Measurements of maize root plasticity under water stress in hydroponic chambers

Under water stress, plants adjust root traits including depth of root system, root diameter, density of root per volume of soil, hydraulic conductance of root. In this experimental study, we present a method to quantify how hydraulic traits of maize roots adapt to drought. The experiments involve a microfluidic flow sensor and a custom-built pressure chamber, made of transparent plastic for visualization purposes. We measured how maize genotypes (PHB47 and PHZ51) grown for a week in deionized (DI) water and one day in hydroponic nutrients solution (called the irrigated condition) respond to one week of water stress. Conditions of water stress (called drought conditions) were created by mixing Polyethylene Glycol with the nutrients solution. Results show that under drought, the roots of both genotypes respond by approximately halving their global hydraulic conductance. This adjustment seems to be achieved mainly by reductions of the total surface area of the roots. Interestingly, the measured hydraulic conductivity of the roots grown under drought was significantly larger. In all, this study sheds light on how plants adapt to water stress in a hydroponic system, by decreasing root area and increasing root permeability.


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Climate change and population growth incite both scientists and engineers to investigate methods to 25 increase food production. Climate change increases drought-index (insufficient soil moisture level to 26 meet the plant needs for water as defined in [1]) all over the world, and in the near future we would have 27 to increase yield and decrease water use. photons m -2 s -1 . Every other day the beakers were refilled with water to maintain the water level at 1.4 L.

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After seven days, the seedlings were taken out of the roll, and roots with similar length were selected for

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Design of pressure chamber and flow sensor 87 We designed and assembled a pressure chamber to measure the hydraulic conductance of whole root 88 systems (see S1 Appendix for the detail). The device is based on the root transport model described in

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[13], where the water flow rate J=L(P-), and , L is the root conductance [m 3 /Pas], P=P 1 -P 2 is the 90 difference of hydrostatic pressure, including gravity, and  is a difference of osmotic pressure, with  is 91 the reflection coefficient. In the device the gradient of water potential (P-) is in the natural 92 direction, that is, the potential is higher around the root system than that at the stem.

Measurement of hydraulic conductance 94
For the measurement, a plant was cut at the stem just above the base of the root system and inserted in the The pressure chamber was filled with DI water. A custom-made compression gasket-fitting was used to 105 hold the cut stem and ensure leak proof. The end of the cut stem was connected to a calibrated 106 microfluidic tube (thick black line), the pressure drop across the calibrated tubing was measured via a 107 differential pressure gauge (P 2 -P atm ). The pressure drop across the root system was measured via another 108 pressure gauge (P 1 -P 2 ).

Measurement of root traits from digital image 110
After hydraulic conductance measurement, the root systems were imaged using a high-resolution scanner,

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First we validated the accuracy, repeatability, and fidelity of our measurements . We, then, quantified and 118 compared hydraulic conductance of the root system for the genotypes, PHB47 and PHZ51. Finally, we 119 measured the total surface area, total length of the root systems using ARIA and investigated the 120 adaptation of the hydraulic conductivity between the genotypes.

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Validation of the hydraulic conductance measurement To validate the accuracy, repeatability, and fidelity of our system, we measured the global root 123 conductance of the hydroponically grown seedlings of an arbitrary maize genotype. The seedlings were 124 grown in irrigated condition ((pure water and nutrient solutions).

Adaptation of root traits under drought 138
Our measurements indicate that seedlings cultivated for seven days under drought (water stress condition) 139 typically exhibit a lower hydraulic conductance than those cultivated in irrigated condition (pure water 140 and nutrient solutions) (Fig 4 (A)). The reduction of hydraulic conductance of the genotypes PHB47 and 141 PHZ51 are, respectively, 53% and 60%. Reduction in hydraulic conductance indicates plant become 142 water conservative, uses less water during drought. They had similar total root volume (via eyeballing),

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after the initial first week in the germination paper, but after the second week in different water stress 144 conditions, the total root volumes were different. Under drought, the total root volumes were smaller than 145 those in the irrigated conditions for both genotypes (Fig 4 (B)), i.e. the root system has less surface area 146 and pathways to uptake water. The overall root surface area under drought was also found around 70% 147 smaller than that in normal/irrigated condition.

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The overall hydraulic conductivity [22] of the genotypes were estimated by dividing overall hydraulic 152 conductance with overall surface area. The hydraulic conductivity under drought was increased 153 significantly for both genotypes (Fig 5), that is 50% for PHB47 and 150% for PHZ51. Similar trends also 154 reported for young maize seedlings grown in pots by Zhang et al. [23].