Abstract
We report the kinetics of embolus formation and collapse in the tracheids of Thuja occidentalis L. stem segments. Radial wood sections were trimmed to 4 mm long paralleling the tracheids by 1 mm wide and 0.1 mm thick. They were observed under a dissecting microscope at 128x while sections were dehydrated and rehydrated. During dehydration, cavitations resulted in the formation of emboli in tracheids, but we concluded that the cavitated tracheids did not immediately fill with air at atmospheric pressure. This conclusion was based on the time required for the emboli to collapse after the rewetting of the dehydrated segment. By hypothesis, the time for the emboli to collapse should be proportional to the amount of air in the emboli. The time for all the emboli to collapse was a linear function of the dehydration time for times up to 15 min. For dehydrations greater than 80 min, the time for collapse after rewetting was constant, and we concluded that the tracheids have saturated with air by 80 min of dehydration. The kinetics of embolus formation is discussed in terms of the air-seeding hypothesis for cavitation, and collapse is discussed in terms of the physics of gas dissolution and diffusion. Embolus formation and dissolution in intact herbaceous and woody plants should follow the same physical laws.
Full Text
The Full Text of this article is available as a PDF (1.8 MB).
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Cochard H., Cruiziat P., Tyree M. T. Use of positive pressures to establish vulnerability curves : further support for the air-seeding hypothesis and implications for pressure-volume analysis. Plant Physiol. 1992 Sep;100(1):205–209. doi: 10.1104/pp.100.1.205. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sperry J. S. Relationship of Xylem Embolism to Xylem Pressure Potential, Stomatal Closure, and Shoot Morphology in the Palm Rhapis excelsa. Plant Physiol. 1986 Jan;80(1):110–116. doi: 10.1104/pp.80.1.110. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sperry J. S., Tyree M. T. Mechanism of water stress-induced xylem embolism. Plant Physiol. 1988 Nov;88(3):581–587. doi: 10.1104/pp.88.3.581. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Tyree M. T., Yang S. Hydraulic Conductivity Recovery versus Water Pressure in Xylem of Acer saccharum. Plant Physiol. 1992 Oct;100(2):669–676. doi: 10.1104/pp.100.2.669. [DOI] [PMC free article] [PubMed] [Google Scholar]