Flow Cytometry and Cell Sorting in Plant Biotechnology
Higher plants comprise approximately 250,000 described species and represent a critical component of the planetary biomass. They contribute functions essential for life, of which the most important is photosynthesis, as it provides the means for conversion of incident solar radiation into biomass accumulation, as well as the oxygen required by aerobic life forms. Fixed carbon in the form of carbohydrate provides the basis of the food chain, and metabolic interconversions within plants provide a variety of essential dietary factors. Plants also provide biomass in the form of structural materials and are the source of many natural products with important biomedical properties. As a consequence, considerable scientific interest is invested in determining the molecular mechanisms underlying plant growth, development, metabolism, and responses to biotic and abiotic stresses. Investment has also been made in developing tools and resources for biological investigations using plants. Notable advances include the development of genetics, of means for transformation using defined DNA sequences, and most recently, of the entire nuclear genome sequences of two plant species (Arabidopsis thaliana and Oryza sativa). On the basis of information of this type and that from other sources, it is evident that higher plants share many features with other eukaryotic organisms. Shared features can be observed at many levels; for example, the overall method of construction of cells, in which a bilamellar plasma membrane separates the cytoplasm from the external milieu and provides primary homeostatic regulation. Eukaryotic cells of different kingdoms share organelles, as well as overall regulatory mechanisms. Shared, or highly similar, protein sequences are observed, and they perform similar functions as enzymes, regulatory molecules, or structural components . Higher land plants have evident differences from other eukaryotes. They contain unique classes of organelles primarily devoted to energy capture from sunlight (plastids and peroxisomes). Of these, chloroplasts contain highly fluorescent pigments devoted to photosynthesis, which, particularly chlorophyll, provide unique and powerful signals that can be employed for flow cytometric analysis. Higher plants are also essentially immobile in the sporophytic stage and hence must be capable of responding to changes in environmental conditions and to biotic attack.