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Song Ping and Ellen B. Peffley

Callus of five onion genotypes representing two species. Allium cepa and A. fistulosum, and their interspecific hybrid were used for establishing suspension cultures. Cultures were derived from callus that had been maintained on solid media and routinely subcultured for four years and from callus induced within six months of this experiment. Long-term callus from which plants were routinely regenerated and newly-induced callus were composed of cells which were, for the most-part, meristem-like with higher mitotic indices than cells from long-term callus which had been maintained as callus but had lost us capability to regenerate plants, these cells were large with small nuclei. Callus from newly-induced and long-term regenerable cultures were selected for further studies. Eight liquid media with factorial combinations of plant growth regulators were tested. Cells cultured in BDS liquid medium supplemented with 0.5 mg/l ABA and 1.0 or 2.0 mg/l 2,4-D without e-BA had higher mitotic indices and plant regeneration percentages than did cells cultured in the same media without ABA and with 6-BA. Suspension cultures from A. fistulosum and interspecific hybrids with A. fistulosum produced the highest numbers of plants regenerated.

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Ping Song, Wanhee Kang, and Ellen B. Peffley

Regenerating calli of Allium fistulosum × A. cepa interspecific F1 hybrids were treated in vitro with colchicine. A factorial experiment (colchicine concentration × time) was used to recover tetraploids from calli treated with colchicine in vitro. Shoot production of regenerating calli following in vitro colchicine treatment decreased with increasing colchicine concentration and treatment time. Cytological analyses of root tip cells from regenerated plantlets showed that chromosomes of control plantlets (not treated with colchicine) were not doubled. Chromosomes of some plantlets regenerated from in vitro colchicine treated calli were doubled, resulting in tetraploids. Calli treated with 0.1 or 0.2% colchicine in BDS (Dunstan & Short, 1977) liquid medium for 48 or 72 hours yielded the highest number of tetraploid plantlets. These results demonstrate that in vitro colchicine treatment of regenerating calli of interspecific F1 hybrids is effective in recovering tetraploids.

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Yuting Meng, Boling Liu, Ping Zhang, Ping Cui, Yuguang Song, Nianwei Qiu, Guoliang Han, and Feng Zhou

2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) is one of the most toxic polybrominated diphenyl ethers (PBDEs). The toxic effects of BDE-47 on Chinese cabbage seedlings were analyzed in this study. After a 30-day hydroponic exposure to BDE-47 at different concentrations (25, 50, 75, and 100 µg·L−1), the fresh weight of Chinese cabbage seedlings was significantly decreased, whereas their root:shoot ratio was increased, indicating that BDE-47 inhibited the growth of the plant, especially the overground parts. The water content, chlorophyll content, and protein content of Chinese cabbage leaves also markedly decreased with the increase of the BDE-47 concentration. In addition, BDE-47 weakened the photosynthetic capacity of the leaves, which was supported by the decreased photosynthetic parameters [net photosynthetic rate (P n) and stomatal conductance (g S)]. Although the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in the leaves were enhanced after exposure to BDE-47, the increased malondialdehyde (MDA) content attested to the existence of membrane lipid peroxidation. The increased plasma membrane permeability and the decreased chlorophyll fluorescence parameters [the maximum quantum yield of PSII photochemistry at t = 0 (F v/F m), photosystem II (PSII) reaction centers (RCs) per cross section (CS) (RC/CS), absorption energy flux per CS (ABS/CS), trapped energy flux per CS (TR o/CS), electron transport flux per CS (ET o/CS), performance index on the absorption basis (PI abs), and driving force for photosynthesis (DF)] further proved that the plasma membrane and photosynthetic membrane were damaged by BDE-47. Our study demonstrated the phytotoxicities of BDE-47 to Chinese cabbage, which can provide valuable information for understanding the toxicity of BDE-47 on vegetables.

Open access

Huihui Zhang, Ping Yu, Min Song, Dalu Li, Qianqian Sheng, Fuliang Cao, and Zunling Zhu

Ginkgo biloba, a relict plant, has been popularized and planted in most areas of China for its leaves, timber, and fruits. In the present study, the dynamic changes in leaf color, leaf pigment content during the color change period, and photosynthetic characteristics in different growth periods were studied to explore the coloring mechanism and adaptability of five late-deciduous superior Beijing G. biloba cultivars (LD1–LD5). The results showed that the leaf color change of each superior cultivar was relatively stable, and the discoloration period of LD3 and LD5 was later than that of others. From September to November, the chlorophyll a, chlorophyll b, and total chlorophyll content in all superior cultivars showed a downward trend, except in LD3, in which the pigment content was slightly higher in October than in September. Except in LD3 and LD4, the ratio of carotene content to total chlorophyll content in other cultivars slightly decreased in October. In May, the photosynthetic capacity of LD5 was stronger than that of other cultivars. The photosynthetic capacity of LD3 was strong in July and October. Our results imply that LD3 and LD5 are suitable for mixed planting with common G. biloba to increase the overall leaf color viewing period. Ginkgo biloba leaves turn yellow in autumn because of both a decrease in the chlorophyll content after leaf senescence and an increase in the Car content during leaf senescence. Although LD5 presented rapid seedling emergence, LD3 grew faster during the vigorous and late growth stages and is thus suitable for agricultural production.

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Zhi-Rong Li, Kang-Di Hu, Fen-Qin Zhang, Shi-Ping Li, Lan-Ying Hu, Yan-Hong Li, Song-Hua Wang, and Hua Zhang

Broccoli (Brassica oleracea var. italica) is an important vegetable crop rich in vitamins and sulforaphane. However, the floral heads of broccoli experience rapid postharvest senescence. Here we found that hydrogen sulfide (H2S) treatment alleviated dark-promoted senescence in broccoli florets. H2S delayed the symptoms of senescence and maintained higher levels of chlorophyll and Rubisco and lower protease activity compared with water control. Gene expression analysis showed that H2S down-regulated the expression of chlorophyll degradation-related genes BoSGR, BoNYC, BoCLH1, BoPPH, and BoRCCR. Expression of lipoxygenase gene BoLOX1 and the genes involved in the ethylene synthesis pathway, BoACS2 and BoACS3, were also down-regulated by H2S. The reduced expression level in cysteine protease gene BoCP3 and aspartic protease gene BoLSC807 suggested the role of H2S in alleviating protein degradation during broccoli senescence. H2S up-regulated the expression of sulfur metabolism genes BoSR and BoOASTL, and the antioxidant gene BoCAT. These results show that H2S plays a vital role in alleviating broccoli senescence through a broad regulation on gene expression of reactive oxygen species (ROS) metabolism genes, ethylene synthesis genes, and protease genes.