**5. Conclusion and prospects**

Among several nutrient elements that are varyingly required by plants, P is the major macronutrient involved in the maintenance of growth, metabolism, and productivity of plants, as well as for their sustenance under adverse conditions. Unfortunately, P is among the less accessible elements for plants mainly as a result of its very low solubility and poor mobility in soil solution, as well as its incorporation into organic compound. The availability of soil-P is modulated by several physical factors (soil texture and moisture), chemical factors (soil solution pH, organic matter, redox potential, and the concentration of Fe, Al, and Ca), and biotic factors (diversity of microorganisms in rhizosphere). Most plants/crops under P-deficiency adopt a range of strategies to facilitate plant/crop P-use efficiency. Pi-uptake and root-toshoot transport are mediated by both low- and high-affinity Pi-transporters, whereas Pi-redistribution at tissue, cellular, and subcellular levels is facilitated by a dedicated sets of transporters. In addition to performing key functions in plants (such as energy transfer, photosynthesis, transformation of sugars and starches, and nutrient

movement within the plant), an adequate P-supply help plants to sustain, develop, and produce under varied abiotic stress factors.

The knowledge of P-recycling and -mobilization may help in improving plant/crop P-use efficiency and thereby minimizing the P-fertilizer input to the environment. In particular, appropriate fertilizer encompassing both the change in the amount and suitability of P-fertilizer, as well as deciding the rate, time, and place of P-fertilizer, may help in achieving sustainable crop production. Exhaustive molecular genetic studies on P-solubilizing microorganisms, understanding Pi-transporters in tonoplast and Pi-uptake by the cells not symplastically connected to guard cells or the developing embryo, and identifying proteins mediating Pi-transport across tonoplast will be promising in the research area aimed at unveiling insights into P in soils and plants.
