The evolution of photosynthetic capacity and the antioxidant enzymatic system during acclimatization of micropropagated Calathea plants

The effects of an increased PPFD on photosynthesis, the functioning of the photosynthetic apparatus and the response of the antioxidant enzymatic syst em were studied during the ex vitro establishment of micropropagated Calath ea 'Maui Queen' plantlets. Measured chlorophyll and carotenoids contents in ex vitro formed leaves were almost three times higher compared to the in v itro formed ones. At the end of the acclimatization, an inverse relation be tween PPFD and the chlorophyll (a + b)/carotenoids ratio was observed. Duri ng the first days after transplantation Calathea plants are not photosynthe tically active, as is illustrated by the photosynthetic light response curv es. With the appearance of new leaves, higher photosynthetic capacities wer e observed and light saturation point increased (days 17 and 25). Also the maximal photosynthetic efficiency enlarged as shown by the increased initia l slope of the curves. F-v/F-m decreased directly after transplantation of the micropropagated plantlets, afterwards a recovery was observed, but high est F-v/F-m values were observed in low light (LL) plants. The photochemica l quenching coefficient increased gradually during the first two weeks of t he acclimatization. In high light (HL) plants, q(P) decreased directly afte r transfer. while this was not observed in LL and medium light (ML). During the acclimatization period to increasing light intensities significant cha nges in the activity of the antioxidant enzymatic system were observed. A d ecrease in superoxide dismutase (SOD) activity was measured during the firs t half of the acclimatization period followed by a recovery in ML and HL pl ants by day 35. Dehydroascorbate reductase (DHAR) activity decreased during acclimatization. At the end of the experimental period the lowest levels w ere measured in ML plants. Catalase (CAT) activity increased significantly during the first two weeks after transfer, a clear inverse relationship to PPFD was detected. The relation between the adquisition of full photosynthe tic capacity and the activation of the enzymatic antioxidant system in the leaves of calathea plants during ex vitro acclimatization is discussed. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.