Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis of dwarf wheat

• Published in: Planta 2005-12, Vol.223 (1), p.46-56
• Main Authors: Stutte, G.W, Monje, O, Goins, G.D, Tripathy, B.C
• Format: Article
• Language: English
• Subjects: Apogees; Biological and medical sciences; Canopies; canopy; Carbon Dioxide; Chlorophyll - metabolism; Compensation; dwarf cultivars; Electron Transport; electron transport chain; Experiments; Fundamental and applied biological sciences. Psychology; Leaves; Life Support Systems; Light; light intensity; Metabolism; Microgravity; Photosynthesis; Photosynthesis, respiration. Anabolism, catabolism; photosystem I; Photosystem I Protein Complex - metabolism; photosystem II; Photosystem II Protein Complex - metabolism; Plant growth; Plant Leaves - metabolism; Plant physiology and development; Plant roots; Plants; Respiration; Space Flight; Space stations; thylakoids; Thylakoids - metabolism; Triticum - growth & development; Triticum - metabolism; Triticum - physiology; Triticum aestivum; Vegetation canopies; Weightlessness; Wheat
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-005-0066-2

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21-24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 micromol m-2 s-1) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 micromol m-2 s-1) and CO2 (4000 micromol mol-1) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at approximately 280 micromol m-2 s-1 were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO2 compensation (121 vs. 118 micromol mol-1) and PPF compensation (85 vs. 81 micromol m-2 s-1) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.