3.2. Cell suspension culture

Characteristics: A suspension culture is developed by transferring the relatively friable portion of a callus as in Figure 11.1B, into liquid medium (Figure 11.2) and is maintained under suitable conditions of aeration, agitation, light, temperature and other physical parameters. The increased cell dissociation means increased culture uniformity. Plant cells are significantly larger and slower growing cells than most microbial organisms. They mostly resemble to parenchymatous cells in having relatively large vacuoles, a thin layer of cytoplasm and thin, rounded cell walls. The species/genotypes and medium composition used can influence in vitro cell morphology and different cell types with different morphological/physiological properties can co-exist within a single culture.

 

Figure 11.2: Cells in liquid medium showing fine suspension of cells

Cell growth: The most commonly used cell suspensions are of the closed (or batch) type where the cells are grown in fixed volume of liquid medium and which are routinely maintained through the transfer of a portion (ca 10%) of a fully-grown culture to fresh medium at regular intervals. The growth curve of a cell suspension culture (Figure 11.3) has a characteristic shape consisting of four essential stages- an initial lag phase, an exponential phase, stationary phase and death phase. The duration of each phase is dependent on the species or genotype selected, explant used, culture medium and subculture regime. The lag phase is shortened when relatively large inocula are used although paradoxically, growth terminates earlier and overall biomass production is reduced.