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

Agar and agarose gels were evaluated as systems to mechanically impede roots of rice (Oryza sativa L.). Two-layer gels were used so that seedlings established in a layer of weak gel (0.35% weight/volume) and then grew downwards to encounter a treatment gel of up to 5.0% (w/v). Agarose gels were stronger than agar gels of the same concentration, reaching a maximum penetrometer resistance of 1.2 MPa at a concentration of 5.0%, compared to 0.3 MPa with 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), but decreased it by 15% in the variety Lac 23. Although increasing agarose concentration decreased seminal axis elongation in both varieties, the seminal axis did not reach the lower layer of treatment gel when the concentration of the treatment gel was greater than 2.0%. The decreased root elongation was therefore a non-mechanical inhibition. In experiments conducted using a different batch of agarose, these inhibitory effects were not seen and strong agarose gels stimulated seminal axis elongation. It was concluded that the agar and agarose gel systems studied were unsuitable for studying the effect of mechanical impedance on the elongation of rice roots and that great care should be taken in interpreting the results of experiments using gels as a growth medium.

[1]  R. Lal,et al.  Response of upland rice varieties to drought stress , 1983, Plant and Soil.

[2]  T. Flowers,et al.  VARIABILITY IN THE RESISTANCE OF SODIUM CHLORIDE SALINITY WITHIN RICE (ORYZA SATIVA L.) VARIETIES , 1981 .

[3]  A. R. Dexter,et al.  Penetration of very strong soils by seedling roots of different plant species , 1991, Plant and Soil.

[4]  U. Zimmermann,et al.  Pressure probe technique for measuring water relations of cells in higher plants. , 1978, Plant physiology.

[5]  A. G. Bengough,et al.  Mechanical impedance to root growth: a review of experimental techniques and root growth responses , 1990 .

[6]  Complete mechanical impedance increases the turgor of cells in the apex of pea roots , 1996 .

[7]  H. Greenway,et al.  The Use of Agar Nutrient Solution to Simulate Lack of Convection in Waterlogged Soils , 1997 .

[8]  W. Armstrong,et al.  The effectiveness of internal oxygen transport in a mesophyte (Pisum sativum L.) , 1972, Planta.

[9]  M. Reid,et al.  Inhibition of ethylene action prevents root penetration through compressed media in tomato (Lycopersicon esculentum) seedlings , 1992 .

[10]  K. Volkmar.  Pre-germination effects on mechanically impeded root growth of barley (Hordeum vulgare L) , 1994, Plant and Soil.

[11]  Comparaison de l'enracinement de quatre variétés de riz pluvial en présence ou absence de travail du sol , 1970 .

[12]  R. T. Cruz,et al.  Shoot and Root Responses to Water Deficits in Rainfed Lowland Rice , 1986 .

[13]  Soil physical behaviour and crop responses to tillage in lowland rice soils of varying clay content , 1990, Plant and Soil.