Phosphoglucomutase
activity in developing endosperms
--David Pan, Lisa Strelow and Oliver
Nelson
The developing endosperms of most plants
investigated have two phosphoglucomutase (PGM) isozymes. One is the amyloplast
enzyme, the other is a cytosolic enzyme, and these isozymes are separable
by starch gel electrophoresis. Assaying extracts of inbred maize endosperms
22 days postpollination by starch gel electrophoresis has shown that the
majority of the inbreds have only one isozyme present. It has been demonstrated
that the isozyme present in all inbreds is the amyloplast form. The inbreds
B73, W22, SDP312, W552, A632, H49, B84, A540, B37, N22, and Oh43 have only
amyloplast PGM. The inbreds W64A, Mo17, and W570 have both isozymes as
does the sweet corn inbred, P39.
The separations by column chromatography
(DEAE-cellulose) of the extracts from N22 and Oh43 reveal only a single
peak of activity, indicating that the single zone of activity observed
on SGE is unlikely to result from two isozymes that migrate to exactly
the same zone.
The lack of the cytosolic isozyme has
no discernible phenotypic consequence. It appears that this enzyme is completely
dispensable for normal endosperm development. It is also possible that
the absence of this enzyme is one of the cryptic deficiencies (along with
many others) that contribute to the lessened vigor and lower productivity
that characterize inbred lines and that is often redressed by crossing
to an unrelated inbred line. This hypothesis is testable, and we are proceeding
to do so.
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