Journal Article

Seed-coat Dormancy in <i>Grevillea linearifolia</i>: Little Change in Permeability to an Apoplastic Tracer after Treatment with Smoke and Heat

Candida L. Briggs and E. Charles Morris

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 101, issue 5, pages 623-632
Published in print April 2008 | ISSN: 0305-7364
Published online February 2008 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcn006
Seed-coat Dormancy in Grevillea linearifolia: Little Change in Permeability to an Apoplastic Tracer after Treatment with Smoke and Heat

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims

Seeds of Grevillea linearifolia germinate following fire, and have seed-coat dormancy broken by smoke and heat shock. Smoke breaks seed coat dormancy in Emmenanthe penduliflora by altering the permeability of the seed coat to an internal germination inhibitor, which subsequently escapes. This model was tested for in G. linearifolia by investigating the permeability of the seed coat to diffusion of high-molecular-weight compounds, and whether this changed after exposure to fire cues.

Methods

Germination response of the seeds to heat shock, smoke or heat + smoke was tested. Penetration of Lucifer Yellow dye into intact seeds was examined after 24 and 48 h of exposure, and penetration of the dye from the inside of the seed coat outwards was examined after 24 h. Histochemical staining with Nile Red and Acridine Orange was used to locate cuticles, suberin and lignin.

Key Results

Twenty-three per cent of untreated seeds germinated; heat shock and smoke increased germination additively up to approx. 80 % for both cues combined. Lucifer Yellow did not penetrate fully through the seed coat of untreated seeds, whether diffusing inwards or outwards. Three barriers to diffusion were identified. Treatment with heat or smoke slightly increased penetration of the dye, but did not completely remove the barriers. Suberin was identified in secondary walls of exotestal and mesotestal cells, and was absent from primary cell walls. Movement of Lucifer Yellow occurred through the middle lamella and primary cell wall of suberized cells; movement of the dye was impeded where suberin was absent.

Conclusions

Fire cues did not significantly decrease barriers to diffusion of high-molecular-weight compounds in the seed coat of Grevillea, and must be breaking dormancy by another mechanism.

Keywords: Fire; germination; smoke; heat shock; Lucifer Yellow; seed coat dormancy; apoplastic tracing; confocal; Grevillea linearifolia; suberin

Journal Article.  6988 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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