Anther and pollen morphology and anatomy in walnut (Juglans regia L.)

Abstract

The morphology and ultrastructure of anthers and pollen grains were described for eight walnut (Juglans regia L.) cultivars (Sebin, Bilecik, Kaman I, Kaplan 86, Yalova 3, Pedro, Hartley, and Franquette) using light microscopy and scanning and transmission electron microscopy. Anther and pollen dimensions and pollen production capabilities were also determined. The mean number of stamens per staminate flower (14.90 to 20.03) and mean anther dimensions (1412.5 to 2553.5 mu m in length and 849.0 to 1145.5 mu m in width) differed significantly among the cultivars. The number of pollen grains per anther also varied significantly and ranged from 4720 to 9840 among the cultivars. The pollen grains of walnut plants are spherical in shape (nearly circular) and pantocolporate (with many colporate apertures on the exine). The pollen surface is microechinate with spiniferous projections. The germination pores are circular and nonbordered. Pollen grain length varied from 33.35 to 37.50 mu m in the examined cultivars. The ultrastructure of the pollen walls was similar between walnut cultivars. The exine was comprised of nexine and sexine, which was thicker than the underlying nexine. The sexine appeared as a strong tectum that was traversed by thin channels and decorated with spinulose processes. The thicknesses of the various layers of the pollen wall were as follows: intine: 82.1 to 200 nm; exine: 793.1 to 1161.1 nm; and total wall: 954.4 to 1327.8 nm.