Keiko Iwabuchi

An environmental control system for growing plants under low total pressures

Abstract An environmental control system including a growth chamber was constructed to study the feasibility of growing plants under low total pressures relating to crop production in space and CELSS. The system could control temperature, relative humidity, light intensity, and total and partial pressures. The chamber was cylindrical, and 63.5cm in diameter and 50cm in height. Thirty samples of leaf vegetables such as spinach could be grown in the chamber by hydroponics under artificial lights. This system could control total pressure, O 2 and CO 2 partial pressures separately, and consequently maintained them at constant during a growth experiment of spinach at a total pressure of 50kPa. Spinach( Spinacia oleracea L.), which was grown under the atmospheric pressure(101kPa), was transplanted in the chamber and exposed to various pressure conditions, and its photosynthetic rate was measured. Photosynthetic photon flux density(PPFD) was maintained at 120μmolm −2 s −1 and the light period was set at 14h. Volume of nutrient solution was 9l, and pH was 6.0 and electric conductivity was 2.2mS/cm. The setting values of temperature and relative humidity(RH) were 20°C and 73 to 75%, respectively. The result indicated that photosynthetic rates of spinach at 50 and 75kPa were almost the same as that at 100kPa.

Measurement of pH in Guard Cells Using a Confocal Laser Scanning Microscope

Two experiments were conducted to establish a method to measure pH in guard cells in situ for analysis of the relationship between pH changes in guard cells and stomatal aperture changes. To measure pH in guard cells of potato plants (Solanum tuberosum L. cv. Benimaru), ratio imaging was conducted using a confocal laser scanning microscope system with SNARF-1/AM as a pH fluorescent probe. Emitted fluorescence was divided into two ranges (580 and 640 nm) and the ratio of fluorescent intensities at 580 and 640 nm (F580/F640) was calculated. In vivo and in vitro calibrations showed an increase in the F580/F640 ratio with decrease in pH. In experiment 1, the relationship between stomatal aperture and pH in guard cells was investigated when the leaf disc was bathed in low pH solution (citric acid solution: pH 2.7). It was observed that stomata opened and F580 increased. Ratio imaging revealed that stomata with guard cells, which were initially at pH 7.0, opened as pH in the guard cells decreased. In experiment 2, to measure pH in guard cells for an attached leaf, 4.4 mM SNARF-1/AM solution was injected into the stem of a potato plant. However, the pH in the guard cells could not be measured because of low fluorescence intensity.

Does Electrolyzed-Reduced Water Protect Plants from Photoinhibition?

Electrolysis of water produces reduced and oxidized water near the cathode and anode respectively. Electrolyzed-reduced water (hereafter referred to as “reduced water”) exhibits high pH, and extremely negative oxidative redox potential (ORP). Reduced water was reported to scavenge active oxygen species that have a high potential to react with biological macromolecules destructively (Shirahata et al., 1997). In plants, photoinhibition of photosynthesis is a well known phenomenon resulting from oxidative damage of photosynthetic apparatus caused by active oxygen species generated in chloroplasts. Photoinhibition is often observed to occur under stressful conditions. Therefore, if the antioxidative function of reduced water can act also in plant cells, it may be possible to improve plant growth under stressful conditions by application of reduced water. In this study, growth of plants irrigated with deionized water or reduced water was studied under two types of stressful conditions: water stress in Experiment 1, and low temperature and high light intensity in Experiment 2. In both experiments, lettuce seeds (Lactuca. sativa L. var. capitata L.) were germinated in reduced water or deionized water in an environmentally controlled room at day/night air temperature of 23/18 °C and 190 ± 20 μmol m-2 s-1 PPF. In Experiment 1, the plants were watered every 2 days for the first 15-day period, then watered every 4 days for the following 15 days to obtain mild drought conditions. In Experiment 2, 25-day-old plants were cultivated at low temperature and high light intensity (5 °C throughout a day and 500 ± 100 μmol m-2s-1 PPF) for following 20 days. Under the both photoinhibitory conditions, leaf yellowing was observed, especially for newly developed leaves. This implied that photoinhibition of photosynthesis occurred in both experiments. However, there were no significant differences in fresh and dry weights, unfolded leaf number, and chlorophyll concentration between reduced water and deionized water treatments in Experiment 1. In Experiment 2, fresh weight was lower in the reduced water treatment than in the deionized water, suggesting that very low pH of reduced water was likely to negatively affect plant growth. These results indicated that mere irrigation with reduced water could not enhance plant growth under photoinhibitory stressful conditions.