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Yee Kwan Chan, Yung Hua Yang and Ning Li

Lychee (Litchi chinensis Sonn.) fruit were harvested at green, pink, and red developmental stages. The fruit of each group were used to determine developmentally and environmentally (chilling) regulated ethylene production. The rate of ethylene production in the fruit was green > pink > red. Storage at either 4 or 10 °C increased C2H4 production as much as 8.6-fold compared with control fruit stored at 25 °C. The green fruit were most responsive to chilling in terms of ethylene production.

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Hua Gao, Zheng-yang Zhao, Lei-cun Wang, Zhen-zhong Liu and Ya-zhou Yang

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Zhong-Hua Bian, Rui-Feng Cheng, Qi-Chang Yang, Jun Wang and Chungui Lu

Light-emitting diodes (LEDs) have shown great potential for plant growth and development, with higher luminous efficiency and more flexible and feasible spectral control compared with other artificial lighting. The combined effects of red and blue (RB) LED with or without green (G) LED light and white LED light on lettuce (Lactuca sativa L.) growth and physiology, including nitrate content, chlorophyll fluorescence, and phytochemical concentration before harvest, were investigated. Continuous light exposure at preharvest can effectively reduce nitrate accumulation and increase phytochemical concentrations in lettuce plants. Nitrate accumulation is dependent on the spectral composition and duration of treatment: lettuce exposed to continuous RB (with or without G) LED light with a photosynthetic photon flux (PPF) of 200 µmol·m−2·s−1 exhibited a remarkable decrease in nitrate content at 24 hour compared with white LED light treatment at the same PPF. In addition, RB LED light (R:B = 4:1) was more effective than white LED light at the same PPF in facilitating lettuce growth. Moreover, continuous LED light for 24 hours significantly enhanced free-radical scavenging activity and increased phenolic compound concentrations. We suggest that 24 hours continuous RB LED with G light exposure can be used to decrease nitrate content and enhance lettuce quality.

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Yayan Feng, Leifeng Xu, Panpan Yang, Hua Xu, Yuwei Cao, Yuchao Tang, Suxia Yuan and Jun Ming

Lilium davidii var. unicolor Salisb is a cultivar of Lilium (Liliaceae) with important edible and ornamental characteristic. The application and production of Lilium davidii var. unicolor Salisb were still facing large problems because of its several disadvantages such as narrow range of adaptability, small annual growth increment, and low fertility. To achieve broader environmental adaptability and obtain a more nutritious germplasm, we used colchicine and oryzalin to induce chromosome doubling via the soaking method. Tissue culture bulbs were treated with colchicine at 0.03%, 0.05%, or 0.08% for 32, 40, or 48 hours or with oryzalin at 0.002%, 0.005%, 0.008%, or 0.01% for 3, 6, 9, 12, or 24 hours before being transferred to a differentiating medium. The results showed that colchicine treatment resulted in the highest induction rate when applied at 0.05% for 48 hours, whereas oryzalin treatment produced fewer tetraploid plants. The chromosome number of induced plants with small stoma density and longer guard cells is twice than that of the diploid. The plants were identified as tetraploid. In this study, a new germplasm of Lilium davidii var. unicolor Salisb was innovative and showed novel genetic characteristic.

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Fure-Chyi Chen, Wan-Ling Wu, Chun-Hua Pan, Irwin Yau-Yuan Chu and Yau-Wen Yang

Molecular markers by random amplified polymorphic DNAs were used to evaluate the genetic variation among different Oncidium accessions. It is possible to distinguish different registered Oncidium hybrids, including Gower Ramsey, Sweet Sugar, and Taka using nine random primers. Furthermore, variation was also detected within different cultivars derived from same hybrids. For example, several cultivars of Gower Ramsey could be distinguished based on molecular markers. Based on dendrogram, the investigated cultivars were clustered into several groups. Onc. Gower Ramsey and its selected cultivars were in one group. Onc. Sweet Sugar, Onc. Taka and Onc. Sharry Baby `Sweet Fragrance' were clustered in separate groups.

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Ji-Lian Zheng, Lan-Ying Hu, Kang-Di Hu, Jun Wu, Feng Yang and Hua Zhang

Hydrogen sulfide (H2S) has been identified as a multifunctional signaling molecule in plants. Here, we show that H2S delayed postharvest senescence of fresh-cut apples (Malus ×pumila) in a dose-dependent manner. Exogenous H2S application maintained significantly higher levels of ascorbic acid, flavonoids, total phenolics, reducing sugars and soluble proteins, and lower levels of free amino acids in apple slices compared with controls. Further investigations showed that H2S significantly reduced the accumulation of superoxide radicals, hydrogen peroxide (H2O2) and malondialdehyde (MDA). Apple fruits fumigated with H2S contained significantly higher activities of ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR), guaiacol peroxidase (POD) and superoxide dismutase (SOD), and lower activities of lipoxygenase (LOX), phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), and protease relative to controls. H2S also upregulated MdDHAR expression and downregulated the expression of MdLOX2, MdPG1, MdPPO, MdACO1, MdERS1, and MdETR1 in postharvest apple tissue. The present study indicates that H2S was involved in delaying postharvest senescence of apples by acting as an antioxidant and by regulating senescence-related gene expression.

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Ting-Ting Li, Zhi-Rong Li, Kang-Di Hu, Lan-Ying Hu, Xiao-Yan Chen, Yan-Hong Li, Ying Yang, Feng Yang and Hua Zhang

Kiwifruit (Actinidia deliciosa) is a typical climacteric fruit, and its ripening is closely associated with ethylene. In this study, we present evidence that H2S alleviated ethylene-induced ripening and senescence of kiwifruit. Kiwifruit were fumigated with ethylene released from 0.4 g·L−1 ethephon solution or H2S with 1 mm sodium hydrosulfide (NaHS) as the donor or in combination. Fumigation with ethylene was found to accelerate kiwifruit ripening and H2S treatment effectively alleviated ethylene-induced fruit softening in parallel with attenuated activity of polygalacturonase (PG) and amylase. Ethylene + H2S treatment also maintained higher levels of ascorbic acid, titratable acid, starch, soluble protein, and reducing sugar compared with ethylene group, whereas suppressed the increase in chlorophyll and carotenoid. Kiwifruit ripening and senescence under ethylene treatment was accompanied by elevation in reactive oxygen species (ROS) levels, including H2O2 and superoxide anion and malondialdehyde (MDA), but combined treatment of ethylene plus H2S alleviated oxidative stress in fruit. Furthermore, the activities of antioxidative enzymes catalase (CAT) and ascorbate peroxidase (APX) were increased by ethylene + H2S treatment in comparison with ethylene alone, whereas the activities of lipoxygenase (LOX) and polyphenol oxidase (PPO) were attenuated by H2S treatment. Further investigations showed that H2S repressed the expression of ethylene synthesis-related genes AdSAM, AdACS1, AdACS2, AdACO2, and AdACO3 and cysteine protease genes, such as AdCP1 and AdCP3. Taken together, our findings suggest that H2S alleviates kiwifruit ripening and senescence by antagonizing the effect of ethylene through reduction of oxidative stress and inhibition of ethylene synthesis pathway.

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Hua Gao, Zheng-yang Zhao, Yu-miao Lu, Yi-zhen Wan, Lei-cun Wang, Jing-jun Yuan and Peter M. Hirst

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Ying Chen, Xinlu Chen, Fei Hu, Hua Yang, Li Yue, Robert N. Trigiano and Zong-Ming (Max) Cheng

Agave species are economically important plants in tropical and subtropical desert ecosystems as ornamentals as well as potential bioenergy crops. However, their relatively long life cycles and the current lack of biotechnology tools hinder their breeding. In this study, an efficient system for micropropagation was developed for Agave americana L. by using basal stems as explants and grown on a modified Murashige and Skoog medium (MSI) or a 1/2 MSI medium supplemented with various concentrations of 6-benzylaminopurine (BA) for shoot proliferation. The highest number of shoots (18.5 shoots/explant) from basal stems was obtained on MSI supplemented with 13.32 μM BA. An efficient shoot regeneration system was also developed from leaf tissues. Combinations of auxin with cytokinin, basal media, and leaf regions were optimized for shoot induction. Adventitious shoot formation from leaf segments was induced and proliferated with combination ranging of 0.54 to 2.68 μM [α-naphthaleneacetic acid (NAA)] with 8.88 to 13.32 μM (BA), and the maximum frequency (≈69%) was obtained with 2.68 μM NAA plus 13.32 μM BA. MSI medium and the basal segment of leaf affected shoot induction. The highest rooting frequency and mean number of shoots occurred in 1/2 MSI containing with 4.92 μM indole-3-butyric acid (IBA) alone (90%, 3.4) or 1.48 μM IBA plus 1.61 μM NAA (92%, 5.2). Survival of in vitro plantlets after transfer and acclimatization to ex vitro conditions was 87%. This is the first complete protocol for micropropagation of A. americana.

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Cui-ping Hua, Zhong-kui Xie, Zhi-jiang Wu, Yu-bao Zhang, Zhi-hong Guo, Yang Qiu, Le Wang and Ya-jun Wang

The autotoxicity of root exudates and the change of rhizosphere soil microbes are two important factors that affect the quality and yield of Lanzhou lily (Lilium davidii var. unicolor). Phthalic acid (PA) is a major autotoxin of the root exudates in Lanzhou lily. In this study, we treated plants with different concentrations of PA from the Lanzhou lily root exudates and then analyzed the effects of autotoxins on fresh weight, shoot height, root length, and Oxygen Radical Absorbance Capacity in root. The diversity of soil fungi in Lanzhou lily soil was analyzed using MiSeq. The results showed that PA induced oxidative stress and oxidative damage of Lanzhou lily roots, improved the level of the membrane lipid peroxidation, reduced the content of antioxidant defense enzyme activity and the nonenzymatic antioxidant, and eventually inhibited the growth of the Lanzhou lily. We found that continuous cropping of Lanzhou lily resulted in an increase in fungal pathogens, such as Fusarium oxysporum in the soil, and reduced the size of plant-beneficial bacteria populations. The results in this study indicate that continuous cropping would damage the regular growth of Lanzhou lily.