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  • Author or Editor: Yi Zou x
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Genetic engineering has the potential to improve disease resistance in taro [Colocasia esculenta (L.) Schott]. To develop a method to produce highly regenerable calluses of taro, more than 40 combinations of Murashige and Skoog (MS) media at full- or half-strength with varying concentrations of auxin [α-naphthaleneacetic acid (NAA) or 2, 4-dichlorophenoxyacetic acid (2, 4-D)], cytokinin [benzyladenine (BA) or kinetin], and taro extract were tested for callus initiation and plant regeneration. The best combination, MS medium with 2 mg·L−1 BA and 1 mg·L−1 NAA (M5 medium), was used to produce regenerable calluses from taro cv. Bun Long initiated from shoot tip explants. After 8 weeks of growth, multiple shoots from these calluses could be induced on MS medium with 4 mg·L−1 BA (M15 medium). The rice chitinase gene (ricchi11) along with the neomycin phosphotransferase (npt II) selectable marker and β-glucuronidase (gus) genes were introduced into these taro calluses through particle bombardment. Transformed calluses were selected on M5 medium containing 50 mg·L−1 geneticin (G418). Histochemical assays for beta-glucuronidase (GUS), polymerase chain reaction (PCR), reverse transcription–PCR, and Southern blot analyses confirmed the presence, integration, and expression of the rice chitinase gene in one transgenic line (efficiency less than 0.1%). Growth and morphology of the transgenic plants appeared normal and similar to non-transformed controls. In pathogenicity tests, the transgenic line exhibited improved resistance to the fungal pathogen, Sclerotium rolfsii, but not to the oomycete pathogen, Phytophthora colocasiae.

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We studied the effects of exogenous spermidine (Spd) on plant growth and nitrogen metabolism in two cultivars of tomato (Solanum lycopersicum) that have differential sensitivity to mixed salinity-alkalinity stress: ‘Jinpeng Chaoguan’ (salt-tolerant) and ‘Zhongza No. 9’ (salt-sensitive). Seedling growth of both tomato cultivars was inhibited by salinity-alkalinity stress, but Spd treatment alleviated the growth reduction to some extent, especially in ‘Zhongza No. 9’. Exogenous Spd may help reduce stress-induced increases in free amino acids, ammonium (NH4 +) contents, and NADH-dependent glutamate dehydrogenase (NADH-GDH) activities; depress stress-induced decreases in soluble protein and nitrate content; and depress nitrate reductase, nitrite reductase, glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT) activities, especially for ‘Zhongza No. 9’. Based on our results, we suggest that exogenous Spd promotes the assimilation of excess toxic NH4 + by coordinating and strengthening the synergistic action of NADH-GDH, GS/NADH-GOGAT, and transamination pathways, all during saline-alkaline stress. Subsequently, NH4 + and its related enzymes (GDH, GS, GOGAT, GOT, and GPT), in vivo, are maintained in a proper and balanced state to enable mitigation of stress-resulted damages. These results suggest that exogenous Spd treatment can relieve nitrogen metabolic disturbances caused by salinity-alkalinity stress and eventually promote plant growth.

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