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  • Author or Editor: Qian Zhang x
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Pothos (Epipremnum aureum Linden & Andre), a climbing vine with leathery, shiny-surfaced, solid green or variegated heart-shaped leaves, is widely grown as an ornamental tropical foliage plant in hanging baskets or on poles as climbers for interiorscaping. Since pothos easily develops roots from nodes, its propagation is mainly from eye cuttings. Eye cuttings, however, frequently carry diseases from stock plants into production greenhouses. The objectives of this study were to investigate if somatic embryogenesis could be induced from a common cultivar `Golden Pothos' and germinated somatic embryos could be a means of clean propagule production. Using a modified MS medium supplemented with 2 mg·L-1 CPPU or TDZ and 0.2 mg·L-1 NAA or 0.5 mg·L-1 2,4-D, somatic embryos formed directly at cut edges of leaf explants, around petiole and stem explant ends, and along their side surfaces. Most somatic embryos maturated and grew into multiple buds or shoots; some of them developed into whole plants on the original medium. Somatic embryos also germinated and developed into plants on MS medium containing 2 mg·L-1 Zeatin and 0.2 mg·L-1 NAA, MS or 1/2 MS containing 2 mg·L-1 BA with or without 0.2 mg·L-1 NAA. Shoots elongated and roots grew on PGR-free medium. Plantlets grew healthy in shaded greenhouses after transferring to soilless substrates. This study suggests that the established method of somatic embryogenesis can be used to generate disease-free propagules of pothos for production.

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Homalomena `Emerald Gem' is an important ornamental foliage plant and widely used for interior plantscaping. Current propagation of this cultivar has been primarily carried out through in vitro culture by organogenesis; regeneration through somatic embryogenesis has not been documented. This report describes successful plant regeneration via direct somatic embryogenesis from explants of different organs. Somatic embryos formed at and around the cut surface of petiole, spathe, and peduncle explants. Embryos also appeared at the base between expanded ovaries of the spadix segment, and around midrib of leaf explants. The optimal treatments for somatic embryo occurrence from petiole, spathe, and peduncle explants were MS medium containing 0.2 mg/L NAA or 0.5 mg/L 2, 4-D with 2.0 mg/L CPPU, and for spadix explants were MS medium with 0.5 mg/L PAA and 2.5 mg/L TDZ. Somatic embryos appeared 6 to 8 weeks after culture and formed large embryo clumps in 3 to 4 months. Somatic embryos produced more secondary embryos and geminated on induction medium. Multiple shoot development and plant regeneration occurred from somatic embryo clusters on MS medium without hormone or with 2 mg/L BA and 0.2 mg/L NAA. The regenerated plants grew vigorously after transplanting to a soilless container substrate in a shaded greenhouse.

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Calcium (Ca) is necessary for plant growth and stress resistance, which are essential for the successful cultivation of Panax quinquefolium L. (American ginseng). However, information about the physiology of Ca nutrition in this species is limited. Therefore, the objective of this study was to determine the effect of Ca on the growth and physiological performance of American ginseng. Two-year-old American ginseng plants were supplemented with the following Ca concentrations [Ca2+] in a hydroponic system: 0, 160.17, 320.34, 640.68, and 961.02 mg⋅L−1. Measurements included growth biomass accumulation, chlorophyll (Chl) content and fluorescence, photosynthetic parameters, antioxidant enzyme activity, root activity, and malondialdehyde content. Biomass, stem height, leaf area, maximum photochemical efficiency, and superoxide dismutase activity peaked at [Ca2+] of 640.68 mg⋅L−1. Actual photochemical efficiency, minimum saturating irradiance, photosynthetic rate, catalase and peroxidase activities, and root activity reached their maximum at [Ca2+] of 320.34 mg⋅L−1. Stem diameter and regulated thermal energy dissipation increased with [Ca2+]. The sum of nonregulated heat dissipation and fluorescence emission and malondialdehyde content decreased to a minimum at [Ca2+] of 320.34 mg⋅L−1. The Chl content reached a maximum at [Ca2+] of 160.17 mg⋅L−1, but the Chl a/b ratio increased with [Ca2+]; the actual photochemical efficiency and photosynthetic rate reached their maximum level at Chl a/b ratios of 2.04 and [Ca2+] of 320.34 mg⋅L−1. Therefore, the optimal [Ca2+] for American ginseng growth was 320.34 mg⋅L−1. Furthermore, an appropriate increase [Ca2+] in the growth medium may improve biomass accumulation, light energy utilization efficiency, and stress resistance in American ginseng.

Open Access

The objective of the present study was to consider the regulatory role of exogenous nitric oxide (NO) supplementation in response to chilling stress impose alterations on different physiological parameters in melon seedlings. Melon seedlings were treated with sodium nitroprusside (SNP, an NO donor), hemoglobin (a NO scavenger), NG-nitro-L-arginine methyl ester (an NO synthase inhibitor), and tungstate (a nitrite reductase inhibitor) under chilling stress conditions. The results showed that exogenous SNP improves the growth of melon seedlings under chilling stress conditions and ameliorates the harmful effects of chilling stress by increasing the levels of chlorophyll and soluble solutes, elevating the activity of sucrose phosphate synthase by enhancing the expression level of CmSPS. Moreover, exogenous NO significantly enhances the expression of genes and activities of antioxidant enzymes under chilling stress, resulting in lower reactive oxygen species accumulation. However, the protective effects of SNP are reversed by both NO scavenging and inhibition. Collectively, our results reveal that NO has the ability to ameliorate the harmful effects of chilling stress on melon seedlings by regulating carbohydrate metabolism and the antioxidant defense system.

Open Access

Quantitative trait loci (QTLs) identified so far in Brassica were mainly generated in the final stage of plant development, which did not apply to the exploitation of genetic effects that were expressed during a specific developmental stage. Thus, the objective of this study was to simultaneously identify unconditional and conditional QTL associated with plant height at various stages of nonheading Chinese cabbage. One hundred twelve doubled haploid (DH) lines developed from the cross between nonheading Chinese cabbage lines ‘SW-13’ and ‘SU-124’ were used for QTL analysis of plant height by the composite interval mapping method combined with mixed genetic model. The map we used for QTL analysis was an updated version of the first genetic map of nonheading Chinese cabbage with 48 additional markers to the same DH population. With data from 2 years, a total of 11 unconditional QTLs in six linkage groups and 23 conditional QTLs in eight linkage groups were identified for plant height. The results indicated that the number and type of QTLs and their genetic effects for plant height were different in a series of measuring stages. Each QTL can explain 7.92% to 28.25% of the total phenotypic variation. Two QTLs (ph8-4 and ph8-5) were identified to be associated with plant height using both unconditional and conditional mapping methods simultaneously in 2 years. These results demonstrated that it is highly effective for mapping QTL of developmental traits using the unconditional and conditional analysis methodology.

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Cornus florida seeds show strong dormancy. In this study, we investigated the causes of the dormancy by assessing the permeability of the stony endocarp, the germination of seeds after mechanical dissection, and the effect of endogenous inhibitors. Water uptake by intact and cracked seeds during imbibition showed that the endocarp formed a strong barrier for water absorption. Meanwhile, extracts from endocarp decreased the germination frequency of chinese cabbage seeds from 99.3% (control) to 2.7%. Therefore, the endocarp was the mechanical barrier and contained endogenous inhibitors for seed germination. However, the germination percentage of decoated seeds and dissected seeds with the exposed radicle were only 13.3% and 28.7%, respectively. It was found that the endosperm also played a role in seed dormancy. Extracts from endosperm decreased the germination frequency of chinese cabbage seeds from 99.3% (control) to 53.0%. By contrast, extracts from embryo did not affect the germination of chinese cabbage seeds. When tested with the excised embryos, germination percentage was up to 85.3% at the 16th day of incubation. Taking these results together, we concluded that the endocarp and endosperm were responsible for seed dormancy in C. florida. To break the seed dormancy of C. florida, stratification and soaking in sulfuric acid are the effective means. The highest germination frequency was achieved by immersing seeds in 98% sulfuric acid for 10 minutes, then soaking the seeds in 500 mg·L−1 gibberellic acid (GA3) for 72 hours before cold stratification at 5 °C for 60 days.

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The past year has brought substantial progress in the development of functional and structural genomic tools for strawberry. Sequencing of cDNA library clones from the cultivated strawberry Fragaria × ananassa and the diploid model species Fragaria vesca has provided more than 3000 new EST sequences. We have also constructed a large (∼40 kb) insert genomic (fosmid) library from F. vesca. About 33,000 fosmid clones have been picked and spotted onto hybridization filters. Filters have been successfully probed with three single copy gene probes, one gene family probe, and chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) probe sets. The combined cpDNA and mtDNA clone content of the library is about 11%. After correction for organelle insert content, the nuclear genome coverage of the library is about 6×. Complete sequencing of two fosmid clones identified 12 putative protein-encoding genes, four of which were organized in colinearity with the corresponding chromosomal region of Arabidopsis thaliana. We will sequence an additional 50 fosmid clones, and use the resulting sequence data as the basis for developing a novel marker technology, to be described. These genomic tools will provide a basis for connecting specific genes to specific traits in the octoploid, cultivated strawberry, paving the way for implementation of gene-based, marker assisted selection as a tool for strawberry breeders. Opportunity for cross-species comparisons of gene sequence and composition, as well as genome organization and linkage group structure, between Fragaria and other members of the economically important Rosaceae family has been significantly enhanced, thus expanding the relevance of the project results to peach, cherry, apple, rose, brambles, and many other Rosaceous species.

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Chinese cymbidiums are important flowering ornamental plants. Traditional propagation via seed or division cannot satisfy growers’ demand for commercialization of new cultivars, and in vitro propagation has a low micropropagation efficiency due to the browning of rhizomes. In this study, rhizomes of Cymbidium ‘14-16-13’ and ‘14-16-5’ were cultured on half-strength Murashige and Skoog (MS) medium supplemented with 6-benzyl aminopurine (BAP), NAA (α-napthaleneacetic acid), or BAP with NAA under either the dark or light. The degree of browning was read, and rhizome proliferation or sprouting (sprout numbers) was evaluated. Results showed that there was significant difference in browning grade of rhizomes between ‘14-16-13’ and ‘14-16-5’ regardless of dark and light culture. Dark culture induced rhizome proliferation but failed to induce sprouts. Light culture slightly elevated the degree of browning but induced sprouting. Among the growth regulators evaluated, BAP was more effective for sprout induction. As rhizome browning appeared to be inevitable in micropropagation of the cymbidiums, a compromise between browning and sprout production could be a realistic approach. Our study showed that rhizomes cultured on half-strength MS medium supplemented with 1.5 mg·L−1 BAP were able to produce more than 16 sprouts per vessel even though browning occurred in the rhizomes. Thus, culturing rhizomes in this medium could be a practical solution for in vitro propagation of Chinese cymbidiums.

Open Access

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.

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To study and model changes in the development of pak choi (Brassica rapa ssp. chinensis Makino), three pak choi cultivars—Xinxiaqing No. 5 (Xinxiaqing 5), Haiqing, and Huawang—were grown in a modern greenhouse. Four structural parameters, including leaf length, leaf width, and plant height and width, were measured regularly every 3 days. The results showed that the changes in plant height and width, and leaf length and width of the three cultivars followed sigmoidal trends. Logistical regression models {Y = K/[1 + (KL 0)/L 0 × exp(–r × t)]; Y = K/[1 + (KL 0)/L 0 × exp(−r × rad)]} of the leaf length and width accumulated with growth days and with accumulated radiation fit the actual data very well, with the correlation coefficient R 2 all greater than 0.98. The R 2 values of the plant width accumulation models were all greater than 0.93, whereas the R 2 values of the plant height regression models were not robust. In this study, the regression models of changes in plant height and width, and leaf length and width of pak choi were used to study the changes of morphological characteristics and analyze the change rules of pak choi growth and development.

Open Access