To understand the functions of transcription factor OsNAC5 in response to abiotic stress, we generated transgenic rice plants with knockdown OsNAC5 by RNA-interfered (RNAi) and overexpressing OsNAC5, and investigated the effects of cold, drought and salt stress on wild-type (WT), RNAi and overexpression rice lines. Our results demonstrated that RNAi lines became less tolerant to these stresses than WT plants, while overexpression of OsNAC5 in Arabidopsis and rice enhanced tolerance to these stresses. The mechanisms underlying the changes in tolerance of the transgenic rice plants to abiotic stresses were explored by measuring free proline (Pro) and soluble sugar contents in WT and transgenic plants. Accumulation of Pro and soluble sugars was positively correlated with OsNAC5 expression levels. The less accumulation of Pro in RNAi lines may be accounted for by inhibition of Pro synthesis and transport at transcriptional levels. In addition, knockdown and overexpression of OsNAC5 enhanced and reduced accumulation of malondialdehyde and H(2)O(2), suggesting that knockdown of OsNAC5 renders RNAi plants more susceptible to oxidative damage. The RNAi lines displayed higher Na(+)/K(+) ratio due to greater accumulation of Na(+) ions than WT under salt stress conditions, and expression of genes encoding tonoplast Na(+)/H(+) antiporter was lower in RNAi lines than in WT under both control and salt-stressed conditions. Seed germination of RNAi and overexpression plants was more and less inhibited by salt and mannitol than that of WT, respectively. Seed germination of overexpression and RNAi plants was more and less sensitive than that of WT to ABA. These findings highlight the important role of OsNAC5 played in the tolerance of rice plants to abiotic stress by regulating downstream targets associated with accumulation of compatible solutes, Na(+) ions, H(2)O(2) and malondialdehyde.
Evidence‐based protection of migratory birds at flyway levels requires a solid understanding of their use of ‘stopping sites’ during migration. To characterize the site use of northward‐migration great knots Calidris tenuirostris in China, we compared length of stay and fuel deposition during northward migration at areas in the south and the north of the Yellow Sea, a region critical for migrating shorebirds. Radio‐tracking showed that at the southern site great knots stayed for only short periods (2.3 ± 1.9 d, n = 40), and bird captures showed that they did not increase their mean body mass while there. In the north birds stayed for 1 month (31.0 ± 13.6 d, n = 22) and almost doubled their mean body mass. Fuel consumption models suggest that great knots departing from the northern Yellow Sea should be able to fly nonstop to the breeding grounds, whereas those from the south would require a refueling stop further north. These results indicate that the study sites in the northern and southern Yellow Sea serve different roles: the southern site acts as a temporary stopover area that enables birds with low fuel stores to make it to main staging areas further north, while the northern site serves as the critical staging site where birds refuel for the next leg of their migration. The rapid turnover rate in the southern Yellow Sea indicates that many more birds use that area than are indicated by peak counts. Differential use of the southern and northern sites indicates that both play crucial roles in the ability of great knots to migrate successfully.
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