The application of plant growth regulators (PGRs), such as abscisic acid (ABA), putrescine (Put), and 2,4-epibrassinolide (EBR), has been shown to enhance a plant's resistance to various abiotic stresses. However, the protective effects of these PGRs on tomato (Solanum lycopersicum) seedlings under suboptimal temperature stress have not yet been evaluated. We also do not know the most effective method of application of PGRs for various tomato cultivars. We studied the effects of three rates of exogenous ABA, Put, or EBR in limiting damage from suboptimal temperature stress on two tomato cultivars, Zhongshu6 (considered sensitive to suboptimal temperatures) and SANTIAM (considered tolerant to suboptimal temperatures). Results showed that application of these PGRs at appropriate concentrations could effectively reduce the decline in the net photosynthetic rate (Pn) and the chlorophyll (Chl) content in leaves caused by suboptimal temperature stress in both ‘Zhongshu6’ and ‘SANTIAM’ and could promote an increase in organic osmolyte (proline and soluble sugar) contents and root 2,3,5-triphenyltetrazolium chloride (TTC)-reducing activity for ‘Zhongshu6’. However, these effects were inferior on ‘SANTIAM’. For both cultivars, the best treatment concentrations are 1 mm ABA, 0.1 mm Put, or 0.02 μM EBR. Results indicate that in tomato production, exogenous application of ABA, Put, or EBR at appropriate concentrations can effectively limit damage from suboptimal temperature stress.
Weijie Jiang, Jie Bai, Xueyong Yang, Hongjun Yu and Yanpeng Liu
Yuee Tian, Zhiping Che, Di Sun, Yuanyuan Yang, Xiaomin Lin, Shengming Liu, Xiaoyu Liu and Jie Gao
Tree peonies are valuable ornamental plants and are widely cultivated in China and many other countries. Gray mold caused by Botrytis cinerea is an increasingly severe disease in Luoyang of China and seriously affects the ornamental value of tree peonies both in the open air and in greenhouses. However, the resistance of different tree peony cultivars to B. cinerea remains unknown. In this study, 15 tree peony cultivars belonging to three different flowering times were evaluated for resistance to B. cinerea by detached leaf assay measure. Results showed that the resistance of early-flowering peonies was stronger than that of later flowering peonies. Moreover, the correlation between flowering time and resistance of tree peonies was extremely significant (P < 0.01). The information obtained in this study can provide theoretical basis both for further exploring the resistance genes of tree peony to B. cinerea and for the prevention and controlling of the gray mold.
Jie Fu, Qiaoyan Xiang, Xianbao Zeng, Mei Yang, Ying Wang and Yanling Liu
To assess the genetic diversity among lotus (Nelumbo) accessions and evaluate the correlation between genetic variation and morphological classification, we sampled 138 accessions: two of N. lutea, 112 of N. nucifera, 17 of hybrids between N. nucifera and N. lutea, and seven Japanese cultivars. The 11 selected combinations of amplified fragment length polymorphism (AFLP) primers produced 138 polymorphic loci, and the percentage of polymorphism was 28.7%. The unweighted pair group method with arithmetic mean (UPGMA) dendrogram clustered all the accessions into two groups: Group I comprised N. lutea and its hybrids with N. nucifera; Group II included N. nucifera and its hybrids with N. lutea and Japanese cultivars. Population structure analysis identified four main clusters: N. lutea clustered mainly in C1, whereas N. nucifera clustered in C2, C3, and C4, which was consistent with the UPGMA and principal coordinate analysis results. The Japanese cultivars were related more closely to N. nucifera (genetic similarity coefficient = 0.74) than to N. lutea (0.46); hence, the Japanese cultivars can be classified as N. nucifera. Moreover, rhizome lotuses formed a separate subclade, whereas seed lotuses were interspersed among flower lotuses, which demonstrated that rhizome lotuses were distinct from flower and seed lotuses. Plant size, flower color, and other morphological criteria used commonly to classify lotuses were correlated with genetic variation to a certain extent but not sufficiently for accurate classification. It appears that it is necessary to use both DNA markers and morphological characteristics to classify lotus species and cultivars.
Yu Bai, Ying Zhou, Xiaoqing Tang, Yu Wang, Fangquan Wang and Jie Yang
The appropriate timing of bolting and flowering is one of the keys to the reproductive success of Isatis indigotica. Several flowering regulatory pathways have been reported in plant species, but we know little about flowering regulatory in I. indigotica. In the present study, we performed RNA-seq and annotated I. indigotica transcriptome using RNA from five tissues (leaves, roots, flowers, fruit, and stems). Illumina sequencing generated 149,907,857 high-quality clean reads and 124,508 unigenes were assembled from the sequenced reads. Of these unigenes, 88,064 were functionally annotated by BLAST searches against the public protein databases. Functional classification and annotation assigned 55,991 and 23,072 unigenes to 52 gene ontology (GO) terms and 25 clusters of orthologous group (COG) categories, respectively. A total of 19,927 unigenes were assigned to 124 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, and 80 candidate genes related to plant circadian rhythm were identified. We also identified a number of differentially expressed genes (DEG) and 91 potential bolting and flowering-related genes from the RNA-seq data. This study is the first to identify bolting and flowering-related genes based on transcriptome sequencing and assembly in I. indigotica. The results provide foundations for the exploration of flowering pathways in I. indigotica and investigations of the molecular mechanisms of bolting and flowering in Brassicaceae plants.
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.
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 184.108.40.206) 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.
Sheng-Xi Liao, Xian-Jie Mi, Ai-Zhong Liu, Kun Li, Zhen-Yin Yang and Bo Tian
The Chinese Incense-cedar (Calocedrus macrolepis Kruz), an important wood and ornamental tree, is native to southwest China and also in northern Vietnam, Laos, Thailand, and Myanmar. As a result of ecological degradation in these areas, Chinese Incense-cedar was considered a vulnerable species according to the criteria of the International Union for the Conservation of Nature and Natural Resources. In the current report, we developed and characterized 13 novel microsatellite markers for this species using the protocol of fast isolation by amplified fragment length polymorphism of sequences containing repeats. Polymorphism of each locus was assessed in 36 individuals from nine geographical populations. The number of alleles per locus ranged from two to nine with an average of 6.08. The observed and expected heterozygosities ranged from 0.0000 to 1.0000 and from 0.1549 to 0.8912 with averages of 0.6688 and 0.6815, respectively. Four of the 13 loci were significantly deviated from Hardy-Weinberg expectations. No significant linkage disequilibrium was detected. These polymorphic microsatellite markers would be useful tools for investigating genetic population structure and diversity to establish conservation strategy for this interesting and vulnerable species.
Qin Yang, Yan Fu, Yalan Liu, Tingting Zhang, Shu Peng and Jie Deng
The xenia effect refers to the phenomenon whereby the pollen genotype directly affects seed and fruit development during the period from fertilization to seed germination, which leads to different characteristics in phenotypic traits. The xenia effect can create differences in the endosperm and embryo formed after double fertilization and can also alter various fruit parameters, such as the fruit-ripening period; the fruit shape, size, and color; the flavor quality, such as sugars and acids; as well as the nutrient quality, such as anthocyanins. The xenia effect manifests in various ways, playing an important role in increasing the yield of fruit trees, improving fruit appearance and internal quality, as well as in directional breeding. Compared with other pomology research areas, our understanding of the xenia effect is still in its infancy. Currently, xenia is classified into two types: xenia and metaxenia. In the former, the direct effects of the pollen genotype are exhibited in the syngamous parts of the ovules; that is, the embryo and endosperm only. In the latter, the effects of the pollen genotype are demonstrated in structures other than the embryo and endosperm; that is, in tissues derived wholly from the mother plant material, in seed parts such as the nucellus and testa, as well as in the carpels and accessory tissues. However, the current classification has various shortcomings. In the present study, we propose a novel classification based on whether the appearance of xenia results from the tissue formed by double fertilization. Three xenia types are proposed: double-fertilization xenia, non–double-fertilization xenia, and combined xenia. The new classification has great theoretical and practical significance for future studies on the xenia effect and its mechanisms and also provides a more effective, broader application of xenia in improving the yield and quality of fruit trees.
Mengzi Zhang, Jie Yang, Huitang Pan and Brian J. Pearson
Baby primrose (Primula forbesii) is a newly cultivated and valuable ornamental plant with great market potential for both indoor and landscape use. As a container plant, baby primrose has long, weak flower stalks that can easily lodge, resulting in poor-quality plants, especially during transportation. To control plant height and subsequently prevent flower peduncle lodging, we investigated the effects of two plant growth regulators (PGRs), chlormequat chloride (CCC) at 0, 250, 500, or 750 ppm and uniconazole (UNI) at 25, 50, or 75 ppm on growth, development, and flowering of two cultivars of baby primrose, Fragrant Luolan and Red Star. Plant growth regulators at the proposed concentrations were applied twice throughout the experiment. Both PGRs significantly suppressed plant height in both cultivars, with a 16% to 27% reduction by CCC and 50% to 59% by UNI compared with untreated plants. Among CCC-treated groups, plants were shortest when CCC was applied at 500 ppm; plant height was suppressed more when treated with UNI. In both cultivars, UNI significantly suppressed the first, second, and third peduncle lengths. Furthermore, CCC affected peduncle length, but to a lesser extent than UNI. Plant growth regulator applications generally had little effect on flower characteristics of baby primrose. Neither PGRs influenced the inflorescence number and flower size; however, PGRs did increase the number of floral whorls and suppressed pedicel length of ‘Red Star’. New leaf growth was suppressed by both PGRs. In addition, peduncle cell length and width were both significantly suppressed by PGR applications. We concluded that two foliar applications of UNI at 25 ppm comprised the most effective method of controlling baby primrose plant height while maintaining desirable flower traits at a relatively low production cost. Results of this study provide guidance for techniques that can be used to effectively control the plant height of potted baby primrose for commercial greenhouse production.
Jun-Bo Yang, Hong-Tao Li, De-Zhu Li, Jie Liu, Lian-Ming Gao, De-Zhu Li, Lian-Ming Gao and Jie Liu
The Himalayan yew, Taxus wallichiana Zucc., is an endangered species with a scatted distribution in the Eastern Himalayas and southwestern China. In the present study, 10 microsatellite markers from the genome of T. wallichiana were developed using the protocol of fast isolation by amplified fragment length polymorphism of sequences containing repeats (FIASCO). Polymorphism of each locus was assessed in 28 samples from four wild populations of the Himalayan yew. The allele number of the microsatellites ranged from two to five with an average of 2.9 per allele. The observed and expected heterozygosity varied from 0.00 to 1.00 and from 0.3818 to 0.7552, respectively. Cross-species amplification in another two yew species showed eight of them holding promise for sister species. Two of the 10 loci (TG126 and TC49) significantly deviated from Hardy-Weinberg expectations. No significant linkage disequilibrium was detected between the comparisons of these loci. These polymorphic microsatellite markers would be useful tools for population genetics studies and assessing genetic variations to establish conservation strategy of this endangered species.