Synthesis of nucleosomal histone variants during wheat grain development.

The synthesis and distribution of histone subfractions (variants) were investigated during early grain development and in mature tissues of wheat (Tritium aestivum L.). Histones were extracted from purified chromatin and separated by two-dimensional polyacrylamide gel electrophoresis. There were no detectable differences in the patterns of histone variants from immature grain (3-16 days after fertilization), from mature embryos, from coleoptiles and roots of 4-day-old, etiolated seedlings and from leaves of 10-day-old, light-grown seedlings. Wheat H2 histones are composed of families of closely related variants. H2A consists of three major variants, and H2B consists of two major and four minor variants. The synthesis of these variants during early grain formation was determined by calculating the specific activities of the [3H]lysine-labeled proteins synthesized between 3 and 10 days after fertilization. The rate of synthesis of the nucleosomal histones closely parallels the declining rate of cell division in developing grains. Our results indicate that all the recognized wheat histone variants are present in developing wheat grains from the earliest time investigated (3 days after fertilization) and persist with no detectable changes in relative quantities throughout grain development and in several mature tissues.