Abstract
Excess Phosphorus (P) in agriculture is causing serious environmental problems like eutrophication of lakes and rivers. Unlike the enormous information available for phosphate starvation response (P0), very few information is available for the effect of excess phosphate Pi on plants. Characterization of Excess Phosphate Response (EPiR) is essential for designing strategies to increase phosphate accumulation and tolerance. We show a significant modulation in the root developmental plasticity under the increasing supply of excess Pi. An excess supply of 20 mM Pi (P20) produces a shallow root system architecture (RSA), reduces primary root growth, root apical meristem size, and meristematic activity in Arabidopsis. The inhibition of primary root growth and development is indeterminate in nature and caused by the decrease in number of meristematic cortical cells due to EPiR. Significant changes occurred in metal nutrients level due to excess Pi supply. A comparative microarray investigation of the EPiR response reveals a modulation in ethylene biosynthesis and signaling, metal ions deficiency response, and root development related genes. We used ethylene-insensitive or sensitive mutants to provide more evidence for ethylene-mediated signaling. A new role of EPiR in regulating the developmental responses of plants mediated by ethylene has been demonstrated.
Highlights
Phosphate (Pi) availability is often limited in the soil, because of its low mobility, creating a major problem in various regions of the world
The shoot to root ratio increased significantly at the P20 as compared to P10, P5, and P2.5 treatments. It indicates that the shoot growth was not as much compromised as root at the high P20 treatment (Fig. 1c)
To summarize the important findings of this study, we proposed a schematic model which shows that the excess phosphate treatment induces the ethylene response may be directly or by altering the nutrient level and attenuates primary root growth by reducing the cell number in root apical meristem (Fig. 10)
Summary
Phosphate (Pi) availability is often limited in the soil, because of its low mobility, creating a major problem in various regions of the world. On the other hand in the developed industrialized world, the excessive application of Pi based chemical fertilizers and phosphate-rich animal manures often results in the accumulation of Pi in the top soil[5,6,7,8]. Swine manure amended paddy soil profile showed an orthophosphate level up to 2610 mg kg−1 with 80% extraction efficiency[16]. To design an effective strategy for P acquisition, accumulation, and tolerance, we need to understand and characterize the plant responses under excess phosphate conditions. Several transcriptomic studies have been carried out in plants to characterize the molecular response to phosphate deficiency or sufficiency using the ATH1 microarray chips[25,26,27,28]. We further provide evidence for the involvement of ethylene by using ethylene-insensitive mutants (etr[1,2,3], ein[4], ein2-T) and constitutive ethylene sensitive mutant (ctr[1])
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