title: Spatial and temporal profiles of cytokinin biosynthesis and accumulation in developing caryopses of maize.
abstract: OBJECTIVE
  Cytokinins are a major group of plant hormones and are associated with various developmental processes. Developing caryopses of maize have high levels of cytokinins, but little is known about their spatial and temporal distribution. The localization and quantification of cytokinins was investigated in maize (Zea mays) caryopsis from 0 to 28 d after pollination together with the expression and localization of isopentenyltransferase ZmIPT1 involved in cytokinin biosynthesis and ZmCNGT, the gene putatively involved in N9-glucosylation.
  
  
  METHODS
  Biochemical, cellular and molecular approaches resolved the overall cytokinin profiles, and several gene expression assays were used for two critical genes to assess cytokinin cell-specific biosynthesis and conversion to the biologically inactive form. Cytokinins were immunolocalized for the first time in maize caryopses.
  
  
  RESULTS
  During the period 0-28 d after pollination (DAP): (1) large quantities of cytokinins were detected in the maternal pedicel region relative to the filial tissues during the early stages after fertilization; (2) unpollinated ovules did not accumulate cytokinins; (3) the maternal nucellar region showed little or no cytokinin signal; (4) the highest cytokinin concentrations in filial endosperm and embryo were detected at 12 DAP, predominantly zeatin riboside and zeatin-9-glucoside, respectively; and (5) a strong cytokinin immuno-signal was detected in specific cell types in the pedicel, endosperm and embryo.
  
  
  CONCLUSIONS
  The cytokinins of developing maize caryopsis may originate from both local syntheses as well as by transport. High levels of fertilization-dependent cytokinins in the pedicel suggest filial control on metabolism in the maternal tissue; they may also trigger developmental programmed cell death in the pedicel.
authors.affiliation: National Institute of Biology, Večna pot 111, Ljubljana, Slovenia.
authors.forename: Tomaz
authors.initials: T
authors.lastname: Rijavec
authors.forename: Mukesh
authors.initials: M
authors.lastname: Jain
authors.forename: Marina
authors.initials: M
authors.lastname: Dermastia
authors.forename: Prem S
authors.initials: PS
authors.lastname: Chourey
mesh_terms: D003583:Cytokinins / Q000096:biosynthesis*; D056625:Endosperm / Q000166:cytology / Q000378:metabolism; D005638:Fruit / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D017403:In Situ Hybridization; D056771:Ovule / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000166:cytology / Q000378:metabolism; D013997:Time Factors; D003313:Zea mays / Q000033:anatomy & histology* / Q000196:embryology / Q000235:genetics / Q000378:metabolism*
chemical_list: D003583:Cytokinins; D010940:Plant Proteins; D012333:RNA, Messenger