International Database for Barley Genes and Barley Genetic Stocks

BGS 474, Laxatum-a, lax-a

BGN  46:113
Stock number: BGS 474
Locus name: Laxatum-a
Locus symbol: lax-a

Previous nomenclature and gene symbolization:

Laxatum-01 = lax-01 (5, 10, 15).
Laxatum-a = lax-a.01 (16).
Hordeum vulgare laxatum-a = HvLax-a (8).


Monofactorial recessive (11, 15).
Located in chromosome 5HL (11, 14); lax-a.8 is about 2.4 cM proximal from the ari-e (breviaristatum-e) locus (7, 17); lax-a.8 is about 3.1 cM from the ert-g (erectoides-g) locus (7, 16, 17); lax-a.8 is associated with SNP markers 2_1065 to 2_1275 (positions 40.91 to 104.73 cM) in 5H of the Bowman backcross-derived line BW457; lax-a.ap is associated with SNP markers 1_0621 to 2_1275 (positions 56.40 to 104.73 cM) in 5H of the Bowman backcross-derived line BW458 (2), the deletion associated with the lax-a.8 mutant mapped near SNP marker 2_0524 (8), in 5H bin 04.


Florets have five anthers with two developing from transformed lodicules (5, 19); however, the extra anthers are deficient in having two rather than four microsporangia (1). The grain is thin and angular and caryopses are exposed between the lemma and palea. The awn has a very wide base, without a distinct notch in the lemma attachment region. Rachis internodes are about 15% longer than normal. Tillers arise at oblique angles giving isolated plants an appearance of a tufty growth habit (10). Treatment of leaves after tillering with GA3 increases rachis internode length (18). Plants of Bowman backcross-derived for lax-a.8, BW457, were 4/5 the height of Bowman and anthesis was delayed by 3 to 4 days. Awns were slightly shorter than normal. Kernels were short and thin and highly variable in size. Compared to Bowman, BW457 plants had kernel weights about 60% of normal, test weights were low, and grain yields were about half of normal (4). The thinner grains are largely exposed due to reduced marginal growth of the palea and lemma. Flowers of the lax-a.8 mutants can open without the impetus force of lodicule swelling (8). The lax-a locus was identified as a homolog of the Arabidopsis genes BLADE-ON-PETIOLE1 (BOP1) and BOP2. The HvLax-a gene and its paralog HvCul4 are involved in primarily regulating spike morphology and tiller number, respectively (8). Evaluation of natural alleles at the Lax-a locus identified one predominant haplotype and nine minor haplotype variants (8).

Origin of mutant:

A gamma-ray induced mutant in Bonus (NGB 14657, PI 189763) (3, 10, 13). More information about the origin and nature of mutants lax-a locus is presented in and by Jost et al. (8).

Mutational events:

lax-a.01 (NGB 116334), -a.4 (NGB 116338), -a.8 (NGB 116342, GSHO 1775), -a.20 (NGB 116354), -a.37 (NGB 116372), -a.39 (NGB 116374), -a.54 (NGB 116388) in Bonus (NGB 14657, PI 189763) (11, 12); lax-a.92 (NGB 116425) in Bonus (12); lax-a.208 (NGB 116435), -a.218 (NGB 116446), -a.222 (NGB 116450), -a.229 (NGB 116457), -a.256 (NGB 116483), -a.278 (NGB 116503), -a.286 (NGB 116510) in Foma (NGB 14659, CIho 11333) (10, 12); -a.353 (NGB 116559), -a.369 (NGB 116578), -a.373 (NGB 116583), -a.398 (NGB 116608), -a.405 (NGB 116613), -a.406 (NGB 116614) in Kristina (NGB 14661, NGB 1500) (11); -a.413 (NGB 116621), -a.434 (NGB 116647), -a.437 (NGB 116650), -a.444 (NGB 116658), -a.448 (NGB 116664), -a.450 (NGB 116667), -a.455 (NGB 116674), -a.472 (NGB 116695) in Bonus (12); a lax-a mutant (Mut 2100/61) in Proctor (PI 280420) (6); lax-a.ap (FN50) in Steptoe (CIho 15229) (9); a lax-a erect2 mutant (NGB 119823 in Bonus (11).

Mutant used for description and seed stocks:

lax-a.8 (NGB 116342, GSHO 1775) in Bonus; lax-a.8 in Bowman (PI 483237)*7 (GSHO 2103, BW457, NGB 20689); lax-a.ap from Steptoe in Bowman*4 (BW458, NGB 22153).


1. Bossinger, G., W. Rohde W, U. Lundqvist U, and F. Salamini F. 1992. Genetics of barley development: mutant phenotypes and molecular aspects. p. 231-264. In P.R. Shewry (ed.) Barley: Genetics, Biochemistry, Molecular Biology and Biotechnology. CAB International, Oxford.

2. Druka, A., J. Franckowiak, U. Lundqvist, N. Bonar, J. Alexander, K. Houston, S. Radovic, F. Shahinnia, V. Vendramin, M. Morgante, N. Stein, and R. Waugh. 2010. Genetic dissection of barley morphology and development. Plant Physiology 155:617-627.

3. Ehrenberg, L., Å. Gustafsson, and U. Lundqvist. 1961. Viable mutants induced in barley by ionizing radiations and chemical mutagens. Hereditas 47:257-278.

4. Franckowiak, J.D. (Unpublished).

5. Gustafsson, Å., A. Hagberg, U. Lundqvist, and G. Persson. 1969. A proposed system of symbols for the collection of barley mutants at Svalöv. Hereditas 62:409-414.

6. Häuser, H., and G. Fischbeck. 1972. Translocations and genetic analysis of other mutants. Barley Genet. Newsl. 2:28-29.

7. Jensen, J. 1981. Construction of a barley chromosome 7 linkage map. p. 927-939. In M.J.C. Asher, R.P. Ellis, A.M. Hayter, and R.N.H. Whitehouse (eds.) Barley Genetics IV. Proc. Fourth Int. Barley Genet. Symp., Edinburgh. Edinburgh Univ. Press, Edinburgh.

8. Jost, M., S. Taketa, M. Mascher, A. Himmelbach, T. Yuo, F. Shahinnia, T. Rutten, A. Druka, T. Schmutzer, B. Steuernagel4, S. Beier, S. Taudien, U. Scholz, M. Morgante, R. Waugh, and N. Stein. 2016. A homolog of Blade-On-Petiole 1 and 2 (BOP1/2) controls internode length and homeotic changes of the barley inflorescence. Plant Physiol. 171:1113-1127.

9. Kleinhofs, A. (Unpublished).

10. Larsson, H.E.B. 1985. Morphological analysis of laxatum barley mutants. Hereditas 103:239-253.

11. Larsson, H.E.B. 1985. Linkage studies with genetic markers and some laxatum barley mutants. Hereditas 103:269-279.

12. Lundqvist, U. (Unpublished).

13. Persson, G. 1969. An attempt to find suitable genetic markers for the dense ear loci in barley II. Hereditas 63:1-28.

14. Persson, G., and A. Hagberg. 1965. Localization of nine induced mutations in the barley chromosomes. Barley Newsl. 8:52-54.

15. Persson, G., and A. Hagberg. 1969. Induced variation in a quantitative character in barley. Morphology and cytogenetics of erectoides mutants. Hereditas 61:115-178.

16. Søgaard, B. 1974. Three-point tests on chromosome 1 and 7. Barley Genet. Newsl. 4:70-73.

17. Søgaard, B. 1977. The localization of eceriferum loci in barley. IV. Three point tests of genes on chromosome 7 in barley. Carlsberg Res. Commun. 42:35-43.

18. Stoy, V., and A. Hagberg. 1967. Effects of growth regulators on ear density mutants in barley. Hereditas 58:359-384.

19. Wettstein, D. von, Å. Gustafsson, and L. Ehrenberg. 1959. Mutationsforschung und Züchtung. p. 7-50. In Arbeitsgemeinschaft für Forschung des Landes Nordrhein-Westfalen, Heft 73. Westdeutscher Verlag Köln und Opladen.


H.E.B. Larsson and U. Lundqvist. 1986. Barley Genet. Newsl. 16:57.


U. Lundqvist and J.D. Franckowiak. 1997. Barley Genet. Newsl. 26:421-422.
U. Lundqvist and J.D. Franckowiak. 2007. Barley Genet. Newsl. 37:273-274.
U. Lundqvist and J.D. Franckowiak. 2010. Barley Genet. Newsl. 40:120-121.
U. Lundqvist and J.D. Franckowiak. 2010. Barley Genet. Newsl. 46:113-115.