Experimental colorimetric determination of inter-root pH

Summary

While absorbing nutrients, the plant root system overflows H+, OH-, HCO3- and other organic substances, which changes the inter-root pH, and thus affects the inter-root nutrient status (e.g., ionic state, solubility, etc.). Therefore, inter-root pH has an important role in plant nutrition either directly or indirectly. The purpose of this experiment is to learn a method for in situ color development of inter-root pH.

Operation method

Experimental colorimetric determination of inter-root pH

Principle

This method is used to test for changes in inter-root pH by using a pH indicator that changes color under varying acidity and alkalinity conditions. The pH indicator is added to agar sol with certain nutrient conditions to form an agar-indicator mixture. Plant roots can directly utilize it as a medium for growth. Due to physiological activities such as root uptake and overflow secretion, the inter-root pH is different from the original medium, resulting in a different color development response. The magnitude and value of the inter-root pH rise or fall can be determined against a standard pH color change range.

Materials and Instruments

Wheat seedlings
Culture solution for NH4+ Bromocresol violet
Petri dish Torsion balance Electric stove pH meter Measuring cylinder Beaker Pipette Glass rod Tweezers Earwash ball Absorbent filter paper Plastic film Agar

Move

I. Materials and equipment

Wheat seedlings, 10 cm diameter Petri dish, torsion balance, electric oven, pH meter, 50 ml measuring cylinder, 100 ml beaker, 0.5 ml pipette, glass rod, tweezers, earwash ball, absorbent filter paper, 10×10 cm plastic film, agar

50pp M culture solution containing NH4+: (1000 ml H2O + 183 M g (NH4)2SO4 + 136 M gCaSO4)

0.6% bromocresol violet: 0.6 g of bromocresol violet dissolved in a small amount of 95% alcohol, then fixed in distilled water to 100 ml

0.01N NaOH, 0.01N HCl

Experimental steps

1. Preparation of color developing substrate: take 50 ml culture solution containing 50pp M NH4+, add 0.5 g agar and 0.5 ml 0.6% bromocresol violet indicator solution, and heat it up to boiling with stirring on an electric stove. It was then cooled to about 40°C when the pH was adjusted to 6.0 (dark red) with dilute NaOH or dilute HCl.

2. Color development: Pour the agar-indicator mixture into a petri dish to make a homogeneous thin layer, cool and solidify for use. Take 1 wheat seedling (root length about 10cm), rinse the root system with distilled water, flatten it on a plastic film (10×10cm), absorb the water on the film and the root surface with blotting paper, invert it onto the solidified agar-indicator mixture, and then press it gently to drive out the air bubbles and make the root system embedded in the gel. The pH indicator showed a color change in about 1 hour at room temperature.

3. Observe the phenomenon and interpret the results: The different colors of the pH-indicator indicate the pH of different inter-root sites. Observe the color change of the agar-indicator mixture around the root system to determine whether the pH of the root system is increasing or decreasing, and to explain the reason for the change in the pH of the root system. This practical can be used as a control with standard agar-indicator to determine the pH of each root zone, and can also be used with microelectrodes for precise determination.

Caveat

1. Bromocresol violet has a color range of pH 5.2-6.8 (yellow-violet) and is suitable for use under slightly acidic conditions;Cresol red color change range is pH7.2-8.8 (yellow-red), suitable for use under alkaline conditions.

2. The water in the plastic film and root surface must be drained, otherwise it will affect the color development results.

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