Chlorophyll (Chl) fluorescence measured on a leaf surface only provides the photosynthetic status of chloroplasts near the surface due to self-shading effect of Chl. Here, we report a laser-induced Chl fluorescence measurement system, which enables measurement of fluorescence induction kinetics at different tissues within a leaf as well as on both leaf surfaces, to assess photosynthetic status within leaves. The logarithmic time-scaled Chl fluorescence induction kinetics obtained from Chenopodium album leaves showed polyphasic transients in which four inflection points designated as O, J, I and P, were observed. Adaxial surface and palisade mesophyll showed significantly higher fluorescence intensities at O than abaxial surface and spongy mesophyll, respectively. In contrast, fluorescence intensities at J, I and P were significantly higher at abaxial surface and spongy mesophyll. Using these fluorescence intensities, the JIP test was performed. The results of JIP test indicated that adaxial surface and palisade mesophyll are characterized by lower maximum quantum yield of photosystem II (PSII) and net rate of PSII closure, but higher rate of energy transfer into electron transport chain than abaxial surface and spongy mesophyll. Considering these dorsiventral and intra-leaf variations in Chl fluorescence parameters, this study suggested the necessity of Chl fluorescence measurements on tissues as well as both surfaces to evaluate photosynthetic status of a whole leaf.

View full abstract

We investigated effects of dim light irradiation (about 11 μmol m⁻² s⁻¹ photon flux density) of the root zone on the growth and development of leaf lettuce (Lactuca sativa ‘Okayama saradana’) plants under nutrient film technique (NFT) hydroponics with monochromatic light emitting diodes (LEDs) of five types with respective peak wavelengths (and colors) of 405 nm (violet), 465 nm (blue), 525 nm (green), 660 nm (red), and 735 nm (far-red). Shoot fresh weight and specific root length in the treatments of dim light irradiation of the root zone with violet, blue, and far-red LEDs were significantly lower than in the control (no irradiation of the root zone). Roots in these treatments developed thickly, probably because of suppressed lateral root initiation because sparsely distributed roots were observed in these treatments. Dim light irradiation of the root zone of leaf lettuce plants did not affect mass production, but it did affect root morphology.

View full abstract

Small amounts of pesticides and their transformation products may exist on edible parts before harvesting tomato (Solanum lycopersicum L.) fruits. For analyzing these compounds, special techniques with minimum preparations and high sensitivity are needed. The capability of a technique for in situ detection of target chemicals can be also a great advantage. Here we report the applicability of ultraviolet matrix-assisted laser desorption/ionization time of flight mass spectrometry (UV-MALDI TOF MS) for direct detection of pesticides and the residues on the tomato fruit surface. Fruits grown in the hydroponic system in a greenhouse were sprayed with a mixture of four pesticides including benomyl, triforine, milbemycin and malathion and collected one week later. The pericarp of sprayed and control fruits was peeled and located on a UV-MALDI plate, air-dried and covered with carbon nanotubes or 2,5-dihydroxybenzoic acid as matrixes. Signals of active and supplementary compounds which are normally present in commercial pesticides could be analyzed and directly detected on the surface of cuticle. A malathion degradation product was also detected on the sprayed fruit pericarp.

View full abstract

The intensity of light falling on the leaf surface of a plant is critical information to accurately evaluate its photosynthetic status and/or the management of the light environment in protected cultivation. In this study, the relationship between the light intensity (expressed as the photosynthetic photon flux density; PPFD) irradiating the leaf surface and the pixel value (PV) in the reflection image was investigated for several plant canopies to examine the possibility of using reflection images to estimate the distribution of light intensity on a canopy surface. Reflection images of the plant canopies were acquired from several directions with a monochrome 14-bit CCD camera through a blue-green band-pass filter. High correlations were observed between the PPFD and the average PVs in the reflection images from three different directions for strawberry canopies under artificial light and tomato and rose canopies in a greenhouse. These results suggest that the distribution of light intensity on a canopy surface could possibly be estimated by reflection images from different directions. A simple method is proposed for the estimation of the PPFD distribution on a plant canopy in a greenhouse using reflection images.

View full abstract

The response in gas exchange and photosystem II (PSII) functions to a flooding condition was characterized with kenaf (Hibiscus cannabinus) by comparing it with napiergrass (Pennisetum purpureum, C₄-plant), corn (Zea mays, C₄-plant) and mungbean (Vigna radiata, C₃-plant). Pot-grown plants were subjected to a 1-week flooding and a 1-week recovery treatment. The flooding treatment had serious effects on the gas exchange of mungbean and corn, while the damages were lenient in kenaf and napiergrass. Kenaf and napiergrass were characterized by keeping a higher stomatal conductance (G_s) and mesophyll conductance (G_m), which resulted in sustaining the CO₂ assimilation under the flooding stress condition. As compared between these two high-yielding species, kenaf was superior in photosynthetic sustainment than napiergrass under the flooding and recovery treatments. The superiority in kenaf is attributable to the fact that this species keeps higher G_s under the flooding, by which photosynthesis was able to continue, and the photosynthetic apparatus prevents the excessive energy accumulation in the leaf. Also, kenaf showed the increase photorespiration and non-photochemical quenching (NPQ) during the treatments.

View full abstract

The transgenic lettuce expressing double repeated Stx2eB (2×Stx2eB) is considered to be an edible vaccine candidate against swine edema disease. For the efficient vaccine protein production in transgenic lettuce grown in a plant factory, the effects of air flow on vaccine protein production in transgenic lettuce were investigated. Plants were grown hydroponically in a closed-type plant factory for 21 days with four airflow patterns: 1) air flow from the side to leaves at 2.0 m s⁻¹; 2) air flow from the top to the inner developing leaves with flexible transparent tubing at 1.0 m s⁻¹; 3) air flow from the bottom to leaves with transparent tubing at 1.0 m s⁻¹; and 4) no air flow. Our results showed that the total leaf number in air flow from the top and the bottom to leaves was significantly increased compared with that in no air flow. While lettuce growth with inner air flow and bottom air flow was enhanced, tipburn at the developing leaves were eliminated by air flow. 2×Stx2eB per plant in bottom air flow to leaves was the highest of the four air flow patterns. These results suggest that bottom air flow to the leaves can enhance vaccine protein productivity in transgenic lettuce.

View full abstract

Aiming at high yield and labor saving production of strawberry, an innovative cultivation system was newly developed by the three dimensional use of the greenhouse space. In this system, a double-seesaw mechanism vertically moves four beds, and the beds can be held at any desired height. Three dimensional use of the greenhouse space creates four times planting density as high as the conventional bench culture. Beds were moved among four heights of 2.8, 2.1, 1.4, and 0.7 m every two hours, but yield increased only 27% over conventional bench culture to a significant decline in integrated solar radiation on individual beds caused by shading. Fixing the beds in a two-height formation (2.1 and 0.7 m) increased integrated solar radiation on beds relative to the moving four-height formation and increased yield twofold. However, photosynthesis of lower-bed plants was only 50% of those on upper beds due to shading by upper beds. By exchanging the upper and lower beds at 11:00 and 14:00, photosynthesis on the beds in the two-height formation was equalized. Consequently, integrated photosynthesis across the moving beds in the two-height formation was 24% higher than on the beds fixed in that formation. Thus, by optimizing the vertical motion of beds based on leaf photosynthesis, the newly-developed system can achieve high yields of high-quality strawberries.

View full abstract

Salinization of crop fields under desertification closely relates to root absorptive functions of the major crops such as corn and sunflower plants. The rate of root salt absorption of corn and sunflower plants under the salinized condition were analyzed by applying the transpiration-integrated model of root ion absorption affected by leaf transpiration. The characteristics of root salt absorption were represented by two model parameters of Q_max and K_M′ which relate to the potential absorbing power and the ion affinity of transport proteins on root cell membranes, respectively. In particular, the model parameter of Q_max can be an explanatory parameter to represent the specificity of plant species and ion species in root ion absorption. Identification of Q_max involved in the transpiration-integrated model of root ion absorption can be effective for simulating salt accumulation in crop fields under desertification.

View full abstract

The improved Temperature Vegetation Dryness Index (iTVDI) can be used as an indicator of transpiration rates in mountainous areas. We investigated the influence of vegetation cover types on differences observed in iTVDI, together with NDVI in vegetation covers around Lake Mashu in a summer day. Based on the results of comparing NDVI and iTVDI values among 14 vegetation cover types, it was shown that the vegetation cover type differences could cause significant differences in iTVDI values. Shrub and grassland categories showed lower NDVI but higher iTVDI values, whereas tall trees except Erman's birch showed relatively higher NDVI but lower iTVDI values. The Erman's birch iTVDI values were higher than the other tall trees. These results suggest that the difference of vegetation cover types could be one of the factors that influence iTVDI values.

View full abstract

Characteristics of direct uptake of organic nitrogen by tomato roots associated with plant growth and water uptake were analyzed quantitatively using a root chamber equipped with a high-pressure flowmeter. The rate of root nutrient uptake was evaluated using the nutrient concentration in the xylem sap collected from the stem stump and the water uptake rate measured by the flowmeter. There was a difference in nutrient content in the xylem sap of the roots grown with or without organic nitrogen (amino acids), suggesting the direct uptake of them. The rate of organic nitrogen uptake was different depending on the type of organic nitrogen used, and was increased with plant growth through water uptake. Furthermore, the increase in water uptake supposed to be daytime transpiration induced a higher rate of organic nitrogen uptake, whereas the rate of nitrate nitrogen uptake either remained the same or increased slightly. As a result, the ratio of organic nitrogen uptake to total nitrogen uptake increased from approximately 15% to 40% with the water uptake increase.

View full abstract

Measurement of the slow phase (the P-S-M-T phase) of the chlorophyll fluorescence induction (CFI) phenomenon is a prospective candidate for plant diagnosis in greenhouses. We applied a methodology, the consecutive measurements of photochemical efficiency of photosystem (PS) II (Ψ_PSII) and non-photochemical quenching (NPQ) during a CFI phenomenon, to clarify the contributions of photochemical and non-photochemical quenching to the slow phase of CFI curves in mature tomato leaves grown in a semi-commercial greenhouse. The Ψ_PSII increased significantly between the inflection points of P and S and decreased between the inflection points of S and M. On the other hand, the NPQ remained at low values during the inflections of P, S and M, but then increased exponentially. These results prove that the shape of the CFI curve during the inflections of P, S and M is predominantly determined by the changes in the status of the photosynthetic electron transport chain, and the shape of the CFI curve after the inflection of M is strongly regulated by non-photochemical quenching, especially of the xanthophyll cycle. Furthermore, the two CFI measurements conducted at an interval of nine days proved that the slight changes in the photosynthetic functions, i.e. decreases in the capacities of the photosynthetic electron transport and the xanthophyll cycle, are detectable by measuring the slow phase of the CFI phenomenon.

View full abstract

In order to improve temperature and water management in the greenhouse cultivation of Satsuma mandarins, short-term water and carbon balance in intact Satsuma mandarin fruits was studied by measuring fruit expansive growth, CO₂ and H₂O gas exchange, sap flux into the fruit through the phloem and xylem, and ¹³C partitioning. Seventy-one days after full bloom, with day/night temperature set at 28°C/23°C and under fine weather conditions, sap flux through the xylem into the fruit showed a dynamic diurnal change which was related to changes of fruit volume. In leaves, ¹³C partitioning decreased from 11:00 until 23:00, remaining constant thereafter, whereas in fruits, ¹³C partitioning increased from 11:00 until 23:00, and then remained contrast. Investigating the cumulative water balance, 19% of water output was lost by fruit transpiration, whereas 81% contributed to fruit growth. In cumulative carbon balance, 39% of carbon output was lost by fruit respiration, whereas 61% contributed to fruit growth. Quantitative analyses of physiological responses to environmental conditions, as measured in this study, are essential for establishing energy-saving temperature management strategies.

View full abstract