What causes turnip leaves to turn purple after frost?

Turnip leaves turn purple after frost due to the accumulation of anthocyanins, which are pigments that can provide protection against cold temperatures. The stress from freezing temperatures can trigger this pigment production as a response to protect the plant’s cells from damage. Additionally, cold weather can affect nutrient uptake, particularly phosphorus, leading to further changes in leaf coloration. This purple hue can be a sign of frost stress but does not necessarily indicate permanent damage to the plant.