Polyploidy in the Differentiation and Function of Tissues and Cells in Plants

SUMMARYThe actually available data on the occurrence of polyploidy in plant tissues and cells have been critically reviewed. The incidence of polyploidy in the plant body, the cytological mechanisms by which the polyploid condition is produced, the physiological and general significance of polyploidy in the « soma » of plant organisms and related questions have been considered.The most common mechanism of polyploidization acting in plant tissues and cells appears to be supernumerary chromosome reproduction. This is responsible for polysomaty in root and shoot meristems as well as for polyploidy in any type of differentiated tissues and for nuclear growth in general. During the development of ephemeral tissues, such as the anther tapetum, supernumerary chromosome reproduction has been sometimes found to occur intermingled with monochromosome mitoses and/or typical endomitosis of the Gerris-type.Abortive mitoses due to spindle disturbances and chromosome stickiness or both are a very common polyploidization mechanism in ephemeral tissues, such as the anther tapetum and the endosperm. The reasons for believing that a tetraploid (or polyploid) cell with a single nucleus is similar to a coenocyte of the same valence of « ploidy » are presented.The problem of the applicability of experimental mitosis stimulation as a tool for cytological studies of differentiated tissues is discussed, also in connection with the actually available methods of DNA determination in the same tissues.Some cases of histological differentiation in a diploid condition and the typical chimerical constitution of the plant body are finally considered.