ROOT ANATOMICAL MECHANISMS INVOLVED IN HOST PLANT CONTROL OF ARBUSCULAR MYCORRHIZAL COLONIZATION
Open Access
- Author:
- Sharda, Jori Nerissa
- Graduate Program:
- Plant Biology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 17, 2008
- Committee Members:
- David M Sylvia, Committee Member
Jonathan Paul Lynch, Committee Member
David Eissenstat, Committee Member
Roger Tai Koide, Committee Chair/Co-Chair - Keywords:
- hypodermal passage cells
arbuscular mycorrhizal colonization
root anatomy
hypodermal suberization
phosphorus
intercellular air space - Abstract:
- Mycorrhizal host plants are widely known to be capable of controlling the degree to which their root systems are colonized by arbuscular mycorrhizal fungi. Previous studies to elucidate mechanisms involved in host plant control of colonization have not considered root anatomical changes as potential control mechanisms. Here, I examined three root anatomical variables hypothesized to influence mycorrhizal colonization: the percentage of root length with a suberized hypodermis, the distribution of hypodermal passage cells, and the percentage of root volume as intercellular air space. To test whether changes in these root anatomical variables influence mycorrhizal colonization, interspecific variation in each trait was correlated with mycorrhizal colonization in a diverse assortment of plant species. Hypodermal passage cell distribution was the only variable capable of influencing mycorrhizal colonization via its effect on fungal penetration point formation. Mycorrhizal colonization was not found to be significantly influenced by either the percentage of root length suberized or the percentage of root volume as intercellular air space. Next, I evaluated the effect of P treatment on each of these variables in order to explore whether they might be potential mechanisms involved in phosphorus-mediated control of mycorrhizal colonization. Fifteen species from 13 families were grown at two P availabilities, and the effect of plant P concentration on each variable was assessed. When each plant species was analyzed as a replicate, only the distribution of passage cells was significantly affected by P status; high P plants possessed a reduced percentage of root length with passage cells. Other examined traits did not respond significantly to P status, and individual species responses to P treatment varied widely. I conclude that, while no single anatomical mechanism appears to be responsible in all species, in species with passage cells, altering the percentage of root length with passage cells could serve as one mechanism for P-mediated control of mycorrhizal colonization.