title: Differential spatial expression of A- and B-type CDKs, and distribution of auxins and cytokinins in the open transverse root apical meristem of Cucurbita maxima.
abstract: OBJECTIVE
  Aside from those on Arabidopsis, very few studies have focused on spatial expression of cyclin-dependent kinases (CDKs) in root apical meristems (RAMs), and, indeed, none has been undertaken for open meristems. The extent of interfacing between cell cycle genes and plant growth regulators is also an increasingly important issue in plant cell cycle studies. Here spatial expression/localization of an A-type and B-type CDK, auxin and cytokinins are reported in relation to the hitherto unexplored anatomy of RAMs of Cucurbita maxima.
  
  
  METHODS
  Median longitudinal sections were cut from 1-cm-long primary root tips of C. maxima. Full-length A-type CDKs and a B-type CDK were cloned from C. maxima using degenerate primers, probes of which were localized on sections of RAMs using in situ hybridization. Isopentenyladenine (iPA), trans-zeatin (t-Z) and indole-3yl-acetic acid (IAA) were identified on sections by immunolocalization.
  
  
  RESULTS
  The C. cucurbita RAM conformed to an open transverse (OT) meristem typified by an absence of a clear boundary between the eumeristem and root cap columella, but with a distinctive longitudinally thickened epidermis. Cucma;CDKA;1 expression was detected strongly in the longitudinally thickened epidermis, a tissue with mitotic competence that contributes cells radially to the root cap of OT meristems. Cucma;CDKB2 was expressed mainly in proliferative regions of the RAM and in lateral root primordia. iPA and t-Z were mainly distributed in differentiated cells whilst IAA was distributed more uniformly in all tissues of the RAM.
  
  
  CONCLUSIONS
  Cucma;CDKA;1 was expressed most strongly in cells that have proliferative competence whereas Cucma;CDKB2 was confined mainly to mitotic cells. iPA and t-Z marked differentiated cells in the RAM, consistent with the known effect of cytokinins in promoting differentiation in root systems. iPA/t-Z were distributed in a converse pattern to Cucma;CDKB2 expression whereas IAA was detected in most cells in the RAM regardless of their proliferative potential.
authors.affiliation: Dipartimento di Ecologia, Università della Calabria, Arcavacata di Rende, Cosenza, Italy.
authors.forename: Adriana
authors.initials: A
authors.lastname: Chiappetta
authors.forename: Leonardo
authors.initials: L
authors.lastname: Bruno
authors.forename: Amelia
authors.initials: A
authors.lastname: Salimonti
authors.forename: Antonella
authors.initials: A
authors.lastname: Muto
authors.forename: Jessica
authors.initials: J
authors.lastname: Jones
authors.forename: Hilary J
authors.initials: HJ
authors.lastname: Rogers
authors.forename: Dennis
authors.initials: D
authors.lastname: Francis
authors.forename: Maria Beatrice
authors.initials: MB
authors.lastname: Bitonti
mesh_terms: D000595:Amino Acid Sequence; D028464:Cucurbita / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D018844:Cyclin-Dependent Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D007210:Indoleacetic Acids / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D017422:Sequence Analysis, DNA
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010940:Plant Proteins; D018844:Cyclin-Dependent Kinases