Matric potential and overburden potential in gels for plant tissue culture

In order to evaluate the effect of matric component on water potential in gel medium for plant tissue culture, matric potential in agar gel and gellan gum gel was studied. Overburden potential was also studied to estimate the effect of overburden pressure to the gels. The suction plate method and the sand column method were used to measure the relationship between matric potential and gel concentration. Mechanical pressure was applied over gel and gel concentration was measured after water in gel and free surface water was in hydrostatical equilibrium. The matric potential for both gels decreased with their concentrations. The potential values were around -0.1 kPa or larger (=less negative) at gel concentrations normally used for plant tissue culture; the values were less than 0.01% of the osmotic potential in MS medium which suggests that they are negligible as a component of water potential in gel medium. The mechanical pressures over gels agreed with the absolute values of matric potentials for the same gel concentrations. This suggests that the solid structure of the gel matrix had no resistance to deformation by the mechanical pressure and all of the mechanical pressure was transferred to the water in the gel to produce overburden potential. The syneresis from gel was concluded to be drainage of excess water during the process of hydrostatical equilibrium among gravitational potential, matric potential, and overburden potential. The amount of syneresis was shown to increase with lower gel concentration (=less negative matric potential) and with larger mechanical pressure. The change of syneresis with gel concentration and/or mechanical pressure by plant growth may influence the water condition of plant tissue in gel medium