Gamma-radiation induces leaf trichome formation in Arabidopsis

Abstract

We observed induction of additional trichome formation on the adaxial surface of mature leaves of Arabidopsis after massive doses (1-3 kilograys) of gamma-radiation from cobalt-60. A typical increase in trichome number was observed in the seventh leaf when the full expansion of the fifth leaf was irradiated. Under normal growth conditions, trichome numbers on the adaxial surface of seventh leaf of the Arabidopsis ecotypes Columbia (Col) and Landsberg erecta (Ler) were 122.5 +/- 22.7 and 57.5 +/- 14.5, respectively. However, gamma-radiation induced additional trichome formation and the numbers rose to 207.9 +/- 43.7 and 95.0 +/- 27.1 in Col and Ler, respectively. In Col the shape of new trichomes was intact and their formation was spatially maintained at equal distances from other trichomes. In Ler trichome morphology was aberrant and the formation was relatively random. Treatment with antioxidants before gamma-irradiation suppressed the increase in trichome number, and treatment with methyl viologen and light induced small trichomes. These results suggest that gamma-radiation-induced trichome formation is mediated by active oxygen species generated by water radiolysis. gamma-Radiation-induced trichome formation was blocked in the trichome mutants ttg-1, gl1-1, and gl2-1. These results suggest that gamma-radiation-induced trichome formation is mediated by the normal trichome developmental pathway.

Figure 1

Increase of trichome number after γ-radiation. Trichome numbers on the adaxial surfaces of sixth and seventh leaves of Col and Ler were counted and their distribution is indicated in green. When the fifth leaf was fully expanded, about 18 d post germination, 2 kGy of γ-rays from cobalt-60 were given. Three days later, the trichome numbers on the sixth and seventh leaves were counted and their distribution is shown in red.

Figure 2

Scanning electron micrographs of the leaf surface. A, Adaxial surface of the seventh leaf of Col. Bar = 1 mm. B, Adaxial surface of the seventh leaf of γ-radiated Col. Bar = 1 mm. C, Adaxial surface of seventh leaf of Ler. Bar = 1 mm. D, Adaxial surface of γ-radiated Ler. Bar = 1 mm. E, Trichome with aberrant branching observed on the adaxial surface of γ-radiated Ler. Bar = 0.2 mm. F, Twin trichome observed on the adaxial surface of γ-radiated Ler. Bar = 0.2 mm.

Figure 3

Scanning electron micrographs of the leaf surface of plant treated with methyl viologen. A, Adaxial surface of the seventh leaf of Col treated with methyl viologen and grown for 3 d under light. Small trichome-like hairs are indicated with “O.” Bar = 0.5 mm. B, Magnified view of A. Bar = 0.2 mm.

Figure 4

Scanning electron micrographs of the leaf surface of trichome mutants treated with γ-radiation. A, Adaxial surface of the seventh leaf of the gl1-2 mutant. Bar = 1 mm. B, Adaxial surface of the seventh leaf of γ-radiated gl1-2 mutant. Bar = 1 mm. C, Adaxial surface of the seventh leaf of the gl2-1 mutant. Bar = 1 mm. D, Adaxial surface of the seventh leaf of γ-radiated gl2-1 mutant. Bar = 1 mm. E, Immaturely branched trichome observed on the surface of leaf shown in D. Bar = 0.2 mm. F, Adaxial surface of the gl3-mutant. Bar = 1 mm. G, Adaxial surface of γ-radiated gl3-1 mutant. Bar = 1 mm. H, New trichomes induced by γ-radiation of the ttg-1 mutant. Bar = 1 mm. I, Immature trichome induced by γ-radiation of the rhd2-1 mutant. Bar = 0.2 mm.