Merab A. Chan1 and Jann Conroy2
Department of Biology, Ateneo de Manila University, Loyola Heights, Quezon City 1108
School of Science, Food and Horticulture, University of Western
Sydney, Hawkesbury, New South Wales, Australia
http://doi.org/10.57043/transnastphl.2000.5394
Abstract
The observation that sucrose supply increased growth, especially in the presence of CO2 in the headspace during the light period and provision of higher photon flux density (PFD), indicated that carbohydrates were limiting at 350 mL CO2·L^-1. Hence, in the present study, CO2 in the headspace was enriched to 2,000 µL·L^-1 to investigate whether sucrose could be eliminated from the media and fully autotrophic Pinus radiata plants could be produced in vitro. In the first experiment, sucrose was supplied at 0%, 3%, and 6% at a PFD of 150 µmol·m^-2·s^-1. Dry matter production and shoot height were greatly enhanced by CO2 enrichment at all sucrose levels, indicating that CO2 enhances autotrophy. In addition, vitrified shoots were never observed at 2,000 µL CO2·L^-1, and the number of senescent shoots was reduced. Increasing the sucrose supply from 0% to 3% stimulated growth even at elevated CO2. On the assumption that more photosynthetic reducing power may have been required to fully develop autotrophy, the PFD was raised to 280 µmol·m^-2·s^-1 in the second experiment, and sucrose was supplied as in the first experiment. Substantial improvement of growth was achieved with a combination of high PFD and elevated CO2, showing that these factors could partially substitute for an external sucrose supply. Maximum growth was achieved at 6% sucrose, 280 µmol·photons·m^-2·s^-1, and 2,000 µL CO2·L^-1. The requirement for extra sucrose was observed despite a large accumulation of starch at high CO2. Although the reason for this starch accumulation is unknown, it may prove beneficial at planting out.