GrainGenes

II.36. Ring chromosome plants in barley.

R. J. Singh and T. Tsuchiya. Department of Agronomy, Colorado State University, Fort Collins, Colorado 80521, U.S.A.

A plant with 14 + 1 ring chromosome was obtained in the progeny of a primary trisomic for chromosome 7 (semierect). The ring chromosome was identified in somatic cells. Morphologically, the plant with 14 + 1 chromosome was similar to the primary trisomic for chromosome 7 (semierect). Meiosis of the plant with 14 + 1 ring chromosome was studied. It is generally difficult to analyze pachytene chromosomes in barley, but the ring chromosome was located outside the main group of chromosomes. At Metaphase I most (82.38%) of the time the ring chromosome did not associate with its homologues and remained as a univalent, while the ring chromosome was associated with its homologous chromosomes to form a trivalent in 17.62% sporocytes. At Anaphase I, 27.05% cells showed 8-8 chromosome separation. This indicates that the ring chromosome was divided at Anaphase I. The ring chromosome did not move to either pole in 38.23% cells and remained in the equatorial region of the cell and in some cells (10.02%) it formed interlocked bridge. No cell without a ring chromosome was observed indicating that this chromosome is fairly stable throughout the development of tissues and organs. This ring chromosome condition is different from those obtained in maize by McClintock (1938) and in Agropyron by Tsunewaki (1959).

Three spikes were obtained after maturity and 11, 13, and 1 seeds were obtained from Spike #1, #2, and #3, respectively. Seeds from each spike were germinated separately and chromosomes were counted in somatic cells. No ring chromosome was observed from the seeds of Spike #1 and #3, indicating that ring chromosome was completely eliminated in these spikes. Three plants having ring chromosomes were obtained from Spike #2 (two plants with 14 + 1 ring and one plant with 14 + 2 ring chromosomes). The frequency of transmission of ring chromosome in Spike #2 was 23.08%.

Morphological characteristics of the three plants with the extra ring chromosome together with diploid and primary trisomic siblings were studied. The ring chromosome plants were morphologically similar and appeared similar to primary trisomics for chromosome 7.

Studies on elimination of the ring chromosome in mitosis were conducted. Root tips were collected at 24 hours and 28 days after germination. The plants with 14 + 1 ring chromosome were fairly stable but 14 + 2 chromosome plants were unstable.

References:

McClintock, B. 1938. Genetics 23:315-376.
Tsunewaki, K. 1959. Can. J. Bot. 37:1271.
(Supported partly by NSF Research Grant GB30493 to T. Tsuchiya.)

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