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961.
We determined the interactive effects of irradiance, elevated CO2 concentration (EC), and temperature in carrot (Daucus carota var. sativus). Plants of the cv. Red Core Chantenay (RCC) were grown in a controlled environmental plant growth room and exposed to 3
levels of photosynthetically active radiation (PAR) (400, 800, 1 200 μmol m−2 s−1), 3 leaf chamber temperatures (15, 20, 30 °C), and 2 external CO2 concentrations (C
a), AC and EC (350 and 750 μmol mol−1, respectively). Rates of net photosynthesis (P
N) and transpiration (E) and stomatal conductance (g
s
) were measured, along with water use efficiency (WUE) and ratio of internal and external CO2 concentrations (C
i/C
a). P
N revealed an interactive effect between PAR and C
a. As PAR increased so did P
N under both C
a regimes. The g
s
showed no interactive effects between the three parameters but had singular effects of temperature and PAR. E was strongly influenced by the combination of PAR and temperature. WUE was interactively affected by all three parameters.
Maximum WUE occurred at 15 °C and 1 200 μmol m−2 s− 1 PAR under EC. The C
i
/C
a
was influenced independently by temperature and C
a. Hence photosynthetic responses are interactively affected by changes in irradiance, external CO2 concentration, and temperature. EC significantly compensates the inhibitory effects of high temperature and irradiance on
P
N and WUE. 相似文献
962.
The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C3), F. floridana (C3–C4), F. brownii (C4-like), and F. trinervia (C4) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in
the C3 species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient
to interpret the net photosynthetic rates (P
N), but, from the decreases in P
N values under high CO2 (C
a = 700 μmol mol− 1) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C3 species. The observed decline in the photosynthesis capacity of the C3–C4 species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum P
N observed in the C4-like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate
(RuBP or PEP) regeneration rates. In the C4 species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS
plants. 相似文献
963.
A controlled growth chamber experiment was conducted to investigate the short-term water use and photosynthetic responses
of 30-d-old carrot seedlings to the combined effects of CO2 concentration (50–1 050 μmol mol−1) and moisture deficits (−5, −30, −55, and −70 kPa). The photosynthetic response data was fitted to a non-rectangular hyperbola
model. The estimated parameters were compared for effects of moisture deficit and elevated CO2 concentration (EC). The carboxylation efficiency (α) increased in response to mild moisture stress (−30 kPa) under EC when
compared to the unstressed control. However, moderate (−55 kPa) and extreme (−70 kPa) moisture deficits reduced α under EC.
Maximum net photosynthetic rate (P
Nmax) did not differ between mild water deficit and unstressed controls under EC. Moderate and extreme moisture deficits reduced
P
Nmax by nearly 85 % compared to controls. Dark respiration rate (R
D) showed no consistent response to moisture deficit. The CO2 compensation concentration (Γ) was 324 μmol mol−1 for −75 kPa and ranged 63–93 μmol mol−1 for other moisture regimes. Interaction between moisture deficit and EC was noticed for P
N, ratio of intercellular and ambient CO2 concentration (C
i/C
a), stomatal conductance (g
s
), and transpiration rate (E). P
N was maximum and C
i/C
a was minimum at −30 kPa moisture deficit and at C
a of 350 μmol mol−1. The g
s and E showed an inverse relationship at all moisture deficit regimes and EC. Water use efficiency (WUE) increased with moisture
deficit up to −55 kPa and declined thereafter. EC showed a positive influence towards sustaining P
N and increasing WUE only under mild moisture stress, and no beneficial effects of EC were noticed at moderate or extreme moisture
deficits. 相似文献
964.
Choi IY Kim SJ Jeong HJ Park SH Song YS Lee JH Kang TH Park JH Hwang GS Lee EJ Hong SH Kim HM Um JY 《Molecular and cellular biochemistry》2007,305(1-2):153-161
The citrus unshiu peel has been used traditionally as a medicine to improve bronchial and asthmatic conditions or cardiac
and blood circulation in Korea, China, and Japan. Here, we report the effects of citrus unshiu peel water extract (CPWE) on
the phorbol myristate acetate (PMA) + calcium ionophore A23187-induced hypoxia-inducible factor-1α (HIF-1α) activation and
inflammatory cytokine production from the human mast cell line, HMC-1 cells. We compared CPWE with hesperidin, a common constituent
of citrus unshiu. CPWE and hesperidin inhibited the PMA + A23187-induced HIF-1α expression and the subsequent production of
vascular endothelial growth factor (VEGF). In addition, CPWE suppressed PMA + A23187-induced phosphorylation of the extracellular
signal-regulated kinase (ERK). We also show that the increased cytokines interleukin (IL)-1β, IL-8, and tumor necrosis factor
(TNF)-α level was significantly inhibited by treatment of CPWE or hesperidin. In the present study, we report that CPWE and
hesperidin are inhibitors of HIF-1α and cytokines on the mast cell-mediated inflammatory responses. 相似文献
965.
Orozco-Segovia A Márquez-Guzmán J Sánchez-Coronado ME Gamboa de Buen A Baskin JM Baskin CC 《Annals of botany》2007,99(4):581-592
BACKGROUND AND AIMS: There is considerable confusion in the literature concerning impermeability of seeds with 'hard' seed coats, because the ability to take up (imbibe) water has not been tested in most of them. Seeds of Opuntia tomentosa were reported recently to have a water-impermeable seed coat sensu lato (i.e. physical dormancy), in combination with physiological dormancy. However, physical dormancy is not known to occur in Cactaceae. Therefore, the aim of this study was to determine if seeds of O. tomentosa are water-permeable or water-impermeable, i.e. if they have physical dormancy. METHODS: The micromorphology of the seed coat and associated structures were characterized by SEM and light microscopy. Permeability of the seed-covering layers was assessed by an increase in mass of seeds on a wet substrate and by dye-tracking and uptake of tritiated water by intact versus scarified seeds. KEY RESULTS: A germination valve and a water channel are formed in the hilum-micropyle region during dehydration and ageing in seeds of O. tomentosa. The funicular envelope undoubtedly plays a role in germination of Opuntia seeds via restriction of water uptake and mechanical resistance to expansion of the embryo. However, seeds do not exhibit any of three features characteristic of those with physical dormancy. Thus, they do not have a water-impermeable layer(s) of palisade cells (macrosclereids) or a water gap sensu stricto and they imbibe water without the seed coat being disrupted. CONCLUSIONS: Although dormancy in seeds of this species can be broken by scarification, they have physiological dormancy only. Further, based on information in the literature, it is concluded that it is unlikely that any species of Opuntia has physical dormancy. This is the first integrative study of the anatomy, dynamics of water uptake and dormancy in seeds of Cactaceae subfamily Opuntioideae. 相似文献
966.
967.
Peeter Nõges Wouter Van de Bund Ana Cristina Cardoso Anna-Stiina Heiskanen 《Hydrobiologia》2007,584(1):373-379
In most cases the negative impacts of climate change to aquatic ecosystems cannot be mitigated by measures in the river basin
management. Ignoring climate change by the Water Framework Directive may have strong implications for the typology and quality
assessment systems used for water bodies. As a result of climate change, water bodies, especially those located near the type
boundaries may change their type. Compared to typology characteristics, water quality parameters are even more labile and
may be easily affected by climate change. The paper exemplifies that the anticipated deterioration of water quality within
the time frame relevant for WFD implementation may be large enough to endanger the fulfillment of the set water quality objectives.
The review of the river basin characterization every six years, as required by the WFD, might also include re-evaluation of
reference conditions according to the changes observed at pristine reference sites. As a consequence, the restoration targets
(i.e., the good ecological status) would also need to be evaluated periodically. 相似文献
968.
External phosphorus load to a wetland with two shallow lakes in the Botshol Nature Reserve, The Netherlands, was reduced,
resulting in a rapid reduction of phytoplankton biomass and turbidity, and after 4 years, explosive growth of Characeae. The
clear water state was unstable, however, and the ecosystem then alternated between clear, high-vegetation and turbid, low-vegetation
states. A model of water quality processes was used in conjunction with a 14-year nutrient budget for Botshol to determine
if fluctuations in precipitation and nutrient load caused the ecosystem instability. The results indicate that, during wet
winters when groundwater level rose above surface water level, phosphorus from runoff was stored in the lake bottom and banks.
Stored phosphorus was released the following spring and summer under anaerobic sediment conditions, resulting in increased
phytoplankton density and light attenuation in the water column. During years with high net precipitation, flow from land
to surface water also transported humic acids, further increasing light attenuation. In years with dry winters, the phosphorus
and humic acid loads to surface water were reduced, and growth of submerged macrophytes was enhanced by clear water. Thus,
the temporal pattern of precipitation and flow from land to water gave a coherent, quantitative explanation of the observed
dynamics in phosphorus, phytoplankton, turbidity, and Characeae. Global warming has caused winters in The Netherlands to become
warmer and wetter during the last 50 years, increasing flow from land to water of humic acids and phosphorus and, ultimately,
enhancing instability of Characeae populations. In the first half of the 20th century interannual variation in precipitation
was not sufficient to cause large changes in internal P flux in Botshol, and submerged macrophyte populations were stable. 相似文献
969.
在实验室条件下观察了小五台山15种蒿属(Artemisia L.)植物种子的基本形态特征,同时进行了种子吸水和发芽试验。结果表明:15种蒿属植物种子近于倒卵形或长卵形,大小差异明显,大籽蒿(A.sieversiana)种子千粒重最大为0.474g,猪毛蒿(A.scoparia)种子千粒重最小仅为0.047g,其余13种种子的千粒重为0.057~0.184g之间。种子吸水率和吸水量与是否有粘液溶出有明显的关系,有粘液溶出的旱生植物种子吸水速率快、吸水量大。15种蒿属植物种子均无明显休眠特性,多数萌发率大于70%,最高可达100%,只有红足蒿(A.rubripes)和魁蒿(A.princeps)萌发率不足50%。蒿属植物种子吸水和萌发特性显示出该属大部分种类能适应北方春季干旱少雨的气候特点,利用少量水可顺利萌发。 相似文献
970.