Structural and Functional Characteristics of Ajuga reptansPhotosynthesis under Cold Climate Conditions

Structural, functional, and biochemical characteristics of the photosynthetic apparatus of a nemoral herbaceous perennial plant Ajuga reptansL. inhabiting the middle taiga subzone were investigated. Plant leaves were characterized by a high content of green (3.1 mg/dm²) and yellow (0.64 mg/dm²) pigments and contained moderate-sized chloroplasts with grana consisting of ten thylakoids or more. The maximum rate of photosynthesis in summergreen leaves (5–8 mg CO₂/(dm²h)) was observed at 14–16°C under a saturating photosynthetically active radiation of 50 W/m². At 6–7°C, the rate of CO₂assimilation was reduced to 60–80% of the maximum one. The temperature optimum of photosynthesis was not constant and shifted by 2–6°C depending on the changes in the ambient temperature. Wintergreen leaves were capable of photosynthesis in late autumn after heavy freezes and in early spring after a long winter. The accumulation of soluble carbohydrates and free amino acids in leaves helps to maintain the functional activity of the photosynthetic apparatus.