Gametophytic expression of beta-glucosidase in maize pollen

Many beta-glucosidase variants have been described in maize sporophytic tissues, such as coleoptile, roots, and seedling. The enzyme is a functional dimer, controlled by a single locus with many alleles (C. W. Stuber et al., Bioch. Gen. 15:383-394, 1977). The locus has been localized on chromosome 10 (A. J. Pryor, MGCNL 52:14, 1978). In this note we present data on the distribution of the enzyme, as determined by starch gel electrophoresis, in pollen and immature endosperm tissues.

Extraction from pollen was obtained only with addition of Triton X to the buffer (Tris-Cl 0.1 M pH 8 + Triton X 1%), thus suggesting that the enzyme is wall-bounded. No bands are visible when electrophoresis of pollen extracts is carried out with L-His-citrate buffer system pH 6.3 (C. W. Stuber et al., Bioch. Gen. 15:383-394, 1977). However, when a different buffer system is used (J. G. Scandalios, Bioch. Gen. 3:37-79, 1969) a single gametophytic band appears in one hour, while only very faint bands from sporophytic tissues are obtained after 24 hr. The staining mixture was the same for both gel types: Fast Blue BB 65 mg, 6-Br-2-naphthyl-beta-d-glucopyranoside 30 mg, in 100 ml phosphate buffer 0.5 M, pH 6.5.

The pollen band was the same for all lines examined, independently of their sporophytic variant. Twelve lines were examined without finding any gametophytic variant. The same band is also clearly visible in pollen extracts from beta-glucosidase null plants (seeds furnished courtesy of Dr. M. M. Goodman). Direct staining of in vitro germinated pollen from null plants by means of the previously reported reaction mixture confirms beta-glucosidase activity both in grain and pollen tube.

It thus appears that different genes for beta-glucosidase are expressed in pollen and in sporophytic tissues.

Immature endosperms from some lines were analyzed for the presence of the enzyme. Neither the electrophoretic system suited for the sporophyte, nor the one used for the pollen, were able to reveal beta-glucosidase activity. It might well be that the enzyme is not expressed in the endosperm, or that another enzymatic form is involved in this tissue. Further analysis is aimed at elucidating this point.

C. Frova, M. Sari Gorla and E. Ottaviano

Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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