High concentration of aluminum ion (Al3+) in acidic soil often negatively affects plant growth. To deepen understanding of the mechanisms of physiological response to Aluminum (Al) toxicity, changes in physiology and cell ultrastructure of oil tea (Camellia oleifera) were investigated under different Al levels. Oil tea plants were grown in pots filled with sand and treated with Al at 0, 0.5, 1.25, 2.0, or 4.0 mm. Results showed that Al at 0.5–2.0 mm improved plant growth, whereas Al at 4.0 mm inhibited root growth and damaged cell ultrastructure. Net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), and photochemical efficiency increased as Al concentration increased from 0 to 2.0 mm; however, all parameters mentioned previously decreased at 4.0 mm. The activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in leaves treated with 2.0 mm Al reached the maximum, which were 29%, 63%, and 28% higher than that of control. When Al was ≤2.0 mm, the content of soluble sugar and soluble protein increased with increasing Al concentration. These results may indicate that oil tea adapted to Al stress through osmotic adjustment and through increasing antioxidant enzyme system. In summary, Al at low concentration (0.5–2.0 mm) improved growth and physiological performance, whereas 4.0 mm negatively impacted performance of oil tea.
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.
As a result of its high photosynthetic efficiency, the tung tree (Vernicia fordii) is a fast-growing heliophile, yielding fruit within 3 years. In addition, tung oil extracted from the fruit seeds is an environmentally friendly paint used widely in China. However, mutual shading inside a tung tree canopy leads to a low yield of fruit because of weak or dead lower branches. In this project, a pot experiment was conducted to understand the growth, physiological, anatomical structure, and biochemical responses of tung trees under various shading levels. Tung tree seedlings were subjected to different light intensities—100% sunlight (no cover), L100; 75% sunlight (25% shading), L75; 50% sunlight (50% shading), L50; and 20% sunlight (80% shading), L20—from June to August. Results indicate that the L75 treatment reduced significantly the net photosynthetic rate (Pn), stomatal conductance (gS), transpiration rate (E), total aboveground and root dry weight (DW), maximum net photosynthetic rate (Amax), and maximum rate of electron transport at saturating irradiance (Jmax) compared with the control, although plant height and leaf area (LA) were not reduced. Lower light intensities (L50 and L20) and longer duration of treatment led to greater reduction in growth, leaf thickness, and photosynthetic potential (Amax and Jmax). Chlorophyll a (Chl a), chlorophyll b (Chl b), and total chlorophyll content were increased in the L50 and L20 treatments compared with L100 and L75. There was no significant reduction in the enzyme activities of ribulose-1,5-bisphosphate carboxylase (Rubisco) and phosphoenolpyruvate (PEPC) of the seedlings using the L75 treatment; however, lower light intensities (L50 and L20) and longer duration of shade treatment resulted in a significant reduction in enzyme activity. In summary, the results suggest that tung trees have greater photosynthetic activity under high light intensity. Shading, even at 20%, especially for the longer term, reduced photosynthetic efficiency and growth. To prevent growth reduction, tung trees should be grown under full sun with a daily light integral (DLI) of ≈46 mol·m‒2·d‒1, and mutual shading should be avoided by proper spacing and pruning.