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Zhiyong Hu, Qing Liu, Meilian Tan, Hualin Yi and Xiuxin Deng

In this article, we describe a novel biological phenomenon that the tips of the juice sac of citrus hybrid HRB turned brown and became tough like many “brown thorns”; HRB is a triploid hybrid regenerated from the cross of diploid tangerine BDZ (Citrus reticulata Blanco cv. Huanongbendizao) with an allotetraploid somatic hybrid HR [Hamlin sweet orange (Citrus sinensis Osbeck) + rough lemon (Citrus jambhiri Lush)]. Histochemical analysis indicated that the “brown thorn” of HRB resulted from lignin deposition. The juice sac of HRB had 4.6- and 3.8-fold content of lignin of its parents tangerine and HR, respectively. Microscopy observation of the cross-sections of the juice sac verified that the cell wall of the “brown thorn” was lignified. Moreover, the cell walls near the “brown thorns” were obviously thickened. Analysis of enzyme activity indicated that the peroxidase (POD) activity of HRB was significantly higher than its parents. Quantitative real-time polymerase chain reaction analysis showed that the transcript abundance of the cinnamate 4-hydroxylase (C4H) gene in HRB was 6.5- and 3.4-fold of its parent BDZ and HR, respectively, but the POD gene transcript abundance was lower than its parent with 1/2-fold of BDZ and 1/7-fold of HR. These facts led to the conclusion that POD and C4H were the key regulating factors for lignin biosynthesis in juice sacs of the hybrid HRB. The POD gene, one member of the POD family, with transcript abundance lower than its parent indicated that this POD isoenzyme was not the regulating factor of lignin biosynthesis, and further study should be carried out to determine which POD isoenzyme is the key factor for lignin biosynthesis.

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Mingxiu Liu, Peng Wang, Xu Wei, Qing Liu, Xiaolin Li, Guolu Liang and Qigao Guo

Triploid loquat (2n = 3x = 51) has stronger growth vigor and larger leaves, flowers, and fruit compared with its diploid parental plant (2n = 2x = 34), but the effects of triploidization on the contents of flavonoids and phenolics in leaves and flowers, which are the most important antioxidant compounds for pharmacological applications, have not been reported. In this report, 58 triploid loquat genotypes and seven corresponding diploid parental cultivars were used to evaluate the effects of triploidization on the contents of total flavonoids and phenolics and the antioxidant activities of leaves and flower buds. The results showed that the contents of total flavonoids and phenolics and their corresponding antioxidant activities were higher in most of the triploid loquat genotypes than their diploid parents. The antioxidant activities of leaves and flower buds were significantly correlated with the total flavonoids and phenolics contents in both diploid loquat and triploid loquat. It could be inferred that triploidization could increase the contents of flavonoids and phenolics in leaves and flower buds of loquat. Notably, the contents of total flavonoids and phenolics of leaves in triploid genotype ‘H3/24’ were the highest, reaching 212.00 mg rutin equivalent (RE)/g DW and 93.06 mg gallic acid equivalents (GAE)/g DW, respectively, which were significantly higher than those previously reported. Such a valuable trait may be stacked with other triploid traits that are already established, such as larger vegetative organs and better tolerance to various stresses, as a feasible strategy for breeding loquat cultivars with high pharmaceutical potency.

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Ze Li, Xiaofeng Tan, Zhiming Liu, Qing Lin, Lin Zhang, Jun Yuan, Yanling Zeng and Lingli Wu

Camellia oleifera Abel. is one of four major woody oil plants in the world. The objective of the current study was to evaluate the effect of different plant growth regulators (PGRs) and concentrations on direct organogenesis using cotyledonary nodes, hypocotyls, and radicle explants. High induction frequency of adventitious shoots were obtained from cotyledonary nodes, hypocotyls, and radicle explants (85.2%, 73.6%, and 41.0%, respectively) when cultured on half-strength Murashige and Skoog (1/2 MS) medium containing 2.0 mg·L−1 6-benzylaminopurine (BA) and 0.1 mg·L−1 indole-3-acetic acid (IAA). Microshoots from cotyledonary nodes, hypocotyls, and radicle explants were then transferred to 1/2 MS medium containing 2.0 mg·L−1 BA and 0.05 mg·L−1 indole-3-butyric acid (IBA) for shoot multiplication, resulting in 6.9 shoots per explant. The shoots were transferred to Woody Plant Medium (WPM) supplemented with various α-naphthalene acetic acid (NAA) and gibberellic acid (GA3) for shoot elongation. The mean length of shoots and the number of leaves per shoot were 3.7 and 6.6 cm, respectively, in WPM supplemented with 0.5 mg·L−1 NAA and 3.0 mg·L−1 GA3. The highest rooting of shoots (90.2%) or the number of roots per shoot (7.2) was obtained when elongated microshoots were transferred to 1/2 MS medium supplemented with 3.5% perlite, 1.0 mg·L−1 IBA and 2.0 mg·L−1 NAA. The rooted plantlets were successfully acclimatized in the greenhouse with a survival rate of 90.0%. The in vitro plant regeneration procedure described in this study is beneficial for mass propagation and improvement of C. oleifera through genetic engineering.

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Ni Jia, Qing-Yan Shu, Dan-Hua Wang, Liang-Sheng Wang, Zheng-An Liu, Hong-Xu Ren, Yan-Jun Xu, Dai-Ke Tian and Kenneth Michael Tilt

Petal anthocyanins were systematically identified and characterized by high-performance liquid chromatography (HPLC)–electrospray ionization–mass spectrometry (MS) coupled with diode array detection among nine wild herbaceous peony (Paeonia L.) species (15 accessions). Individual anthocyanins were identified according to the HPLC retention time, elution order, MS fragmentation patterns, and by comparison with authentic standards and published data. Six main anthocyanins, including peonidin-3,5-di-O-glucoside, peonidin-3-O-glucoside-5-O-arabinoside (Pn3G5Ara), peonidin-3-O-glucoside, pelargonidin-3,5-di-O-glucoside, cyanidin-3,5-di-O-glucoside, and cyanidin-3-O-glucoside (Cy3G), were detected. In addition to the well-known major anthocyanins, some minor anthocyanins were identified in herbaceous peony species for the first time. Detection of the unique anthocyanins cyanidin-3-O-glucoside-5-O-galactoside and pelargonidin-3-O-glucoside-5-O-galactoside in both Paeonia anomala L. and P. anomala ssp. veitchii (Lynch) D.Y. Hong & K.Y. Pan indicated these two species should belong to the same taxon. Pn3G5Ara was found only in European wild species and subspecies suggesting different metabolic pathways between European and Chinese accessions. Anthocyanins conjugated with galactose and arabinose were observed in the genus Paeonia for the first time. The North American species, Paeonia tenuifolia L., had high Cy3G content in flower petals. This anthocyanin composition is distinct from the anthocyanin composition in Asian and European species and possibly is responsible for the vivid red coloration in flowers.

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Min Zhang, Xiuxin Deng, Changping Qin, Chunli Chen, Hongyan Zhang, Qing Liu, Zhiyong Hu, Linlin Guo, Wenhua Song, Yong Tan and Shengcai Liao

‘Zaohong’ navel orange [Citrus sinensis (L.) Osbeck + C. unshiu Marc.], a new strain of citrus from a graft chimera, was discovered in China. It was diploid and arose at the junction where a ‘Robertson’ navel orange scion was top-worked onto a Satsuma mandarin (C. unshiu). Some characteristics determined by the L1 cell layer, such as juice sacs of fruit and stoma length, were similar to those of Satsuma mandarin, while others, including leaf index, fruit shape, navel, and color and aroma of the rind, were determined by the L2 cell layer, were similar to ‘Robertson’ navel orange. High-performance liquid chromatography analysis of the carotenoid extracts of the flesh of ‘Zaohong’ navel orange indicated that it had the carotenoids profile of Satsuma mandarin with β-cryptoxanthin as the predominant component in the juice sacs in mature fruit. Simple sequence repeats (SSR) and chloroplast simple sequence repeats (cpSSR) analysis showed that both nuclear and chloroplast genomes of ‘Zaohong’ navel orange were composed of both donor plants. On the basis of these facts, ‘Zaohong’ navel orange was found to be a periclinal chimera consisting of L1 derived from Satsuma mandarin and L2/L3 from ‘Robertson’ navel orange. It combined the valuable traits of both donor plants, matured ≈1 month earlier than the present navel orange cultivars, and therefore had good potential in citrus fresh market.