Effect of low temperature on the nucleolus of larkspur (Delphinium Ajacis L.) meiocytes.

In comparison with stage specific modifications of nucleolus in the early stages of meiotic prophase in Delphinium Ajacis meiocytes, the effect of low temperature is described. On the contrary to control leptotene nucleolus, exhibiting intermingled fibrillar and granular components, cold induced a disappearance of fibrillar material from these organelles. Disappearance of fibrillar material was accompanied by marked diminishment of 3H-uridine incorporation. NOR in control as well as in cold treated material was present. Zygotene nucleolus being in eccentric position displayed segregation of granular and fibrillar components, especially well visible in cold treated cells. In the area occupied in control material by NOR, cold treated cells were found to contain the numerous dark granules. The application of Bernhard's EDTA technique and enzymatic digestion with RNase, DNase and pepsine have proved that the dark granules are composed of RNA. Although pachytene nucleolus still pressed to nuclear envelope exhibited compact structure, composed probably of fibrillar and granular elements, in cold treated meiocytes it showed only the presence of granular component. Moreover, in cold treated cells some dark granules of RNA character were visible at the surface of nucleolus. No was absent. In addition to these changes, in the cytoplasm of cold treated cells in pachytene stage a material of nucleolar origin has appeared. The meiotic irregularities described in the present paper are discussed in relation to the partial male sterility that occurs in Delphinium meiocytes growing in a low temperature.