ROOT ETIOLATION AS A STRATEGY FOR PHOSPHORUS ACQUISITION IN COMMON BEAN
Open Access
- Author:
- De la Riva, Laurie Morrow
- Graduate Program:
- Horticulture
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 02, 2010
- Committee Members:
- Jonathan Paul Lynch, Thesis Advisor/Co-Advisor
- Keywords:
- phosphorus
root anatomy
root etiolation - Abstract:
- It has been proposed that roots should favor primary growth (elongation) over secondary growth (thickening) in response to low phosphorus availability, in order to increase soil exploration, a process termed “root etiolation” by analogy with shoot responses to low light intensity. The objectives of this study were to evaluate the role of root etiolation in phosphorus acquisition under sub-optimal phosphorus conditions as an adaptive trait and to confirm genotypic variation for this response. Two common bean (Phaseolus vulgaris L.) genotypes known for their differing efficiency under low P, DOR 364 and G19833, were grown in sand culture in a greenhouse at two rates of buffered P availability. Twenty-seven days after planting, basal root axis length was longest under low P. Root and stele cross sectional areas increased over time under high P but not under low P. Low P root and stele cross sectional areas ultimately measured only 50% and 30% of high P, leading to a significantly higher stele to root area ratio under high P at basal and middle segments of the basal root. Reduced secondary development was also observed as reduced xylem vessel development under low P. These developmental differences were not observed to be due to allometry. Older sections of the basal root axis under high P respired almost 70% more per unit length than under low P. DOR 364 had significantly larger specific root length than G19833, especially under low P. This genetic difference was also apparent in significantly reduced root cross sectional area for DOR 364 under low P. Our results verify that roots etiolate under phosphorus stress and that etiolated roots are metabolically ‘cheaper’ due to their reduced respiration per unit length. There also appears to be a genetic component to root etiolation that could be included in a breeding program for plants better adapted to low phosphorus soils.