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Zhou Li, Yan Peng and Bingru Huang

Gama-aminobutyric acid (GABA) is a nonprotein amino acid in plant cells, which responds to changes in environmental factors. The objectives of this study were to evaluate the effects of foliar spray of GABA on drought and heat tolerance in creeping bentgrass (Agrostis stolonifera), and to investigate physiological factors altered by GABA application that contribute to improved drought tolerance and heat tolerance. GABA-treated plants (cv. Penncross) or non-GABA-treated control plants were then subjected to the following three treatments in growth chambers: 1) nonstress control [plants irrigated every 2 days to maintain soil water content at the pot capacity and maintained at 21/19 °C (day/night) for 35 days], 2) heat stress [plants exposed to 35/30 °C (day/night) and well-watered conditions for 35 days], and 3) drought stress [plants unirrigated for 9 days and maintained at 21/19 °C (day/night), and then rewatered for 2 days]. As compared with untreated plants, GABA-treated plants showed 22% to 39% and 8% to 21% significantly lower leaf electrolyte leakage (EL) and 35% to 143% and 21% to 24% significantly higher turf quality (TQ), 8% to 17% and 17% to 24% relative water content (RWC), 22% to 39% and 25% to 27% chlorophyll content, 7% to 11% and 6% to 17% photochemical efficiency, and an 84% to 683% and 57% to 76% osmotic adjustment (OA) exposed to heat or drought stress across days of treatment, respectively. GABA-treated plants accumulated 7% to 10% more water-soluble carbohydrates (WSC) and 11% to 43% more free proline than nontreated plants under heat stress, and 12% to 30% higher accumulation of WSC under drought stress. After 2 days of rewatering, a significantly better recovery also was observed in GABA-treated plants than that in nontreated plants previously exposed to drought stress. The results suggest that foliar application of GABA significantly improved heat and drought tolerance of creeping bentgrass, which was associated with maintenance of cell membrane stability, delaying in leaf senescence, and enhancing OA. The effectiveness of exogenous GABA application was more pronounced under heat stress than under drought stress.

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Li-ping Chen, Yan-ju Wang and Man Zhao

In this study, in vitro induction of tetraploid Lychnis senno Siebold et Zucc. and its cytological and morphological characterization were conducted. For polyploid induction, nodal segments with axillary buds from in vitro grown plants were kept for 3 days in MS (Murashige and Skoog, 1962) liquid or solid media added with a series of concentrations of colchicine. Out of total 588 recovered plants, 15 tetraploids and 6 mixoploids determined by flow cytometry analysis were obtained. The tetraploid contained 48 chromosomes, twice the normal diploid number of 24, as observed under light microscope. The tetraploid plants exhibited much larger but less stomata than diploid plants. Moreover, significant differences in stem height and leaf size between the diploid and tetraploid plants were noted. The tetraploid plants were more compact than diploids.

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Qianqian Shi, Long Li, Lin Zhou and Yan Wang

Paeonia delavayi is a species endemic to Southwest China and an important genetic resource for flower color breeding of tree peonies. The mechanisms underlying the flower coloration of this plant have not been fully elucidated. In this article, the petals of yellow-colored individual (Pl) and purple–red-colored individual (Pd) of P. delavayi were studied. And anatomical observations revealed that a large amount of yellow protoplasts and a small amount of colorless protoplasts were located in the yellow-colored Pl petals, whereas a mixture of purple, red, and pink protoplasts were observed in the purple–red-colored Pd petals. The Pl cells were subrotund and flat, whereas the Pd cells were irregularly polygon-shaped and bulging. Chemical analyses were performed, and the results indicated that significant differences occurred between the cell sap pH of the Pl and Pd flowers and large differences occurred in the contents of Fe and Al between Pl and Pd. Cyanidin- and peonidin-based anthocyanins with flavones and flavonols as copigments determined the Pd flower color, whereas chalcone 2 ′G with apigenin 7-O-neohesperidoside and chrysoeriol 7-O-glucoside as copigments determined the yellow color of Pl. Correspondingly, the genes dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) were significantly highly expressed in Pd, whereas chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavone synthase (FNS), flavonol synthase (FLS), flavonoid 7-O-glycosyltransferase (7GT), and 2′4′6′4-tetrahydroxychalcone 2′-glucosyltransferase (THC) had high transcript levels in Pl relative to Pd. The results indicate that the color variation of P. delavayi petals may be related to a delicately controlled balance of the aforementioned factors.

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Mou Zong-min, Yan Ning, Li Shu-yun and Hu Hong

Paphiopedilum armeniacum S. C. Chen et F. Y. Liu is endemic to China and has great ornamental value. Little is known about its nutrient requirement for growth and reproduction after deflasking (transplantation of seedlings from culture vessels to pots). We studied the effects of adding nitrogen (N) (0, 105, 210, and 420 mg·L−1) on the vegetative growth and reproduction of P. armeniacum. N enrichment improved leaf area and lengthened the leaf lifespan during the vegetative stage. The effects of N application on flower size were minor. The intermediate N level of 210 mg·L−1 (MN) increased the seed capsule weight, seed germination rate, and improved the growth of seedlings that developed from seeds of MN-treated plants. N fertilizer exerted little influence on ramet emergence and ramet number per plant, but a low N concentration of 105 mg·L−1 promoted the leaf number and leaf area of ramets. Appropriate N levels for P. armeniacum in production and cultivation should be determined according to different production objectives.

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Zhaohui Li, Yan Ma, Wanyuan Yin, Dekui Zang and Xianfeng Guo

Pteroceltis tatarinowii Maxim, the only species of the genus Pteroceltis (family Ulmaceae), is an endemic rare tree species in China. This study was performed to explore vegetative propagation techniques for P. tatarinowii using stem cuttings. First, the effects of exogenous indole-3-butyric acid (IBA) and cutting positions on rooting performance were investigated to screen the appropriate exogenous auxin treatment and to determine the proper cuttings type. The results showed that the control cuttings pretreated with no exogenous IBA, irrespective of whether the stem cuttings were terminal, middle, or basal, rooted in a manner significantly inferior to that of cuttings pretreated with IBA. Their rooting percentage was less than 50%. Among the IBA-treated cuttings, the middle cuttings pretreated with 1000 mg·L−1 IBA rooted best, with the shortest number of days until rooting emergence (20 days), the highest rooting percentage (84.0%), the lowest mortality rate (4.0%), the greatest root number (average of 6.7 per cutting), and the longest roots per cutting (44.4 cm per cutting). Terminal cuttings pretreated with 1000 mg·L−1 IBA acquired satisfactory rooting traits and had the same shortest rooting duration (20 days) and the following parameters: rooting, 70.7%; mortality, 10.7%; average roots per cutting, 5.2; and longest root, 29.1 cm. To further determine the optimum cutting propagation time for this plant, a second experiment was performed and the cuttings were collected beginning in early June, when the growth of the current season was feasible for harvesting cuttings. Stem cuttings collected in late June and middle July had significantly higher rooting percentages (≥80%) compared with those collected in early June (66.7%). The other three rooting parameters were not significantly affected by the collection date. However, according to the overall rooting traits, the cuttings collected in both late June and middle July remarkably outperformed those collected in early June regarding the number of roots and the total root length per cutting. The initial nutrient reserves in the cuttings were also determined. A significant difference in the soluble carbohydrate level was found among collection times, but the nitrogen level in the cuttings was similar. The study revealed that stem cutting propagation of P. tatarinowii was achievable, and it was best achieved with cuttings collected from the terminal and middle positions of the branches of the current season from late June to middle July and treated with 1000 mg·L−1 IBA using the quick dip method.

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Yong Zhang, Chunxia Fu, Yujing Yan, Xiaodan Fan, Yan’an Wang and Ming Li

Application of sugar alcohol zinc (SA-Zn) spray to apple trees at certain developmental stages can improve fruit quality. Increasing the Zn concentration of fruit can improve nutritional content and promote human health. We conducted foliar application of SA-Zn to 13-year-old ‘Fuji’ apple trees at different developmental stages. The effects of SA-Zn application on Zn concentration, reducing sugar content, and carbohydrate metabolism-related enzyme activity in fruit were investigated. The foliar treatment increased Zn and reducing sugar concentrations significantly in mature fruit. Sorbitol dehydrogenase activity was higher in the fruit of trees treated before budbreak and 3 weeks after flowering compared with the control at the early fruit stage and was higher during fruit expansion in plants treated after termination of spring shoot growth. Mature fruit of trees treated during the fruit expansion stage showed higher sorbitol dehydrogenase activity than the control. Foliar SA-Zn treatment did not have a significant effect on sorbitol oxidase activity in apple fruit. Treatment before budbreak and at 3 weeks after flowering led to a significant increase in the activity of sucrose synthase and acid invertase at the early fruit stage. Treatment during the fruit expansion stage significantly increased the activity of acid invertase at maturity but had no effect on the activity of neutral invertase. Our results indicate that foliar SA-Zn application resulted in biofortification of Zn in apples, which led to higher activity of carbohydrate metabolism-related enzymes and accumulation of sugars.

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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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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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Meiling Yang, Fang Li, Hong Long, Weiwei Yu, Xiuna Yan, Bin Liu, Yunxiu Zhang, Guorong Yan and Wenqin Song

As a wild apple species native to central Asia, Malus sieversii (Ledeb.) Roem. is distributed in a wide region covering most of the Tienshan Mountains. Malus sieversii is a useful genetic pool for apple breeding since rich with diversity. In this paper, we first describe the species range of this endangered species. We then describe an in situ reserve that has been established. We also investigated some reproductive characteristics of M. sieversii including pollen germination, seed dormancy, and seed viability. Both stratification and seedcoat removal efficiently released seed dormancy and accelerated seed germination. Pollen germination rate is around 60%. Our data suggest that injurious insects and human activities, rather than reproductive characters, limit the renewal of M. sieversii.

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Yong Zhang, Chunxia Fu, Yujing Yan, Yan’an Wang, Ming Li, Meixiang Chen, Jianping Qian, Xinting Yang and Shuhan Cheng

This research was initiated to determine the response of apple (Malus ×domestica) fruit quality to sprays of zinc sulfate (ZnSO4) and sugar alcohol zinc. Two apple cultivars Fuji and Gala were evaluated, the leaf zinc (Zn) concentration of which were about 14.3 mg·kg−1 dry weight without Zn deficiency symptoms. The trees were sprayed with ZnSO4 and sugar alcohol zinc separately during four different developmental stages: 2 weeks before budbreak (P1), 3 weeks after bloom (P2), the termination of spring shoot growth (P3), and 4 weeks before harvest (P4). The fruit was harvested at maturity and analyzed for fruit quality and fruit Zn concentration. Zinc sprays during the four different developmental stages increased Zn concentration of peeled and washed fruit at harvest, without phytotoxicity. The treatments at stages P2 and P4 increased average fruit weight of ‘Gala’ and ‘Fuji’, respectively. The treatments at stages P1 and P4 increased the fruit firmness of ‘Gala’, while the treatments at stages P1 and P2 increased the fruit firmness of ‘Fuji’. The treatments at stages P1, P2, and P4 increased the soluble sugar and vitamin C of ‘Gala’ fruit, while the treatments at all the stages increased the soluble sugar and vitamin C of ‘Fuji’. And the effects of sugar alcohol zinc were equal and more pronounced than those of ZnSO4. Thus, Zn sprays at critical periods can improve fruit quality of apple trees, which show no Zn deficiency symptoms with leaf Zn concentration less than 15 mg·kg−1 dry weight.