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Leaf Sections (leaf + section)
Selected AbstractsLeaf photoacclimatory responses of the tropical seagrass Thalassia testudinum under mesocosm conditions: a mechanistic scaling-up studyNEW PHYTOLOGIST, Issue 1 2007Napo M. Cayabyab Summary ,,Here, the leaf photoacclimatory plasticity and efficiency of the tropical seagrass Thalassia testudinum were examined. ,,Mesocosms were used to compare the variability induced by three light conditions, two leaf sections and the variability observed at the collection site. ,,The study revealed an efficient photosynthetic light use at low irradiances, but limited photoacclimatory plasticity to increase maximum photosynthetic rates (Pmax) and saturation (Ek) and compensation (Ec) irradiances under high light irradiance. A strong, positive and linear association between the percentage of daylight hours above saturation and the relative maximum photochemical efficiency (FV/FM) reduction observed between basal and apical leaf sections was also found. ,,The results indicate that T. testudinum leaves have a shade-adapted physiology. However, the large amount of heterotrophic biomass that this seagrass maintains may considerably increase plant respiratory demands and their minimum quantum requirements for growth (MQR). Although the MQR still needs to be quantified, it is hypothesized that the ecological success of this climax species in the oligotrophic and highly illuminated waters of the Caribbean may rely on the ability of the canopy to regulate the optimal leaf light environment and the morphological plasticity of the whole plant to enhance total leaf area and to reduce carbon respiratory losses. [source] Water vapour isotopic exchange by epiphytic bromeliads in tropical dry forests reflects niche differentiation and climatic signalsPLANT CELL & ENVIRONMENT, Issue 6 2008CASANDRA REYES-GARCÍA ABSTRACT The 18O signals in leaf water (,18Olw) and organic material were dominated by atmospheric water vapour 18O signals (,18Ovap) in tank and atmospheric life forms of epiphytic bromeliads with crassulacean acid metabolism (CAM), from a seasonally dry forest in Mexico. Under field conditions, the mean ,18Olw for all species was constant during the course of the day and systematically increased from wet to dry seasons (from 0 to +6,), when relative water content (RWC) diminished from 70 to 30%. In the greenhouse, progressive enrichment from base to leaf tip was observed at low night-time humidity; under high humidity, the leaf tip equilibrated faster with ,18Ovap than the other leaf sections. Laboratory manipulations using an isotopically depleted water source showed that ,18Ovap was more rapidly incorporated than liquid water. Our data were consistent with a Craig,Gordon (C-G) model as modified by Helliker and Griffiths predicting that the influx and exchange of ,18Ovap control ,18Olw in certain epiphytic life forms, despite progressive tissue water loss. We use ,18Olw signals to define water-use strategies for the coexisting species which are consistent with habitat preference under natural conditions and life form. Bulk organic matter (,18Oorg) is used to predict the ,18Ovap signal at the time of leaf expansion. [source] crinkled leaves 8 , A mutation in the large subunit of ribonucleotide reductase , leads to defects in leaf development and chloroplast division in Arabidopsis thalianaTHE PLANT JOURNAL, Issue 1 2007Sarah Garton Summary The crinkled leaves8 (cls8) mutant of Arabidopsis thaliana displays a developmental phenotype of abnormal leaf and flower morphology, reduced root growth and bleached leaf sections. Map-based cloning identified the mutation as being within the gene encoding the large subunit of ribonucleotide reductase (RNR1), the enzyme that catalyses the rate-limiting step in the production of deoxyribonucleoside triphosphates (dNTPs) for DNA synthesis and repair. Levels of dTTP and dATP were significantly reduced in cls8. Two further mutant cls8 alleles and cls8::RNAi plants show similar or more severe phenotypes. The cls8-1 mutant has fewer copies of the chloroplast genome, and fewer, larger chloroplasts than wild-type plants. The ultrastructure of the chloroplast, however, appears normal in cls8-1 leaves. We present evidence that, under conditions of limited dNTP supply, the inhibition of chloroplast DNA replication may be the primary factor in inducing aberrant growth. [source] Acclimation of photosynthesis to elevated CO2 in onion (Allium cepa) grown at a range of temperaturesANNALS OF APPLIED BIOLOGY, Issue 1 2004T R WHEELER Summary Onion (Allium cepa) was grown in the field within temperature gradient tunnels (providing about -2.5°C to +2.5°C from outside temperatures) maintained at either 374 or 532 ,mol mol,1 CO2. Plant leaf area was determined non-destructively at 7 day intervals until the time of bulbing in 12 combinations of temperature and CO2 concentration. Gas exchange was measured in each plot at the time of bulbing, and the carbohydrate content of the leaf (source) and bulb (sink) was determined. Maximum rate of leaf area expansion increased with mean temperature. Leaf area duration and maximum rate of leaf area expansion were not significantly affected by CO2. The light-saturated rates of leaf photosynthesis (Asat) were greater in plants grown at normal than at elevated CO2 concentrations at the same measurement CO2 concentration. Acclimation of photosynthesis decreased with an increase in growth temperature, and with an increase in leaf nitrogen content at elevated CO2. The ratio of intercellular to atmospheric CO2 (C1/C3 ratio) was 7.4% less for plants grown at elevated compared with normal CO2. Asat in plants grown at elevated CO2 was less than in plants grown at normal CO2 when compared at the same C1. Hence, acclimation of photosynthesis was due both to stomatal acclimation and to limitations to biochemical CO2 fixation. Carbohydrate content of the onion bulbs was greater at elevated than at normal CO2. In contrast, carbohydrate content was less at elevated compared with normal CO2 in the leaf sections in which CO2 exchange was measured at the same developmental stage. Therefore, acclimation of photosynthesis in fully expanded onion leaves was detected despite the absence of localised carbohydrate accumulation in these field-grown crops. [source] Fluctuations in concentration of two potyviruses in garlic during the growing period and sampling conditions for reliable detection by ELISAANNALS OF APPLIED BIOLOGY, Issue 1 2002C I DOVAS Summary To optimise sampling conditions for the detection by ELISA of Onion yellow dwarf virus (OYDV) and Leek yellow stripe virus (LYSV), the most important viral pathogens of garlic worldwide, relative virus concentrations were determined during the growing period and in different leaf parts by DAS-ELISA. Both viruses were found to have uneven distributions in garlic plants, with the tips of the two latest fully developed leaves showing the highest concentrations and the oldest leaves the lowest concentrations. The tips of the youngest leaves were found to have higher virus concentrations than their middle and basal sections. In the older leaves, viruses were distributed more uniformly in the three leaf sections. In the oldest leaves virus levels in the leaf tips were significantly decreased. The concentrations of OYDV and LYSV increased until March, whereas later on they decreased. During storage of leaf samples at 6°C for 15 days, a loss was found of both virus antigens of more than 80%, and during 109 days of storage at ,30°C a loss of more than 90% was found. [source] | ||||||||||