Importance of in vitro pretreatment for ex vitro acclimatization and growth

The influence of in vitro pretreatment on the physiology and growth of toba cco (Nicotiana tabacum L. cv. Samsun) plantlets during ex vitro transfer an d acclimatization was studied. Nodal cuttings were cultured on solid Murash ige-Skoog medium with 3% sucrose or without sucrose, and in low (60 mu mol m(-2) s(-1)) or high (200 mu mol m(-2) s(-1)) photosynthetic photon flux de nsities. 35 days old plantlets were transferred to soil. After a 20-days-pe riod of acclimatization in the greenhouse the plants were transferred to th e open air. The distinctive effects of the different in vitro culture condi tions on pigments and photosynthetic parameters disappeared during greenhou se acclimatization. Both the transfers were accompanied by a transient incr ease in starch content and the transfer to open air by a transient decrease in maximum photochemical efficiency of Photosystem II. In the open air, ph otosynthetic capacity and starch content started to increase with only smal l effects of the different pretreatments. Pretreatment had a pronounced eff ect on growth under these conditions. Growth was highest in plants original ly grown with 3% sucrose under high irradiance, and lowest in plants origin ally grown without sucrose under high irradiance (plantlets suffering from photoinhibition in vitro). Thus, photomixotrophic in vitro culture at eleva ted photon flux density is most suitable for later ex vitro development of the plants. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.