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101.
Leaf lifespan and lifetime carbon balance of individual leaves in a stand of an annual herb, Xanthium canadense 总被引:1,自引:0,他引:1
Leaf lifespan in response to resource availability has been documented in many studies, but it still remains uncertain what determines the timing of leaf shedding. Here, we evaluate the lifetime carbon (C) balance of a leaf in a canopy as influenced by nitrogen (N) availability. Stands of Xanthium canadense were established with high-nitrogen (HN) and low-nitrogen (LN) treatments and temporal changes of C gain of individual leaves were investigated with a canopy photosynthesis model. Daily C gain of a leaf was maximal early in its development and subsequently declined. Daily C gain at shedding was nearly zero in HN, while it was still positive in LN. Sensitivity analyses showed that the decline in the daily C gain resulted primarily from the reduction in light level in HN and by the reduction in leaf N in LN. Smaller leaf size in LN than in HN led to higher light levels in the canopy, which helped leaves of the LN stand maintain for a longer period. These results suggest that the mechanism by which leaf lifespan is determined changes depending on the availability of the resource that is most limiting to plant growth. 相似文献
102.
Hironaka Tsukagoshi Takamasa Suzuki Kouki Nishikawa Sakae Agarie Sumie Ishiguro Tetsuya Higashiyama 《PloS one》2015,10(2)
Understanding the molecular mechanisms that convey salt tolerance in plants is a crucial issue for increasing crop yield. The ice plant (Mesembryanthemum crystallinum) is a halophyte that is capable of growing under high salt conditions. For example, the roots of ice plant seedlings continue to grow in 140 mM NaCl, a salt concentration that completely inhibits Arabidopsis thaliana root growth. Identifying the molecular mechanisms responsible for this high level of salt tolerance in a halophyte has the potential of revealing tolerance mechanisms that have been evolutionarily successful. In the present study, deep sequencing (RNAseq) was used to examine gene expression in ice plant roots treated with various concentrations of NaCl. Sequencing resulted in the identification of 53,516 contigs, 10,818 of which were orthologs of Arabidopsis genes. In addition to the expression analysis, a web-based ice plant database was constructed that allows broad public access to the data. The results obtained from an analysis of the RNAseq data were confirmed by RT-qPCR. Novel patterns of gene expression in response to high salinity within 24 hours were identified in the ice plant when the RNAseq data from the ice plant was compared to gene expression data obtained from Arabidopsis plants exposed to high salt. Although ABA responsive genes and a sodium transporter protein (HKT1), are up-regulated and down-regulated respectively in both Arabidopsis and the ice plant; peroxidase genes exhibit opposite responses. The results of this study provide an important first step towards analyzing environmental tolerance mechanisms in a non-model organism and provide a useful dataset for predicting novel gene functions. 相似文献
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104.
Plant communities around natural CO2 springs have been exposed to elevated CO2 levels over many generations and give us a unique opportunity to investigate the effects of long-term elevated CO2 levels on wild plants. We searched for natural CO2 springs in cool temperate climate regions in Japan and found three springs that were suitable for studying long-term responses
of plants to elevated levels of CO2: Ryuzin-numa, Yuno-kawa and Nyuu. At these CO2 springs, the surrounding air was at high CO2 concentration with no toxic gas emissions throughout the growth season, and there was natural vegetation around the springs.
At each site, high-CO2 (HC) and low-CO2 (LC) plots were established, and three dominant species at the shrub layers were used for physiological analyses. Although
the microenvironments were different among the springs, dicotyledonous species growing at the HC plots tended to have more
starch and less nitrogen per unit dry mass in the leaves than those growing at the LC plots. In contrast, monocotyledonous
species growing in the HC and LC plots had similar starch and nitrogen concentrations. Photosynthetic rates at the mean growth
CO2 concentration were higher in HC plants than LC plants, but photosynthetic rates at a common CO2 concentration were lower in HC plants. Efficiency of water and nitrogen use of leaves at growth CO2 concentration was greatly increased in HC plants. These results suggest that natural plants growing in elevated CO2 levels under cool temperate climate conditions have down-regulated their photosynthetic capacity but that they increased
photosynthetic rates and resource use efficiencies due to the direct effect of elevated CO2 concentration. 相似文献
105.
Kouki?HikosakaEmail author Yusuke?Onoda Toshihiko?Kinugasa Hisae?Nagashima Niels?PR?Anten Tadaki?Hirose 《Ecological Research》2005,20(3):243-253
Elevated CO2 enhances photosynthesis and growth of plants, but the enhancement is strongly influenced by the availability of nitrogen. In this article, we summarise our studies on plant responses to elevated CO2. The photosynthetic capacity of leaves depends not only on leaf nitrogen content but also on nitrogen partitioning within a leaf. In Polygonum cuspidatum, nitrogen partitioning among the photosynthetic components was not influenced by elevated CO2 but changed between seasons. Since the alteration in nitrogen partitioning resulted in different CO2-dependence of photosynthetic rates, enhancement of photosynthesis by elevated CO2 was greater in autumn than in summer. Leaf mass per unit area (LMA) increases in plants grown at elevated CO2. This increase was considered to have resulted from the accumulation of carbohydrates not used for plant growth. With a sensitive analysis of a growth model, however, we suggested that the increase in LMA is advantageous for growth at elevated CO2 by compensating for the reduction in leaf nitrogen concentration per unit mass. Enhancement of reproductive yield by elevated CO2 is often smaller than that expected from vegetative growth. In Xanthium canadense, elevated CO2 did not increase seed production, though the vegetative growth increased by 53%. As nitrogen concentration of seeds remained constant at different CO2 levels, we suggest that the availability of nitrogen limited seed production at elevated CO2 levels. We found that leaf area development of plant canopy was strongly constrained by the availability of nitrogen rather than by CO2. In a rice field cultivated at free-air CO2 enrichment, the leaf area index (LAI) increased with an increase in nitrogen availability but did not change with CO2 elevation. We determined optimal LAI to maximise canopy photosynthesis and demonstrated that enhancement of canopy photosynthesis by elevated CO2 was larger at high than at low nitrogen availability. We also studied competitive asymmetry among individuals in an even-aged, monospecific stand at elevated CO2. Light acquisition (acquired light per unit aboveground mass) and utilisation (photosynthesis per unit acquired light) were calculated for each individual in the stand. Elevated CO2 enhanced photosynthesis and growth of tall dominants, which reduced the light availability for shorter subordinates and consequently increased size inequality in the stand. 相似文献
106.
Background and Aims
Understorey evergreen species commonly have a higher leaf nitrogen content in winter than in summer. Tested here is a hypothesis that such changes in leaf nitrogen content maximize nitrogen-use efficiency, defined as the daily carbon gain per unit nitrogen, under given temperature and irradiance levels.Methods
The evergreen shrub Aucuba japonica growing naturally at three sites with different irradiance regimes in Japan was studied. Leaf photosynthetic characteristics, Rubisco and leaf nitrogen with measurements of temperature and irradiance monthly at each site were determined. Daily carbon gain was determined as a function of leaf nitrogen content to calculate the optimal leaf nitrogen content that maximized daily nitrogen-use efficiency.Key Results
As is known, the optimal leaf nitrogen content increased with increasing irradiance. The optimal leaf nitrogen content also increased with decreasing temperature because the photosynthetic capacity per Rubisco decreased. Across sites and months, the optimal leaf nitrogen content was close to the actual leaf nitrogen content and explained the variation in actual leaf nitrogen by 64 %. Sensitivity analysis showed that the effect of temperature on optimal nitrogen content was similar in magnitude to that of irradiance.Conclusions
Understorey evergreen species regulate leaf nitrogen content so as to maximize nitrogen-use efficiency in daily carbon gain under changing irradiance and temperature conditions. 相似文献107.
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109.
110.
Mechanisms for modulation of mouse gastrointestinal motility by proteinase-activated receptor (PAR)-1 and -2 in vitro 总被引:3,自引:0,他引:3
Sekiguchi F Hasegawa N Inoshita K Yonezawa D Inoi N Kanke T Saito N Kawabata A 《Life sciences》2006,78(9):950-957
Proteinase-activated receptor (PAR)-1 or -2 modulates gastrointestinal transit in vivo. To clarify the underlying mechanisms, we characterized contraction/relaxation caused by TFLLR-NH2 and SLIGRL-NH2, PAR-1- and -2-activating peptides, respectively, in gastric and small intestinal (duodenal, jejunal and ileal) smooth muscle isolated from wild-type and PAR-2-knockout mice. Either SLIGRL-NH2 or TFLLR-NH2 caused both relaxation and contraction in the gastrointestinal preparations from wild-type animals. Apamin, a K+ channel inhibitor, tended to enhance the peptide-evoked contraction in some of the gastrointestinal preparations, whereas it inhibited relaxation responses to either peptide completely in the stomach, but only partially in the small intestine. Indomethacin reduced the contraction caused by SLIGRL-NH2 or TFLLR-NH2 in both gastric and ileal preparations, but unaffected apamin-insensitive relaxant effect of either peptide in ileal preparations. Repeated treatment with capsaicin suppressed the contractile effect of either peptide in the stomach, but not clearly in the ileum, whereas it enhanced the apamin-insensitive relaxant effect in ileal preparations. In any gastrointestinal preparations from PAR-2-knockout mice, SLIGRL-NH2 produced no responses. Thus, the inhibitory component in tension modulation by PAR-1 and -2 involves both apamin-sensitive and -insensitive mechanisms in the small intestine, but is predominantly attributable to the former mechanism in the stomach. The excitatory component in the PAR-1 and -2 modulation may be mediated, in part, by activation of capsaicin-sensitive sensory nerves and/or endogenous prostaglandin formation. Our study thus clarifies the multiple mechanisms for gastrointestinal motility modulation by PAR-1 and -2, and also provides ultimate evidence for involvement of PAR-2. 相似文献