Objectives Phosphorus (P) is an essential macronutrient element in the process of plant growth and development. Due to its low mobility in soil, the root system has limited access to phosphorus. To meet the demand of phosphorus for growth, plants have evolved a series of biological processes to maximize the re-use of internal phosphorus, reduce the P fertilizer input and P effluence in the aquatic ecosystem. This review summarizes recent advances in the understanding of mechanisms by which plant utilize the organic P pools and inorganic P pools. Further, the relevant molecular mechanisms involved in the transport of released inorganic P (Pi) in different tissues and organs are explored and an insight on how to further study the relevant directions of P utilization in the future is provided.
Major advances P in higher plants mainly includes Pi and organic P. The excess Pi absorbed by plants is temporarily stored in vacuoles and this part of Pi is released to cytoplasm under low-P stress to buffer the demand for Pi via phosphate transporter located in the tonoplast. Enzymes such as nuclease, phospholipase and purple acid phosphatase hydrolyze organophosphate such as nucleic acid, phospholipid and release Pi to facilitate its redistribution and utilization in plants. When plants suffer from low P stress, Pi is exported from vegetative organs (old leaves, etc.) and transported to growth centers such as young leaves for use via phosphate transporters, thereby significantly improving P re-use efficiency. Reducing the accumulation of P in grains and controlling grain P within a reasonable range through phosphate transporters is of great significance for improving grain PUE and alleviating eutrophication.
Prospects Numerous studies have elaborated the mechanisms of P recycling and utilization in plants, but the involvement of phosphate transporters in specific P transport processes is still not clear. For example, vacuolar Pi can be re-used to meet P demand when plant suffer P deficiency. However, few transporters related to its efflux have been identified, and the relevant regulation factors need further exploration. Holistically exploring the role of PHT1, PHT2, PHT3 and PHT4 proteins on P from source to sink is pertinent. The contribution of Pi mobilized from vacuole and the Pi recycled from organophosphate to cope with phosphate deficiency needs to be quantified. Therefore, analyzing the biological regulatory mechanisms underlying the transportation and utilization of P in plants can provide a scientific basis for reducing P fertilizer input, improving P utilization efficiency and cultivating P-efficient crop varieties.
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