Temperature responses of roots: impact on growth, root system architecture and implications for phenotyping

Abstract

Abstract. Root phenotyping is a challenging task, mainly because of the hidden nature of this organ. Only recently, imaging technologies have become available that allow us to elucidate the dynamic establishment of root structure and function in the soil. In root tips, optical analysis of the relative elemental growth rates in root expansion zones of hydroponically-grown plants revealed that it is the maximum intensity of cellular growth processes rather than the length of the root growth zone that control the acclimation to dynamic changes in temperature. Acclimation of entire root systems was studied at high throughput in agar-filled Petri dishes. In the present study, optical analysis of root system architecture showed that low temperature induced smaller branching angles between primary and lateral roots, which caused a reduction in the volume that roots access at lower temperature. Simulation of temperature gradients similar to natural soil conditions led to differential responses in basal and apical parts of the root system, and significantly affected the entire root system. These results were supported by first data on the response of root structure and carbon transport to different root zone temperatures. These data were acquired by combined magnetic resonance imaging (MRI) and positron emission tomography (PET). They indicate acclimation of root structure and geometry to temperature and preferential accumulation of carbon near the root tip at low root zone temperatures. Overall, this study demonstrated the value of combining different phenotyping technologies that analyse processes at different spatial and temporal scales. Only such an integrated approach allows us to connect differences between genotypes obtained in artificial high throughput conditions with specific characteristics relevant for field performance. Thus, novel routes may be opened up for improved plant breeding as well as for mechanistic understanding of root structure and function.

Analyzing Lateral Root Development: How to Move Forward

“…For plants grown in soil, x-ray CT techniques and magnetic resonance imaging (Heeraman et al, 1997;Nagel et al, 2009;Tracy et al, 2010;Lucas et al, 2011;Zhu et al, 2011) have recently increased our capabilities to visualize root system architecture in situ nondestructively. For example, the x-ray CT technique can be used to study root architectures under varying nutrient, moisture, temperature, and soil density conditions in a physiologically relevant way over time.…”

“…In all these techniques, a compromise must be made between the disturbance required to allow observations and the resolution and throughput provided by the imaging device. To obtain relevant high-throughput phenotyping data, new (automated) methods and combinations are still required to provide more natural and nondestructive environmental conditions (Nagel et al, 2009;Zhu et al, 2011).…”

Quantitative 3D Analysis of Plant Roots Growing in Soil Using Magnetic Resonance Imaging

“…Other approaches, such as rhizotrons or mini-rhizotron tubes, where root growth is observed along transparent windows (Nagel et al, 2009), monitor only a fraction of the roots. Methods in which the whole root system is visible are typically based on artificial media such as paper pouches (Chen et al, 2011;Le Marié et al, 2014), three-dimensional (3D) gels (Iyer-Pascuzzi et al, 2010), and hydro-or aeroponics (Herdel et al, 2001).…”

Soil thermal diffusivity estimated from data of soil temperature and single soil component properties

“…Chemically, it affects the equilibrium and reaction rates, thus influencing the decomposition of organic matter and agrochemicals. Biologically, it impacts the functioning of enzymes and other more complex biological systems, affecting microbial and root growth (Bowen, 1970;Barber et al, 1988;Nagel et al, 2009). …”