The culture vessels placed in suitable trays or racks, are stored on the shelves in a hygienically maintained culture room, under controlled conditions of light and temperature. If possible the relative humidity should not fall below 50% to prevent rapid desiccation of the medium. To minimize the infection of cultures during incubation, the culture room should be dust free. It is often provided with double doors and entry of people is restricted. The requirement for light and temperature varies considerably. The cultures of high altitude plants as well as those of desert species grow well at 25? c-28?c. However, induction of pollen embryogenesis requires a high temperature treatment (35? C). As mentioned earlier, in cultures even green tissues and shoots do not exhibit active photosynthesis and are largely heterotrophic. The differentiation of shoots from callus or explants and axillary shoot proliferation are favored by light.
A callus is defined as an unrecognized mass of tissue varying widely in texture, appearance and growth rate. Such cultures should be maintained in continuous diffuse light (1-3K lux) provided by fluorescent tubes. You should know that unorganized callus and freshly isolated protoplast cultures are often sensitive to light and are incubated in darkness. Total darkness is also favorable for rooting and for the initial stages of pollen and somatic embryogenesis.