Biomedical subjects

Li-Song Chen

Publications and source records attributed to Li-Song Chen.

5 recordsLinked to original sources

PubMed2005

Effects of aluminum on light energy utilization and photoprotective systems in citrus leaves.

BACKGROUND AND AIMS: Under high photon flux, excitation energy may be in excess in aluminum (Al)-treated leaves, which use a smaller fraction of the absorbed light in electron transport due to decreased CO2 assimilation compared with normal leaves. The objectives of this study were to test the hypothesis that the antioxidant systems are up-regulated in Al-treated citrus leaves and correlate with protection from photoxidative damage, and to test whether xanthophyll cycle-dependent thermal energy dissipation is involved in dissipating excess excitation energy. * METHODS: 'Cleopatra' tangerine seedlings were fertilized and irrigated daily for 8 weeks with quarter-strength Hoagland's nutrient solution containing Al at a concentration of 0 or 2 mM from Al2(SO4)3.18H2O. Thereafter, leaf absorptance, chlorophyll (Chl) fluorescence, Al, pigments, antioxidant enzymes and metabolites were measured on fully expanded leaves. * KEY RESULTS: Compared with control leaves, energy was in excess in Al-treated leaves, which had smaller thermal energy dissipation, indicated by non-photochemical quenching (NPQ). In contrast, conversion of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) at midday increased in both treatments, but especially in Al-treated leaves, although A + Z accounted for less 40 % of the total xanthophyll cycle pool in them. Activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and catalase (CAT), and concentrations of ascorbate (AsA), dehydroascorbate (DASA), reduced glutathione (GSH) and oxidized glutathione (GSSG) were higher in Al-treated than in control leaves. * CONCLUSIONS: These results corroborate the hypothesis that, compared with control leaves, antioxidant systems are up-regulated in Al-treated citrus leaves and protect from photoxidative damage, whereas thermal energy dissipation was decreased. Thus, antioxidant systems are more important than thermal energy dissipation in dissipating excess excitation energy in Al-treated citrus leaves.

Aluminum↗

PubMed2005

Aluminum-induced decrease in CO2 assimilation in citrus seedlings is unaccompanied by decreased activities of key enzymes involved in CO2 assimilation.

'Cleopatra' tangerine (Citrus reshni Hort. ex Tanaka) seedlings were irrigated daily for 8 weeks with 1/4 strength Hoagland's nutrient solution containing 0 (control) or 2 mM aluminum (Al). Leaves from Al-treated plants had decreased CO2 assimilation and stomatal conductance, but increased intercellular CO2 concentrations compared with control leaves. On a leaf area basis, 2 mM Al increased activities of key enzymes in the Calvin cycle, including ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), stromal fructose-1,6-bisphosphatase (FBPase), and a key enzyme in starch synthesis, ADP-glucose pyrophosphorylase (AGPase), compared with control leaves. Aluminum had no effect on cytosolic FBPase activity, but it decreased sucrose phosphate synthase (SPS) activity. Aluminum had no effect on area-based concentrations of carbohydrates, glucose-6-phosphate (G6P) and fructose 6-phosphate (F6P) or the G6P:F6P ratio, but it decreased the area-based concentration of 3-phosphoglycerate (PGA). Photochemical quenching coefficient (qP) and electron transport rate through PSII were greatly reduced by Al. Non-photochemical quenching coefficient (NPQ) was less affected by Al than qP and electron transport rate through PSII. We conclude that the reduced rate of CO2 assimilation in Al-treated leaves was probably caused by a combination of factors such as reduced electron transport rate through PSII, increased closure of PSII reaction centers and increased photorespiration.

Aluminum Compounds↗

PubMed2004

Day-night changes of energy-rich compounds in crassulacean acid metabolism (CAM) species utilizing hexose and starch.

BACKGROUND AND AIMS: Plants with crassulacean acid metabolism (CAM) can be divided into two groups according to the major carbohydrates used for malic acid synthesis, either polysaccharide (starch) or monosaccharide (hexose). This is related to the mechanism and affects energy metabolism in the two groups. In Kalanchoë pinnata and K. daigremontiana, which utilize starch, ATP-dependent phosphofructokinase (tonoplast inorganic pyrophosphatase) activity is greater than inorganic pyrophosphate-dependent phosphofructokinase (tonoplast adenosine triphosphatase) activity, but the reverse is the case in pineapple (Ananas comosus) utilizing hexose. To test the hypothesis that the energy metabolism of the two groups differs, day-night changes in the contents of ATP, ADP, AMP, inorganic phosphate (Pi), phosphoenolpyruvate (PEP) and inorganic pyrophosphate (PPi) in K. pinnata and K. daigremontiana leaves and in pineapple chlorenchyma were analysed. METHODS: The contents of energy-rich compounds were measured spectrophotometrically in extracts of tissue sampled in the light and dark, using potted plants, kept for 15 d before the experiments in a growth chamber. KEY RESULTS: In the three species, ATP content and adenylate energy charge (AEC) increased in the dark and decreased in the light, in contrast to ADP and AMP. Changes in ATP and AEC were greater in Kalanchoë leaves than in pineapple chlorenchyma. PPi content in the three species increased in the dark, but on illumination it decreased rapidly and substantially, remaining little changed through the rest of the light period. Pi content of Kalanchoë leaves did not change between dark and light, whereas Pi in pineapple chlorenchyma increased in the dark and decreased in the light, and the changes were far greater than in Kalanchoë leaves. Light-dark changes in PEP content in the three species were similar. CONCLUSIONS: These results corroborate our hypothesis that day-night changes in the contents of energy-rich compounds differ between CAM species and are related to the carbohydrate used for malic acid synthesis.

Adenosine Diphosphate↗

PubMed2003

Both xanthophyll cycle-dependent thermal dissipation and the antioxidant system are up-regulated in grape (Vitis labrusca L cv Concord) leaves in response to N limitation.

One-year-old grapevines (Vitis labrusca L. cv. Concord) were supplied with 0, 5, 10, 15, or 20 mM nitrogen (N) in a modified Hoagland's solution twice weekly for 4 weeks. As leaf N decreased in response to N limitation, leaf chlorophyll (Chl) decreased linearly whereas leaf absorptance declined curvilinearly. Compared with high N leaves, low N leaves had lower quantum efficiency of PSII as a result of both an increase in non-photochemical quenching (NPQ) and an increase in closure of PSII reaction centres at midday under high photon flux density (PFD). Both the xanthophyll cycle pool size on a Chl basis and the conversion of violaxanthin (V) to antheraxanthin (A) and zeaxanthin (Z) at noon increased with decreasing leaf N. NPQ was closely related to A+Z expressed either on a Chl basis or as a percentage of the xanthophyll cycle pool. As leaf N increased, superoxide dismutase (SOD) activity on a Chl basis decreased linearly; activities of catalase (CAT) and glutathione reductase (GR) on a Chl basis increased linearly; activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDAR) and dehydroascorbate reductase (DHAR) expressed on the basis of Chl decreased rapidly first, then gradually reached a low level. In response to N limitation, the contents of ascorbate (AsA), dehydroascorbate (DAsA), reduced glutathione (GSH), and oxidized glutathione (GSSG) increased when expressed on a Chl basis, whereas the ratios of both AsA to DAsA and GSH to GSSG decreased. It is concluded that, in addition to decreasing light absorption by lowering Chl concentration, both xanthophyll cycle-dependent thermal energy dissipation and the antioxidant system are up-regulated to protect low N leaves from photo-oxidative damage under high light.

Antioxidants↗

PubMed2002

A comparative study on diurnal changes in metabolite levels in the leaves of three crassulacean acid metabolism (CAM) species, Ananas comosus, Kalanchoë daigremontiana and K. pinnata.

A comparative study on diurnal changes in metabolite levels associated with crassulacean acid metabolism (CAM) in the leaves of three CAM species, Ananas comosus (pineapple), a hexose-utilizing species, and Kalanchoë daigremontiana and K. pinnata, two starch-utilizing species, were made. All three CAM species showed a typical feature of CAM with nocturnal malate increase. In the two Kalanchoë species, isocitrate levels were higher than citrate levels; the reverse was the case in pineapple. In the two Kalanchoë species, a small nocturnal citrate increase was found and K. daigremontiana showed a small nocturnal isocitrate increase. Glucose 6-phosphate (G-6-P), fructose 6-phosphate (F-6-P) and glucose 1-phosphate (G-1-P) levels in the three CAM species rose rapidly during the first part of the dark period and decreased during the latter part of the dark period. The levels of the metabolites also decreased during the first 3 h of the light period, then, remained little changed through the rest of the light period. Absolute levels of G-6-P, F-6-P and G-1-P were higher in pineapple than in the two Kalanchoë species. Fructose 1,6-bisphosphate (F-1,6-P(2)) levels in the three CAM species increased during the dark period, then dramatically decreased during the first 3 h of the light period and remained unchanged through the rest of the light period. The extent of nocturnal F-1,6-P(2) increase was far greater in the two Kalanchoë species than in pineapple. Absolute levels of F-1,6-P(2) were higher in the two Kalanchoë species than in pineapple, especially during dark period. Diurnal changes in oxaloacetate (OAA), pyruvate (Pyr) and phosphoenolpyruvate (PEP) levels in the three CAM species were similar.

Carboxylic Acids↗