title: Growth and cellular patterns in the petal epidermis of Antirrhinum majus: empirical studies.
abstract: OBJECTIVE
  Analysis of cellular patterns in plant organs provides information about the orientation of cell divisions and predominant growth directions. Such an approach was employed in the present study in order to characterize growth of the asymmetrical wild-type dorsal petal and the symmetrical dorsalized petal of the backpetals mutant in Antirrhinum majus. The aims were to determine how growth in an initially symmetrical petal primordium leads to the development of mature petals differing in their symmetry, and to determine how specific cellular patterns in the petal epidermis are formed.
  
  
  METHODS
  Cellular patterns in the epidermis in both petal types over consecutive developmental stages were visualized and characterized quantitatively in terms of cell wall orientation and predominant types of four-cell packets. The data obtained were interpreted in terms of principal directions of growth (PDGs).
  
  
  RESULTS
  Both petal types grew predominantly along the proximo-distal axis. Anticlinal cell walls in the epidermis exhibited a characteristic fountain-like pattern that was only slightly modified in time. New cell walls were mostly perpendicular to PDG trajectories, but this alignment could change with wall age.
  
  
  CONCLUSIONS
  The results indicate that the predominant orientation of cell division planes and the fountain-like cellular pattern observed in both petal types may be related to PDGs. The difference in symmetry between the two petal types arises because PDG trajectories in the field of growth rates (growth field) controlling petal growth undergo gradual redefinition. This redefinition probably takes place in both petal types but only in the wild-type does it eventually lead to asymmetry in the growth field. Two scenarios of how redefinition of PDGs may contribute to this asymmetry are considered.
authors.affiliation: Department of Biophysics and Morphogenesis of Plants, University of Silesia, Jagiellońska 28,40-032 Katowice, Poland.
authors.forename: Magdalena
authors.initials: M
authors.lastname: Raczyńska-Szajgin
authors.forename: Jerzy
authors.initials: J
authors.lastname: Nakielski
mesh_terms: D032161:Antirrhinum / Q000166:cytology* / Q000254:growth & development*; D002455:Cell Division; D002473:Cell Wall / Q000378:metabolism; D035264:Flowers / Q000166:cytology / Q000254:growth & development; D008954:Models, Biological; D019441:Plant Epidermis / Q000166:cytology / Q000254:growth & development
keywords: Antirrhinum majus; Principal directions of growth, cellular pattern; backpetals mutant; cell wall orientation; dorsal petal; epidermis; symmetry; tetrad types