Photosynthetic capacity and dry mass partitioning in dwarf and semi-dwarf wheat (Triticum aestivum L.)

Efficient use of space and high yields are critical for long-term food prod uction aboard the International Space Station. The selection of a full dwar f wheat (less than 30 cm tall) with high photosynthetic and yield potential is a necessary prerequisite for growing wheat in the controlled, volume-li mited environments available aboard long-term spaceflight missions. This st udy evaluated the photosynthetic capacity and carbon partitioning of a full -dwarf wheat cultivar, Super Dwarf, which is routinely used in spaceflight studies aboard U.S. space shuttle and NASA/Mir missions and made comparison s with other dwarf and semidwarf wheat cultivars utilized in other ground-b ased studies in plant space biology. Photosynthetic capacity of the flag le af in two dwarf (Super Dwarf, BB-19), and three semi-dwarf (Veery-10, Yecor a Rojo, IBWSN 199) wheat cultivars (Triticum aestivum L.) was assessed by m easuring: net maximum photosynthet ic rate, RuBP carboxylation efficiency, chlorophyll concentration and flag leaf area. Dry mass partitioning of carb ohydrates to the leaves, sheaths, stems and ear was also assessed. Plants w ere grown under controlled environmental conditions in three replicate stud ies: slightly enriched CO2 (370 mu mol mol(-1)), high photosynthetic photon flux (1000 mu mol m(-2) s(-1); 58 mol m(-2) d(-1)) for a 16 h photoperiod, 22/15 degrees C day/night temperatures, ample nutrients and water provided by one-half strength Hoagland's nutrient solution (Hoagland and Amen, 1950 ). Photosynthetic capacity of the flag leaf was determined at anthesis usin g net CO2 exchange rate versus internal CO2 concentration curves measured u nder saturating light (2000 mu mol m(-2) s(-1)) and CO2 (1000 mu mol mol(-1 )). Dwarf wheat cultivars had greater photosynthetic capacities than the ta ller semi-dwarfs, they averaged 20 % higher maximum net photosynthetic rate s compared to the taller semi-dwarfs, but these higher rates occurred only at anthesis, had slightly greater carboxylation efficiencies and significan tly increased chlorophyll concentrations per unit leaf area. The reduced-he ight wheat had significantly less dry mass fraction in the stem but greater dry mass partitioned to the ear than the taller semi-dwarfs (Yecora rojo, IBWSN-199). Studies with detached heads confirm that the head is a signific ant sink in the shorter wheat cultivars.