Abstract
ABSTRACTThe rice root system consists of three types of roots; main root, L-type and S-type lateral root (LR). These component roots are morphologically and histologically different, which is termed as heterorhizy. Root system hydraulic architecture is related to the unique features of component roots. We hypothesized that each component root contributes in different degrees to water uptake of the whole root system. Rice varieties IRAT 109 and Taichung 65 were grown in pots filled with soil under continuous waterlogged (CWL) and drought (CD) conditions until two weeks after heading. Morphology and histological structures of roots, which may regulate radial water movement, were compared among the three component roots. Moreover, hydraulic conductivity (Lpr) of the root system, which represents the water uptake ability, were measured with a pressure chamber. Based on a model that Lpr of the whole root system is a product of Lpr of each of the component roots and their surface areas, we found that the differences in Lpr between the two varieties and the plants grown under different soil water conditions for any of the component roots did not support the corresponding differences in the measured Lpr of the whole root system. In contrast, a significant and positive correlation was found between Lpr of the whole root system and the percentage of surface area of S-type LR but not for the other component roots. These results indicate S-type LR might have a higher contribution to Lpr of the whole root system than the other component roots.
Highlights
The rice root system consists of a number of component roots; main roots including one seminal root and nodal roots, and two types of lateral roots (LRs) (L-type LR and S-type LR) (Kono et al, 1972; Yamauchi et al, 1996)
Based on a model that Lpr of the whole root system is a product of Lpr of each of the component roots and their surface areas, we found that the differences in Lpr between the two varieties and the plants grown under different soil water conditions for any of the component roots did not support the corresponding differences in the measured Lpr of the whole root system
Three types of component roots were compared in their morphology and histological features for the plants grown under continuous waterlogged (CWL) condition
Summary
The rice root system consists of a number of component roots; main roots including one seminal root and nodal roots, and two types of lateral roots (LRs) (L-type LR and S-type LR) (Kono et al, 1972; Yamauchi et al, 1996). Our studies showed that L-type LR production and elongation were promoted in response to mild drought stress, which implied the differences in responses to environmental conditions between L-type LR and S-type LR (Bañoc et al, 2000: Kano et al, 2011; Suralta et al, 2010, 2018). Such developmental response is known as root plasticity and is one of the key traits of plant adaption to various abiotic stresses (Suralta et al, 2018)
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