Institute of Genetics and Cytology, Belarus Academy of Sciences,
Zhodinslaya 14, 220023 Minsk, Belarus

To elucidate cytoplasmic effects on the expression and recombination of nuclear genes in barley, a collection of iso- and alloplasmic substituted lines was created. Kihara (1951) first to proposed the idea of cytoplasm substitution in wheat. Collections of cytoplasm substituted lines were developed later for Avena, Helianthus, Brassica, Gossypium, Solanum, and Nicotiana. Barley, Hordeum vulgare, was chosen for this study because the nuclear genome is frequently investigated and many morphological and molecular markers are mapped. The creation of substituted barley lines, differing from each other at specific loci in chloroplast and mitochondrial genomes, will facilitate the study of nucleo-cytoplasmic interactions and make barley more useful as a genetic tool.

The nuclear genomes of seven barley cultivars used by breeders in Belarus were combined by repeated backcrosses with each of 12 cytoplasmic variants (kindly provided by M.Clegg). The cytoplasm donor lines included the wild H. spontaneum lines: W1, W3, W4, W5, W7, W8, W9, and W10 (originating from Israel and Iran) and four H. vulgare forms: primitive landraces L1 and L2 from Iran and two cultivars, Himalaya (Iran) and Atlas (California). With this collection of nucleo-cytoplasm substitution lines, we plan to select specific nucleoplasmic combinations that increase the expression of some desirable characteristics and/or inhibit the expression of others.

According to our preliminary results, specific cytoplasms affect the recombination processes in nuclear genomes as well as the sister chromatid exchange (SCE) frequencies (Sychjova et al. 1997). The aim of our investigation is to determine the influence of cytoplasmic genes or gene complexes on the expression of specific nuclear genes and recombination frequencies. Using RFLP techniques, we analyzed the cytoplasmic variants for mitochondrial DNA polymorphisms (Table 1) and compared the results with chloroplast DNA data reported by M.Clegg et al. (l984).

Nine endonucleases were used in the study. Diversity in the mtDNA was found using restriction enzymes EcoRI, BamHl, Pst, Pvu, Hind, and Bsp. Four of the H. spontaneum lines and all H. vulgare cultivars had identical mtDNA patterns (called type A). Each of the other four H. spontaneum lines had an unique mtDNA pattern (types B, C, D, and E). The differences included additional fractions, lack of fragments, and displacement of definite zones (Table 2).

Comparing these results with M. Clegg's data on chloroplast DNA polymorphism, we can identify nine different cytotypes in our collection, each having either unique chlDNA, mtDNA, or both. The most common type of chlDNA is type 3, according to Clegg's classification, which is coupled with four different types of mtDNA. Type A mtDNA is coupled with all five chlDNA types; types B, C, and D mtDNA are found only in combination with type 3 chlDNA; and type E mtDNA is found only with type 4 chlDNA (Table 2).

Certainly, there exist other differences in the primary structure of organelle genomes that can be detected by more precise methods. That is why the next step in our work is to find the exact genes or gene complexes in the defined cytotypes that change the expression of the nuclear genes. This study may help find a means by which the barley breeder can modify gene expression in a favorable manner.

Clegg, M.T., A.H.D. Brown, and P.R. Whitfeld. 1984. Chloroplast DNA diversity in wild and cultivated barley: implications for genetic conservation. Gen. Res. 43:339-343.

Kihara, H. 1951. Substitution of nucleus and its effect on genome manifestations. Cytologia 16:117-193.

Sychjova, I. M., H. A. Aksjonova, and O. G. Davydenko, 1997. The effect of cytoplasm interspecies substitutions on chiasmata and sister chromatid exchanges frequency and on marker gene segregation distortion. p. 48. In Int. Symp. on Current Topics in Plant Cytogenetics Related to Plant Improvement. February 21-22, 1997. Tulln, Austria.

Table 1. Sources of the barley nuclear and cytoplasmic genotypes used generate combinations (84) nuclear and cytoplasmic variants for the barley germplasm collection at Minsk, Belarus.

Table 2. Diversity of the organellar genotypes in the barley collection held at Minsk, Belarus.