We carried out investigations on the effects of different soil temperatures caused by artificial heating and cooling on the thickening growth and the quality, such as factors that determine the market value as skin color, dry matter percentage, starch and sugar of the tuberous root of sweetpotatoes (Ipomoea batatas (L.) Lam.) during the latter period of their growth. The soil temperatures of the heating and the cooling treatments were within the range of 20 and 36°C, and 13 and 31°C, respectively. The leaf and stem weight was the smallest in the cooling treatment. The number of roots increased in each plant when the soil was heated and decreased when cooled. There was an inverse relationship between the average root weight and the number of roots. Dry matter percentage, starch and total sugar contents were the highest in the cooling treatment and the lowest in the heating treatment. The skin color of the root was brilliant red in the cooling treatment, but almost white in the heating treatment. From these results, we can surmise that starch and total sugar contents increase in the root of sweetpotatoes cultivated in cooler soil temperature, with a vivid red skin color.

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Two cultivars of spray chrysanthemum (Dendranthema grandiflorum), ‘Sei Aloha’ (summer-to-autumn flowering cultivar) and ‘Pinky’ (autumn flowering cultivar), were grown in NFT system and the effects of varying nutrient solution volumes (0.25, 0.50, 0.75, 1.00, 2.00 L plant^-1) on mineral uptake and cut flower quality were investigated. The N, P and K uptake remained unaffected with the varying nutrient solution volumes. Nutrient solution volumes of <0.75 L plant^-1 resulted into considerable reduction in the shoot length and shoot weight, thus giving rise to poor cut flower quality. Root growth inhibition was observed under 0.25 L plant^-1. Reduction in plant growth under smaller nutrient solution volumes occurred possibly via unstable root environment, large fluctuation in EC and pH, and excess accumulation of root exudates in the recirculated nutrient solution. Charcoal addition did not alleviate the reduction in plant growth under 0.25 L plant^-1. Also, weekly renewal of nutrient solution with 0.25 L plant^-1 resulted in less plant growth compared to 1.00 L plant^-1 without renewal.

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Solutions of 1- (2-chloro-4-pyridyl) -3-phenylurea (CPPU), α-napthalenacetic acid (NAA), and p-chlorophenoxyacetic acid (4-CPA) applied once or twice to the parthenocarpic fruit induced by CPPU at anthesis, and their effects on the growth and quality of the fruit were investigated. Non-pollinated flowers treated with CPPU produced parthenocarpic fruit with 100% fruit set. CPPU treatment at anthesis enlarged fruit until 5 d after anthesis, but then the growth of the fruit was exceeded by the seeded fruit (control) . Both the 2nd CPPU treatments to the CPPU induced parthenocarpic fruit on the 10th day after anthesis and the 3rd CPPU treatment on the 25th day after anthesis enhanced the fruit growth. The first NAA and 4-CPA treatment to the fruit on the 10th day after anthesis and/or the second treatment on the 25th day after anthesis enhanced the fruit growth. No significant difference existed in enhancing the fruit growth between the three plant growth regulators. CPPU treatment to the pollinated flower did not influence the sugar accumulation of the fruit. The sugar content in parthenocarpic fruit induced by CPPU was significantly lower than in seeded fruit, this difference was more substantial in the placenta than in the mesocarp. Both the 2nd and 3rd CPPU treatments and the 1st and 2nd NAA treatments to the CPPU induced parthenocarpic fruit did not improve sucrose accumulation of those fruits. However, the 1st and 2nd 4-CPA treatment to these CPPU induced parthenocarpic fruit could remarkably enhanced the sugar accumulation of the fruit. These results suggest that 4-CPA treatment is practical for improving of the growth and the sugar accumulation of parthenocarpic fruit induced by CPPU.

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The effects of these dwarfing genes at the sd1 locus, d18-k (kotaketamanishiki dwarf) and d12 (yukara dwarf) on the chilling tolerance at the seedling stage of rice plants (Oryza sativa L.) were investigated. We used isogenic lines developed by backcrosses, and artificial or natural dwarf mutants, together with their parental varieties, i.e., ‘Fujiminori’ and ‘Shiokari’ and ‘Tamanishiki’. Chilling treatments at 2°C without illumination for three, four and five d were conducted at the 1- and/or 2-leaf stages. The chilling tolerances of the lines were evaluated by survival percentages 22 d after the treatments. The isogenic lines of the dwarfing genes at the sd1 locus showed lower survival percentages than their respective parental varieties in the 3-or 4-day treatments at the 1-leaf stage. The survival percentages of ‘Kotaketamanishiki’ and the isogenic line of ‘Shiokari’ were higher than those of their respective parental varieties through all the treatments. Fukei 71 containing d12 showed lower survival percentages than ‘Fujiminori’ in the 3- and 4-day treatments at the 1-leaf stage. It is inferred from the results in the present study that the dwarfing genes at the sd1 locus and d12 lower the chilling tolerance at the seedling stage whereas d18-k enhances it.

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Norin-PL8 (“PL8”) is an extremely cool-tolerant variety, which contains genes for cool tolerance introduced from a javanica indigenous variety, ‘Silewah.’ The effect of d18-k on the cool tolerance at the booting stage was examined under the genetic background of PL8, by using the isogenic line regarding d18-k of the recurrent parent, PL8. This line was denoted by “D8.” We performed cool treatments at 12°C for five d with and without deep water at a depth of 15 cm, i.e., DW and CA, respectively. The light intensities in day time in the DW and CA were about 30, 000 and 7, 000 lx, respectively. L₅ (the mean value of the lowest five spikelet fertilities on five consecutive days in each treatment in each line) was used to evaluate the cool tolerances of the lines. In the CA, the L₅ of D8 was higher than that of PL8, indicating that the former is more tolerant than the latter. There was a trend in each line that spikelet fertilities in the DW were higher than those in the CA. The height of panicle of D8 was always lower than that of PL8 throughout the booting stage. This indicated that d18-k makes it easy to protect developing panicles under the surface of irrigation water which is ordinary warmer than the ambient air in cool weather districts.

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The mathematical modeling used to predict the steady-state O₂ partial pressures for design of modified atmosphere (MA) packages of avocado (Persea americana ‘Fuerte’) fruits was developed. The rate of O₂ uptake (R_O2) was determined as a function of O₂ partial pressures by mathematical characterization of O₂ depletion data collected by avocado fruits in a closed system with time. R_O2 was used to describe the modeling of packaging ratios (A/W_p) characteristics (film surface area (A), fruit weight in packages (W_p) ) as a function of film permeability to O₂ (P_O2) (O₂ permeability coefficient, thickness) to achieve desired O₂ partial pressures of the sealed package for MA packages of avocado fruits. Prediction curves showing steady-state O₂ partial pressures for packaging ratios in the range of 1.5 to 8.6 closely resembled the curves of experimental data. Maximum benefits (for example, weight loss, firmness, visually assessed mean pericarp coloration (brownness) and visual quality of fruit) for avocado fruits in MA packages were obtained when the O₂ partial pressures inside the package was maintained in the range of 1.5 kPa at 20°C. As a result, film specifications and optimization of packaging ratios for avocado fruits in MA packages were calculated based on desired steady-state O₂ partial pressures.

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In order to quantify water movement and solute diffusion in gel medium for plant tissue culture, hydraulic conductivity and diffusion coefficient in agar gel and gellan gum gel were studied. The falling-head method was used to measure the hydraulic conductivity. The diffusion coefficient was evaluated from solute concentration profiles in gels after contacting gel samples with and without solute. The hydraulic conductivity decreased from 3.15 × 10^-5 to 3.45 × 10^-7 kg s m^-3 as agar gel concentration increased from 0.5 to 3.0 wt% and also decreased from 4.20 × 10^-5 to 4.25 × 10^-7 kg s m^-3 as gellan gum gel concentration increased from 0.1 to 1.0 wt%. The conductivity in agar gel changed steeper than that in gellan gum gel at normal gel concentrations for plant tissue culture (= around 0.6 wt% for agar gel and 0.2 wt% for gellan gum), which implies that the change of gel concentration in agar gel could effect water supply to plant tissue. Pore diameters in gels were estimated by the hydraulic conductivity and Hagen-Poiseuille equation. The estimated diameters were 1, 050 nm for 0.2 wt% gellan gum gel and 542 nm for 1.0 wt% agar gel, which was approximately equal to the actual diameter. The diffusion coefficient of solute in gel was almost constant in any gel concentrations and was close to that in water. This implies that diffusion coefficient does not restrict the growth of tissue except for diffusion of macromolecules. The possibility of inhibiting of diffusion by the collision of the macromolecules with the agar pore was indicated from the examination of a equation by Ackers and Steere (Biochim. Biophys. Acta 59: 137-149, 1962) .

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In order to know the effect of anaerobiosis on alcohol fermentation in early developmental stage of alfalfa (Medicago sativa L.), 6-d-old seedlings were subjected to anaerobic stress and alcohol dehydrogenase (ADH) activity and ethanol concentration in the seedlings were determined. The anaerobic stress caused increases in ADH activity and ethanol concentration. At 48 h after onset of the stress, ADH activity and ethanol concentration in the seedlings were 4.2- and 20-fold greater than those in non-stressed seedlings, respectively. These results suggest that anaerobic stress accelerates the alcohol fermentation pathway in the alfalfa seedlings.

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