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The objective of this study was to investigate ascorbic acid (AsA) accumulation, mRNA expression of genes involved in AsA biosynthesis as well as recycling, activity of key enzymes, and the relationship of them to AsA levels during the development of apple fruit (Malus ×domestica cv. Gala). AsA concentration, which mainly depends on biosynthesis, was the highest in young fruit post-anthesis and then decreased steadily toward maturation. However, AsA continued to accumulate over time because of the increase in fruit mass. Transcript levels of guanosine diphosphate (GDP)-L-galactose phosphorylase, GDP-mannose pyrophosphorylase, D-galacturonate reductase, and the post-transcriptionally regulated L-galactono-1,4-lactone dehydrogenase were not correlated with AsA accumulation in apple. In contrast, patterns of expression for L-galactose dehydrogenase, L-galactose-1-phosphate phosphatase, and GDP-mannose-3′,5′-epimerase showed a pattern of change similar to that of AsA accumulation. Although activities and expression levels of monodehydroascorbate reductase and dehydroascorbate reductase in fruit, which had less capacity for AsA recycling, were much lower than in leaves, they were not clearly correlated with AsA level during fruit development.

Light and temperature are two crucial factors affecting plant growth. Light intensities vary considerably with season and weather conditions. Reasonable light regulation at different temperatures is a key issue in environmental regulation. In this study, we determined the effects of light intensity and temperature on crop growth and development. Furthermore, we determined an optimal light value and a suitable light range at different temperatures for producing the lettuce Lactuca sativa L. Artificial climate chamber experiments were conducted at five light intensities (100, 200, 350, 500, and 600 μmol·m⁻²·s⁻¹), as well as at low (15 °C/10 °C), medium (23 °C/18 °C), and high (30 °C/25 °C) temperatures. In these experiments, we investigated the photosynthetic rate; chlorophyll fluorescence parameters; total N, P, and K uptake; and growth of lettuce plants. The results indicated that at a low temperature, the values of effective quantum yield of photosystem II photochemistry (Φ_PSII), net photosynthetic rate (P _n ), stomatal conductance (g _S), and transpiration rate (T _r ) —as well as those of N, K, and P uptake—were the highest at 350 μmol·m⁻²·s⁻¹, followed by 500 μmol·m⁻²·s⁻¹, which resulted in higher values for leaf number (LN), leaf area (LA), dry weight (DW), and fresh weight (FW). At the medium temperature, the values of Φ_PSII, P _n , g _S, and T _r , as well as those of N, K, and P uptake were higher at 350, 500, and 600 μmol·m⁻²·s⁻¹ than at other light intensities, resulting in high values for LN, LA, DW, and FW of lettuce plants. The LN, LA, and FW of lettuce plants were the highest at 500 μmol·m⁻²·s⁻¹, whereas DW was the highest at 600 μmol·m⁻²·s⁻¹. At a high temperature, lettuce plants exhibited the highest values of F _v/F _m, Φ_PSII, P _n , g _S , and T _r , as well as those of N, K, and P uptake for the 500 μmol·m⁻²·s⁻¹ treatment; whereas LN, LA, FW, and DW were the highest at 600 μmol·m⁻²·s⁻¹. In addition, the values of F _v/F _m indicated that lettuce plants were under stress under the following combinations: 600 μmol·m⁻²·s⁻¹ at the low temperature, 100 μmol·m⁻²·s⁻¹ at the medium temperature, and 100–350 μmol·m⁻²·s⁻¹ at the high temperature. Based on these results, an optimal regulation strategy for light intensity at different temperature environments was proposed for lettuce cultivars similar to L. sativa L. in some regions, such as the subtropical regions of China. Specifically, for low temperatures, light intensities of 350 to 500 μmol·m⁻²·s⁻¹are recommended for production, and an intensity of 350 μmol·m⁻²·s⁻¹ provides optimal supplementary light during early spring and winter in greenhouses. For medium temperatures, light intensities of 350 to 600 μmol·m⁻²·s⁻¹ are recommended, and 500 μmol·m⁻²·s⁻¹ is the optimal value during the middle of spring and autumn. For high temperatures, light intensities of 500 to 600 μmol·m⁻²·s⁻¹are recommended, and 600 μmol·m⁻²·s⁻¹ is the optimal value of light intensity during late spring and early autumn.