Differential Regulation of Trichome Formation on the Adaxial and Abaxial Leaf Surfaces by Gibberellins and Photoperiod in Arabidopsis thaliana (L.) Heynh

Abstract

In wild-type (WT) Columbia and Landsberg erecfa ecotypes of Arabidopsis fhaliana (L.) Heynh., trichomes are present on the adaxial surfaces of all rosette leaves but are absent from the abaxial surfaces of the first-formed leaves. We have determined that both long-day (LD) photoperiod and gibberellin (CA) stimulate trichome formation. WT plants grown in L D conditions produce the first abaxial trichome on earlier leaves than plants grown in short-day (SD) conditions. Photoperiod sensitivity of abaxial trichome formation on WT plants develops gradually over time, reaching the maximum sensitivity about 24 d after germination. Application of gibberellic acid t o WT plants growing in SD conditions accelerates the onset of abaxial trichomes. Conversely, application of 20 to 80 mg LU' paclobutrazol, a CA biosynthesis inhibitor, t o wild-type plants suppresses trichome initiation on the abaxial epidermis. The CAdeficient mutants ga7-5 and ga4-7 and the GA-insensitive mutant g a t l exhibit delayed onset of abaxial trichomes when grown i n L D conditions. l h e null mutant gal-3 produces completely glabrous leaves when grown in SD conditions. Application of gibberellic acid to glabrous ga7-3 plants consistently induces earlier formation of trichomes on the adaxial epidermis than on the abaxial epidermis, demonstrating a difference between the adaxial and abaxial surfaces in their response to CA with regard t o trichome formation.A common feature of the leaves of dicotyledonous species is their dorsiventral asymmetry. If a leaf is cut through its midrib along the long axis of the leaf, the two sides separated by the incision are typically mirror images of each other. However, if the cut is made through the center of the mesophyll layer, parallel to the plane of the leaf surface, the two portions separated by the incision are dorsiventrally asymmetrical. This is because palisade mesophyll occurs immediately below the adaxial epidermis, whereas spongy mesophyll occurs immediately above the abaxial epidermis. Superficial features such as stomata, wax deposition, and trichomes are also often differentially distributed on the two leaf surfaces. Despite the widespread occurrence of dorsiventrality in leaf development, relatively little is known about the genes and the mecha-

Gibberellins Promote Flowering of Arabidopsis by Activating the LEAFY Promoter

“…A similar differential effect on vegetative phase change has been observed in ga1-3 and other late-flowering mutants. The production of abaxial trichomes on leaves and bracts, an indicator of vegetative phase change, is blocked by the ga1-3 mutation in both long and short days (Chien and Sussex, 1996;Telfer et al, 1997). Similar to the observations for LFY promoter activity, none of the late-flowering mutations examined by Telfer et al (1997) abolished abaxial trichome production, although several flowered later than did ga1-3 mutants in long days.…”

Efeitos da radiação ultravioleta-B sobre a morfologia foliar de Arabidopsis thaliana (L.) Heynh. (Brassicaceae)

“…Alguns estudos indicam que a formação de tricomas, principalmente da face adaxial parece ser regulada, diferentemente da formação de tricomas da face abaxial, por fitohormônios como a giberelina (Telfer et al 1997;Traw & Bergelson 2003). Devido a diferenças fisiológicas entre as duas faces da folha, a formação de tricomas na face abaxial é mais tardia durante o desenvolvimento foliar (Chien & Sussex 1996;Telfer et al 1997). Provavelmente, a ausência de tricomas na face adaxial das folhas tratadas com UV-B, seja resultado do efeito direto e negativo da radiação UV-B associado à ação dos fitohormônios sobre as células da protoderme durante o desenvolvimento foliar.…”

GeBP and GeBP-Like Proteins Are Noncanonical Leucine-Zipper Transcription Factors That Regulate Cytokinin Response in Arabidopsis

“…Cytokinins, which positively regulate cell division (RiouKhamlichi et al, 1999;Howell et al, 2003;Ferreira and Kieber, 2005), are required for meristem function and maintenance (Giulini et al, 2004;Leibfried et al, 2005;Kurakawa et al, 2007). GAs and auxin act antagonistically to cytokinins with GAs promoting cell differentiation (Chien and Sussex, 1996;Ogas et al, 1997;Perazza et al, 1998;Hay et al, 2002) and auxin promoting organ initiation (Reinhardt et al, 2000). Cytokinin signaling in plants is similar to the bacterial two-component phosphorelay system composed of a His kinase sensor and a response regulator.…”