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An Qin, Xiaosan Huang, Huping Zhang, Juyou Wu, Jie Yang and Shaoling Zhang

Ascorbic acid (AsA) is a major antioxidant and redox buffer in plants. Dehydroascorbate reductase (DHAR; EC 1.8.5.1) catalyzes the conversion of dehydroascorbate (DHA) to AsA and is crucial for AsA regeneration. In this study, we developed transgenic tomato plants that overexpressed PbDHAR2 to investigate whether PbDHAR2 could limit the deleterious effects of salt and chilling stresses. These transgenic plants contained significantly higher AsA levels than the wild-type (WT) plants. Overexpression of PbDHAR2 increased the expression of the AsA-glutathione (GSH) cycle genes in transgenic lines under salt and chilling stresses. In addition, the transgenic lines subjected to salt and chilling stresses showed higher levels of antioxidant enzyme activity, lower malondialdehyde (MDA) levels, and higher chlorophyll contents than the WT. Thus, our results demonstrate that the regulation of PbDHAR2 during AsA regeneration contributes to enhanced salt and chilling tolerance in tomato.

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Soohyun Kang, Yating Zhang, Yuqi Zhang, Jie Zou, Qichang Yang and Tao Li

Ultraviolet-A (UV-A) is the main component of UV radiation in nature. However, its role on plant growth, to a large extent, remains unknown. In this study, tomato (Solanum lycopersicum ‘Beijing Cherry Tomato’) seedlings were cultivated in an controlled environment in which UV-A radiation was provided by UV-A fluorescent lamps (λmax = 369 nm) with a fluence rate of 2.28 W·m−2. The photoperiod of UV-A radiation was 0, 4, 8, and 16 hours, which corresponds to control, UV-A4, UV-A8, and UV-A16 treatments, respectively. The photosynthetic photon flux density (PPFD) was 220 μmol·m−2·s−1, which was provided by light-emitting diodes (LEDs) with a blue/red light ratio of 1:9, the photoperiod of PPFD was 16 hours. We showed that supplementing 8 and 16 hours of UV-A to visible radiation (400–700 nm) stimulated plant biomass production by 29% and 33%, respectively, compared with that of control. This resulted mainly from larger leaves (i.e., 22% and 31% in 8 and 16 hours UV-A, respectively), which facilitated light capture. Supplemental UV-A also enhanced photosynthetic capacity, as indicated by greater net photosynthesis rates in response to CO2 under saturating PPFD. Furthermore, the greatest stomatal conductance (g S) value was observed in UV-A16, followed by UV-A8, which correlated with the greater stomatal density in the corresponding treatments. Moreover, supplemental UV-A did not induce any stress, as the maximum quantum efficiency of photosynthetic system II (PSII) (F v/F m) remained ≈0.82 in all treatments. Similarly, chlorophyll content and leaf mass area (LMA) were also unaffected by UV-A radiation. Taken together, we conclude that supplementing reasonable levels of UV-A to visible radiation stimulates growth of indoor cultivated tomato seedlings.

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Zhiyong Hu, Min Zhang, Qigen Wen, Jie Wei, Hualin Yi, Xiuxin Deng and Xianghua Xu

Seedlessness is of commercial importance in citrus (Citrus L.). Seedless ‘Ougan’ mandarin (C. suavissima) was selected from a bud sport mutation that occurred in ‘Ougan’ mandarin. We analyzed their pollen viability through KI-I2 and FDA staining, and examined the anthers of wild-type (seedy) and seedless mutant ‘Ougan’ mandarin using histological and cytochemical methods to characterize the process of pollen development. No pollen fertility was detected in this mutant. Pollen abortion in anthers of the mutant occurred at the tetrad stage of microspore development, and almost all the tetrads were abnormal. The mutant had heterogeneous microspore populations, including monads, dyads, triads, tetrads, and polyads in the same microsporangium. Pollen grain number per anther of the mutant was 21.9% less than the wild type. Morphology of mature pollen grains using SEM showed that the shape of mature pollen grains from both wild type and mutant is similar, but the microsporangia of the latter contained pollen grains of more variable sizes. At the early mature pollen grain stage, abundant starch grains and lipids appeared in the wild type's pollen, but fewer amounts were observed in the mutant. Moreover, the tapetal cells of the wild type accumulated lipids, but not those of the mutant. Results indicated that the abnormal development of the microspore led to pollen abortion in the mutant, and this could be the reason for its seedlessness. However, the genetic reasons for the aberrant tetrads are not clear and are under investigation.

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Ji Tian, Zhen-yun Han, Li-ru Zhang, Ting-Ting Song, Jie Zhang, Jin-Yan Li and Yuncong Yao

Anthocyanins are protective pigments that accumulate in plant organs such as fruits and leaves, and are nutritionally valuable components of the human diet. There is thus considerable interest in the factors that regulate synthesis. Malus crabapple leaves are rich sources of these compounds, and in this study we analyzed leaf coloration, anthocyanin levels, and the expression levels of anthocyanin biosynthetic and regulatory genes in three crabapple cultivars (Royalty, Prairifire, and Flame) following various temperature treatments. We found that low temperatures (LTs) promoted anthocyanin accumulation in ‘Royalty’ and ‘Prairifire’, leading to red leaves, but not in ‘Flame’, which accumulated abundant colorless flavonols and retained green colored leaves. Quantitative reverse transcript PCR (RT-PCR) analyses indicated that the expression of several anthocyanin biosynthetic genes was induced by LTs, as were members of the R2R3-MYB, basic helix–loop–helix (bHLH) and WD40 transcription factor families that are thought to act in a complex. We propose that anthocyanin biosynthesis is differentially regulated in the three cultivars by LTs via the expression of members of this anthocyanin regulatory complex.

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Ji Tian, Ke-ting Li, Shi-ya Zhang, Jie Zhang, Ting-ting Song, Yong-jun Zhu and Yun-cong Yao

Anthocyanins are protective pigments that accumulate in plant organs such as fruits and leaves, and are nutritionally valuable components of the human diet. The MYB10 transcription factor (TF) plays an important role in regulating anthocyanin biosynthesis in Malus crabapple leaves. However, little is known about how the promoter regulates McMYB10 expression and influences the substantial variation in leaf anthocyanin accumulation and coloration that is observed in different crabapple cultivars. In this study, we analyzed leaf coloration, anthocyanin levels, and the expression levels of McMYB10 in the leaves of 15 crabapple cultivars with three leaf colors at various development stages, and showed that the expression of McMYB10 correlates positively with anthocyanin accumulation. We also examined the relationship between the number of R6 and R1 elements in the McMYB10 promoters of the different cultivars and the pigmentation of the new buds of spring-red cultivars, as well as the methylation level of the McMYB10 promoters at different development stages in three representative crabapple cultivars. The ratio of R6/R1 minisatellites in the promoters correlated with the color and anthocyanin accumulation in new crabapple buds, and we concluded that the differences in promoter structure and methylation level of the McMYB10 promoters coordinately affect the leaf color of crabapple cultivars.

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Haiying Zhang, Jianguang Fan, Shaogui Guo, Yi Ren, Guoyi Gong, Jie Zhang, Yiqun Weng, Angela Davis and Yong Xu

Watermelon belongs to the genus Citrullus. There have been continuing interests in breeding of watermelon for economic benefits, but information on the scope and utilization of genetic variations in Citrullus is still limited. The present study was conducted in 2012–13, to evaluate the genetic diversity and population structure of the 1197 line watermelon collection maintained by the Beijing Vegetable Research Center (BVRC), which belongs to seven Citrullus species including Citrullus naudinianus, Citrullus colocynthis, Citrullus rehmii, Citrullus ecirrhosus, Citrullus amarus, Citrullus mucosospermus, and Cirullus lanatus subsp. vulgaris. Twenty-three highly informative microsatellite markers evenly distributed in the watermelon genome were used to assess genetic diversity in this collection. The markers detected on an average of 6.05 alleles per locus with the average value of polymorphism information content (PIC) at 0.49. A high level of gene diversity [Nei’s gene diversity index (Nei) = 0.56] and a low observed heterozygosity (H o = 0.10) were revealed within the collection. Structure analysis grouped the 1197 accessions into two main populations (Pop I and Pop II) and an admixture group. Pop I contained 450 accessions from C. lanatus subsp. vulgaris (446) and C. mucosospermus (4). Pop II comprised 465 accessions, 379 of which belonged to C. lanatus subsp. vulgaris and 86 to C. naudinianus (3), C. ecirrhosus (2), C. rehmii (2), C. colocynthis (11), C. amarus (58), and C. mucosospermus (10). The remaining 282 accessions were classified as an admixture group. The two main populations were further subdivided into four subgroups. The groupings were consistent with the estimation of F statistics (F st) and Nei’s genetic distances in collections. We confirmed the distinct genetic backgrounds between American and East Asian ecotypes. Subsequently, we defined a core set consisting of 130 accessions including 47 from Pop I, 68 from Pop II, and 15 from the Admixture group. This core set was able to capture all 133 alleles detected by 23 simple sequence repeats (SSRs) in 1197 accessions. These results will facilitate efficient use of genetic variations in Citrullus in watermelon breeding and help optimization of accessions in genomewide association studies.

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Jie Zhang, Hong-yan Liu, Xin-yu Qi, Ya-nan Li and Ling Wang