Demonstration of osmotically dependent promotion of aerenchyma formation at different levels in the primary roots of rice using a 'sandwich' method and X-ray computed tomography

Background and Aims

The effect of environmental factors on the regulation of aerenchyma formation in rice roots has been discussed for a long time, because aerenchyma is constitutively formed under aerated conditions. To elucidate this problem, a unique method has been developed that enables sensitive detection of differences in the development of aerenchyma under two different environmental conditions. The method is tested to determine whether aerenchyma development in rice roots is affected by osmotic stress.

Methods

To examine aerenchyma formation both with and without mannitol treatment in the same root, germinating rice (Oryza sativa) caryopses were sandwiched between two agar slabs, one of which contained 270 mm of mannitol. The roots were grown touching both slabs and were thereby exposed unilaterally to osmotic stress. As a non-invasive approach, refraction contrast X-ray computed tomography (CT) using a third-generation synchrotron facility, SPring-8 (Super photon ring 8 GeV, Japan Synchrotron Radiation Research Institute), was used to visualize the three-dimensional (3-D) intact structure of aerenchyma and its formation in situ in rice roots. The effects of unilateral mannitol treatment on the development of aerenchyma were quantitatively examined using conventional light microscopy.

Key Results

Structural continuity of aerenchyma was clearly visualized in 3-D in the primary root of rice and in situ using X-ray CT. Light microscopy and X-ray CT showed that the development of aerenchyma was promoted on the mannitol-treated side of the root. Detailed light microscopic analysis of cross-sections cut along the root axis from the tip to the basal region demonstrated that aerenchyma developed significantly closer to the root tip on the mannitol-treated side of the root.

Conclusions

Continuity of the aerenchyma along the rice root axis was morphologically demonstrated using X-ray CT. By using this ‘sandwich’ method it was shown that mannitol promoted aerenchyma formation in the primary roots of rice.     

On the reflex coactivation of ankle flexor and extensor muscles induced by a sudden drop of support surface during walking in humans.

Recent studies have revealed that the stretch reflex responses of both ankle flexor and extensor muscles are coaugmented in the early stance phase of human walking, suggesting that these coaugmented reflex responses contribute to secure foot stabilization around the heel strike. To test whether the reflex responses mediated by the stretch reflex pathway are actually induced in both the ankle flexor and extensor muscles when the supportive surface is suddenly destabilized, we investigated the electromyographic (EMG) responses induced after a sudden drop of the supportive surface at the early stance phase of human walking. While subjects walked on a walkway, the specially designed movable supportive surface was unexpectedly dropped 10 mm during the early stance phase. The results showed that short-latency reflex EMG responses after the impact of the drop (<50 ms) were consistently observed in both the ankle flexor and extensor muscles in the perturbed leg. Of particular interest was that a distinct response appeared in the tibialis anterior muscle, although this muscle showed little background EMG activity during the stance phase. These results indicated that the reflex activities in the ankle muscles certainly acted when the supportive surface was unexpectedly destabilized just after the heel strike during walking. These reflex responses were most probably mediated by the facilitated stretch reflex pathways of the ankle muscles at the early stance phase and were suggested to be relevant to secure stabilization around the ankle joint during human walking.     

Chromatic Regulation of Photosystem Composition in the Cyanobacterial Photosynthetic System: Kinetic Relationship between Change of Photosystem Composition and Cell Proliferation

Kinetics of the change of photosystem (PS) composition in cyanobacteriainduced by chromatic light were studied in relation to cellproliferation. The study was made for two unicellular strains,Synechococcus NIBB 1059 and Synechocystis (Aphanocapsa) PCC6714. We found that (1) the change to a higher or lower PS I/IIratio was due to acceleration or suppression of apparent PSI formation, and (2) it progressed on a similar time scale tothat of the cell proliferation. The apparent rate constant ofthe change in the PS I/II ratio was proportional to that ofcell proliferation, µ, when this was low, but at highvalues of µ the increase in the rate constant of the changein the PS I/II ratio became smaller, causing a deviation fromthe linear relationship. Results indicate that under autotrophicconditions, the photoregulated composition change occurs asa result of thylakoid development, which accompanies cell proliferation. (Received June 23, 1986; Accepted December 5, 1986)     

Incorporation of ZP1 into perivitelline membrane after in vivo treatment with exogenous ZP1 in Japanese quail (Coturnix japonica)

In birds, the egg envelope surrounding the oocyte prior to ovulation is called the perivitelline membrane and it plays important roles in fertilization. In a previous study we demonstrated that one of the components of the perivitelline membrane, ZP3, which is secreted from the ovarian granulosa cells, specifically interacts with ZP1, another constituent that is synthesized in the liver of Japanese quail. In the present study, we investigated whether ZP1 injected exogenously into the blood possesses the ability to reconstruct the perivitelline membrane of Japanese quail. When ZP1 purified from the serum of laying quail was injected into other female birds, the signal of this exogenous ZP1 was detected in the perivitelline membrane. In addition, we revealed, by means of ligand blot analysis, that serum ZP1 interacts with both ZP1 and ZP3 of the perivitelline membrane. By contrast, when ZP1 derived from the perivitelline membrane was administered, it failed to become incorporated into the perivitelline membrane. Interestingly, serum ZP1 recovered from other Galliformes, including chicken and guinea fowl, could be incorporated into the quail perivitelline membrane, but the degree of interaction between quail ZP3 and ZP1 of the vitelline membrane of laid eggs from chicken and guinea fowl appeared to be weak. These results demonstrate that exogenous ZP1 purified from the serum, but not ZP1 from the perivitelline membrane, can become incorporated into the perivitelline membrane upon injection into other types of female birds. To our knowledge, this is the first demonstration that the egg envelope component, when exogenously administered to animals, can reconstruct the egg envelope in vivo.     

Assembly of the mitochondrial membrane system: isolation of nuclear and cytoplasmic mutants of Saccharomyces cerevisiae with specific defects in mitochondrial functions.

A selection procedure is described which permits a large number of Saccharomyces cerevisiae mutants to be screened for specific lesions in mitochondrial respiratory enzymes and the adenosine triphosphatase. The method has been used to isolate nuclear mutant strains with specific lesions in coenzyme QH2-cytochrome c reductase, cytochrome oxidase, and adenosine triphosphatase. In addition, two cytoplasmic mutants have been found whose primary defect is in cytochrome oxidase, and others have been found that show variable degrees of abnormalities in their mitochondrial translation products.     

Assembly of the mitochondrial membrane system. Characterization of nuclear mutants of Saccharomyces cerevisiae with defects in mitochondrial ATPase and respiratory enzymes.

Mutants of Saccharomyces cereviaiae showing defects in cytochrome oxidase, coenzyme QH2-cytochrome c reductase, and rutamycin-sensitive ATPase are described. The mutations have been established to be nuclear, based on complementation with a cytoplasmic petite tester strain and 2:2 segregation of tetrads. Genetic analysis indicate the coenzyme QH2-cytochrome c reductase and cytochrome oxidase mutants fall into 9 and 10 different complementation groups, respectively. The mutants also form distinct classes based on absorption spectra of the mitochondrial cytochromes. Two of the ATPase mutants lack detectable F1 ATPase, while the third synthesizes F1 but does not integrate it into a membrane complex. The latter mutant is missing one of the mitochondrially synthesized subunits of the rutamycin-sensitive ATPase complex.     

Embryonic development of the sea butterfly Desmopterus papilio (Gastropoda: Thecosomata)

The embryonic development of the thecosome Desmopterus papilio is described for the first time. The mature individual produced a round-shaped egg mass containing ca. 200 fertilised eggs. First cleavage was observed 15 min after the release of the egg mass. Embryos showed typical molluscan spiral cleavage: macromeres produced the first and second quartets of micromeres in clockwise and counterclockwise directions, respectively. A trochophore larva hatched from the egg capsule 28 h after the release of the egg mass. Thereafter, the larva secreted a primary shell at the posterior part, developing into the veliger stage. These findings may be useful for future work on postembryonic development, especially on the loss of the veliger shell, in the genus Desmopterus which is the only group of thecosome species without a shell in the adult stage.     

Uncertainty of knee joint muscle activity during knee joint torque exertion: the significance of controlling adjacent joint torque.

In the single-joint torque exertion task, which has been widely used to control muscle activity, only the relevant joint torque is specified. However, the neglect of the neighboring joint could make the procedure unreliable, considering our previous result that even monoarticular muscle activity level is indefinite without specifying the adjacent joint torque. Here we examined the amount of hip joint torque generated with knee joint torque and its influence on the activity of the knee joint muscles. Twelve healthy subjects were requested to exert various levels of isometric knee joint torque. The knee and hip joint torques were obtained by using a custom-made device. Because no information about hip joint torque was provided to the subjects, the hip joint torque measured here was a secondary one associated with the task. The amount of hip joint torque varied among subjects, indicating that they adopted various strategies to achieve the task. In some subjects, there was a considerable internal variability in the hip joint torque. Such variability was not negligible, because the knee joint muscle activity level with respect to the knee joint torque, as quantified by surface electromyography (EMG), changed significantly when the subjects were requested to change the strategy. This change occurred in a very systematic manner: in the case of the knee extension, as the hip flexion torque was larger, the activity of mono- and biarticular knee extensors decreased and increased, respectively. These results indicate that the conventional single knee joint torque exertion has the drawback that the intersubject and/or intertrial variability is inevitable in the relative contribution among mono- and biarticular muscles because of the uncertainty of the hip joint torque. We discuss that the viewpoint that both joint torques need to be considered will bring insights into various controversial problems such as the shape of the EMG-force relationship, neural factors that help determine the effect of muscle strength training, and so on.     

Kin recognition affects plant communication and defence

The ability of many animals to recognize kin has allowed them to evolve diverse cooperative behaviours; such ability is less well studied for plants. Many plants, including Artemisia tridentata, have been found to respond to volatile cues emitted by experimentally wounded neighbours to increase levels of resistance to herbivory. We report that this communication was more effective among A. tridentata plants that were more closely related based on microsatellite markers. Plants in the field that received cues from experimentally clipped close relatives experienced less leaf herbivory over the growing season than those that received cues from clipped neighbours that were more distantly related. These results indicate that plants can respond differently to cues from kin, making it less likely that emitters will aid strangers and making it more likely that receivers will respond to cues from relatives. More effective defence adds to a growing list of favourable consequences of kin recognition for plants.