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

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\ud 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

Reduction of enzymatic browning of harvested 'Daw' longan exocarp by sodium chlorite

ABSTRACT: Post-harvest exocarp browning is a major problem resulting in reduced shelf-life of longan fruits. The objective of this study was to evaluate the possibility of using sodium chlorite (SC) as an anti-browning agent for controlling enzymatic browning of harvested longan fruits during storage at ambient conditions. Longan fruits cv. Daw were dipped in 0.001%, 0.005%, 0.01%, and 0.05% SC (W/V) for 10 min. The fruits were packed in cardboard boxes and stored at 25 ± 1°C with a relative humidity of 82 ± 5% for 72 h. Changes in browning index, colour parameter (L* and b* values), polyphenol oxidase (PPO) activity, peroxidase (POD) activity, and total phenolic content were measured. The results showed that the fruits treated with SC had lower browning index, but higher L* (lightness) and b*(yellowness) values than those of the control group during storage for 48 h. SC at a concentration of 0.01% was the most effective in reducing exocarp browning. The application of SC reduced PPO and POD activities and delayed a decrease in the total phenolic content. The treatment with 0.01% and 0.05% SC had the lowest PPO and POD activities, and maintained the highest total phenolic content. It was concluded that an application of SC is an alternative method for reducing exocarp browning and maintaining quality of harvested longan fruits

The role of lateral roots in bypass flow in rice (Oryza sativa L.)

Although an apoplastic pathway (the so-called bypass flow) is implicated in the uptake of Na+ by rice growing in saline conditions, the point of entry of this flow into roots remains to be elucidated. We investigated the role of lateral roots in bypass flow using the tracer trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS) and the rice cv. IR36. 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 revealed that the exodermis is absent in the lateral roots. We conclude that PTS can move freely through the cortical layers of lateral roots, enter the stele and be transported to the shoot via the transpiration stream

Phospholipases Dζ1 and Dζ2 have distinct roles in growth and antioxidant systems in Arabidopsis thaliana responding to salt stress

International audienceLipid signalling mediated by phospholipase D (PLD) plays essential roles in plant growth including stress and hormonal responses. Here we show that PLDζ1 and PLDζ2 have distinct effects on Arabidopsis responses to salinity. A transcriptome analysis of a double pldζ1pldζ2 mutant revealed a cluster of genes involved in abiotic and biotic stresses, such as the high salt-stress responsive genes DDF1 and RD29A. Another cluster of genes with a common expression pattern included ROS detoxification genes involved in electron transport and biotic and abiotic stress responses. Total superoxide dismutase (SOD) activity was induced early in the shoots and roots of all pldζ mutants exposed to mild or severe salinity with the highest SOD activity measured in pldζ2 at 14 days. Lipid peroxidation in shoots and roots was higher in the pldζ1 mutant upon salt treatment and pldζ1 accumulated H2O2 earlier than other genotypes in response to salt. Salinity caused less deleterious effects on K+ accumulation in shoots and roots of the pldζ2 mutant than of wild type, causing only a slight variation in Na+/K+ ratio. Relative growth rates of wild-type plants, pldζ1, pldζ2 and pldζ1pldζ2 mutants were similar in control conditions, but strongly affected by salt in WT and pldζ1. The efficiency of photosystem II, estimated by measuring the ratio of chlorophyll fluorescence (Fv/Fm ratio), was strongly decreased in pldζ1 under salt stress. In conclusion, PLDζ2 plays a key role in determining Arabidopsis sensitivity to salt stress allowing ion transport and antioxidant responses to be finely regulated