There are several methods of evaluating growth kinetics of plant cells. Selected examples include, fresh cell weight, settled volume, packed cell volume, cell optical density, cell size, nitrogen content, protein content, nucleic acid content, mitotic index, electrical conductivity, respiration, and pH measurement. In addition, concentrations of substrate and extracellular product have also been used for such purpose of selecting the best method of studying growth kinetics, especially from the bioprocess engineering point of view.
Figure 35.2: Cell growth and nutrient uptake in L. camara cells
3. Parameters of growth efficiency
3.1. Growth index
As described by Loyola-Vargas and V á zquez-Flota (2006) that at a given sampling time, both fresh and dry weights are measurements of complete biomasses of the tissues. No reference to the actual growth capacity is taken in consideration. Growth index (GI) is a relative estimation of such capacity as it correlates the biomass data at the sampling time to that of the initial condition. It is calculated as the ratio of the accumulated and the initial biomass. The accumulated biomass corresponds to the difference between the final and the initial masses.
Where in this equation, GI is growth index while Wf is final cell mass and Wi is the initial cell mass. Both Wf and Wi are taken either as fresh or dry weight.
3.2. Specific growth rate
As explained by Loyola-Vargas and V á zquez-Flota (2006), the specific growth rate (µ) refers to the steepness of a curve, and it is defined as the rate of increase of biomass of a cell population per unit of biomass concentration. It can be calculated in batch cultures, since during a defined period of time, the rate of increase in biomass per unit of biomass concentration is constant and measurable. This period of time occurs between the lag phase and stationary phases. During this period, the increase in the cell population fits a straight-line equation between ln x and t.
Where, xo is the initial biomass (or cell density), x is the biomass (or cell density) at time t, and µ is the specific growth rate. Mu can be calculated from the above relationship, which is the slope of the line between ln x and t.
3.3. Doubling time
Doubling time (td) is the time required for the concentration of biomass of a population of suspension cells to double. One of the greatest contrasts between the growths of cultured plant cells refers to their respective growth rates. The doubling time (dt) can be calculated according to the following equation (Loyola-Vargas and V á zquez-Flota, 2006)
