Evaluation of agar and agarose gels for studying mechanical impedance in rice roots

Agar and agarose gels were evaluated as systems to mechanically impede root s of rice (Oryza sativa L.). Two-layer gels were used so that seedlings est ablished in a layer of weak gel (0.35% weight/volume) and then grew downwar ds to encounter a treatment gel of up to 5.0% (w/v). Agarose gels were stro nger than agar gels of the same concentration, reaching a maximum penetrome ter resistance of 1.2 MPa at a concentration of 5.0%, compared to 0.3 MPa w ith agar. The 5.0% agar gel stimulated elongation of the seminal axis by 40 % in seedlings of variety TN1 (compared with elongation in the 0.2% gel), b ut decreased it by 15% in the variety Lac 23. Although increasing agarose c oncentration decreased seminal axis elongation in both varieties, the semin al axis did not reach the lower layer of treatment gel when the concentrati on of the treatment gel was greater than 2.0%. The decreased root elongatio n was therefore a non-mechanical inhibition. In experiments conducted using a different batch of agarose, these inhibitory effects were not seen and s trong agarose gels stimulated seminal axis elongation. It was concluded tha t the agar and agarose gel systems studied were unsuitable for studying the effect of mechanical impedance on the elongation of rice roots and that gr eat care should be taken in interpreting the results of experiments using g els as a growth medium.