The effect of genetic variation in root hair length of common bean (phaseolus vulgaris) on the acquisition of potassium from a low potassium environment

Open Access
- Author:
- Esterhuizen, Kristelle
- Area of Honors:
- Horticulture
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Jonathan Paul Lynch, Thesis Supervisor
Kathleen Marie Kelley, Thesis Honors Advisor - Keywords:
- root hair length
common bean
potassium deficiency - Abstract:
- The purpose of this project was to study the effect of genetic variation of root hair length in common bean (Phaseolus vulgaris) on the acquisition of potassium from low potassium environments. Preliminary experiment one tested two growth media mixtures and a fertigation regime to determine how to best induce potassium stress. The media mixture with 10% sub-soil, 30% medium grade sand and 60% coarse perlite had more stable results with larger variation in shoot dry weight and therefore was chosen to be used for the remainder of the experiments as opposed to the media mixture of 20% sub-soil, 30% sand and 50% perlite. In preliminary experiment two the amount of potassium (K) in the nutrient solutions was reduced for the low and medium K treatments. This was done because the K stress in preliminary experiment one was not severe. The K treatments had no effect on shoot dry weight or root hair length in preliminary experiment two and therefore preliminary experiment tree was set up to test a new fertigation regime. Instead of continually adding K to the pots at varying concentrations, as was done in the first two experiments, the K treatments were regulated based on molar amounts of K added to each pot. The phosphorus (P) supplied to the plants was decreased to determine whether adequate P caused root hairs to show no variation in length. Preliminary experiment three was compromised by poor management of K levels and therefore the results were inconclusive. Preliminary experiment four was similar to preliminary experiment three and tested a lower P level and whether supplying plants with K only once at the beginning of the experiment was a better fertigation regime. The adequate/high K treatment had significantly longer root hairs than the medium and low K treatment but no significant effect on shoot dry weight was observed. A root hair survey was done to determine which genotypes to select for the final experiment. While root hair length did not vary much between genotypes (root hair length ranged from 0.33mm to 0.54mm) significant differences were observed. The recombinant inbred lines selected for the final experiment with longer root hairs included DG 13, 37, and 47 and those chosen with shorter root hairs included DG 32, 52, and 67. The final experiment included a control treatment of adequate P and K and included three K treatments with a reduced level of P. All low P treatments received 1.0mmol of P total. The low K treatment received 0.75mmol K and the medium K treatment received 1.50mmol K. The high K treatment was fertigated with a quarter strength Epstein solution (with no P) which supplied the plants with 1.50mM K. The K treatments had no effect on shoot dry weight, leaf area, root hair length or root system length even though the K shoot concentration was significantly affected by the K treatments. This can be explained because K follows Liebig’s Law of the Minimum in which case the inadequate P caused the varying K treatments to have no effect on growth since P was the nutrient limiting plant growth (Rubio et. al 2003). The P treatment had a significant effect on plant growth parameters but no effect on root hair length. The shoot dry weight of the low P treatments was reduced by 50% compared to the high P treatments. The root to shoot ratio had a significant increase from 0.19 under adequate P to 0.29 under low P. This shows the importance of P as a plant growth regulator. Plants that were supplied with low P but adequate K had a lower K shoot concentration than those supplied with adequate P and K. This was not expected since low P suppressed plant growth and increased the root to shoot ratio which seems as though it would cause high K shoot concentrations. It is thought that the low P affected K uptake because it reduced shoot growth and ultimately the supply of carbohydrates produced through photosynthesis. With fewer carbohydrates there is less energy in the form of ATP to actively take up K+ ions from the external environment. Comparing the low K to the medium K treatment, the low K treatment took up 68% of the 0.75mmol K supplied, while the medium K treatment took up 42% of the 1.50mmol K supplied, indicating that the plants growing under more severe K deficiency conditions were more efficient in K acquisition. Further experiments are needed to determine the best way to induce K stress and why no significant differences were observed in root hair length.