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991.
Gross photosynthetic capacity (P
G
) of greenhouse-grown tomato plants (Lycopersicon esculentum Mill.) decreased as the leaf aged. The P
G
of the 10th, 15th and 18th leaves from the top was only 76, 37, and 18 % of P
G
of the 5th leaf, respectively. Quantum yield (Y
Q
) and dark respiration rate (R
D
) were also lower in older leaves than in the younger ones. Net photosynthetic rate (P
G
) was apparent in young fruits (about 10 g FM) or young petioles but no P
N
was found in large fruits (40 g or more FM) and stems because of high R
D
. Both P
G
and R
D
were lower in older fruits and petioles or in lower parts of the stem compared to the younger ones or upper parts of stem.
A sharp decrease in chlorophyll (Chl) content was only measured in the senescing 18th leaf. The Chl content in petioles, stems
and fruits was proportional to P
G
. Decreases in P
G
of older leaves were attributed to decreases in content rather than activity of ribulose-1,5-bisphosphate carboxylase/oxygenase
(RuBPCO) since soluble protein content was lower in older leaves than in the younger ones but the specific activity (activity
per unit of protein) of RuBPCO was not so. The estimated values of P
N
of the 10th, 15th and 18th leaves inside the canopy were only 50, 21, and 7 % of that in the 5th leaf. Therefore, leaves
below the 18th can be removed in order to ensure a good air circulation and prevent diseases. The significance of photosynthesis
in fruit, stem and petioles is not negligible because photosynthesis re-fixes the respired CO2.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
992.
Effect of root zone carbon dioxide enrichment on ethylene inhibition of carbon assimilation in potato plants 总被引:2,自引:0,他引:2
Potato plants ( Solanum tuberosum L. var. Russet Burbank) treated with 1 μl ethylene 1−1 of air showed an inhibition of CO2 assimilation by 18%. The inhibition occurred after 3 h of exposure to ethylene and was not mediated through closure of the stomata. The enrichment of the root zone with CO2 almost completely abolished the ethylene inhibition of CO2 assimilation which was apparently due to an increase in the intercellular concentration of CO2 in leaves following enrichment. The effect of application of CO2 to the root zone on ethylene inhibition of CO2 assimilation seemed to last for a few days. Potato plants treated with aminoethoxyvinlglycine (AVG) showed an increase in fresh and dry weight as compared to non-treated plants. Our results indicate that both CO2 and AVG alter the effect of ethylene and promote growth in plants by inhibiting ethylene action and biosynthesis, respectively. 相似文献
993.
A list of plant species documented over the past 25 years to exhibit Crassulacean Acid Metabolism (CAM) is presented. The list compiles all available information on these species including their growth habits, succulent parts, carbon isotope discrimination values, CAM types, CAM inducers, and CAM modifications. 相似文献
994.
995.
996.
Phosphoenolpyruvate carboxylase (PEPC) from higher plants is usually assayed by using malate dehydrogenase (MDH) as a coupling enzyme. To avoid erroneous readings caused by metal ions, which convert oxaloacetate (OAA) to pyruvate, lactic dehydrogenase can be included. Reporting the total NADH used by both coupling enzymes gives the total OAA production. Microbial PEPC has been assayed by employing citrate synthase (CS) as a coupling enzyme which detects the reaction of CoA with Ellman's reagent. Comparable Km values for MgPEP are found with the two assays. When MDH alone is used as the coupling system, the Vmax value is about 60% larger than the one found with the CS assay. However, when MDH is added to the CS assay without the NADH cofactor, Vmax is brought back to the same level as that with the NADH-coupled enzyme. Malate inhibition of PEPC assayed with the CS coupling system is blocked by low concentrations of citrate in the range produced in the assay. High concentrations of citrate inhibit PEPC. Glucose-6-phosphate in concentrations higher than 1 m M blocks the response of PEPC to added MDH in the CS assay. 相似文献
997.
998.
999.
L. Nadeau D.A. Patten A. Caron L. Garneau E. Pinault-Masson M. Foretz P. Haddad B.G. Anderson L.S. Quinn K. Jardine M.W. McBurney E.E. Pistilli M.E. Harper C. Aguer 《Biochimica et Biophysica Acta (BBA)/General Subjects》2019,1863(2):395-407
Background
IL-15 is believed to play a role in the beneficial impact of exercise on muscle energy metabolism. However, previous studies have generally used supraphysiological levels of IL-15 that do not represent contraction-induced IL-15 secretion.Methods
L6 myotubes were treated acutely (3?h) and chronically (48?h) with concentrations of IL-15 mimicking circulating (1–10?pg/ml) and muscle interstitial (100?pg/ml ?20?ng/ml) IL-15 levels with the aim to better understand its autocrine/paracrine role on muscle glucose uptake and mitochondrial function.Results
Acute exposure to IL-15 levels representing muscle interstitial IL-15 increased basal glucose uptake without affecting insulin sensitivity. This was accompanied by increased mitochondrial oxidative functions in association with increased AMPK pathway and formation of complex III-containing supercomplexes. Conversely, chronic IL-15 exposure resulted in a biphasic effect on mitochondrial oxidative functions and ETC supercomplex formation was increased with low IL-15 levels but decreased with higher IL-15 concentrations. The AMPK pathway was activated only by high levels of chronic IL-15 treatment. Similar results were obtained in skeletal muscle from muscle-specific IL-15 overexpressing mice that show very high circulating IL-15 levels.Conclusions
Acute IL-15 treatment that mimics local IL-15 concentrations enhances muscle glucose uptake and mitochondrial oxidative functions. That mitochondria respond differently to different levels of IL-15 during chronic treatments indicates that IL-15 might activate two different pathways in muscle depending on IL-15 concentrations.General significance
Our results suggest that IL-15 may act in an autocrine/paracrine fashion and be, at least in part, involved in the positive effect of exercise on muscle energy metabolism. 相似文献1000.