Age and Adaptive Changes in the Photosynthetic Apparatus of Leaves in Winter Green Herbaceous Plant Ajuga reptans L. in the Natural Conditions of the Taiga Zone

Abstract

The formation and functioning of the photosynthetic apparatus (PSA) is under the general control of the plant organism and constantly changing environmental conditions. The authors studied age-related and adaptive changes in the pigment complex, spectral properties, and the state of photosystem II (PSII) leaves of partial shoots of a summer-winter-green herbaceous perennial Ajuga reptans L. (bugle) in connection with overwintering. Rosette leaves of a new generation appearing in May–June quickly accumulated photosynthetic pigments and formed PSA with a maximal quantum efficiency of PSII (Fv/Fm) and actual quantum yield of PSII (ФPSII). In autumn (September–October), the content of chlorophylls was 10 mg/g dry weight, the value of Fv/Fm was 0.8 rel. units, and the level of ФPSII at PAR 130 µmol quanta/(m2 s) was approximately 0.7 rel. units. Overwintered leaves contained half as much photosynthetic pigments, accumulated a significant amount of anthocyanins, and were characterized by low photochemical activity and a high level of de-epoxidation of pigments of the violaxanthin cycle. With the resumption of active vegetation of plants (May), a partial restoration of the pigment pool and the repair of PSA of overwintered leaves were noted, as evidenced by an increase in the quantum yield PSII. The completion of the leaf life cycle was accompanied by a decrease in ФPSII up to 0.5 rel. units and a sharp increase in the thermal dissipation of absorbed excitation energy (NPQ) to 0.9 rel. units. Seasonal changes of spectral properties of leaves and photochemical reflectance indices generally corresponded to the dynamics content pigments and the efficiency of the use of light in photosynthesis. The results obtained indicate a significant transformation of the structural and functional organization of PSA in the ontogeny of overwintering leaves. The genetically fixed property of winter green plants to preserve leaves is based on the ability of their PSA to restore functional activity after the shock impact of overwintering, which is facilitated by a complex of adaptive and protective mechanisms.