Periplasmic multilamellar membranous structures in Nicotiana tabacum L. pollen grains treated with Ni2+ or Cu2+

Essential trace elements Ni²⁺ and Cu²⁺ can block pollen germination without causing cell death. Mechanisms of this effect remain unclear. Using TEM, we studied the effects of Ni²⁺ or Cu²⁺ treatment on the ultrastructure of the aperture regions in tobacco pollen preparing to germinate in vitro, since in these zones, the main fluxes of water, ions, and metabolites cross the plasmalemma. Neither Ni²⁺ nor Cu²⁺ altered the cytoplasm ultrastructure, but both affected the reorganization of apertural periplasm during pollen activation. Numerous multilamellar membranous structures continuous with the plasma membrane could be seen in hydrated but not yet activated pollen. When the normal activation was completed, the structures disappeared and the plasmalemma became smooth. In the presence of 1 mM Ni²⁺ or 100 μM Cu²⁺, these structures preserved its original appearance. It is assumed to be the storage form for the membrane material, which is to provide an initial phase of the pollen tube growth. Ni²⁺ and Cu²⁺ affect the utilization of these membranes, thereby, blocking the pollen germination.