Temporal and tissue specificity of enzyme coding genes in the developing kernel

--Carla Frova and Gloria Padoani

Data in the literature indicate that in maize several enzyme coding genes are developmentally regulated during the male gametophytic phase (Frova et al., 1987, in Curr. Topics Biol. Med. Res., vol. 15), seed germination (Scandalios et al., Dev. Gen. 4:281-293, 1984) and in the endosperm of immature kernels (Chandlee and Scandalios, Dev. Gen. 4:99-115, 1983). Here we report data on gene expression in different tissues of the developing kernel at 7, 14, 21 and 25 days after pollination (DAP). Four tissues--scutellum+embryo, endosperm, aleurone, pericarp--were analyzed in two genotypes: F198 and W22Rsc. The latter (kindly provided by Prof. G. Gavazzi) is characterized by a strong pigmentation in the aleurone layer, so that separation of this tissue is easy.

The following enzymatic systems were considered: ADH, GOT, CAT, B-GLU, for a total of 6 isozymes. Extracts from each sample were analyzed by native PAGE followed by specific staining for each enzyme. The results allow the identification of three patterns of expression:

1) Genes showing both tissue and temporal specificity. Glu1 belongs to this group. This enzymatic activity was found only in scutella up to 14 DAP. A residual activity was present at 21 DAP but not in later stages.

2) Genes which reveal only quantitative variations between tissues and stages. This is the case for Cat1. The strongest activity is expressed by the aleurone, the weakest by the endosperm, scutellum and pericarp showing an intermediate level. In all tissues the activity increases with development.

3) Genes which show quantitative variations between tissues but not developmental stages. In this preliminary survey this was the most represented group. Adh1, Got1, Got2 and Got3 show this type of regulation. In all of them enzymatic activity was lowest in the pericarp. Differences between enzymes were found with regard to the other tissues. While ADH-1 and GOT-1 are mainly expressed in scutella and endosperms, and to a lesser extent in the aleurone, GOT-2 activity is stronger in scutella than in triploid tissues (endosperm and aleurone); the reverse is found for GOT-3. This difference in the level of activity between GOT-2 and GOT-3 is not found in other sporophytic tissues, including the scutellum of germinating seeds (24 hrs of imbibition).

We are now extending the analysis of these enzymatic systems to very early (0-7 DAP) and late (21-40 DAP) kernel development.


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