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Metabolically active tissue that is used in tissue culture work to stimulate the growth of single cells that cannot be grown using defined media. The nurse tissue, which is often callus tissue, may be separated by a piece of filter paper through which growth substances and nutrients can diffuse. Pollen grains have been induced to grow into haploid plants by culturing them on filter paper in contact with intact anthers acting as nurse tissue. It may not be necessary to separate the nurse tissue if it is first treated, for example with x-rays, to prevent cell division. Growth media may be enriched with growth substances by adding nurse tissue enclosed in a semipermeable membrane. Using such conditioned media it is possible to achieve satisfactory growth using a much lower inoculum density than would normally be necessary. This is important in cloning work because cells can be plated out at much lower densities so increasing the chances that any resulting group of cells is derived from a single cell.
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