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Bypass flow and sodium transport in rice (Oryza sativa L.)

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posted on 2023-06-07, 15:44 authored by Bualuang Faiyue
An apoplastic pathway, the so-called bypass flow, is important for Na+ uptake in rice under saline conditions. The primary aim of this thesis was to identify the point of entry for bypass flow into rice roots subjected to salinity. Investigations using lateral rootless mutants (lrt1, lrt2), a crown rootless mutant (crl1), their wild types (Oochikara, Nipponbare and Taichung 65, respectively) and seedlings of rice cv. IR36 showed that the entry point, quantified using trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), was not at the sites of lateral root emergence. However, PTS was identified in the vascular tissue of lateral roots using both epifluorescence microscopy and confocal laser scanning microscopy. Cryo-scanning electron microscopy and epifluorescence microscopy of sections stained with berberine-aniline blue and Fluorol Yellow 088 revealed that an exodermis was absent in the lateral roots, suggesting that the lack of the exodermis allowed PTS to pass through the cortical layers, enter the stele and be transported to the shoot via the transpiration stream. These findings suggest a role for the lateral roots of rice in bypass flow. The addition of polyethylene glycol (PEG) and silicon (Si) to the culture solution significantly reduced Na+ uptake to the shoot by reducing bypass flow through the lateral roots. PEG was found to be more effective than Si. It was also shown that changing the relative humidity in the air around the shoots had a significant effect on the magnitude of bypass flow and the flux of water across the roots: the greater the flux of water through the roots, the greater the Na+ uptake and bypass flow. Furthermore, results showed that recombinant inbred lines of rice with low Na+ transport possessed low magnitudes of bypass flow, whereas lines with high Na+ transport had a high degree of bypass flow, indicating that bypass flow could be used as a criterion for screening salt resistance in rice varieties.


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