Composite Transport Model and Water and Solute Transport across Plant Roots: An Update.

Yangmin X Kim,Deogbae Lee,Yejin Lee,Seulbi Lee,Jwakyung Sung,Kosala Ranathunge

doi:10.3389/fpls.2018.00193

Yangmin X Kim, Deogbae Lee + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2018.00193

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Abstract

The present review examines recent experimental findings in root transport phenomena in terms of the composite transport model (CTM). It has been a well-accepted conceptual model to explain the complex water and solute flows across the root that has been related to the composite anatomical structure. There are three parallel pathways involved in the transport of water and solutes in roots – apoplast, symplast, and transcellular paths. The role of aquaporins (AQPs), which facilitate water flows through the transcellular path, and root apoplast is examined in terms of the CTM. The contribution of the plasma membrane bound AQPs for the overall water transport in the whole plant level was varying depending on the plant species, age of roots with varying developmental stages of apoplastic barriers, and driving forces (hydrostatic vs. osmotic). Many studies have demonstrated that the apoplastic barriers, such as Casparian bands in the primary anticlinal walls and suberin lamellae in the secondary cell walls, in the endo- and exodermis are not perfect barriers and unable to completely block the transport of water and some solute transport into the stele. Recent research on water and solute transport of roots with and without exodermis triggered the importance of the extension of conventional CTM adding resistances that arrange in series (epidermis, exodermis, mid-cortex, endodermis, and pericycle). The extension of the model may answer current questions about the applicability of CTM for composite water and solute transport of roots that contain complex anatomical structures with heterogeneous cell layers.

Highlights

Water and solutes, taken up by plant roots, use different pathways or routes, such as apoplastic and cell-to-cell, to transport them into the vascular tissue in the stele (Steudle and Peterson, 1998; Steudle, 2000a; Ranathunge et al, 2017)
After the composite transport model (CTM) has been developed, many experimental research works on water and solute transport across the root were conducted and they have been explained in terms of the CTM (Knipfer et al, 2011; Hachez et al, 2012; Fricke et al, 2013; Suku et al, 2014; Vandeleur et al, 2014)
Ranathunge et al (2017) suggested to extend the CTM by adding components arranged in a series of the root in addition to the currently included components arranged in parallel

Summary

Introduction

Taken up by plant roots, use different pathways or routes, such as apoplastic and cell-to-cell (symplastic and transmembrane), to transport them into the vascular tissue in the stele (Steudle and Peterson, 1998; Steudle, 2000a; Ranathunge et al, 2017). This model successfully explains the results of greater Lpr with increasing water flow across roots (Steudle and Peterson, 1998).

Results

Conclusion