Inheritance and expression of gametophyte gene Adh-P causing modification of alcohol dehydrogenase in pollen grains of the beet (Beta vulgaris L.)

An additional alcohol dehydrogenase (ADH) activity zone denoted ADH-P ("pollen") has a slightly lower mobility than the major protein ADH1 (the product of structural locus Adh1). This zone is detected in maturing and mature pollen grains and has not been found in any other tissue. ADH-P is detected by electrophoresis in a neutral medium (at pH 7.0-7.2). In an alkaline medium (pH > 8), protein ADH-P is completely inactivated, whereas protein ADH1 retains its activity. ADH-P is a modified variant of the major protein ADH1. Both alleles of the main structural gene (Adh1-F and Adh1-S) undergo modification. The pollen of an FS heterozygote has two variants of the modified enzyme: ADH-PS and ADH-PF. Analysis of segregation in F2 offsprings and test crosses has confirmed that this character is controlled by the only gene Adh-P with allelic variants Adh-P+ (the presence of the modified ADH protein in the pollen) and Adh-P- (the normal protein). Allele Adh-P+ is transmitted through female gametes at a normal frequency (about 1) and through male gametes at a decreased frequency (0.2-0.6), the mean frequency being about 0.4. The frequency of the transmission of allele Adh-P+ through male gametes depends on the genotype of the female parent and the conditions of pollination. Cytoembryological study of microsporogenesis in the Adh-P+/Adh-P- heterozygotes demonstrated an absence of any disturbances in the formation of microspores and pollen grains. Some differences in the formation of pollen tubes on an artificial medium have been observed. It is assumed that the differences between the Adh-P+ and Adh-P- microgametophytes manifest themselves at the progamic phase of fertilization. The possible mechanisms of the formation of the modified ADH-P protein are discussed in connection with the differential activity of genes in the microgametophytes of angiosperms.