Physiology of polyploids.

Polyploidy, a multiplication of the whole chromosomal complement, is a very widespread phenomenon in higher plants. Natural polyploids have been suggested to be more successful than their diploid progenitors under certain conditions. This success may be due to "balance hybridity," i.e., the combination of the advantage of hybridity together with the balancing of excessive segregation and sterility by chromosome doubling, and possibly also to the effect of genome multiplication per se. The latter effect can be studied independently of the effect of other genetic changes only in autopolyploid newly derived from single ancestral strains. The existing knowledge on the effect of genome multiplication on the physiology of the plant is fragmentary and based on too narrow a representation of plant types; much of the information available on the effect of genome multiplication pertains to the tomato. Various aspects of polyploidy are discussed according to levels of function and organization: gene action, cell characteristics, growth substance, water balance, ion balance, stability of phenotypic expression and the response of polyploid plants to stress. Future work on the physiology of autopolyploid plants should be directed towards: (1) the investigation of more representative experimental systems that should include genetically homogeneous and heterogeneous species of both wild and cultivated plants; and (2) diploid-polyploid comparisons on the level of isolated tissues and cells, in addition to the whole plant.