The late embryoidogenesis in maize anther culture and the composition
of mature embryoids provides further regeneration and secondary callusogenesis.
We observed that the majority of embryoids in the moment of their departure
from an anther had the organs typical for mature zygotic embryos, such
as scutellum and root and shoot points of growth, but often they were abnormally
altered. In the scutellum a 1-2-layer epidermis with very little starch
was seen. In some cases it was modified into multilayer epidermal tissue,
or nipple-shaped epidermis with a large amount of starch. The subepidermal
layer usually developed into multicellular tissue and differed with superproduction
of starch. The filling of its cells with plenty of starch grains, often
huge, led to different cellular abnormalities, such as the crushing of
the nucleus with growing starch grains, the appearance of nuclei of irregular
form, the formation of 2-nuclear cells due to disruption of the cell wall
and fusion of two nuclei. In parenchyma of the central part of the scutellum
great starch accumulation was also observed but nuclei here were normal,
and cells were not compact. In the central part of the scutellum sometimes
single, extremely large cells with nuclei of irregular shape occurred.
We observed also abnormalities of root and shoot points of growth leading
to the decline of regeneration ability, such as the absence of meristematic
zone in the well-formed root eminence or stem bud; the development of callus
on the coleoptile; or the squeezing of the stem bud with neighboring embryoids,
which did not allow it to emerge normally. These abnormalities partially
explain the fact that the number of embryoids which had given the seedlings
by emergence was considerably lower than the number of embryoids transferred.
Thus, for genotypes B14xWf9, B14xAnd44 and And44xDK201 the regeneration
frequencies were correspondingly 24.14, 40.54 and 54.55%. The critical
size of embryoids at the time of their departure from an anther also apparently
had great value. If the length of embryoid had been less than 3mm, only
22.95% were able to undergo the regeneration of seedlings. If it had been
from 3mm to 6mm and more, the regeneration frequency increased to 36.31%.
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