Efficiency of the induction of cytomixis in the microsporogenesis of dicotyledonous (N. tabacum L.) and monocotyledonous (H. distichum L.) plants by thermal stress

The efficiencies of the induction of cytomixis in microsporogenesis by thermal stress are compared in tobacco (N. tabacum L.) and barley (H. distichum L.) It has been shown that different thermal treatment schedules (budding tobacco plants at 50°C and air-dried barley grains at 48°C) produce similar results in the species: the frequency of cytomixis increases, and its maximum shifts to later stages of meiosis. However, the species show differences in response. The cytomixis frequency increase in tobacco is more pronounced, and its maximum shifts from the zygotene–pachytene stages of meiotic prophase I to prometaphase–metaphase I. Later in the meiosis, aberrations in chromosome structure and meiotic apparatus formation typical of cytomixis are noted, as well as cytomixis activation in tapetum cells. Thermal stress disturbs the integration of callose-bearing vesicles into the callose wall. Cold treatment at 7°C does not affect cytomixis frequency in tobacco microsporogenesis. Incubation of barley seeds at 48°C activates cytomixis in comparison to the control, shifts its maximum from the premeiotic interphase to zygotene, and changes the habit of cytomictic interactions from pairwise contacts to the formation of multicellular clusters. Thermal treatment induces cytomictic interactions within the tapetum and between microsporocytes and the tapetum. However, later meiotic phases show no adverse consequences of active cytomixis in barley. It is conjectured that heat stress affects callose metabolism and integration into the forming callose wall, thereby causing incomplete closure of cytomictic channels and favoring intercellular chromosome migration at advanced meiotic stages.