Kenji Kurata

Automation of somatic embryo production

Automation could enhance the use of somatic embryogenesis for micropropagation in two ways: as effective tools for research on somatic embryogenesis, and for improving the efficiency of embryo production by reducing labor costs. Processes expected to be automated for somatic embryo production are: (1) evaluation of embryogenic cultures, (2) embryo development, (3) harvesting, (4) post-harvesting (pre-delivery) processes for enhancing conversion and preparing for delivery. In this review, the techniques related to the automation of each process are introduced and discussed.

Analysis of the relationship between blue-light photon flux density and the photosynthetic properties of spinach (Spinacia oleracea L.) leaves with regard to the acclimation of photosynthesis to growth irradiance

Abstract Blue light has been suggested to participate in the acclimation of photosynthesis to growth irradiance. We analyzed the effects of blue light intensity on the photosynthetic properties of leaves with regard to acclimation to irradiance. Spinach (Spinacia oleracea L.) plants were grown under mixtures of blue and red light with blue-light photon flux densities (PFDs) of 0, 30, 100 and 150 µmol m−2 s−1 at a total photosynthetic PFD of 300 µmol m−2 s−1. The light-saturated rate of photosynthesis under white light, leaf N content per unit leaf area, leaf dry weight per unit leaf area and the ratio of cytochrome (Cyt) f content to light-harvesting chlorophyll-binding protein of photosystem II (LHCII) content were evaluated. The photosynthetic rate tended to increase with increasing blue-light PFD up to 100 µmol m−2 s−1, and this was associated with an increase in leaf N content per unit leaf area. However, the increase in leaf N content per unit leaf area did not necessarily result from an increase in leaf dry weight per unit leaf area. The Cyt f to LHCII content ratio increased linearly with increasing blue-light PFD up to 100 µmol m−2 s−1, indicating that plants grown under higher blue-light PFD up to this value resembled plants grown under higher irradiance in terms of N partitioning between electron-transport components and light-harvesting components. This result suggests that the level of blue light is involved only in the acclimation to relatively low growth irradiances at the chloroplast level.

Growth of rice plants under red light with or without supplemental blue light

Abstract The effects of blue light supplementation to red light on growth, morphology and N utilization in rice plants (Oryza sativa L. cv. Sasanishiki and Nipponbare) were investigated. Plants were grown under two light quality treatments, red light alone (R) or red light supplemented with blue light (RB; red/blue-light photosynthetic photon flux density [PPFD] ratio was 4/1), at 380 mol m−2 s−1 PPFD. The biomass production of both cultivars grown under RB conditions was higher than that of plants grown under R conditions. This enhancement of biomass production was caused by an increase in the net assimilation rate (NAR). The higher NAR was associated with a higher leaf N content per leaf area at the whole-plant level, which was accompanied by higher contents of the key components of photosynthesis, including Rubisco and chlorophyll. In Sasanishiki, preferential biomass investment in leaf blades and expansion of wider and thinner leaves also contributed to the enhancement of biomass production. These morphological changes in the leaves were not observed in Nipponbare. Both the changes in physiological characteristics, including leaf photosynthesis, and the changes in morphological characteristics, including leaf development, contributed to the enhancement of biomass production under RB conditions, although the extent of these changes differed between the two cultivars.

Short-term and long-term effects of low total pressure on gas exchange rates of spinach

In this study, spinach plants were grown under atmospheric and low pressure conditions with constant O2 and CO2 partial pressures, and the effects of low total pressure on gas exchange rates were investigated. CO2 assimilation and transpiration rates of spinach grown under atmospheric pressure increased after short-term exposure to low total pressure due to the enhancement of leaf conductance. However, gas exchange rates of plants grown at 25 kPa total pressure were not greater than those grown at atmospheric pressure. Stomatal pore length and width were significantly smaller in leaves grown at low total pressure. This result suggested that gas exchange rates of plants grown under low total pressure were not stimulated even with the enhancement of gas diffusion because the stomatal size and stomatal aperture decreased.

Relationship between production of carrot somatic embryos and dissolved oxygen concentration in liquid culture

To evaluate the relationship between somatic embryogenesis and dissolved oxygen concentration, somatic embryo cultures of carrot (Daucus carota L.) were cultured under various dissolved oxygen concentration levels (bubble free aeration with 4%, 7%, 20%, 30%, and 40% oxygen in flasks). The system used allows dissolved oxygen concentration control without bubble aeration or mixing speed modification. The total number of somatic embryos was not affected by the dissolved oxygen (DO) concentration tested. Even if globular-stage embryos were induced at a low level of oxygen aeration, heart-stage embryo formation was still repressed. Oxygen enrichment (20%, 30% and 40% oxygen) enhanced torpedo and cotyledonary-stage embryo production. The oxygen-enriched aeration was effective in promoting the growth of the late developmental stages. Sugar consumption did not increase when the oxygen concentration was enriched above the ambient level. The number of heart-stage embryos increased as oxygen concentration increased up to the 7% level, while above the 20% level no change in production was observed. The production of cotyledonary-stage embryos was directly related to oxygen concentration. These results support that oxygen-enriched aeration provides oxygen to the low oxygen areas in somatic embryo. After the heat-stage embryos, which were grown at the 7% level were transferred to a flask with ambient, they developed an elongated root part and eventually grew to normal plantlets.

Role of reflection in light transmissivity of greenhouses

Abstract Analyses of light transmissivity of greenhouses so far published have not correctly considered the effects of structural members. In particular, the effects of structural members on the internal reflection at the cover have been neglected; this results in an overestimation of the importance of reflection. This report presents a method of analyzing the light transmissivity of greenhouses, including the effects of structural members. Analyses using this method elucidate the role of reflection in the light environment in greenhouses.

Nutrient Solution Prepared with Ozonated Water does not Damage Early Growth of Hydroponically Grown Tomatoes

Ozonated water as a water source for nutrient solution was investigated in hydroponically grown tomatoes. Nutrient solution was prepared by diluting concentrated nutrient solutions with ozonated water with dissolved ozone (DO3) concentrations of 0 to 10 mg L−1. Manganese concentration in the nutrient solution decreased with increasing DO3 concentrations. Initial growth of tomato plants supplied with nutrient solution prepared with ozonated water with a DO3 concentration of 1.5 mg L−1 was greater than that with a DO3 concentration of 0 mg L−1. These results indicate that ozonated water can be used as a disinfectant for source water in hydroponics during the early growth stage of tomatoes.

SYSTEM FOR MICROPROPAGATION BY NUTRIENT MIST SUPPLY

ABSTRACT Systems were developed for investigating optimal conditions for plant tissue culture using nutrient mist supply. A system in which a growth chamber and a mist generator were combined into a single unit operated reliably. An experiment that restricted the mist wafting region in the culture space resulted in better growth of potato nodal explants than that attained with a conventional culture method using agar media. KEYWORDS. Plant tissue culture, Micropropagation, Potato, Nutrient mist culture.

Scale-model experiments of applying a Fresnel prism to greenhouse covering

Abstract Effects of applying a Fresnel prism to a south roof of an EW-oriented single-span greenhouse were studied using scale models and artificial lights as well as under a natural light condition. The experiments confirmed the theoretical predictions that the application of a Fresnel prism increases the light transmissivity in winter and decreases it in summer. The experiments also revealed, however, large spatial variations of the light transmissivity in the greenhouse.

A new relative referencing method for crop monitoring using chlorophyll fluorescence

The measurement of plant chlorophyll fluorescence has been used for many years as a method to monitor a plants health status. These types of methods have been mostly relegated to the laboratory. The newly developed Relative Referencing Method allows for the measurement of chlorophyll fluorescence under artificial lighting conditions. The fluorescence signal can be determined by first taking a reference signal measurement, then a second measurement with an additional fluorescence excitation source. The first signal can then be subtracted from the second and the plants chlorophyll fluorescence due to the second lighting source can be determined. With this simple approach, a photosynthesizing plant can be monitored to detect signs of water stress. Using this approach experiments on tomato plants have shown that it was possible to detect water stress, while the plants were continuously illuminated by fluorescent lamps. This method is a promising tool for the remote monitoring of crops grown in a CELSS-type application.