title: Cytokinin inhibits lateral root initiation but stimulates lateral root elongation in rice (Oryza sativa).
abstract: Research in lateral root (LR) development mainly focuses on the role of auxin. This article reports the effect of cytokinins (kinetin and trans-zeatin) on LR formation in rice (Oryza sativa L.). Our results showed that cytokinin has an inhibitory effect on LR initiation and stimulatory effect on LR elongation. Both KIN and ZEA at a concentration of 1 microM and above completely inhibited lateral root primordium (LRP) formation. The inhibitory effect of cytokinin on LR initiation required a continuous presence of KIN or ZEA in the growth solution. Cytokinin did not show any inhibitory effect on LR emergence from the seminal root once LRPs had been formed. The LRPs that developed in cytokinin-free solution can emerge normally in the solution containing inhibitory concentration (1 microM) of KIN and ZEA. The KIN and ZEA treatment dramatically stimulated LR elongation at all the concentrations tested. Maximum LR elongation was observed at a concentration of 0.01 microM KIN and 0.001 microM ZEA. The epidermal cell length increased significantly in LRs of cytokinin treated seedlings compared to those of untreated control. This result indicates that the stimulation of LR elongation by cytokinin is due to increased cell length. Exogenously applied auxin counteracted the effect of cytokinin on LR initiation and LR elongation, suggesting that cytokinin acts on LR elongation through an auxin dependent pathway.
authors.affiliation: Faculty of Agriculture, Kagawa University, Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0701, Japan. bakuldebi@yahoo.com
authors.forename: Bakul
authors.initials: B
authors.lastname: Rani Debi
authors.forename: Shin
authors.initials: S
authors.lastname: Taketa
authors.forename: Masahiko
authors.initials: M
authors.lastname: Ichii
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology; D048429:Cell Size / Q000187:drug effects; D003583:Cytokinins / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D007210:Indoleacetic Acids / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D007701:Kinetin; D012275:Oryza / Q000187:drug effects* / Q000254:growth & development*; D019441:Plant Epidermis / Q000166:cytology; D018517:Plant Roots / Q000187:drug effects* / Q000254:growth & development*; D036226:Seedlings / Q000187:drug effects / Q000502:physiology; D015026:Zeatin / Q000378:metabolism / Q000494:pharmacology
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D007211:Indoles; C014612:indolebutyric acid; C030737:indoleacetic acid; D015026:Zeatin; D000225:Adenine; D007701:Kinetin