Introduction Directory UMM :Data Elmu:jurnal:P:PlantScience:PlantScience_Elsevier:Vol155.Issue1.2000:

Plant Science 155 2000 59 – 66 The evolution of photosynthetic capacity and the antioxidant enzymatic system during acclimatization of micropropagated Calathea plants J.M. Van Huylenbroeck a, , A. Piqueras b , P.C. Debergh c a Department of plant genetics and breeding D6P , CLO Gent, Ministry of Small Enterprises, Traders and Agriculture, Caritasstraat 21 , 9090 Melle, Belgium b Departamento de Nutricion y Fisiologia Vegetal, CEBAS CSIC , PO BOX 4195 , 30080 Murcia, Spain c Faculty of Agricultural and Applied Biological Sciences, Department of Plant Production, Horticulture, Uni6ersity Gent, Coupure links 653 , B- 9000 Gent, Belgium Received 18 October 1999; received in revised form 8 December 1999; accepted 6 January 2000 Abstract The effects of an increased PPFD on photosynthesis, the functioning of the photosynthetic apparatus and the response of the antioxidant enzymatic system were studied during the ex vitro establishment of micropropagated Calathea ‘Maui Queen’ plantlets. Measured chlorophyll and carotenoids contents in ex vitro formed leaves were almost three times higher compared to the in vitro formed ones. At the end of the acclimatization, an inverse relation between PPFD and the chlorophyll a + bcarotenoids ratio was observed. During the first days after transplantation Calathea plants are not photosynthetically active, as is illustrated by the photosynthetic light response curves. With the appearance of new leaves, higher photosynthetic capacities were observed and light saturation point increased days 17 and 25. Also the maximal photosynthetic efficiency enlarged as shown by the increased initial slope of the curves. F v F m decreased directly after transplantation of the micropropagated plantlets, afterwards a recovery was observed, but highest F v F m values were observed in low light LL plants. The photochemical quenching coefficient increased gradually during the first two weeks of the acclimatization. In high light HL plants, q P decreased directly after transfer, while this was not observed in LL and medium light ML. During the acclimatization period to increasing light intensities significant changes in the activity of the antioxidant enzymatic system were observed. A decrease in superoxide dismutase SOD activity was measured during the first half of the acclimatization period followed by a recovery in ML and HL plants by day 35. Dehydroascorbate reductase DHAR activity decreased during acclimatization. At the end of the experimental period the lowest levels were 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 photosynthetic capacity and the activation of the enzymatic antioxidant system in the leaves of calathea plants during ex vitro acclimatization is discussed. © 2000 Elsevier Science Ireland Ltd. All rights reserved. Keywords : Acclimatization ex vitro; Antioxidant enzymes; Photosynthesis; Calathea; Micropropagation www.elsevier.comlocateplantsci

1. Introduction

In vitro culture is an efficient vegetative propa- gation system for many high-value cultivars. Nev- ertheless, micropropagation is in some cases restricted due to considerable losses during the ex vitro acclimatization in greenhouse or field. Therefore improvement in survival and a better knowledge of the physiology of in vitro cultured plants are of considerable interest. Directly after transfer to ex vitro conditions, micropropagated plants are very susceptible to various stresses, because they have not yet devel- oped adequate patterns of resource allocation and Corresponding author. Tel.: + 32-9-2722862; fax: + 32-9- 2722901. E-mail address : jvanhuylenbroeckclo.fgov.be J.M. Van Huylen- broeck 0168-945200 - see front matter © 2000 Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 2 0 1 - 6 morphological and physiological features required by the new environment [1]. Low photosynthesis rates [2,3] and the malfunctioning of the water housekeeping system [4] are two of the major constrains of tissue cultured plants. A switch to autotrophy and changes in stomatal functioning and cuticula composition are observed during ac- climatization [5 – 7]. Plantlets are exposed to low photosynthetic photon flux densities PPFD. Once in the greenhouse, PPFD is much higher and plants become very susceptible to light stress. Ex- cessive radiation during acclimatization can even lead to chronic photoinhibition [8,9]. Besides pho- toinhibition, plants also suffer due to the differ- ence between in vitro and ex vitro relative humidity [10]. Both phenomena, photoinhibition and water stress, can generate toxic O 2 species [11 – 13]. As protection against the latter, plant cells have developed several antioxidant and enzy- matic scavenging systems as superoxide dismutase SOD, catalase CAT, peroxidase, dehydroascor- bate redutase DHAR and gluthathione reductase GR [14]. Accordingly, there are many examples relating SOD and enzymes of the H 2 O 2 scavenging pathway to environmental stresses in plants [15]. However, limited information on the possible role of these protective enzymatic systems during the acclimatization process and their relation with photoinhibition and malfunctioning in the transpi- ration system of micropropagated plants is avail- able. Recently, it was demonstrated that micropropagated plants develop antioxidant mechanisms during acclimatization [16]. In the present study we investigated the effects of an increased PPFD during the ex vitro estab- lishment of micropropagated Calathea ‘Maui Queen’ on photosynthesis, the functioning of the photosynthetic apparatus and the enzymatic activ- ities in the scavenging systems of activated oxygen.

2. Materials and methods