FIELD MEASUREMENTS AND COMPUTER SIMULATIONS OF VEGETATIVE EXPANSION (GROWTH, CELL DIVISION)

A general plant cell growth module is developed which describes known aspects of cell expansion and cell division. Expansion is governed by water flux as determined by the total water potentials inside and outside the cells, the hydraulic conductance of the cell wall-plasmalemma boundary and the cell wall extensibility. Division is accomplished through the use of a daughter ratio versus time function. Temperature is coupled to the water flow equations through its influence on the cell cycle rate which is a function of both the water parameters and the cell temperature. The equations are neither species nor organ specific. The module forms the basis of two plant growth simulators. The first deals with the growth of a group of cells arranged in a file. The second is a model of leaf expansion in monocots. Model outputs are compared with field measurements of leaf expansion in maize and sorghum. The predicted file or leaf length increase, the proliferative fractions in the expanding zone and the relative growth rates in the expanding region show kinetics which match the field measurements quite well. The length of the expanding zones in both simulators overestimates that measured in the field. The models are quite sensitive to variations in the water flux parameters and somewhat less sensitive to the temperature inputs. These sensitivities are discussed in relation to leaf expansion in field plants grown under well watered and water limiting environments. An extension to the leaf model is described which considers the mass balance of the system in relation to photosynthetic production in the mature portion of the leaf and carbon utilization by the expanding cells