Effects of different temperature treatments on physiological and biochemical parameters and bolting in Lactuca sativa

This study investigates the effects of temperature on the growth, development, and bolting characteristics of Lactuca sativa , utilizing the late-maturing variety WS1 and the early-maturing variety WS3 as experimental materials. Three temperature gradients were established: 18 °C/4 °C (low temperature), 25 °C/18 °C (control), and 35 °C/18 °C (high temperature), with treatment durations of 2 d, 6 d, and 10 d, respectively. Each treatment included three biological replicates, allowing for a systematic analysis of changes in agronomic traits, physiological and biochemical indicators, and bolting characteristics of the seedlings. The results indicated that temperature stress significantly influenced seedling growth, although responses varied between the two varieties. Regarding agronomic traits, the plant height and leaf length of WS1 were significantly reduced compared to the control at both 6 d and 10 d of treatment. In contrast, WS3 exhibited significant changes in leaf length, petiole thickness, and fresh weight of the aboveground portion after just 2 d of high-temperature treatment, indicating an early sensitivity to temperature stress. At the physiological level, the activities of catalase (CAT), superoxide dismutase (SOD), and the content of malondialdehyde (MDA) in WS1 significantly increased after 6 d and 10 d of high-temperature treatment. In contrast, the CAT activity in WS3 exhibited a significant increase only during the early stages, while the MDA content was notably higher than that of the control at 2 d and 10 d of treatment. A comparison of the bolting rates among the different varieties indicated that WS1 had a lower bolting rate than WS3, with both varieties showing increased bolting rates over time. Furthermore, the bolting speed of WS3 demonstrated greater sensitivity to temperature fluctuations. In summary, the bolting rates of both varieties increased to varying degrees following stress, with a more pronounced rise observed at elevated temperatures. This finding suggests that high temperatures are more effective than low temperatures in inducing bolting, indicating enhanced adaptability to temperature stress under the experimental conditions. This study elucidates the response characteristics of the late-maturing variety WS1 and the early-maturing variety WS3 to temperature stress, highlighting the differences in tolerance among the varieties.