title: Inherited phenotype instability of inflorescence and floral organ development in homeotic barley double mutants and its specific modification by auxin inhibitors and 2,4-D.
abstract: OBJECTIVE
  Barley (Hordeum vulgare) double mutants Hv-Hd/tw2, formed by hybridization, are characterized by inherited phenotypic instability and by several new features, such as bract/leaf-like structures, long naked gaps in the spike, and a wide spectrum of variations in the basic and ectopic flowers, which are absent in single mutants. Several of these features resemble those of mutations in auxin distribution, and thus the aim of this study was to determine whether auxin imbalances are related to phenotypic variations and instability. The effects of auxin inhibitors and 2,4-D (2,4-dichlorophenoxyacetic acid) on variation in basic and ectopic flowers were therefore examined, together with the effects of 2,4-D on spike structure.
  
  
  METHODS
  The character of phenotypic instability and the effects of auxin inhibitors and 2,4-D were compared in callus cultures and intact plants of single homeotic Hv-tw2 and Hv-Hooded/Kap (in the BKn3 gene) mutants and alternative double mutant lines: offspring from individual plants in distal hybrid generations (F9-F10) that all had the same BKn3 allele as determined by DNA sequencing. For intact plants, two auxin inhibitors, 9-hydroxyfluorene-9-carboxylic acid (HFCA) and p-chlorophenoxyisobutyric acid (PCIB), were used.
  
  
  RESULTS
  Callus growth and flower/spike structures of the Hv-tw2 mutant differed in their responses to HFCA and PCIB. An increase in normal basic flowers after exposure to auxin inhibitors and a decrease in their frequencies caused by 2,4-D were observed, and there were also modifications in the spectra of ectopic flowers, especially those with sexual organs, but the effects depended on the genotype. Exposure to 2,4-D decreased the frequency of short gaps and lodicule transformations in Hv-tw2 and of long naked gaps in double mutants.
  
  
  CONCLUSIONS
  The effects of auxin inhibitors and 2,4-D suggest that ectopic auxin maxima or deficiencies arise in various regions of the inflorescence/flower primordia. Based on the phenotypic instability observed, definite trends in the development of ectopic flower structures may be detected, from insignificant outgrowths on awns to flowers with sterile organs. Phenotypically unstable barley double mutants provide a highly promising genetic system for the investigation of gene expression modules and trend orders.
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania Raimondas.Siuksta@gf.vu.lt.
authors: Raimondas
authors: R
authors: Šiukšta
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Virginija
authors: V
authors: Vaitkūnienė
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Greta
authors: G
authors: Kaselytė
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Vaiva
authors: V
authors: Okockytė
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Justina
authors: J
authors: Žukauskaitė
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Donatas
authors: D
authors: Žvingila
authors: Department of Botany and Genetics, Faculty of Natural Sciences, Vilnius University, M. K. Čiurlionis Str. 21/27, LT-03101 Vilnius, Lithuania and Botanical Garden of Vilnius University, Kairėnai Str. 43, LT-10239 Vilnius, Lithuania.
authors: Vytautas
authors: V
authors: Rančelis
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology*; D002264:Carboxylic Acids / Q000494:pharmacology; D002995:Clofibric Acid / Q000494:pharmacology; D035264:Flowers / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D001467:Hordeum / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D007210:Indoleacetic Acids / Q000037:antagonists & inhibitors*; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002264:Carboxylic Acids; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D015084:2,4-Dichlorophenoxyacetic Acid; D002995:Clofibric Acid
keywords: 2; 4-D; Auxin inhibitors; Hordeum vulgare; barley; double mutants; floral organ growth; flower development; flower structure; homeotic mutants; phenotypic instability; specific normalization