how to quantify root hair development on the root systems allows
for student creativity and problem solving. In light of the results of
this experiment, students are asked to reflect on the following questions (answers in italics):
1. How would a plant benefit from changing its root architecture
in a low-phosphate environment? A plant relies on its root as
the primary organ of absorption of water and nutrients from the
environment (typically soil). If nutrients are scarce (such as low
phosphate levels), the plant can explore more soil by increasing the
surface area of its root system via branching and root hair development, resulting in more root surface area for uptake.
2. What roles does phosphorus play in the life of a plant? Phosphorus is a key component of ATP, nucleic acids, and phospholipids of plant cells.
3. How do plant growth regulators influence root architecture?
Auxins are the primary plant growth regulators that promote lateral
root formation. The action of auxins in root development involves ethylene and strigolactones. Cytokinins suppress lateral root initiation.
4. What soil factors influence phosphorus availability to plants?
Due to fixation to soil cations, phosphorus availability is optimal
at pH values between 6 and 7.5. Phosphorus can be lost to soil via
erosion. Release of phosphorus from decaying soil organic matter
is an important source of input for phosphorus.
5. Describe how lateral roots arise. Lateral root growth is a type of
primary plant growth that originates from meristematic cells of the
pericycle, the outermost layer of the vascular cylinder of the root.
Some Tips to Consider
• Crowded root systems on the agar plates make it difficult to
count lateral roots. Use three seeds per plate and ensure they
are well spaced to make it easier to count lateral roots.
• Different seed sources may require different conditions of pregermination. For example, kale seeds typically pregerminate
slowly at 4°C in comparison to Fast Plant seeds.
• Don’t confuse root hairs and lateral roots. Root hairs appear as
tiny fuzzy growth along a root, whereas lateral roots are distinct
branches off of another root (see Figure 1A). Root hair development may vary between phosphate concentrations, so this can
be a point of discussion with the students.
Mineral Salts Agar
Composition and preparation of MSA is as follows (modified
from Murashige & Skoog, 1962): 2 mM NH4NO3, 1.9 mM
KNO3, 0.3 mM CaCl2-2H2O, 0.15 mM MgSO4-7H2O, 0.1 mM
FeSO4-7H2O, 1% agar, pH 5.7; a stock solution of 10 mM
Na2H2PO4 is prepared and sterilized separately; aliquots of the
stock solution are added to quantities of MSA, resulting in agar
varying in phosphate concentration from 0 to 1 mM. Prepare all
solutions in distilled water, sterilize via autoclaving, and dispense
the resulting agar into 100-mm-diameter Petri plates (teacher
preparation time: three hours).
Linkohr, B., Williamson, L., Fitter, A. & Leyser, H. (2002). Nitrate and
phosphate availability and distribution have different effects on root
system architecture of Arabidopsis. Plant Journal, 29, 751–760.
Lopez-Bucio, J., Hernandez-Abreu, E., Sanchez-Calderon, L., Nieto-Jacobo,
M., Simpson, J. & Herrera-Estrella, L. (2002). Phosphate availability
alters architecture and causes changes in hormone sensitivity in the
Arabidopsis root system. Plant Physiology, 129, 244–256.
Murashige, T. & Skoog, F. (1962). A revised medium for rapid growth and
bio assays with tobacco tissue cultures. Physiologia Plantarum, 15,
Niu, Y., Chai, R., Jin, G., Wang, H., Tang, C. & Zhang, Y. (2013). Responses of
root architecture development to low phosphorus availability: a
review. Annals of Botany, 112, 391–408.
Strgar, J. (2007). Increasing the interest of students in plants. Journal of
Biology Education, 42, 19–23.
Torrey, J. (1950). Induction of lateral roots by indoleacetic acid and root
decapitation. American Journal of Botany, 37, 257–264.
Uno, G. (1994). The state of precollege botanical education. American
Biology Teacher, 56, 263–267.
Urry, L., Cain, M., Wasserman, S., Minorsky, P. & Reece, J. (2017). Campbell
Biology, 11th ed. New York, NY: Pearson.
Williamson, L., Ribrioux, S., Fitter, A. & Leyser, H. (2001). Phosphate
availability regulates root system architecture in Arabidopsis. Plant
Physiology, 126, 875–882.
ROBERT E. ZDOR is a Professor in the Department of Biology, Andrews
University, Berrien Springs, MI 49104; e-mail: email@example.com.
1 0.1 0.01
Figure 2. Effect of phosphate levels on lateral root numbers
of Brassica sp. Each bar represents the average of 75–89 plants
from four years of student data collection.