The Biology of Pomegranate Pollen: All about Formation, Morphology, Viability, Germination and Events relating to Sperm Nuclei

Investigation of pollen biology (i.e. morphology, viability, germination capacity, development of pollen tube and sperm nuclei) of pomegranates, an andromonoecious species, was aimed in this study with the aid of microscopy. Pollens were collected from the Punica granatum L. cv. ‘Caner II’ at different phenological stages. Morphological features showed that the pollen is prolate with smooth exine surface. Viability was higher in the staminate flowers but germination capacity was better in the bisexuals. Pollen germination begins after it leaves the microsporangium. During pollen tube elongation, the pollen cytoplasm, vegetative nucleus and generative cells are transported within the pollen tube. Before entering the pollen tube, the generative cell undergoes mitosis and form two haploid generative cells. Differences in pollen viability and germination ratio of the flower types were found to be insignificant. Polar length was maximum (28.5 μm) in both sexual morphs and minimum (26.8 μm) in the perfect flower. The width of pollen grains ranged from 15.9 μm to 17.1 μm in both types. Perfect and functional male flowers had small pollen (15.9-27.3 μm) with grooves on the surface without perforations. The surface displayed regular continuities where it was between the protrusions. The surface of pollen grains from both of flowers was striate, with more parallel longitudinal ridges in functional male flower. The pollen from both sexes is about the same size. These findings not only provide information on basic features of pomegranate pollen and its pollination biology, but also can help understand breeding and decide strategies to develop better cultivars.