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For centuries in Asia, Rhodiola coccinea has been used as a valuable adaptogen medicinal plant known for its remarkable resistance to various stress factors. Physiological tolerance in chloroplasts is believed to be an important factor, which affects the geographic distribution of plant species. However, there is currently no report on how the physiological tolerance in the chloroplasts of R. coccinea varies along an altitudinal gradient in a semiarid mountain region. In this work, we investigated the physiological variations of the chloroplasts of R. coccinea plants along an altitudinal gradient in the Tianshan Mountains, which are located in northwest China. It was found that the physiological parameters of chloroplasts in R. coccinea plants, including superoxide generation, fatty acid compositions, thylakoid membrane fluidity, chlorophyll a/b ratios and photosynthetic electron transport rates (ETRs), varied nonlinearly with altitude. Indeed, an inflection point was observed at approximately 3,800 m. For altitudes were higher or lower than 3,800 m, the ETR, index of unsaturated fatty acids in the thylakoid membrane and Chl a/b ratios decreased with increasing altitude, whereas the superoxide generation and DPH polarisation of thylakoid membranes increased. In addition, variations in the AsA and GSH contents of chloroplasts could be divided into two distinct phases along the altitudinal gradient. The AsA content slowly decreased with increasing altitudes up to 3,800 m and rapidly decreased above 3,800 m. However, there was a gradual increase in the GSH content between 3,570 and 3,750 m, followed by an abrupt rise to a plateau level. These results demonstrate that the physiological tolerance of chloroplasts widely varies with altitude and have a tight relationship with the range of growth altitude of R. coccinea in Tianshan Mountains.
Leaf color mutants are not only ideal resources for studying the physiological mechanisms of plant photosynthesis, but they are also selection markers for hybrid production. In this study, the chlorosis mutant ‘564Y’ and its wild-type counterpart ‘564’ were used to explore physiological characteristics and gene expression in pak choi. Compared with those of wild type, the dry weight and fresh weight of ‘564Y’ were significantly reduced, but the hypocotyl length of ‘564Y’ was longer. Pigment analysis showed that the chlorophyll a and carotenoid contents of ‘564Y’ were lower than those of wild type. However, there was no significant difference in chlorophyll b content between these two varieties. The photosynthetic capacity of ‘564Y’ was lower than that of ‘564’, and the photosynthetic electron transfer ability and light energy conversion efficiency were weaker in the former. Transmission electron microscopy showed that the chloroplast structure of ‘564Y’ was not compact, the thylakoid structure was irregular, and the number of matrix, grana, and stacking layers was decreased. Transcriptome analysis revealed 2958 differentially expressed genes (DEGs), and 78 gene ontology terms and 35 Kyoto Encyclopedia of Genes and Genomes pathways were significantly enriched. Among the DEGs, nine genes were associated with the chlorophyll synthesis pathway (Bra031690, Bra012595, Bra005677, Bra022628, Bra026410, Bra032155, Bra039206, Bra029875, and Bra012511) and one gene was associated with photosynthesis (Bra038011). Among these genes, 3 were identified as related to auxin metabolism too (Bra032155, Bra039206, and Bra029875). Their differential expression in the ‘564Y’ mutant and wild-type plant was confirmed by qRT-PCR. These results lay the foundation for future genetic and functional genomic studies in pak choi.
This study investigated heavy metals in soils and agricultural products near an industrial district in Dongguan City. The concentrations of Cu, Zn, Pb, Cd, Hg, and As in soil and agricultural products from vegetable and banana fields were determined. Results indicated that except for Zn in one sample and Cd in five samples, the majority of the samples were notably enriched by heavy metals compared with background values. The concentrations of heavy metals (mg·kg⁻¹ dry soil) in agricultural soils in the study area ranged from 22.2 to 93.0 for Cu, 31.2 to 213.6 for Zn, 47.6 to 133.5 for Pb, 0.01 to 0.67 for Cd, 0.15 to 0.56 for Hg, and 20.5 to 28.9 for As. Among these soil samples, concentrations of Cu, Zn, Cd, and Hg in 20.6%, 8.8%, 29.4% and 38.2% soil samples, respectively, exceeded Chinese maximum allowable concentrations (MAC) for agricultural soil. The concentrations of Zn, Pb, and Cd were significantly higher in vegetable than in banana fields. Cu, Zn, Pb, Cd, and Hg accumulated in the topsoil of vegetable fields, but only Pb and Hg accumulated in banana fields. Zn, Cd, and Hg accumulated more easily in flowering cabbage than other vegetables. Cu, Zn, and As were accumulated more easily in banana than lettuce, bunching onion and eggplant. Therefore, the findings suggest more attention should be focused on the accumulation of heavy metals in banana. This study presents a practical methodology for screening crops with lower bio-concentration factors for heavy metals to reduce metal contaminants in the general food supply chain.
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