Low night temperature-induced feedback inhibition of photosynthesis through sucrose accumulation in sugar beet (Beta vulgaris L.) leaves

Sugar beet (Beta vulgaris L.) is a globally important sugar crop that is mainly used to produce sucrose. However, its cultivation is limited by poor growth and seedling necrosis under low night temperatures (LNT). The aim of this study was to investigate the effects of LNT on growth, photosynthetic characteristics, and sucrose accumulation in sugar beet. LNT stress reduced growth, photosynthesis, membrane stability, and dark respiration. Following LNT stress, we observed thicker leaves and a reduction in diameter of the stem vascular bundle. LNT stress also decreased sucrose synthase, resulting in decreased sucrose decomposition. Under low night temperature, the reduction of sucrose decomposition, nocturnal respiratory consumption, and sucrose output from leaves to roots resulted in significant sucrose accumulation in leaves, which in turn inhibited photosynthesis and sucrose phosphate synthase. The sucrose accumulation in leaves subjected to lower night temperature (4 ℃) was higher than that in leaves at 12 ℃, resulting in stronger inhibition of photosynthetic feedback. The results of this study confirmed that LNT stress can decrease photosynthesis via feedback inhibition of sucrose in leaves, providing a theoretical basis for the improvement and cultivation of sugar beet.