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Shi-Lin Tian, Li Li, Yue-Qin Tian, S.N.M. Shah and Zhen-Hui Gong

Abscisic acid (ABA) is an important plant hormone that plays an important role in stress responses. Previous studies have suggested that ABA can also accelerate ripening in climacteric and nonclimacteric fruit. Capsanthin is a carotenoid that confers red coloration to mature pepper (Capsicum annuum) fruit. However, the effect of ABA on capsanthin accumulation in pepper fruit has not been thoroughly studied. Herein, we aimed to evaluate the effects of ABA treatment on capsanthin accumulation in pepper fruit and on the expression of key genes involved in the capsanthin biosynthetic pathway. For this purpose, we treated pepper fruit with ABA at green mature stage. Our results indicate that ABA treatment increased capsanthin content in pepper fruit, with the best result obtained with 150 mg·L−1 ABA solution. Application of exogenous ABA also increased the expression levels of the capsanthin synthesis genes phytoene synthase (Psy), lycopene β-cyclase (Lcyb), β-carotene hydroxylase (Crtz), and capsanthin/capsorubin synthase (Ccs), likely explaining the significant capsanthin content increase in pepper fruit.

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Shujuan Yang, Li Peng, Han Bao and Huiqiao Tian

Our goal was to determine the ultrastructure features and the dynamic changes in polysaccharides and neutral lipids in developing anthers of rose balsam (Impatiens balsamina), and to better understand the mechanisms controlling male reproductive development. Transmission electron microscope (TEM) techniques were used to study the ultrastructural characteristics of the anthers, and histochemical methods were used to determine levels of polysaccharides and lipids. The cytokinesis in the microsporocyte meiosis was simultaneous type, and microspore tetrads were mainly tetrahedral. The pollen exine began to form at the tetrad stage. The mature pollen grains were oval-shaped and bicellular. Accumulation of reserve substances began at the late microsporogenesis stage, and an abundance of starch grains and lipids were stored in pollen grains at anthesis. Polysaccharides and lipids changed in different stages and played an important role in anther development. Moreover, the calcium oxalate crystals may protect the pollen and suggest that calcium distribution is related to anther development.

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He Li, Cheng-Jiang Ruan, Li Wang, Jian Ding and Xing-Jun Tian

Sea buckthorn (Hippophae rhamnoides) is an ecologically and economically valuable species that has been widely cultivated as a new berry crop rich in nutritional and medicinal compounds. RNA Sequencing (RNA-Seq) simple sequence repeat (SSR) markers were developed to evaluate the genetic relationships among 91 plants of 31 cultivars from two subspecies, mongolica and sinensis, as well as intraspecific hybrids between them. A total of 7540 RNA-Seq SSRs were identified as potential molecular markers, in which AG/CT (27.57%) was the most abundant unit type. AT/AT (9.93%), and AAG/CTT (11.95%) are the other main repeat motifs. A total of 110 primer pairs were randomly selected for validation of amplification. Seventeen SSR loci, located in genes encoding metabolic processes and cellulose synthases, were identified to be polymorphic among different sea buckthorn cultivars. These SSR loci generated 48 alleles, ranging from 2 to 5 per locus. Cluster analysis based on the proportion of shared alleles and unweighted pair group method with arithmetic average (UPGMA) algorithm divided all the genotypes into two main groups, with all of the ssp. sinensis cultivars (native to China) and hybrids in one group and ssp. mongolica cultivars (introduced from Russia) in the other group, which was in good agreement with their taxonomic classification. The RNA-Seq SSRs developed in this study have a potential use in the conservation of sea buckthorn germplasm and marker-assisted breeding (MAB).

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Li-Juan Zhang, Tian-Xiu Zhong, Li-Xin Xu, Lie-bao Han and Xunzhong Zhang

Soil water deficit impacts cold acclimation and freezing tolerance in creeping bentgrass (Agrostis stolonifera L.), but the mechanisms underlying have not been well understood. The objectives of this study were to investigate the effects of deficit irrigation before and during cold acclimation on osmoprotectants, antioxidant metabolism, and freezing tolerance in creeping bentgrass. The grass was subjected to three-soil moisture levels: well-watered [100% container capacity (CC)], deficit irrigation induced-mild drought stress (60% CC), and severe drought stress (30% CC) for 35 days including 14 days at 24/20 °C (day/night) and then 21 days under cold acclimation treatment (2 °C) in growth chambers. Leaf proline and total soluble sugar (TSS) levels were higher in the grass under mild drought stress relative to that under severe drought stress. Superoxide (O2 −·), hydrogen peroxide (H2O2), and malondialdehyde (MDA) content were higher in the grass under severe drought relative to that under well-watered and mild drought stress at day 35. Mild drought stress increased catalase (CAT) and guaiacol peroxidase (POD) activity, induced new isoforms and increased band intensities of superoxide dismutase (SOD), CAT, and POD during cold acclimation (days 14 to 35). No differences in osmoprotectants, antioxidant metabolism, and freezing tolerance were found between mild drought and well-watered treatments. The results of this study suggest deficit irrigation-induced mild drought stress in late fall and winter could induce accumulation of osmoprotectants and improve antioxidant metabolism, and freezing tolerance, but severe drought stress could reduce freezing tolerance of creeping bentgrass in the region with limited precipitation.

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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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Yan Li, Hongyan Qi, Yazhong Jin, Xiaobin Tian, Linlin Sui and Yan Qiu

The catabolism of fatty acid (FA) is regarded as a key pathway of aroma volatile compounds in oriental sweet melon (Cucumis melo var. makuwa). In our research, two cultivars of oriental sweet melon, Caihong7 and Tianbao, were employed to illuminate which step of the biosynthetic pathway of aroma compounds could be regulated by ethylene (ETH). The role of ETH in determining the profiles of straight-chain aroma volatile compounds, levels of FA as aroma precursors, activities of aroma-related enzymes derived from FA pathway, and expression patterns of key enzymes were investigated. Overall, exogenous application of ETH increased the production rates of endogenous ETH and levels of FA. Compared with control, the level of straight-chain esters, especially the acetate, hexanoate, and hexyl esters, was significantly increased by ETH, whereas the content of alcohol and aldehyde reduced. In addition, the metabolism of free FA included linoleic acid (LA), linolenic acid (LeA), and oleic acid (OA) appeared to be ETH-dependent. The activities of lipoxygenase (LOX), alcohol dehydrogenase (ADH), and alcohol acetyltransferase (AAT) as well as the expression patterns of Cm-ADH1, Cm-ADH2, Cm-AAT1, and Cm-AAT4 were positively regulated by ETH. In contrast, hydroperoxide lyase (HPL) and Cm-AAT2 and Cm-AAT3 seemed to be independent of ETH modulation. These results suggested that the dissimilation of FA included LA, LeA, and OA into the acetate, hexanoate, and hexyl esters mainly through ETH regulating the LOX pathway by enhancing the expression of particular members of aroma-related key enzyme gene families as well as the activities of dehydrogenation and esterification.

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Jing Tian, Li-Ping Wang, Yan-Juan Yang, Jin Sun and Shi-Rong Guo

Heat tolerance is considered to be an essential feature for cucumber (Cucumis sativus) production, and it has been suggested that higher antioxidant ability could prevent the oxidative damage in plants caused by high-temperature stress. We aimed to investigate whether the application of exogenous spermidine (Spd) increases antioxidant activities and, therefore, elevates the heat tolerance of cucumber. Cucumber seedlings (cv. Jinchun No. 4) showing moderate heat tolerance were grown in climate chambers to investigate the effects of exogenous Spd (1 mm) foliar spray treatment on the activities and isozyme levels of antioxidative enzymes under both high-temperature stress 42/32 °C (day/night) and normal temperature 28/18 °C (day/night). On high-temperature stress, the activities of superoxide dismutase and ascorbate peroxidase were significantly reduced; the catalase activity was initially lower and then increased, whereas the peroxidase activity was initially higher and then decreased. The levels of these isozymes also changed differently. On treatment with exogenous Spd, the activities of these antioxidant enzymes were noticeably enhanced, and the isozyme zymogram expression had some changes. It was concluded that foliar spray with Spd effectively improved the total antioxidant ability of cucumber seedlings and, therefore, enhanced the tolerance of the plants to high-temperature stress.

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Ying Qu, Xue Bai, Yajun Zhu, Rui Qi, Geng Tian, Yang Wang, Yonghua Li and Kaiming Zhang

Leaves of Begonia semperflorens accumulate anthocyanins and turn red under low temperature (LT). In the present work, LT increased H2O2 content and superoxide anions production rate, causing significant increases in the activities of enzymes and contents of reduced components involved in the ascorbate-glutathione cycle (AsA-GSH cycle). As a result, LT-exposed seedlings increased the expression of genes involved in anthocyanin biosynthesis, and accumulated anthocyanin. Based on LT condition, application of N,N'-dimethylthiourea (DMTU) decreased reactive oxygen species (ROS) content, and unbalanced the AsA-GSH-controlled redox homeostasis. As a result, seedlings in the LT + DMTU group did not accumulate anthocyanin. Our results suggest that ROS may act as an important inducer in LT-induced anthocyanin biosynthesis.

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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.

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Quan Liu, Yan Lan, Feng Tan, Yunbiao Tu, Yingying Sun, Gajue Yougu, Zeshen Yang, Chunbang Ding and Tian Li

Water is essential for crops and plays a vital role in olive (Olea europaea) growth. Three irrigation treatments, rain-fed (CK), flood irrigation (FI), and drip irrigation (DI), were applied from late November to late May in a 2-year study (Nov. 2015 to Oct. 2017) on two olive cultivars, Coratina and Koroneiki. Shoot growth, flower and fruit characteristics, and olive and oil yields were measured. Compared with CK, FI had significantly higher values of vegetative growth, olive and oil yields, moisture content, and oil content. Although the fruit weight, pulp rate, and oil content with DI were the lowest, our results support that DI had the greatest positive effects on olive vegetative growth, flowers, fruit set, and olive and oil yields. It is suggested that DI in winter and spring is the best irrigation strategy for olive productivity in southwest China.