Stereological Analysis of Floral Development and Quantitative Histochemistry of Nucleic Acids in Fertile and Base-sterile Varieties of Wheat

Abstract

The speltoid series of mutations provides a genetic tool for investigating the control of flower development. In fertile Gabo wheat and in Si2 and S73 basal sterile speltoids, the changes in RNA staining patterns have been followed histochemically as a marker of cellular activity. Sterile floret sites are characterized by a reduced RNA content. Use of dual-wavelength microspectrophotometry has provided evidence that RNA content is similar in lemma primordia subtending presumptive fertile and sterile primordia, but is strikingly different in the floral meristems in the two types. The total nucleic acid content of the floral primordia has been related to the number of epidermal cells in the subtending lemma primordium as a marker of development, using a linear model analysis of covariance. There is a linear increase in nucleic acid content during fertile floret development, but no significant increase in RNA content in sterile St3 primordia. The rate constant is only 1/1 0th to 1 /20th of that of Gabo. A stereological analysis shows that cell number in the floral meristems of Gabo increases exponentially during development. In contrast, in St3 , while there is a significant increase in cell number, it is at a drastically reduced rate. The intercept values are close to zero, indicating that only one or two cells initiate floral meristem development. The fertility-controlling alleles exert their effect prior to the appearance of a visible floral primordium, and probably after initiation of the lemma.