Hydraulic Strategy of Cactus Root-Stem Junction for Effective Water Transport.

Hyejeong Kim,Sang Joon Lee,Kiwoong Kim

doi:10.3389/fpls.2018.00799

Hyejeong Kim, Sang Joon Lee + Show 1 more

Open Access

https://doi.org/10.3389/fpls.2018.00799

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Abstract

Cactus roots function as a hydraulic safety valve by conducting available water quickly and preventing water loss under drought condition. In particular, the root–stem (R–S) junction is responsible for effective water transport by direct coupling of the water absorptive thin roots and the moisture-filled bulky stem. In this study, the morphological features of the R–S junction were observed by using X-ray micro-imaging technique. Their structural and functional characteristics were also elucidated according to a hydrodynamic viewpoint. With regard to the axial water transport through xylem, the R–S junction prevents water leakage by embolizing large-scale vessels with relatively high hydraulic conductivity. In addition, the axial theoretical hydraulic conductivity of xylem vessels from the roots to the stem drastically increases to facilitate water absorption and prevent water loss. The cortex cell layer of a cactus is thinner than that of other plant species. In the viewpoint of radial conductivity, this property can be the hydraulic strategy of the cactus R–S junction to transport water quickly from the root surface into the xylem. These results suggest that the R–S junction functions as a hydraulic safety valve that can maximize water uptake in axial and radial directions at limited rainfall. This junction can also prevent the stem from leaking water under drought condition.

Highlights

Deserts receive considerably limited rainfall and plants have evolved for a long time to establish a special hydraulic strategy for effective water transport and conservation for survival in adverse desert environments (North and Nobel, 1997; Nobel, 2003)
At the position 800 μm above the R-S junction, only the mucilage cells exist in the stem, and lots of calcium oxalates are distributed around the endodermis having numerous air spaces (Figure 1Ciii)
Cactus roots are crucial as a flow regulator by conducting available water quickly and preventing the loss of absorbed water (Lopez and Nobel, 1991; Huang and Nobel, 1993; North and Nobel, 1997)

Summary

Introduction

Deserts receive considerably limited rainfall and plants have evolved for a long time to establish a special hydraulic strategy for effective water transport and conservation for survival in adverse desert environments (North and Nobel, 1997; Nobel, 2003). A representative desert plant, cacti, can manage water effectively under drought conditions and their anatomical features related to water uptake, transport, and storage have been investigated in the last decades (North and Nobel, 1997; Dubrovsky and North, 2002). Their needles can collect water droplets from wet air or fog (Ju et al, 2012). Rhizosheath enables the cactus roots to absorb a large amount of water rapidly and prevent the water inside the cortex cell from evaporation (Huang and Nobel, 1992)

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