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Medium pH is generally adjusted to 5.8 to 6.0 for plant tissue culture. Our research indicated that pH generally falls between 5.5 and 7.5 in an ordinarily made medium which can be directly used for apple tissue culture without adjusting pH. Repeated adjustment of pH by adding NaOH and HCl leads to the increase in Na⁺ and Cl⁻ concentration and decrease in Mg²⁺ and Ca²⁺ concentration in the medium due to precipitation. To determine the pros, cons, and necessity of pH levels while making medium in plant tissue culture, subculture proliferation, adventitious root induction, and organ regeneration, the apple cultivars Fuji, Golden Delicious, Jonagold, and Gala were used and hardness of the medium and the ion content of Na⁺, Cl⁻, Mg²⁺, and Ca²⁺ in the medium under different pH were measured. In the lower pH range of 5.0–5.5, plantlets could be subcultured and grew normally; however, the medium did not solidify or solidified poorly resulting in problems associated with handling. No significant difference was found among the treatments when pH ranged 6.0–8.0 in terms of proliferation, adventitious root induction, and adventitious bud regeneration from leaves, except a slight decrease in shoot number proliferation in ‘Jonagold’ and in adventitious bud regeneration from leaves in ‘Fuji’ and ‘Golden Delicious’ at pH above 7.5. The hardness of the medium increased with the increased pH. The superfluous Cl⁻ and Na⁺ generated during the process of overadjusting pH to 7.0 by adding NaOH and then readjusting to 6.0 by adding HCl significantly affected the proliferation, rooting, and organ regeneration of apple plantlets. A relative broad range of medium pH (5.5–7.5) is suitable for apple tissue culture. We suggest that it is not necessary to always adjust medium pH to 5.8–6.0 in apple tissue culture; especially the repeated adjustment should be avoided.

Aquaporin (AQP) proteins serve important roles in regulating water movement across cellular membranes and affect plant responses to drought stress. The objective of this study was to characterize and examine functions of an AQP gene FaPIP2;1, isolated from a drought-tolerant perennial grass species tall fescue (Festuca arundinacea), for involvement in leaf dehydration status during water stress by overexpressing the gene in arabidopsis (Arabidopsis thaliana). FaPIP2;1 had characteristic transmembrane domains and Asn–Pro–Ala motifs and was similar to PIP2;1 in rice (Oryza sativa) and maize (Zea mays). Quantitative real-time reverse transcriptase polymerase chain reaction analysis showed that FaPIP2;1 was upregulated during moderate water stress (hydroponic culture, osmotic potential (Ψ_S) at −0.47 and −0.78 MPa) and the transcript level decreased as Ψ_S further decreased. Transgenic arabidopsis plants overexpressing FaPIP2;1 showed greater number of leaves per plant and improved survival rate compared with the wild type (WT) during drought stress. Transgenic plants also maintained higher leaf relative water content (RWC), chlorophyll content (Chl), net photosynthetic rate (Pn), and lower leaf electrolyte leakage (EL) than the WT. However, there was no difference in root length between the transgenic and WT plants following drought stress. The results demonstrated that overexpressing FaPIP2;1 could improve plant tolerance to drought stress by enhancing leaf water status, Chl, and photosynthetic rate, as well as maintaining improved cellular membrane stability relative to the WT plants. FaPIP2;1 may be used as a candidate gene for genetic modification of perennial grasses to develop new drought-tolerant germplasm and cultivars.

Tobacco is traditionally an industrial crop that is used for manufacturing cigarettes. However, due to health concerns and global tobacco control movements, alternative uses of tobacco are urgently needed to support tobacco farmers and vendors. Tobacco is also an oilseed crop with an oil yield ranging from 30% to 40 of its dry weight. However, there is still no information on the effects of nitrogen application on tobacco seed yield and seed oil production. The objective of this study was to evaluate the effects of N fertilization (90, 120, 150, and 180 kg·ha⁻¹ N) on the seed yield, oil content, fatty acid composition, and seed germination characteristics of tobacco plants at two locations. The results showed that applying increasing amounts of N to tobacco plants significantly increased their total seed yields and oil content. Nitrogen application also modified the fatty acid composition of the seed oil, as more unsaturated fatty acids were produced under the increasing N application rate treatments than under the control. Moreover, increasing the N application rate generally significantly increased the yields of individual fatty acids as well. Nevertheless, the increased seed oil content and altered fatty acid composition did not affect seed germination traits, as the seed germination potential and rate showed no obvious change among treatments or the control. The height and size of the tobacco plants also increased with the increasing N application rate, which would be beneficial for increasing biomass production for bioenergy. This study shows for the first time the feasibility of increasing the seed and oil yields and modifying the fatty acid composition of tobacco plants by increasing N addition.

The aim of this study was to quantitatively investigate the impacts of nitrogen on growth dynamics and yield, so as to facilitate the optimization of nitrogen management for muskmelon crop in plastic greenhouse. For this purpose, four experiments with different levels of nitrogen treatment and planting dates on muskmelon (Cucumis melo L. ‘Nanhaimi’ and ‘Xizhoumi 25’) were conducted in plastic greenhouse located at Sanya from Nov. 2012 to Sept. 2014. The quantitative relationship between leaf nitrogen content and growth dynamics and yield of muskmelon was determined and incorporated into a photosynthesis-driven crop growth model (SUCROS). Independent experimental data were used to validate the model. The critical leaf nitrogen content at flowering stage for muskmelon ‘Nanhaimi’ and ‘Xizhoumi 25’ were 19.8 and 21.0 mg·g⁻¹. The coefficient of determination (r ²) and the relative root-mean-squared error (rRMSE) between the predicted and measured value of growth dynamics and yield were, respectively, 0.91 and 10.8% for leaf area index (LAI), 0.90 and 19.6% for dry weight of shoot (DWSH), 0.76 and 30.3%, 0.82 and 21.1%, and 0.92 and 11.9% for dry weight of leaf (DWL), stem (DWST), and fruit (DWF), 0.91 and 17.3%, 0.89 and 13.9%, 0.86 and 27.8%, and 0.88 and 20.6% for soluble sugar content (SU), soluble protein content (PR), vitamin C content (VC), and soluble solids content (SO) of fruit, and 0.90 and 10.1% for fresh weight of fruit (FWF). The model could be used for the optimization of nitrogen management for muskmelon production in plastic greenhouse. Further calibration and test would be needed during the application of the model in wider range of conditions and muskmelon cultivars.