidoblack and Lacmoid. For transmission microscopy we processed samples on resin and stained with toluidine blue. For scanning electron microscopy, we fixed and dehydrated in 2.2-dimethoxypropane, critically dried and coated with gold. Results: Anthers differentiated by a cellular mass at the ends distal to the staminal filaments. During development, the anther wall has several cellular layers reduced, at maturity, to the epidermis and endothecium. Microspore mother cells divide by meiosis to form tetrads. The tapetum is secretory and intact until the grains are released, to later degenerate. Pollen grains are isopolar, spheroidal, small, tricolpate. Ultrastructure has a semi-tectate sporodermis, with reticulate ornamentation, and heterobrochated reticulum with the muri without ornamentation. Exine is deposited before intine. The orbicles are individual, smooth, and varied in size. There is abundant pollenkitt on the tectum and between the columellae. The intine is thin, but develops widely in the colpus areas, forming a compact internal intine and an unusual external intine with a columellated appearance. Conclusion: Anther structure and development follows the angiosperm pattern. Simultaneous microsporogenesis and centripetal deposition of the sporodermis are known from Malvaceae, but intine characters are novel for the family. Key words: cocoa; Malvaceae; microspore; palynology; pollen ontogeny; sporodermis; tapetum. Introduccion: No conocemos estudios sobre la microsporogenesis de la planta de cacao, y poco se sabe sobre la ultraestructura de sus granos de polen. Objetivo: Describir la microsporogenesis y ultraestructura de los granos de polen en T. cacao. Metodos: Procesamos mas de 30 flores para cada etapa floral, tenidas con Safranina-Azul Alcian, PAS-Amidoblack y Lacmoid. Para la microscopia de transmision procesamos las muestras en resina y las tenimos con azul de toluidina. Para microscopia electronica de barrido, fijamos y deshidratamos en 2.2-dimetoxipropano, secamos hasta un punto critico y recubrimos con oro. Resultados: Anteras diferenciadas por una masa celular en los extremos distales a los filamentos est