Sap flow is an important indicator of transpiration and plant growth. The objectives of this study were to develop a simple method to measure sap flow in stems or petioles of herbaceous plants and monitoring sap flow under low gravity in space. We created an index of sap flow (ISF) based on the petiole surface temperature distribution around a tiny heated point in a simulated plant and sweetpotato plants. In results, the ISF was related linearly (r=0.90) with the sap flow rate actually measured in sweetpotato petioles and usefulness and convenience of this method were confirmed easily monitoring sap flow.
The effects of hypergravity on growth and dynamics of actin filaments were examined in azuki bean (Vigna angularis) epicotyls. Elongation growth occurred mainly in the apical region of epicotyls, which was inhibited by hypergravity at 300 G. The density of actin filaments in epidermal cells decreased from the apical to the basal regions of epicotyls, irrespective of the gravitational conditions, and in the apical region of epicotyls, hypergravity decreased the density. Actin filaments were arranged with longitudinal or radial direction in the epidermal cells of apical region of 1 G-grown epicotyls. On the other hand, actin filaments with transverse direction were observed in basal region of epicotyls grown at 1 G. Similar changes in the arrangement of actin filaments toward the basal region were observed even under hypergravity conditions. Hypergravity had no effects on the growth and reorientation of cortical microtubules, when actin filaments were disrupted by cytochalasin D treatment. These results suggest that modification of dynamics of actin filaments is responsible for reorientation of cortical microtubules, which leads to inhibition of elongation growth in azuki bean epicotyls under hypergravity conditions.
Our previous spaceflight experiment CERISE showed that gene and protein expression levels of muscular components, cytoskeleton, and mitochondrial enzymes are altered in space flown wild-type C. elegans. To confirm and clarify whether the C. elegans muscle fibers and mitochondrial network are physically altered in response to microgravity, this Nematode Muscles project was designed with wild-type and several mutant lines with GFP expression. This investigation also studied whether microgravity could affect the insulin/IGF-1 (Insulin-like growth factor -1) and/or TGF-β signaling by imaging DAF-16::GFP fusion protein. Wild-type and several mutants were grown in a culture bag kept under microgravity or 1G centrifuge conditions on board ISS for 4 days starting from L1 larva. All samples were fixed on board and recovered, to be analyzed on the earth. The worms did not grow well in the μG culture bag probably due to unexpected air bubbles. Therefore, DAF-16 activation observed in larval worms in μG and not in 1G may be attributed to starvation instead of μG response. In 1G samples, we could successfully find normal mitochondrial network. We also found that chemical fixation using CFA is an effective method for preservation of GFP containing C. elegans in space environment.
We propose radiation shielding using Martian magnetic anomalies to protect human crews on the Martian surface. We have simulated the trajectories of energetic protons using the Buneman-Boris method to measure how magnetic anomalies affect the impact rate on the Martian surface. Protons from the west can be completely eliminated, while those from the east are concentrated on the area between the magnetic poles. This would mean crews would need to concern themselves about radiation from the vertex and east only. A Martian magnetic anomaly can therefore be used to realize continuous and efficient radiation shielding.