Shuhei Fujii

Growth promotion and an increase in cell wall extensibility by silicon in rice and some other Poaceae seedlings.

Abstract The effect of silicon on organ growth and its mechanisms of action were studied in rice (Oryza sativa L. cv. Koshihikari), oat (Avena sativa L. cv. Victory), and wheat (Triticum aestivum L. cv. Daichino-Minori) seedlings grown in the dark. Applying silicon in the form of silicic acid to these seedlings via culture solution resulted in growth promotion of third (rice) or second (oat and wheat) leaves. The optimal concentration of silicon was 5–10 mM. No growth promotion was observed in early organs, such as coleoptiles or first leaves. In silicon-treated rice third leaves, the epidermal cell length increased, especially in the basal regions, without any effect on the number of cells, showing that silicon promoted cell elongation but not cell division. Silicon also increased the cell wall extensibility significantly in the basal regions of rice third leaves. These results indicate that silicon stimulates growth of rice and some other Poaceae leaves by increasing cell wall extensibility.

Growth and Development, and Auxin Polar Transport in Higher Plants under Microgravity Conditions in Space: BRIC-AUX on STS-95 Space Experiment

The principal objectives of the space experiment, BRIC-AUX on STS 95, were the integrated analysis of the growth and development of etiolated pea and maize seedlings in space and a study of the effects of microgravity conditions in space on auxin polar transport in these segments. Microgravity significantly affected the growth and development of etiolated pea and maize seedlings. Epicotyls of etiolated pea seedlings were the most oriented toward about 40 to 60 degrees from the vertical. Mesocotyls of etiolated maize seedlings were curved at random during space flight but coleoptiles were almost straight. Finally the growth inhibition of these seedlings in space was also observed. Roots of some pea seedlings grew toward to the aerial space of Plant Growth Chamber. Extensibilities of cell walls of the third internode of etiolated pea epicotyls and the top region of etiolated maize coleoptiles, which were germinated and grown under microgravity conditions in space, were significantly low as compared with those grown on the ground of the earth. Activities of auxin polar transport in the second internode segments of etiolated pea seedlings and coleoptile segments of etiolated maize seedlings were significantly inhibited and promoted, respectively, under microgravity conditions in space. These results strongly suggest that auxin polar transport as well as the growth and development of plants is controlled under gravity on the earth.

Effects of sodium chloride on the fatty acids composition in Boekelovia hooglandii (Ochromonadales, Chrysophyceae)

Composition of fatty acids in Boekelovia hooglandii Nicolai et Baas Becking (Chrysophyceae) was investigated as a function of salinity. It was confirmed by gas chromatography that the composition of fatty acids in cells cultured in a 50 mmol L−1 NaCl medium consisted of C14:0, C15:0, C16:0, C16:1, C18:0, C18:1, C18:2, C18:3, C18:4, C20:0, C20:4, C20:5, C22:5 and C22:6, in which C14:0, C16:0, C16:1, C18:4, C20:0, C20:5, C22:5 and C22:6 were main constituents. When the cells were cultured in a medium with different concentrations of NaCl ranging from 50 to 800 mmol L−1, the mole percentage of fatty acids such as C14:0, C16:0 and C16:1 decreased with increases in the salinity, while the mole percentage of highly polyunsaturated fatty acids such as C18:4, C20:5, C22:5 and C22:6 increased. When the cells were transferred from a 200 mmol L−1 NaCl medium to a 600 mmol L−1 NaCl medium, a decrease in mole percentage of C14:0, C16:0 and C16:1, and an increase in C18:4, C20:5, C22:5 and C22:6 were observed within 4 h. However, no change in the compositions of fatty acids was observed within 4 h when the cells were transferred from a 600 mmol L−1 NaCl medium to a 200 mmol L−1 NaCl one. The increase in the content of highly polyunsaturated fatty acids was considered to reflect the rapid response to upshock and to be the characteristic of salt tolerance in B. hooglandii.

Occurrence of jasmonic acid in Dunaliella (Dunaliellales, Chlorophyta)

The occurrence of jasmonic acid and related compounds in Dunaliella species was investigated using gas‐liquid chromatography/mass spectroscopy (GCY MS). Jasmonic acid was identified in the ethyl acetate soluble‐acidic fraction of Dunaliella tertiolecta and Dunaliella salina (Dunal) Teodoresco, The concentration of jasmonic acid in D. salina. which is extremely halophilic, was much higher than that in D. tertiolecta Butcher, These results indicate that jasmonic acid might play an important role in salt‐tolerance in Dunaliella.

Growth and Development in Arabidopsis thaliana through an Entire Life Cycle under Simulated Microgravity Conditions on a Clinostat

Arabidopsis thaliana ecotype Columbia and Landsberg erecta were studied. Horizontal clinorotation affected little germination of seeds, growth and development of rosette leaves and roots during early vegetative growth stage, and the onset of the bolting of inflorescence axis and flower formation in reproductive growth stage, although it suppressed elongation of inflorescence axes. The clinorotation substantially reduced the numbers of siliques and seeds in Landsberg erecta, and completely inhibited seed production in Columbia. Seeds produced in Landsberg erecta on the clinostat were capable of germinating and developing rosette leaves normally on the ground. On the other hand, growth of pin-formed mutant (pin/pin) of Arabidopsis ecotype Enkheim, which has a unique structure of inflorescence axis with no flower and extremely low levels of auxin polar transport activity, was inhibited and the seedlings frequently died during vegetative stage on the clinostat. Seed formation and inflorescence growth of the seedlings with normal shape (pin/+ or +/+) were also suppressed on the clinostat. These results suggest that the growth and development of Arabidopsis, especially in reproductive growth stage, is suppressed under simulated microgravity conditions on a clinostat. To complete the life cycle probably seems to be quite difficult, although it is possible in some ecotypes.

The influence of applied hydrostatic pressure on gel formation of a (1→3)-β-d-glucan

Abstract Aqueous suspensions of (1→3)-β- d -glucan were gelated under high pressure (1–10000 atm) at temperatures of 57.4, 59.0, 61.0, and 64.5°. The elasticity of the gel, prepared under defined conditions, was determined by measuring the change of gel size under low compression (0.6 gw/cm2). The results indicate that the elasticity decreases initially with increasing pressure, but then increases as the pressure is increased. Raising the temperature shifted to higher pressure the range of applied pressure at which the minimum elasticity was observed. The lowering of elasticity by high-pressure treatment may be attributed to a decrease of free water as solvent, brought about by compression. Increasing elasticity with application of higher pressure may arise from the promotion of hydrogen bonding by compression.

Two Types of Water Passages in Okra Hypocotyls

Abrasion of okra hypocotyl segments with carborundum enhances the rate of water uptake into segments, while it decreases the response to auxin. Incubation of abraded segments in buffer recovers the decreased response to auxin. In abraded segments, mercuric chloride is found to inhibit auxin-induced cell elongation. When abraded segments were soaked in 0.3M sorbiiol, they maintained the ability to shrink in the presence of mercury. In contrast, when abraded segments were soaked in a 0.1M sorbitol solution, mercury completely suppressed osmotic shrinkage. These results suggest that water flows through at least two types of passages; One, which is resistant to mercury, requires a high osmotic pressure such as that provided by 0.3 M sorbitol. The other, which is vulnerable to mercury, requires a low osmotic pressure for water to pass through it.

Graviresponse in Eichhornia cressipes (water hyacinth) II. Hormone involvement in graviresponse in the peduncle

Summary The effects of decapitation of the inflorescence and application of hormones and related substances on the bending of the peduncle cutting and the isolated peduncle segment were observed and the following results were obtained. (1) With isolated cuttings excised at the base of the peduncle cultured in test tubes, the bending of the peduncle normally occurred at a slower rate than in intact plants. (2) Removal of whole flowers and flower buds 10 or more h before full flowering inhibited the bending but that of petals did not. Flower removal at or after full flowering did not affect the bending response. (3) The bending in intact plants was eliminated when 2,3,5-triiodobenzoic acid (TIBA), an antiauxin preventing polar transport of auxin, was applied to the upper most region of the peduncle in a lanolin ring. However, indole-3-acetic acid (IAA) at a concentration of 10 −6 to 10 −4 and gibberellin (GA) at 10 −4 M exogenously applied from the basal cut ends of the peduncle in the test tube inhibited the bending. IAA, 3 mg/g lanolin, and GA, 3 mg/g lanolin, applied to the top cut end of the peduncle also inhibited the bending. (4) Exogenously applied hormones showed no significant effect on elongation of the isolated peduncles but GA applied to intact plants promoted the elongation of petioles and inhibited the formation of floats on the petiole. (5) Aminooxy-acetic acid (AOA), 3 mg/g lanolin, an ethylene inhibitor, applied to the segments of the peduncle excised at the time of full flowering inhibited the curvature. (6) Segments excised less than 6 h after the start of flowering showed a negative response and those excised after the flowering phase showed a bending response. From the above results it appears that a subtle balance of IAA and ethylene in the peduncle is necessary for the manifestation of the bending, whereas gibberellins and relatively high concentrations (more than 10 −6 M) of auxins serve to maintain the normal negative gravitropic response in the peduncle.