Hiroaki Hirai

Effects of gravity on transpiration of plant leaves.

To clarify effects of gravity on the water vapor exchange between plants and the ambient air, we evaluated the transpiration rate of plant leaves at 0.01, 1.0, and 2.0 g for 20 s each during parabolic airplane flights. The transpiration rates of a strawberry leaf and a replica leaf made of wet cloth were determined using a chamber method with humidity sensors. Absolute humidity at 3 and 8 mm below the lower surface of leaves was measured to evaluate the effect of gravity on humidity near leaves and estimate their transpiration rate. The transpiration rate of the replica leaf decreased by 42% with decreasing gravity levels from 1.0 to 0.01 g and increased by 31% with increasing gravity levels from 1.0 to 2.0 g. Absolute humidity near the intact strawberry leaf was 5 g m−3 at ambient absolute humidity of 2.3 g m−3 and gravity of 1.0 g. The absolute humidity increased by 2.5 g m−3 with decreasing gravity levels from 1.0 to 0.01 g. The transpiration rate of the intact leaf decreased by 46% with decreasing gravity levels from 1.0 to 0.01 g and increased by 32% with increasing gravity levels from 1.0 to 2.0 g. We confirmed that the transpiration rate of leaves was suppressed by retarding the water vapor transfer due to restricted free air convection under microgravity conditions.

Growth characteristics and yield of carrots grown in a soil ridge with a porous tube for soil aeration in a wet lowland

The growth characteristics and yield of carrots grown in a soil ridge with an aeration treatment were compared with those of carrots grown in a conventional ridge as a control under wet lowland field conditions. For the aeration treatment, a plastic porous tube was placed in the soil ridge. Water depth between the ridges in the aeration treatment and the control was kept at 20 mm throughout the growing period in order to imitate the wet soil conditions in tropical and subtropical lowlands. The fresh and dry weights of the storage root were 1.9 and 1.7 times greater, respectively, in the aeration treatment than in the control. The maximum root length in the aeration treatment was 1.8 times greater than in the control. The length of the leaf lamina and the leaf area per plant were greater in the aeration treatment than in the control. The fresh and dry weights of the total phytomass per plant were approximately 1.6 times greater in the aeration treatment than in the control. The fresh weight of the above-ground part was 1.3 times greater in the aeration treatment than in the control. The net photosynthetic rate and edible biomass index were greater in the aeration treatment than in the control. Carrot production in wet lowlands is possible if adequate aeration of the soil ridges is provided.

Hypolipidemic Effects of Starch and γ-Oryzanol from wx/ae Double-Mutant Rice on BALB/c.KOR-Apoe shl Mice

waxy/amylose-extender (wx/ae) double-mutant japonica rice (Oryza sativa L.) produces resistant starch (RS) and a large amount of γ-oryzanol. Our previous study has shown the hypolipidemic effect of wx/ae brown rice on mice. To identify the functional constituents of the hypolipidemic activity in wx/ae rice, we prepared pure wx/ae starch and γ-oryzanol from wx/ae rice and investigated their effect on the lipid metabolism in BALB/c.KOR/Stm Slc-Apoe shl mice. The mice were fed for 3 weeks a diet containing non-mutant rice starch, non-mutant rice starch plus γ-oryzanol, wx/ae starch, or wx/ae starch plus γ-oryzanol. γ-Oryzanol by itself had no effect on the lipid metabolism, and wx/ae starch prevented an accumulation of triacylglycerol (TAG) in the liver. Interestingly, the combination of wx/ae starch plus γ-oryzanol not only prevented a TAG accumulation in the liver, but also partially suppressed the rise in plasma TAG concentration, indicating that wx/ae starch and γ-oryzanol could have a synergistic effect on the lipid metabolism.

Growth and ajoene concentrations in garlic plants cultured hydroponically with different aeration regimes

Summary A hydroponic culture system was developed for producing garlic bulbs and roots containing a precursor of ajoene. Garlic plants were cultured in a growth chamber under artificial lighting for 2 months at air temperatures of 25º/21ºC (light/dark), relative humidities of 75%/90% (light/dark), a photosynthetic photon flux density of 450 µmol m–2 s–1, and a photoperiod of 12 h d–1. The growth and ajoene concentrations of garlic plants cultured hydroponically with different aeration regimes were compared in order to examine the effects of dissolved O2 levels on these parameters. The four aeration treatments included 12 h dark-time aeration (12 h-D), 12 h illuminated-time aeration (12 h-L), 24 h continuous aeration (24 h) using a pump, or no aeration (control). Dissolved O2 concentrations increased in the order: 24 h >12 h-L >12 h-D > control. Fresh weights (FW), dry weights (DW), and ajoene concentrations were increased in each part of the garlic plants by increasing the levels of dissolved O2. The FWs of bulbs, leaves, and roots in the 24 h aeration treatment were 27.7, 41.4, and 80.3 g per plant, respectively. These values were 4.3-, 2.0-, and 5.6-times higher, respectively, than those in the controls. The ajoene contents of bulbs, leaves, and roots were 18.7, 6.7, and 14.6 mg per plant, respectively, in the 24 h treatment, which were 6.4-, 5.2-, and 11.2-times higher, respectively, than those in the controls. In conclusion, garlic plants grown at higher levels of dissolved O2 showed higher growth rates and greater ajoene contents. The roots of garlic plants cultured hydroponically contained ajoene, and were expected to be a healthy food, as are the bulbs.