In last year's issue we reported evidence of HSP synthesis in immature pollen, 12 days after meiosis. In this note we present data on HSPs induced at different stages of microspore maturation.
Pollen development within the anther was divided into three stages: (A) From meiosis to first mitotic division, (B) First and second mitotic division, and (C) Trinucleate pollen maturation. Each stage was analyzed for HSP synthesis by SDS-PAGE in a gradient 5-20% gel system.
High molecular weight HSPs approximately 84 and 72 Kd are induced in all stages following heat-shock (37 C). Some genotypes show an additional 94 Kd band starting from stage B.
In the 40-69 Kd range two stage-specific HSPs were found: a 46 Kd band appeared only in stage A, while a 66 Kd band is synthesized through stages B and C. These two HSPs are not inducible in sporophytic tissues.
In the low molecular weight range only an 18 Kd HSP was detectable, but the pattern through development is not very clear because overall incorporation of 35S-methionine in immature microspores is low and therefore this non-prominent HSP appears very faint. Further analysis is under way to clarify this point.
The analysis of sporophytic HSPs was continued on additional genotypes. Genetic variability for several HSPs was detected. In particular, a low molecular weight 17 Kd band, additional to the normal HSP pattern, was found in several inbred lines. A preliminary genetic analysis shows that the F1 hs17+/hs17- also synthesizes this band.
C. Frova, G. Binelli and E. Ottaviano
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