ABSTRACT
Fresh pollen grains of Welwitschia mirabilis were irradiated with CuKα X-ray at 35 KV, 20 mA for 35 s and investigated by means of LM and TEM. The aim of this study was to investigate whether pollen tube growth would occur, because our previous research has shown that such development in irradiated pollen is a phenomenon characteristic of angiosperm grains only. In addition our past work has indicated that the degree of degradation or disintegration of the different wall layers at the ultrastructural level to be different in various taxa. This factor appears to depend on the molecular system of the sporopollenin. As Welwitschia mirabilis is important from the taxonomic, phylogenetic and ecological points of view, we initiated this study. In LM analysis we observed pollen tube development, as a result of irradiation, in 17.0% of the investigated pollen grains. Based on TEM data we established the following: The outer layer of the ectexine (tectum) was extremely resistant to irradiation. The granular infratectal layer became damaged; sometimes the granular elements disappeared. Lamellar elements appeared on the inner surface of the foot layer — probably a secondary ultrastructural feature. Important intine thickening, also resulting from irradiation, was also observed in this species. These findings are significant for the study of the effect of radioactivity in recent sediments.
