Abstract
In vitro regenerated shoots of Spathiphyllum from bioreactor were hydroponically cultured for 30 days. The response of plant growth and photosynthesis to different substrates, photosynthetic photon flux (PPF), nutrient scheduling and electrical conductivity (EC) of hydroponic solution were studied. The best plant growth response was observed in perlite based substrates with moderate PFF (70-100 mu mol m(-2) s(-1)). Highest fresh weight, dry weight, shoot length, root length, root number and photosynthetic characteristics (chlorophyll, carotenoids and Fv/Fm) was observed in continuous immersion system. Plant growth responses, photosynthetic rate, stomatal conductance and transpiration rate were also found to be affected by EC levels. The optimum EC of a balanced nutrient solution was recorded as 1.2 dS m(-1). Photosynthetic activity was also characterized in terms of photochemical efficiency using measurements of chlorophyll fluorescence. Fv/Fm (it is a measure of the intrinsic or maximum efficiency of PSII i.e. the quantum efficiency if all PSII centers were open) also decreased significantly in plants grown under higher EC level; a decrease in this parameter indicates down regulation of photosynthesis or photoinhibition. Antioxidant defense enzymes such as catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) significantly elevated in the leaves and roots of plantlets at higher EC levels. This increase could reflect a defense response to the cellular damage provoked by higher EC levels in the nutrient solution.