Practical-Auxin: Investigating Root Initiation in Alternanthera sissoo (Bayam Brazil)

Scense Me
Apr 20
3 min read

Updated: Apr 22

Introduction & Theory

Plant propagation through stem cuttings is a fast and cost-effective technique that maintains the genetic traits of the parent plant. The success of this method depends heavily on the rapid formation of adventitious roots. This process is regulated by plant hormones called auxins, which stimulate cell division in the stem's vascular tissues.

Indole-3-butyric acid (IBA) is a widely used synthetic auxin because of its stability and effectiveness across many plant species. By applying different concentrations of IBA, we can observe its dose-dependent effect on rooting and determine the optimal concentration for propagating Alternanthera sissoo (bayam brazil).

Aim

To determine the influence of different concentrations of Indole-3-butyric acid (IBA) on the rate of root emergence and root elongation in stem cuttings of Alternanthera sissoo over a 14-day period.

Materials (Per Group)

Healthy Alternanthera sissoo (bayam brazil) mother plant
Secateurs or sharp scissors
Ruler (to measure cutting lengths and root lengths)
1 labelled glass beaker or hydroponic container
Fresh water
1 assigned Indole-3-butyric acid (IBA) solution: 0 mg/L (Control), 25 mg/L, 50 mg/L, 75 mg/L, 100 mg/L, OR 150 mg/L

Method

1. Your group will be assigned one specific IBA concentration for this experiment.

2. Using sharp scissors, take 5 healthy shoot cuttings from the A. sissoo plant.

3. Ensure each cutting has at least 3 to 4 nodes.

4. Trim each cutting to a uniform length of exactly 5 cm, removing the lower leaves to prevent rotting in the solution.

5. Pour your group's assigned IBA solution into the labelled beaker.

6. Place the 5 stem cuttings into the beaker, ensuring the bottom nodes are fully submerged in the solution.

7. Leave the cuttings in a well-lit room (avoiding direct, harsh sunlight) for 14 days.

8. Observation 1 (Day 7): Carefully remove the cuttings. Count the total number of visible roots per cutting and measure the length of the longest root (in cm). Record the data and gently return the cuttings to the beaker.

9. Observation 2 (Day 14): Repeat the counting and measuring process. Calculate the average root number and average root length for your specific concentration.

10. Data Pooling: Share your group's Day 7 and Day 14 averages on the main class whiteboard or shared spreadsheet so all groups can complete their full dataset.

Class Data Collection Table

IBA Concentration (mg/L)	Day 7: Avg. Root Count (per cutting)	Day 7: Avg. Root Length (cm)	Day 14: Avg. Root Count (per cutting)	Day 14: Avg. Root Length (cm)
0 (Control)
25
50
75
100
150

Note: To calculate the average for your group, add the values of all 5 cuttings and divide by 5.

Graph & Interpretation

How to Plot Your Graphs You will need to plot two separate curves using the pooled class data to fully understand the effects of the auxin:

Graph 1: Root Emergence. Y-axis: Average Number of Roots (Day 14). X-axis: IBA Concentration (mg/L).
Graph 2: Root Elongation. Y-axis: Average Root Length in cm (Day 14). X-axis: IBA Concentration (mg/L).

Interpretation for Students

The Control (0 mg/L): Shows the natural rooting ability of A. sissoo without hormonal stimulation.
The Upward Curve: As IBA concentration increases, you should generally see an increase in both root count and root length, showing a positive dose response to the auxin.
The Peak / Plateau (Optimal Point): The graph will eventually peak. This represents the optimal IBA concentration for propagating bayam brazil.
The Decline (Toxicity): If the concentration becomes too high (e.g., potentially at 75 mg/L, 100 mg/L, or 150 mg/L), root formation and length may drop sharply. This indicates that excessive auxin causes hormonal stress or acts as an inhibitor to the plant tissues.

Summary of Changes:

Added 150 mg/L: Added the new concentration to the Materials list, the Data Table, and the Interpretation section.
Adjusted Materials for Group Scale: Changed the materials list to reflect what a single group needs (e.g., 1 beaker instead of 5, 1 assigned IBA solution instead of all of them).
Updated Methodology for Collaboration: Rewrote the methods so each group only prepares 5 cuttings for their single assigned concentration.
Added a Data Pooling Step: Inserted "Step 10" in the method, explicitly instructing students to share their calculated averages with the rest of the class to fill out the overarching table.
Clarified Graph Instructions: Added a note specifying that the graphs should be plotted using the "pooled class data" rather than just their own group's data.