Abstract
Seeds and young seedlings often encounter high soluble salt levels in the upmost soil layers, impeding vigorous growth by affecting root establishment. Computed tomography (CT) scanning used at low X-ray doses can help study root development in such conditions non-destructively, because plants are allowed to grow throughout the experiment. Using a high-resolution Toshiba XVision CT scanner, we studied corn (Zea mays L.) root growth under optimal and salt-stressed conditions in 3D and on a weekly basis over 3 weeks. Two groups of three corn plants were grown in the controlled environment of a growth chamber, in mid-sized plastic pots filled with sieved and autoclaved sand. Seedlings were subjected to first CT scanning 1 week after seed planting. Our main research objectives concerning root systems were: (i) to quantify structural complexity from fractal dimensions estimated on skeletal 3-D images built from CT scanning data; (ii) to measure growth from volumes and lengths and the derived relative rates and increments, after isolating primary and secondary roots from the soil medium in CT scanning data; and (iii) to assess differences in complexity and growth per week and over Weeks 1–3 for groups of corn plants. Differences between groups were present from Week 1; starting in Week 2 secondary roots were present and could be isolated, which refined the complexity and growth analyses of root systems. Besides expected Week main effects (P < 0.01 or 0.05), Week × Group interaction (P < 0.05 or 0.10), and Group main effects were observed. Graphical, quantitative, and statistical analyses of CT scanning data were thus completed at an unprecedented level, and provided new and important insights regarding root system development. Repeated CT scanning is the key to a better understanding of the establishment in the soil medium of crop plants such as corn and the assessment of salt stress effects on developing root systems, in complexity, volume, and length.
Highlights
Plants encounter various abiotic and biotic stressors during their life cycle
Three-Dimensional Image Analyses From the skeletal 3-D images of root systems constructed from the Computed tomography (CT) scanning data collected on a weekly basis for individual plants in the control and salt-stressed groups (Figures 2A,B), it is clear that germinated seeds of the control group in Week 1 show the development of embryonic roots with two subsets of roots called “upper roots” and “lower roots” here, whereas the onset of upper roots is delayed in the salt-stressed plants and upper roots in this group are present and visible only from Week 2 on
Studies of root system architecture under laboratory conditions mostly use platforms such as WinRhizo that can help generate data for plants grown in solid medium
Summary
Plants encounter various abiotic and biotic stressors during their life cycle. Two of the most prevalent abiotic stressors confronting global agriculture are soil salinity and drought. Salinization is one of the more serious agricultural limitations, especially in the arid and the semi-arid regions of the CT monitoring of plant stress world. Land clearing and irrigation are among the major contributors to salinization of agricultural lands. Their general impact has been reported (Munns, 2005; Rengasamy, 2008), and this is aggravated by a number of factors, including climate, the degree of water deficit, the inherent salt content of soils, topography, and the underlying geology and hydrology (Wiebe et al, 2007)
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