Effects of day and night temperature on photosynthesis, antioxidant enzyme activities, and endogenous hormones in tomato leaves during the flowering stage

To study the effects of day and night temperature difference (DIF) on tomato growth, a controlled experiment using Solanum lycopersicum L., cv. Jinguan 5 was conducted. The daily mean temperature (T-m) was maintained at 18 degrees C and 25 degrees C, and the DIF was set at 0 degrees C, 6 degrees C, and 12 degrees C. The results indicated that chlorophyll a (Chl a) and chlorophyll b (Chl b) gradually increased as DIF rose. At 18 degrees C T-m, the carotenoid content reached a maximum at 12 degrees C DIF. The Chl a/Chl b, net photosynthetic rate (P-N), photosynthetic rate at irradiation saturation (P-max), stomatal conductance (g(s)), intercellular CO2 concentration (C-i), stomatal limitation value, the maximum assimilation rate (A(max)), apparent quantum efficiency (A(q)), carboxylation efficiency (C-e), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), gibberellin A(3) (GA(3)), and indole-3-acetic acid (IAA) were highest, while malondialdehyde (MDA) was lowest at 6 degrees C DIF. At 25 degrees C T-m, P-N, P-max, A(max), A(q), C-e, g(s), C-i, CAT, POD, GA(3), IAA, and zeatin reached the maximum under 6 degrees C DIF, while SOD and MDA reached the maximum under 12 degrees C DIF. Furthermore, the morphological index peaked at 6 degrees C DIF under 18 degrees C and 25 degrees C T-m. The results suggested that 6 degrees C DIF improved the growth and development of tomato during the flowering stage.