3 ALKALOIDS IN TISSUE CULTURES
The quantum growth and progress in the past three decades especially with regard to the legitimate utilization of plant tissue cultures in the exclusive bioproduction of naturally occurring chemical compounds under specific asceptic conditions through various well established means and methods almost identical to those employed to culture microorganisms has virtually opened up an altogether new and virgin horizon in the latest field of biotechnology. Therefore, the application of tissue culture techniques in the context of the biosynthesis of important secondary metabolites from plants viz., alkaloids, not only holds a well-deserved promise for the rational controlled production of plant constituents but also supports the fact that higher plants do provide an important source of medicinally active chemical entities.
Although it has been established beyond any reasonable doubt that most of the work carried but on ‘alkaloid biosynthesis’ has been more or less directly concerned with the intact plants or parts thereof, for instance: leaves, roots or shoots, there have been certain evidence and investigations using tissue cultures. This type of work is particularly beneficial in locating and establishing the site of alkaloid synthesis. It is, however, pertinent to mention here that the inferences drawn from various experimental findings that tobacco stem callus tissue will not synthesize alkaloids unless and until the root formation has started either spontaneously or by means of chemical stimulation.
Likewise, it has been observed interestingly that the latex isolated from the capsule of the opium poppy (Papaver somniferum) will synthesize morphine either from dopa or tyrosine, but the latex obtained from the stem will not.
Tissue cultures do not always essentially behave exactly as the intact plant, as has been observedwith Catharanthus roseus, wherein the cultures of either leaf or stem effectively carried out the synthesis of certain alkaloids found in the intact plant, but no dimeric alkaloids could either be observed or detected. On the contrary, tissue cultures of tobacoo might convert thebaine to morphine; however, no benzylisoquinoline alkaloids have been noticed in Nicotiana tabacum.
