FROM CELL-GROWTH TO LEAF GROWTH .1. COUPLING CELL-DIVISION AND CELL EXPANSION

An area of plant growth modeling that appears to have been neglected is incorporation of current knowledge regarding fell expansion and cell division into the growth models. The objective of this research was to incorporate this knowledge into a quantitative description of plant growth. A general cell growth module is described that combines known aspects of cell expansion and cell division. Cell expansion is governed by water Bur equations. The cells start at a fixed minimum volume and expand to a final (fixed) volume. The wall extensibility of a cell is considered to be a function of its volume. Cell division is described through use of a daughter ratio vs. time function that categorizes the cells resulting from a division as either proliferative or nonproliferative. Temperature is coupled to the water flow equations through its influence on cell cycle time. The daughter ratio vs. time function is of paramount importance. The influence of a number of daughter ratio functions on the rate of cell production and the rate of total cell volume accumulation are considered. Exponential, linear, and sigmoidal increases in both cell numbers and total cellular volume are shown to result from the various daughter ratios examined. A comparison was made of simulations using a constant wall extensibility to those made using the wall extensibility vs. volume function. The difference between these two cases was much less than the differences obtained by varying the daughter ratio function.