II. 34. Mitotic and meiotic chromosomal aberrations and pollen fertility in plants grown from artificially aged barley seeds.
M. Murata, T. Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, and E.E. Roos, National Seed Storage Laboratory, USDA-SEA-AR, Fort Collins, Colorado 80523.
Continuing the studies on chromosomal aberrations in barley seeds (Murata et al., 1979), the authors investigated the frequencies of mitotic and meiotic chromosomal aberrations and pollen fertility in plants grown from artificially aged seeds (12% moisture content stored at 32 C).
1. Changes in mitotic chromosomal aberrations with plant growth.
After collecting the primary roots at the first mitotic stage, 20 seedlings per aging treatment were grown in Jiffy-7 pots for 3 weeks in a growth chamber under short-day conditions (8 hours-light at 18 C and 16 hours-dark at lOC) to increase the number of tillers. After 3 weeks' growth, three roots per plant were collected for cytological studies and the plants transplanted to 4-inch pots in a greenhouse at long-day conditions. Two weeks after transplanting (5 weeks' growth), three roots per plant were again cytologically checked.
The frequency of aberrant anaphases at three different growth stages is shown in Table 1. As reported previously (Murata et al., 1979), the frequency of aberrant anaphases at the first mitosis increased with increased time in storage and decreased germination. However, after 3 weeks' growth, their frequency was reduced by 0.25% in the control and about 0.5% and 1.0% in plants from seeds showing 85% and 59% germination. Further reductions in the frequency of chromosomal aberrations were evident after 5 weeks of growth. The frequency of aberrant anaphases appeared to stabilize at 1.13% to 1.40% in spite of larger percentage difference at the first mitosis. This suggests that the chromosomal aberrations induced by seed aging are reduced by some metabolic and/or genetic system during cell divisions.
2. Meiotic chromosomal aberrations and pollen fertility
In order to learn the frequency of chromosomal aberrations at meiosis, ten plants per aging treatment and three tillers per plant were sampled. Meiosis was investigated at the first metaphase (MI), first anaphase (AI), second anaphase (AII) and tetrad stages in the pollen mother cells. After checking the meiotic stages by using one anther out of three in the same flower, the remaining two anthers were fixed in acetic alcohol (1:3) solution. Squash preparation of fixed anthers were made in acetocarmine staining solution (0.8%).
Pollen grains were collected from mature anthers in the middle of spikes. Three spikes per plant and ten plants per treatment were sampled to determine the pollen fertility of each treatment. Pollen grains were stained by acetocarmine solution (0.4%). About 500 grains per preparation were counted and classified according to Kihara's classification (1937).
All plants studied showed the normal configuration with 14 bivalents at the MI stage. Some aberrations were found at AI, AII and tetrad stages (Table 2). However, there were no significant differences among the three different aging treatments. The frequencies of aberrant anaphases at AI were 1.5% to 1.7%. This data confirmed that the mitotic chromosomal aberrations in roots were reduced with plant growth. Furthermore, aberrations at AII were reduced further (0.3% to 0.8%). With respect to the number of micronuclei at the tetrad stage, their frequency was about 0.1% in plants from each aging treatment. This indicates that some cells with chromosomal aberrations were lost between the AI and AII stage and still more between the AII and tetrad stage.
Pollen fertility in plants grown from aged seeds was not significantly different from that of the control plants (Table 2).
Based on these results, it may be concluded that the chromosomal aberrations induced by artificial seed aging are reduced with repeated mitotic cell divisions, with further reduction occurring at meiosis. The effect of the chromosomal aberrations induced by seed aging on pollen fertility was not significant.
References:
Kihara, H. 1937. Genom analyse bei Triticum und Aegilops. VII. Kurze Ubersicht Uber die Ergebnisse der Zare. 1934-1936. Mem. Coll. Agr. Kyoto Imp. Univ. 41:1-61.
Murata, M., E.E. Roos, and T. Tsuchiya. 1979. Relationship between loss of germinability and the occurrence of chromosomal aberrations in artificial seed aging of barley. BGN 9:65-67.
