Estimation of parthenogenesis frequency on the grounds of genetical and embryological data --Tyrnov, VS, Smolkina, YV, Titovets, VV We have investigated the line AT-3, described before (Tyrnov, MNL 71:73-74, 1997), characterized by pseudogamous reduced parthenogenesis. The frequency of this phenomenon depend on delays in pollination and can reach 50-100%.

In these experiments, we pollinated a week after appearance of silks. We used the pollen of a purple tester; matroclinic haploids and diploids were diagnosed by colour and plant morphology.

For embryological analysis the ears were fixed in acetoalcohol 7-8 days after appearance of silks. Enzymatic maceration of ovaries was used for isolation of embryo sacs. The usual frequency of haploid plants reached 12.1%, with 6.7% of haploids in monoembryonic seedlings, and 5.4% in twins and triplets. The frequency of diploid matroclinic plants was small, about 0.2%.

Among twins the following cytological types were revealed: n-n, n-n-n, n-2n, n-2n-n, n-n-2n, 2n-2n. Diploid twins were mainly of hybrid origin. Only one was matroclinic.

Approximately 100 embryo sacs from each ear were examined cytoembryologically. In all, 535 embryo sacs were examined. Non-typical, for maize, events included: 1) autonomous embryo - 16.3%; 2) autonomous endosperm - 4.7%; 3) some eggs - 11.2%; 4) egg-like synergids - 7.1%; 5) additional embryo sacs - 3.2%.

The above embryological peculiarities were manifested independently or in combination as follows: a) separate or simultaneous embryo- and endospermogenesis; b) globular embryo + one or some eggs; c) one or some globular embryos; d) some eggs + two synergids; e) egg + egg-like synergids; f) two embryos + two eggs + two synergids.

Apparent additional embryo sacs were observed in the region of antipodal disposition. They were in different stages of formation ( from unicellular to 5-6-cellular) and reached one half the size of a normal embryo sac. They may be of aposporic origin. However this question needs additional investigation.

Observation showed formation of mono- and polyembryonic haploids, even triplets of n-n-n type. The potential opportunities for egg-like synergids remain unclear: are these cells able to produce embryos or not? The high frequency (more than 7%) of egg-like synergids in parthenogenetical lines indicates an obvious connection of this phenomenon with parthenogenesis. It could be used as an indicator of embryo capability for parthenogenesis.

As a whole, the frequency of phenomena connected with parthenogenesis on an embryological level is significantly higher (about 40%) than the frequency of their manifestation in plants (about 12-13%). This can be explained by an earlier discovery that endospermogenesis in lines of the AT series does complete (Enaleeva, Tyrnov, MNL 67:74-75, 1997), so that a portion of autonomous embryos perish. In addition, embryogenesis also probably can not always complete, since a rather great number of seeds without embryos (approximately from 1 to 20%) was observed.

This work was supported by a grant from the Russian Foundation for basic Research.
 
 


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