H. Schreiber¹ and A. Habekuß²
In crosses involved the completely linked loci v and lk on chromosome 2 and the B locus on chromosome 5 it could be proved that changed gene expression, aberrant ratios and somatic instabilities are due to a high frequency of somatic non-reciprocal recombination events (SCHREIBER, 1992a,b,c). In further analyses of the crosses of the mutant line 152 with the initial variety `Saale' and marker stocks somatic instability at heterozygot loci was frequently exhibited (Table 1). Three marker loci dispersed on the chromosomes 1, 4 and 5 tested in detail showed similar patterns of somatic instability, i.e. sectors, mosaics, spots and twin sectors of wild or mutant phenotype, respectively, dependent on the stage of the somatic events.
Table 1. Frequencies of plants with somatic sectoring
___________________________________________________________________________ |Cross |Character |Number of | |Rate of | | | |plants tested|with |somatic | | | | |somatic |sectoring | | | | |sectoring| | |________________________|____________|_____________|_________|___________| |Master x Line 152 |Waxy | | | | | |starch | 237 | 18 | 7,6x10^-2^| |EP.79 x Line 152 |Black lemma | | | | | |and pericarp| 791 | 86 |10,9x10^-2^| |Master x (H5 x Line 152)|Black lemma | | | | | |and pericarp| 12 | 1 | 8,3x10^-2^| |Saale x Line 152 |Blue | | | | | |aleurone | 1808 | 291 |16,1x10^-2^| |________________________|____________|_____________|_________|___________|Only a fraction of these genetic changes came into germinal cells and was transferred to the next generation. This resulted in various degrees of deviations from the expected 3:1 segregation ratio. Table 2 shows that of a total of 76 tested progenies 34 (44,7 %) exhibited a aberrant ratio in aleurone colour and 8 (10,5 %) in the waxy character. Surprisingly, 20 (26,3%) of the 76 progenies revealed aberrant ratios in both aleurone colour and waxy character.
In the same manner the somatic instability of the B-marker was connected with a deviation in the ratio of the waxy character (Fig. 1). Furthermore, changes in neighbouring endosperm cells were observed. A increased intensity of blue aleurone colour was correlated with darker iodine stained adjacent starch cells (Fig. 2).
Table 2. Number of aberrant ratios and normal 3:1 segregating in common between the two characters aleurone colour (blue/white) and starchy/waxy starch (iodine stained endosperm) in comparison to single character ratios of the cross Master (blbl wxwx) x Line 152 (BlBl WxWx)
_______________________________________________________________________ |Number of progenies|Aberrant ratio |3:1 ratio | |tested |Aleurone Waxy In common|Aleurone Waxy In common| |___________________|________________________|________________________| | 76 | 34 8 20 | 7 33 15 | |___________________|________________________|________________________|
_______________________________________ | |Number of kernels | | | | Normal Waxy |X²3:1| | |___________________|______| |Observed | 61 | 5 | 10,7 | |Expected | 49,5 | 16.5 | | |__________|____________|______|______|
Fig. 1: Ear with white-black variegated and black coloured kernels (B-locus, chromosome 5) shows simultaneously a deviation of the expected 3:1 ratio in the waxy character (wx-locus, chromosome 1)
Moleculargenetic investigations will be carried out to understand the nature of the genetic changes and to find out eventually the structural component mediated the coordinated events. Besides the question arrises whether this recombination system can be used for gene targeting.
References:
SCHREIBER, H. 1992: High non-reciprocal recombination in a barley cross. BGN
22: 63-64
SCHREIBER, H. 1992: Genetische Instabilität bei der Gerste: Beweise für nicht reziproke Rekombinationsereignisse in der v-lk Region. Biol.Zent.-bl. 111: 228-240
SCHREIBER, H. 1992: Kontinuierliche genetische Veränderungen in der vom B-Locus der Gerste kodierten Spelzen- und Perikarpfärbung. Biol. Zent.-bl. 111: 241-253