Roots of spinach plants (Spinacia oleracea L.) were exposed to temperature of 10°C, 15°C and 30°C to induce the effect of the moderate stress with low and high root temperatures, respectively. The excessive growth depression and the consumption of electric energy for the root zone cooling are the main consideration to apply moderately low temperature to roots of spinach for induction of adaptive functions of osmoregulation and antioxidation, where enrichment of healthful substances and reduction of harmful substances were expected. Spinach plants were grown in the soil-less culture system, where the temperature of the nutrient solution in the root zone was set in the four different temperature regimes during two weeks before the harvest (i.e. two weeks 20°C with no temperature stresses (20°C), two weeks 10°C with the moderate low temperature stress (10°C), the first week 30°C and the second week 15°C (30°C/15°C), and the first week 30°C and the second week 10°C (30°C/10°C). Absorption depression in roots and adaptive functions of osmoregulation and antioxidation were induced by the combination of the one week treatment with a moderately high root temperature of 30°C and the one week treatment with a moderately low root temperature of 10°C (30°C/10°C), while the two weeks treatment with a moderately low root temperature of 10°C induced no significant adaptive functions of osmoregulation and antioxidation. The treatment of 30°C/10°C only enabled to produce value-added spinach shoots with high content of healthful substances such as sugars, Fe2+, ASA and SOD and with low content of harmful substances such as NO3− and oxalic acid.
Ralstonia solanacearum undergoes spontaneous phenotypic conversion (PC) from a wild-type pathogenic to non-pathogenic form in plant. Little is known about the dependence of bacterial PC on the strength of plant resistance to bacterial wilt. Furthermore, bacterial PC conditions in plants have not been elucidated. We inoculated R. solanacearum into resistant Solanum plants and susceptible eggplants grown in aseptic and non-aseptic culture, and investigated bacterial proliferation and PC in stems at various wilting stages. PC mutants were detected among all susceptible and resistant Solanum species. The pathogen underwent PC in 47–78% of plants that recovered from wilting and those that were in the final stages of wilting (bacteria lived stems for a long period with high density). On the other hand, only 0–22% of plants that were in the initial stage of wilting (bacteria existed stems for a short period with high density) and those that did not wilt (bacteria inhabited stems for a long period with low density) were isolated PC mutants. These results suggest that R. solanacearum spontaneously undergoes PC in plants regardless of the plants' resistance to bacterial wilt, and this mutation occurs after it had infected the host plants for a certain period at a high density.
A fast-maturing carrot cultivar that produces small storage roots termed “mini carrot” was grown in a solid substrate, sub-irrigation culture system placed in a phytotron glass room with a controlled air temperature of 23°C and relative humidity of 70%. Patterns of storage root growth and accumulation of chemical compounds in the roots were investigated. Optimal time for harvest determined by the root size was limited to 1 week—between 9 and 10 weeks after seeding. Fresh weight of the storage root increased by the greatest amount between 8 and 9 weeks after seeding. However, increase in length, diameter, and fresh weight of the storage roots reached a plateau at 11 weeks after seeding. The increase in β-carotene and sucrose content was slow until 9 weeks after seeding—just before the optimal harvest time. Thereafter, accumulation of these nutrients became more active, and their contents increased by approximately 2-fold at 3 weeks after the optimal harvest time.
Contamination of agricultural soil by fecal pathogenic bacteria poses a potential risk of infection to humans. As a way of biosafety control, soil solarization in a closed greenhouse was examined for the efficiency on the inactivation of Escherichia coli which was inoculated into soil as a model microorganism for fecal pathogenic bacteria. Soil solarization greatly increased the soil temperature (depth of 15 cm), which reached up to 40°C within the first one week of solarization, thereafter fluctuated between 40 and 46°C in most of the solarization periods. The population of E. coli in the solarized soil decreased dramatically from 105 CFU g−1 dry soil to undetectable level (‹0.1 CFU g−1 dry soil) within one week as a result, whereas E. coli was detected even after four weeks in the non-solarized soil in an open greenhouse. Soil solarization, however, had little effect on the total direct count and total viable count of bacteria in the soil. These results indicate that soil solarization would be useful for the rapid biosafety control of soil contaminated by human pathogens via immature compost or animal feces under greenhouse environments.
In this study, a leaf gas exchange system was constructed and tested over an extended range of external CO2 concentrations (ca) while the concentration inside the leaves (ci) was directly and continuously determined. For ca, an infrared analyzer was used to compare ca with a reference gas at concentrations as high as 50,000 μmol•mol−1. For ci, a glass cup sealed to the abaxial leaf surface equilibrated with internal CO2, and the gas was circulated to another infrared analyzer. When stomata were open in the light in a sunflower (Helanthus annuus L.) leaf, ci was about 275 μmol•mol−1 in ca of 400 μmol•mol−1. If stomata closed in the dark, ci increased until it exceeded ca but in the light the reverse occurred and ci decreased to only 60 μmol•mol−1. When ca increased in light, stomata began to close but ci could be increased to 50,000 μmol•mol−1, overcoming the closure. But inward CO2 diffusion was further inhibited by water vapor diffusing outward. The inhibition agreed with theoretical calculations of von Caemmerer and Farquhar (1981). The system expanded the CO2 concentrations at which CO2 fixation could be measured while avoiding complications from calculating ci when stomata close.
We investigated the effects of high temperature and water stress on fruit growth and levels of anthocyanins and their precursors in pot-grown strawberry (Fragaria×ananassa Duch.) plants. Nursery seedlings in pot were grown at a greenhouse. For simplicity, fruit set was fixed at one per plant. After pollination by honeybees, plants were transferred to growth chambers for high temperature (30/15°C day/night) or control (20/15°C) treatments, both with a 14L/10D photoperiod. Water stress was applied in both temperature regimes. After fruit weights were measured, the fruits were divided into three portions: inner (pith), middle (cortex), and outer parts. The anthocyanin, flavonoid, and cinnamic acid derivative contents were then analyzed. The harvest time (days after anthesis) was shorter at the high temperature. Anthocyanin content decreased in all three parts of the fruit at high temperature but was not affected by water stress. Cinnamic acid derivative content decreased (but not significantly) in all three parts of the fruit at high temperature but flavonoid content did not differ from the levels in the control. In the anthocyanin biosynthesis pathway, high temperature affected for anthocyanins and cinnamic acid derivatives inside the strawberry fruit.
We cultivated dent corn as a catch crop for controlling soil salt conditions in field plots at different densities, namely, 7.3 (low), 59.7 (normal) and 119.5 (high) plants m−2 in a greenhouse, where environmental elements and plant growth were measured for analyses of evapotranspiration components relating to the catch crop effects. Using the Penman-Monteith model with specific parameters incorporated for the crop and greenhouse, leaf transpiration and soil evaporation were estimated. Further crop coefficients were analyzed by dividing actual evapotranspiration by a reference evapotranspiration determined from meteorological data. Leaf area index for the normal and high density treatments reached 14 and 22, respectively, which were extremely high values compared to those for various other crops. Transpiration and its ratio to evapotranspiration increased with plant growth and density. Crop coefficients also increased with leaf area index and transpiration, and the coefficients for the normal and high density treatments reached high values of 1.5–2 and 2–3, respectively. These findings reveal characteristic features of plant growth and water dynamics in a catch crop field. The results of this study will contribute to the optimization of catch crop cultivation and to elucidate the crop's effects on soil salt conditions in greenhouses.
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