Chlorophyll fluorescence as an indicator of photosynthetic functioning of in vitro grapevine and chestnut plantlets under ex vitro acclimatization

This study reports the effects of light availability during the acclimatiza tion phase on photosynthetic characteristics of micropropagated plantlets o f grapevine (Vitis vinifera L.) and of a chestnut hybrid (Castanea sativa x C. crenata). The plantlets were acclimatized for 4 weeks (grapevine) or 6 weeks (chestnut), under two irradiance treatments, 150 and 300 mu mol m(-2) s(-1) after in vitro phases at 50 mu mol m(-2) s(-1.) For both treatments and both species, leaves formed during acclimatization (so-called 'new leav es') showed higher photosynthetic capacity than the leaves formed in vitro either under heterotrophic or during acclimatization (so-called 'persistent leaves'), although lower than leaves of young potted plants (so-called 'gr eenhouse leaves'). In grapevine, unlike chestnut, net photosynthesis and bi omass production increased significantly with increased light availability. Several parameters associated with chlorophyll a fluorescence indicated ph otoinhibition symptoms in chestnut leaves growing at 300 mu mol m(-2) s(-1) . The results taken as a whole suggest that 300 mu mol m(-2) s(-1) is the u pper threshold for acclimatization of chestnut although grapevine showed a better response than chestnut to an increase in light.