**3.2 Callus and cell culture systems**

Quatrano (1968) and Nag and Street (1973) reported the first successful experiments on cryopreservation of plant cells. Since then a large number of cell suspension and calli cultures have been successfully cryopreserved (Engelmann *et al* 1994). In general, callus cultures are more difficult to cryopreserve than cell suspensions, because of the relative volume of the callus, its slow growth rate and the cellular heterogeneity (Withers 1987). One successful cryopreservation procedure that is applicable to all different cell suspensions or calli cultures has not been developed yet. Research focuses on optimizing the factors on which successful cryopreservation of plant organs cells suspensions and calli depends, such as: (i) starting material, (ii) pretreatment, (iii) cryopreservation procedure, and (iv) postthaw treatment.

Plant cells cultured *in vitro* produce wide range of primary and secondary metabolites of economic value. Production of phytochemicals from plant cell cultures has been presently used for pharmaceutical products. Production of flavour components and secondary metabolites *in vitro* using immobilised cells is an ideal system for spices crops. Production of saffron and capsaicin was reported using such system (Ravishankar *et al.,* 1988; 1993, Johnson *et al.,* 1996; Venkataraman and Ravishankar 1997). Johnson *et al* (1996) reported biotransformation of ferulic acid vanillamine to capsacin and vanillin in immobilised cell cultures of *Capsicum frutescens.* Reports on the *in vitro* synthesis of crocin, picrocrocin and safranel from saffron stigma (Himeno and Sano, 1995) and colour components from cells derived from pistils (Hori *et al,* 1988) are available for further scaling up. Callus and cell cultures were established in nutmeg, clove, camphor, ginger, lavender, mint, thyme, celery etc. Cell immobilization techniques have been standardized in ginger, sage, anise and lavender (Ilahi and Jabeen, 1992; Ravindran *et al*, 1996; Sajina *et al*, 1997).

Studies on conservation of cell lines is yet o become popular in spices. Suspensions of embryogenic cell lines of fennel, conserved at 4 0C for up to 12 weeks produced normal plants upon transfer to normal laboratory conditions (Umetsu *et al*, 1995).
