Tree peony (Paeonia section Moutan DC.) is a famous ornamental plant, and P. ostii has been used for seed oil production in China because it is rich in α-linolenic acid. P. ostii has some resistance to drought, but lack of water can severely hinder its growth and development in arid areas. In order to clarify drought stress induced physiological and molecular changes of P. ostia, its physiological and transcriptomic analyses were performed under drought stress, and we found that P. ostii leaves drooped significantly 12 days after treatment and observed a significant increase in all detected physiological indices in response to drought treatment except leaf water content, chlorophyll, and carotenoid content. Meanwhile, the activity of three antioxidant enzymes basically increased under drought treatment. Moreover, drought treatment significantly reduced photosynthetic and chlorophyll fluorescence parameters except non-photochemical quenching (qN), and maintained more intact mesophyll cell structures. Additionally, many differentially expressed genes (DEGs) were found by transcriptome sequencing, which play an important role in P. ostia drought tolerance by controlling a variety of biological processes, including the reactive oxygen species (ROS) system, chlorophyll degradation and photosynthetic competency, fatty acid metabolism, proline metabolism, biosynthesis of secondary metabolism, and plant hormone metabolism. These results provide a better understanding of P. ostii responses to drought stress.
Graphene oxide (GO) is considered to be an emerging environmental pollutant with its inevitable release into the environment. Thus, its potential environmental risks and biosafety are receiving increased attention. In this study, Paeonia ostii was exposed to GO under drought stress. The results demonstrated that GO prevented soil water from evaporating due to its hydrophilic oxygen-containing functional groups and did not change the soil pH. Moreover, GO treatment resulted in lower increases in reactive oxygen species, relative electrical conductivity and free proline content, and greater increases in the antioxidant enzyme activities of P. ostii under drought stress compared with those in the control. And under drought stress, higher photosynthesis, more intact mesophyll cells and organelles and open stomata were found in P. ostii under GO treatment. Furthermore, GO treatment induced greater changes in the expression patterns of genes required for lignin biosynthesis, photosynthesis-antenna proteins, carbon fixation in photosynthetic organisms, and glyoxylate and dicarboxylate metabolism. Additionally, GO did not accumulate in P. ostii due to the soil environment and the electrostatic repulsion between GO and the roots. GO did not have toxic effects on P. ostii and was an effective soil water retention agent; therefore, it could be economically beneficial for the production of plants under drought stress.
Paeonia ost ii has become an economically important oil crop in recent years, but its growth is seriously affected by drought stress in dry areas. In this study, the alleviating effect of fulvic acid (FA) on potted P. ostii under natural drought stress was investigated. The natural drought stress adopted in this experiment was mainly characterized by the low soil water content, and the roots of plants cannot absorb enough water to compensate for the consumption of transpiration, which affects the normal physiological activities and causes damage. The results showed that FA treatment significantly increased the leaf water content and antioxidant enzyme activities and decreased reactive oxygen species (ROS) accumulation, the proline (Pro) content, and the relative electrical conductivity (REC). Moreover, FA treatment improved photosynthetic parameters and chlorophyll (Chl) fluorescence parameters, maintained the integrity of chloroplasts and mesophyll cells, and increased the expression level of drought-tolerant genes. These results indicated that FA treatment could induce antioxidant enzymes to eliminate ROS, reduce membrane lipid peroxidation and decrease damage to photosynthesis in P. ostii under drought stress, which would provide a measure for alleviating the damage of P. ostii caused by drought stress.
Herbaceous peony (Paeonia lactiflora Pall.) is one of the color-leaved ornamental spring plants, with graceful appearance and splendid color. However, the underlying mechanism of this coloration variation from purple to green has not been studied in P. lactiflora. In th study, the leaves in purple, purple-green, and green stages were compared in terms of anatomical, physiological, and molecular. We found that the variation of leaf color from purple to green was mainly determined by the change in pigments distributed in the leaf surface. Physiological experiments showed a significant increase in chlorophyll contents and a notable reduction in anthocyanin contents in leaves from the purple to green stages. We further found that the anthocyanin biosynthesis-related dihydroflavonol 4-reductase (DFR) gene and anthocyanin synthase (ANS) gene as well as chlorophyll biosynthesis-related glutamyl-tRNA reductase (HEMA) gene showed a decreased trend in leaves from purple to green stages, whereas the chlorophyll degradation-related chlorophyll b reductase (NYC) gene showed a rising trend. Alteration of DFR and ANS gene expression might reduce anthocyanin accumulation, whereas increased HEMA gene expression would enhance chlorophyll biosynthesis and reduced NYC gene expression would inhibit chlorophyll degradation. Consequently, reduction in anthocyanins and enhanced deposition of chlorophylls resulted in leaf coloration variation from purple to green in P. lactiflora, which could improve our understanding of its mechanism for further studies.
Tree peony (Paeonia section Moutan DC.) is an excellent ornamental plant, of which Paeonia ostii (P. ostii) has a high oil value. It is widely cultivated in China, but severe drought affects its growth. In this study, the effects of exogenous calcium on drought-induced damage of P. ostii were studied. The results showed that under drought stress, leaf water content showed a downward trend, while reactive oxygen species (ROS), relative electrical conductivity (REC), proline (Pro) content, and related antioxidant enzymes increased significantly. Spraying CaCl2 could effectively slow leaf wilting and water loss, induced an increase in enzyme activity of the antioxidant enzyme system, and reduced the accumulation of ROS caused by drought stress. Simultaneously, REC and Pro content could be alleviated, and the degree of cell membrane damage could be reduced. In addition, CaCl2 improved photosynthetic characteristics and chlorophyll fluorescence parameters. These results indicated that CaCl2 reduced the harmful effects of drought stress on the growth of P. ostii by regulating infiltration, activating photosynthesis, and enhancing the antioxidant system. These findings suggested that CaCl2 can be used to manage drought stress in P. ostii cultivation.Additional key words: ascorbate peroxidase; gas exchange; physiological index; relative water content; superoxide dismutase; water stress. (J. Tao) Abbreviations: APX -ascorbate peroxidase; Ci -intercellular CO2 concentration; DAB -diaminobenzidine; DM -dry mass; E -transpiration rate; F0 -minimal fluorescence yield of the dark-adapted state; Fm -maximal fluorescence yield of the dark-adapted state; FM -fresh mass; Fv/Fm -maximal quantum yield of PSII photochemistry; gs -stomatal conductance; PN -net photosynthetic rate; POD -peroxidase; Pro -free proline; qN -nonphotochemical quenching coefficient; REC -relative electrical conductivity; ROS -reactive oxygen species; SOD -superoxide dismutase; Y(II) -effective quantum yield of PSII photochemistry. Acknowledgments: The authors wish to thank two anonymous reviewers for their input and constructive criticism.
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