Effect of Abnormal Light/Dark Cycles on the Pigment Complex of Brassicaceae and Solanaceae Plants

Under controlled environmental conditions, the authors studied the effect of extended light/dark cycles of 24/12, 48/24, 96/48, and 120/60 h and continuous lighting on the content and ratio of photosynthetic and nonphotosynthetic pigments in a number of Solanaceae (eggplant ( Solanum melongena L.), sweet pepper ( Capsicum annuum L.), tobacco ( Nicotiana tabacum L.), and tomato ( Solanum lycopersicum L.)) and Brassicaceae (broccoli ( Brassica oleracea var. italica Plenck), mizuna ( Brassica rapa ssp nipposinica (L.H. Bailey) Hanelt), arugula ( Eruca vesicaria sp . sativa Mill.), and cauliflower ( Brassica oleracea L. var. botrytis L.)) plants. Plants were grown in controlled-climate chambers at 23°С and light intencity of 270 µmol/(m 2 s) PAR. Control plants were grown under photoperiod of 16/8 h. Continuous lighting decreased the content of chlorophyll, its share in light-harvesting complex and chlorophyll to carotenoids ratio, but increased chlorophyll a / b ratio and the content of anthocyanins and flavonoids; these effects were differently manifested depending on plant species. At all other examined light/dark cycles (24/12, 48/24, 96/48, and 120/60 h) where average daily light integral did not differ from such under common photoperiod (16/8 h), changes in pigment complex were often observed similar to photoprotective reactions occurring upon exposure of plants to excess illumination (a decrease in the content of photosynthetic pigments, modification of their ratios, and accumulation of protective, nonphotosynthetic pigments). At the same time, plant responses were species-specific. On the whole, the obtained results have shown that changes within the plant pigment complex may be induced not only by excessive light energy coming to plants, but also by distribution of daily light integral in time as it occurs in response to abnormal light/dark cycles that, in the authors’ opinion, cause a circadian asynchrony.