Why do putting green grasses turn red, blue, or purple? The cool to cold temperatures trigger the color responses. During mid to late October, many regions experience relatively warm days (65 to 75°F; 17 to 24°C), but cool nights (32 to 55°F; 0 to 13°C). The sunny, bright, and warm days stimulate plants to produce large amounts of sugars (through photosynthesis) in leaf blades and sheathes. At night, the sugars must be translocated out of the leaves to crowns for storage or use in other physiological processes. When nights are very cool or frosty the sugars are not completely moved out of the leaves and they accumulate. There are many types of sugars. Glucose is a common plant sugar and sometimes glucose molecules are chemically bound with anthocyanins. Anthocyanins are pigments and their function in plants is unclear. They provide the red, purple, and blue colors in flowers. Anthocyanins are always present in leaves, but normally are masked by the presence of chlorophyll. They are expressed in the foliage of trees during cool and bright weather to provide the spectacular colors in autumn leaves. Hence, bentgrasses may experience a similar accumulation of sugar, and therefore anthocyanins, following the first cool or frosty night of fall. Frost injury may denature the green chlorophyll, thereby exposing the anthocyanin pigment. These colors may intensify and persist throughout winter months and slowly disappear in mid-spring after the turf begins active growth.
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