Effects of continuous hypergravity stimuli on the amounts and composition of cell wall constituents were investigated in wheat shoots. Hypergravity (300 g) treatment for three days after germination increased the net amount of cell wall polysaccharides such as hemicellulose and cellulose, but reduced the shoot elongation. As a result, the amount of cell wall polysaccharides per unit length of shoot increased under hypergravity. The hemicellulose fraction contained polysaccharides in the middle and low molecular mass range (5 kDa-1 MDa) and increased in response to hypergravity. Also, the amounts of arabinose (Ara) and xylose (Xyl), the major sugar components of the hemicellulose fraction, increased under hypergravity conditions. In addition to wall polysaccharides, hypergravity increased the amounts of cell wall-bound phenolic acids, such as ferulic acid (FA) and diferulic acid (DFA). Furthermore, the activity of phenylalanine ammonia-lyase (PAL, EC 184.108.40.206) was enhanced under hypergravity conditions. These results suggest that continuous hypergravity stimulates the synthesis of cell wall constituents, especially hemicellulosic arabinoxylans and cell wall-bound FA and DFA in wheat shoots. The increased PAL activity may promote the formation of FA and DFA. These changes in cell wall architecture may be involved in making rigid and tough cell walls under hypergravity conditions and thereby contribute to the ability of plant to sustain their structures against gravitational stimuli.
Research Containing: Wheat
Increase in the level of arabinoxylan–hydroxycinnamate network in cell walls of wheat coleoptiles grown under continuous hypergravity conditions
Changes in the amount and composition of cell wall constituents in response to continuous hypergravity stimuli were studied in wheat (Triticum aestivum L.) coleoptiles. The lengths of coleoptiles grown under hypergravity (300 g) conditions for 2–4 days from germination stage were 60–70% of those of 1 g control. However, the net amounts of hemicellulosic polysaccharides and cellulose in hypergravity-treated coleoptiles increased progressively as much as those in the control coleoptiles. As a result, their contents per unit length of coleoptile largely increased under hypergravity conditions. In the hemicellulose fraction, the amounts of arabinose and xylose, the major components of the fraction, prominently increased in response to hypergravity. When hemicellulosic polysaccharides were separated into neutral and acidic polymers by an anion-exchange column, the amounts of the acidic fraction consisting of (glucurono)arabinoxylans were higher in hypergravity-treated coleoptiles than in control coleoptiles. The amounts of cell wall-bound ferulic acid and diferulic acid (DFA) increased dramatically in both 1 g control and hypergravity-treated coleoptiles. Particularly, the amounts of DFA in hypergravity-treated coleoptiles were significantly higher than those in control coleoptiles during the incubation period. These results suggest that continuous hypergravity increases the rigid network structures via arabinoxylan–hydroxycinnamate cross-links within cell wall architecture in wheat coleoptiles. These structures may have a load-bearing function and contribute to construct the stable cell wall against the gravitational force.
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 (microg) 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 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, CO(2), and planting density were used as ground controls. At the morphological level, there was little difference in the development of cells of wheat under microg conditions. Leaves developed in mug have thinner cross-sectional area than the 1g grown plants. Ultrastructurally, the chloroplasts of microg grown plants were more ovoid than those developed at 1g, 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 microg or 1g conditions. Furthermore, no differences in gene expression were detected leaf samples collected at microg from 24-day-old leaves, suggesting that the spaceflight environment had minimal impact on wheat metabolism.
Wheat (Triticum Aesativum L. cv. USU Apogee) Growth Onboard the International Space Station (ISS): Germination and Early Development
A series of experiments to determine the effects of microgravity on growth and development of wheat were conducted during a 73-day period onboard the International Space Station. The experiment relied upon telescience for the remote operation, monitoring, and management of the experiment. Growth and development of wheat was measured directly by the ISS crew, estimated from analysis of telemetry data, and quantified with digital image analysis. On-orbit germination rates of stowed root modules containing seed cassettes were greater than 95%. Absolute growth rates of ~4.25 cm per day were observed in both the flight and ground control plants. Final height of plants on orbit was approximately 10% greater than comparable ground controls. The results suggest that early growth and development of wheat can be consistently achieved in long-duration space experiments.
The PESTO (Photosynthetic Experiment System Testing and Operation) experiment flew in the Biomass Production System (BPS) to International Space Station (ISS) on STS-110 (Atlantis) April 8, 2002, and returned on STS-111 (Endeavour) June 19, 2002, after 73 days in space. The ground control was conducted on a two-week delay at Kennedy Space Center in a BPS unit under environmental conditions comparable to ISS. Wheat ( Triticum aestivum cv Apogee) and Brassica rapa cv Astroplant were independently grown in root modules for multiple grow-outs. On-orbit harvests, root modules exchanges and primings, seeds imbibitions, and gas and water samplings occurred at periodic intervals; all were replicated in ground controls. Many operations required crew handling and open access to individual chambers, allowing the exchange of microorganisms between the crew environment and the BPS modules. Upon landing, BPS surfaces, containment bags, root modules, and plant material were swabbed for recovery of microbes. Water samples were collected from BPS nutrient delivery and humidity control systems (HCS), root modules, and wastewater bags. Swabs and liquid samples were plated onto selective media; microbial and fungal colonies were identified to the species level by metabolic profiling when possible. Differences in bacterial and fungal species and the number of species identified were detected between the flight and ground controls.