We examined the effects of continuous ultraviolet-B (UV-B) irradiation (0.58 W m−2) for 15 d on pumpkin seedlings. Continuous irradiation for 15 d slightly reduced the expansion of epidermal cell area and leaf area, whereas total epidermal cell number did not change in cotyledons. Only normal trichomes consisting of three cells were observed on the surface of control cotyledons. On the UV-B-irradiated cotyledon surface from 3–7 d, smaller trichomes consisting of single cells were observed along with normal trichomes. The total number of trichomes increased after UV-B irradiation for 5–9 d compared with that of control cotyledons. Expansion of true leaves was disrupted by UV-B irradiation for 15 d. Expansion of epidermal cell area and leaf area was reduced substantially, and the total number of epidermal cells was reduced considerably after UV-B irradiation for 15 d. Thus, continuous UV-B irradiation of pumpkin seedlings induces endoreduplication and trichome formation in tissues lacking active cell division (cotyledons), and reduces cell division in tissues that are actively growing (shoot apical meristem including first leaves).
An understanding of ongoing changes in biogeochemistry of carbon (C) as influenced by increasing atmospheric deposition (AD) of nutrients is important for integrated water resource management and for exploring options for balancing C sink and fluxes. To determine whether AD-nutrients would increase phytoplankton production and catchment carbon flushing in lakes, we analyzed NO3−, NH4+ and PO4−3 in atmospheric deposits, microbial biomass and activity in catchment, nutrient and dissolved organic carbon (DOC) in runoff and, phytoplankton production and sediment-C in six freshwater lakes from 1999 to 2008. Although N: P stoichiometry of AD did not change over time, there was over 1.5 fold increase in AD-NO3−, NH4+ and PO4−3 overtime. Microbial biomass and activity in catchments and, DOC and nutrients in runoff increased consistently over time. Lake nutrients, DOC, gross primary productivity, chlorophyll a biomass and sediment-C also showed positive relationship with AD-nutrients. The study indicates that rising input of AD-nutrients steer freshwater lakes towards greater productivity, whereas such inputs in catchment enhance microbial processes and consequently runoff DOC flush and the-coupled effects of these may cause long-term shift in water quality and C balance of these ecosystems.
Soybean plant growth during reproductive stage controls strongly seed yield. Two field experiments were conducted to analyze whether water condition improve soybean plant growth from flowering to the beginning of seed developing stage and which growth factors were related. One experiment was the comparison in plant growth between 2008, a wetter season, and 2009, a drier season. Crop growth rate (CGR) from flowering to beginning seed stage in 2008 was higher than that of 2009 and this was associated with higher mean leaf area index (LAI). Relative growth rate (RGR) in 2008 was as high as that of 2009 and this was associated with higher mean specific leaf area (SLA) in spite of lower net assimilation rate (NAR). The other was the irrigation experiment where we irrigated a half of experimental field during emergence to maturity. Although the differences between the treatments were smaller, CGR, LAI and mean SLA increased by irrigation. These results indicate that the improvement of soil water condition increased CGR with the increase in LAI and keep RGR by high SLA in spite of high total dry weight at flowering and lower NAR during reproductive stage.
The effects of shading on growth and photosynthetic potential was analyzed with 8 cultivars with greengram (Vigna radiata (L.) Wilczek). Plants grown in 5 L pots were subjected to 2-week shading treatment and after 2-week recovery by removing a black-cheese cloth. Photosynthetic potential was evaluated by electron transport rate sealed on the both leaf surfaces by vaseline, which is close relationship to gross photosynthetic rate because CO 2 released by the reaction of photorespiration is recycled by stroma in chloroplast. Shading treatment reduced total dry weight of all cultivars. In particular, significant reduction in total dry weight was found in Nyangoo, Magwe and VC. Leaf specific area under shading treatment showed increment tendency and remarkable increase in this parameter was found in Nyangoo and VC, which cultivars decreased total dry weight under shading, indicating that shading treatment lead to thin of the leaf thickness. The ratio of plant height to diameter of stem was significantly decreased in R-288-8, Kanti and Yezin-5 by shading, indicating the restriction of succulent growth under shading condition and these cultivars are superior in lodging resistance to other cultivars. Photosynthetic rate as evaluated by electron transport rate sealed by vaseline was decreased by shading treatment. The extent of decrease in photosynthetic potential was found cultivaral difference. According to these results, Kanti is capable of applicable to the highest in resistance to shading and its recovery.
The purpose of this study was to develop a technique for designing modified atmosphere packaging (MAP) for suppressing chilling injury (CI) in cucumber fruit using a mathematical model. The respiratory quotient (RQ) changes from 0.2% to 4% of O2 at 5°C was measured to determine the critical low O2 limit and was found to be 0.5%. Next, respiration rates of cucumber fruit stored at 5°C under various O2 concentrations were measured and modelled with the Michaelis-Menten equation as a function of O2 concentration. The model provided a good prediction of the respiration rate of cucumber fruit at any O2 concentration. A mathematical model incorporating the respiration rate and gas mass transfer through film packaging was developed to estimate the optimal O2 permeance, leading to equilibration of O2 concentration in the package at the established critical low O2 limit. To verify the effect of CO2 accumulation inside the package on CI suppression, the malondialdehyde (MDA) of the fruit packed in a low-density polyethylene (LDPE) bag with and without a CO2 absorber was evaluated. The results suggested that reducing CO2 in the package is effective for suppressing CI. Further study such as optimal design for the active MAP with a CO2 absorbent is needed to realize the maximum performance of MAP in alleviating CI in cucumber fruit.
In Japan, Bulbophyllum drymoglossum is a unique species without pseudobulbs in the genus Bulbophyllum. A normal form of B. drymoglossum was described as having an obtuse leaf tip and unclear midrib but we found many B. drymoglossum individuals with an acute leaf tip adding clear midrib in Kochi Prefecture, Japan. It is questionable whether the individuals having an acute leaf tip and/or a clear midrib are simply morphological variants of this species. To reveal the status of the individuals, we performed morphological and molecular analyses using B. drymoglossum having acute/obtuse leaf tips and clear/unclear midribs and two related sympatric species, B. inconspicuum and B. japonicum. Morphological analyses showed that B. drymoglossum with an acute leaf tip had a longer leaf and rhizome internode than those with an obtuse leaf tip, though the two types of leaf tip shape of B. drymoglossum overlapped with the two character ranges. Individuals of B. drymoglossum with unclear midribs were twice as many as those with clear midribs regardless of leaf tip shape. Molecular analysis showed no evidence of genetic differentiations between the two types of B. drymoglossum. Because a local floral variation of B. drymoglossum (described as B. somai) was reported from Taiwan, this species might have various morphological variations adapted for local regions.
Japanese red pine (Pinus densiflora Sieb. et Zucc.) was reported to have strong allelopathic activity. However, the allelopathic activity of the pine has not been monitored throughout a year. In this research, the seasonal change in the allelopathic activity of the extracts of Japanese red pine needles was determined. The extracts of pine needles inhibited the growth of cress (Lepidium sativum L.) and the inhibitory activity of the extracts showed the seasonal variation. The inhibitory activity of June extract was significantly greater than that of December extract. The extracts also inhibited the barnyard grass (Echinochloa crus-galli (L.) Beauv.), but the seasonal change was not apparent. The present research suggests Japanese red pine needles have allelopathic activity throughout a year and the patterns of the change in the inhibitory activity were different with cress and barnyard grass, which may be due to the different sensitivity of cress and barnyard grass to a mixture of allelopathic substances in the pine needles.
The life cycle of a community of variegated Japanese butterbur (Petasites japonicus) found in a field at the Fukuoka University of Education (FUE) campus in April 2012 was investigated. The prevalence and morphology of white sectors in newly regenerated leaves of the same variegated Japanese butterbur plants were greater in April, but less in August and December. The community of normal Japanese butterbur identified in the field at the FUE campus in April 2012 did not exhibit variegation changes during the year. To investigate temperature effects on variegation regeneration, we exhumed variegated Japanese butterbur plants from the field, replanted them in clay pots, removed the aerial portions by mowing, and allowed regrowth in a growth cabinet at 25°C or 18°C for 11 d. The percentage of regenerated leaves exhibiting variegation was 12.8% at 25°C and 28.0% at 18°C. The variegation pattern and morphology in regenerated leaves was diffuse and indistinct at 25°C, whereas the variegation pattern was distinct and robust at 18°C. These results suggest that lower temperatures promote regeneration of variegation patterns in variegated Japanese butterbur leaves. It is possible that regeneration of vivid variegation patterns in variegated Japanese butterbur requires cold temperatures during the winter.