Microgravity effects on leaf morphology, cell structure, carbon metabolism and mRNA expression of dwarf wheat

The use of higher plants as the basis for a biological life support system that regenerates the atmosphere, purifies water, and produces food has been proposed for long duration space missions. The objective of these experiments was to determine what effects microgravity (mu g) had on chloroplast development, carbohydrate metabolism and gene expression in developing leaves of Triticum aestivum L. cv. USU Apogee. Gravity naive wheat plants were sampled from a series of seven 21-day experiments conducted during Increment IV of the International Space Station. These samples were fixed in either 3% glutaraldehyde or RNAlater (TM) or frozen at -25 degrees C for subsequent analysis. In addition, leaf samples were collected from 24- and 14-day-old plants during the mission that were returned to Earth for analysis. Plants grown under identical light, temperature, relative humidity, photoperiod, CO2, and planting density were used as ground controls. At the morphological level, there was little difference in the development of cells of wheat under mu g conditions. Leaves developed in mu g have thinner cross-sectional area than the 1 g grown plants. Ultrastructurally, the chloroplasts of mu g grown plants were more ovoid than those developed at 1 g, and the thylakoid membranes had a trend to greater packing density. No differences were observed in the starch, soluble sugar, or lignin content of the leaves grown in mu g or 1 g conditions. Furthermore, no differences in gene expression were detected leaf samples collected at mu g from 24-day-old leaves, suggesting that the spaceflight environment had minimal impact on wheat metabolism.