The Water Status Measurements Associated with Plant Growth

The process of cell elongation from the viewpoint of plant-water relations and the effect of excision in the zone of elongation on changes in the water status are discussed. The excision effect on changes in water potential was evaluated after measuring turgor before excision and after excision in growing tulip tepals, and it was found that the size of wall relaxation was about 0.04 MPa. In mature tissues, there is no wall relaxation due to excision, and thus, the water status can be cross-checked by using a pressure chamber, a pressure probe and psychrometers. It was found that water potential of the apoplast is equal to the sum of the matric potential and the osmotic potential of the apoplast solution in the mature tissue. The symplast water potentials of epidermal cells and mesophyll cells were measured with the cell pressure probe, having the same values of water potentials measured with the psychrometer. Volume-averaged cell turgor and osmotic potentials were similar to the corresponding values measured in tissues with the psychrometer. In elongating tissues and mature tissues, it was confirmed that water potential can be expressed as the sum of pressure potential and osmotic potential in both the apoplast and symplast.