Photosynthetic capacity, growth and water relations in 'Golden' papaya cultivated in vitro with modifications in light quality, sucrose concentration and ventilation

This study assessed the ecophysiological aspects of the in vitro multiplication of 'Golden' papaya in response to different light qualities, ventilation systems and sucrose concentrations related to photosynthesis, chlorophyll fluorescence, water balance and growth. The treatments were performed in a complete, randomised split-plot design with four replicates. These treatments consisted of white and red light, closed and ventilated culture systems and four sucrose concentrations (10, 20, 30 and 40 g L-1) in the culture medium. The lowest plantlet water loss rate was obtained using the ventilated culture system. The photochemical damage was attributable to the reduced maximum PS II quantum yield and the efficiency of the oxygen-evolving complex (OEC). The increase in the production of papaya dry biomass was due to the exogenous carbon source, the sucrose that was added to the culture medium. In this study, there was no photosynthetic carbon assimilation (A(actual), actual photosynthetic rate) or oxygen evolution (A(pot), potential photosynthetic rate) due to the damage caused by the presence of sucrose in the culture medium to the photochemical capacity of the oxygen-evolving complex (OEC) and PS II activity. Further studies are needed using a sucrose concentration below 10 g L-1 in association with the increased irradiance of the culture chamber (red lights) as well as carbon dioxide enrichment (over 400 mu L L-1 of air). These conditions may stimulate the autotrophic metabolism of this species for in vitro cultivation and increase the rate of biomass production.