Fast dehydration reduces bundle sheath conductance in C maize and sorghum.

In the face of anthropogenic warming, drought poses an escalating threat to food production. C plants offer promise in addressing this threat. C leaves operate a biochemical CO concentrating mechanism that exchanges metabolites between two partially isolated compartments (mesophyll and bundle sheath), which confers high-productivity potential in hot climates boosting water use efficiency.

The operation of PEPCK increases light harvesting plasticity in C NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study.

The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase (PEPCK) subtypes of C photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea.

C maize and sorghum are more sensitive to rapid dehydration than C wheat and sunflower.

The high productive potential, heat resilience, and greater water use efficiency of C over C plants attract considerable interest in the face of global warming and increasing population, but C plants are often sensitive to dehydration, questioning the feasibility of their wider adoption. To resolve the primary effect of dehydration from slower from secondary leaf responses originating within leaves to combat stress, we conducted an innovative dehydration experiment. Four crops grown in hydroponics were forced to a rapid yet controlled decrease in leaf water potential by progressively raising roots of out of the solution while measuring leaf gas exchange.

Physiological responses to low CO over prolonged drought as primers for forest-grassland transitions.

Savannahs dominated by grasses with scattered C trees expanded between 24 and 9 million years ago in low latitudes at the expense of forests. Fire, herbivory, drought and the susceptibility of trees to declining atmospheric CO concentrations ([CO]) are proposed as key drivers of this transition. The role of disturbance is well studied, but physiological arguments are mostly derived from models and palaeorecords, without direct experimental evidence.

Upregulation of bundle sheath electron transport capacity under limiting light in C Setaria viridis.

C photosynthesis is a biochemical pathway that operates across mesophyll and bundle sheath (BS) cells to increase CO concentration at the site of CO fixation. C plants benefit from high irradiance but their efficiency decreases under shade, causing a loss of productivity in crop canopies. We investigated shade acclimation responses of Setaria viridis, a model monocot of NADP-dependent malic enzyme subtype, focussing on cell-specific electron transport capacity.

Response of photosynthesis, growth and water relations of a savannah-adapted tree and grass grown across high to low CO2.

Background And Aims: By the year 2100, atmospheric CO2 concentration ([CO2]a) could reach 800 ppm, having risen from ~200 ppm since the Neogene, beginning ~24 Myr ago. Changing [CO2]a affects plant carbon-water balance, with implications for growth, drought tolerance and vegetation shifts. The evolution of C4 photosynthesis improved plant hydraulic function under low [CO2]a and preluded the establishment of savannahs, characterized by rapid transitions between open C4-dominated grassland with scattered trees and closed forest.

A Dynamic Hydro-Mechanical and Biochemical Model of Stomatal Conductance for C Photosynthesis.

C plants are major grain (maize [] and sorghum []), sugar (sugarcane []), and biofuel ( spp.) producers and contribute ∼20% to global productivity. Plants lose water through stomatal pores in order to acquire CO (assimilation []) and control their carbon-for-water balance by regulating stomatal conductance ().

Anatomical constraints to C4 evolution: light harvesting capacity in the bundle sheath.

In C4 photosynthesis CO2 assimilation and reduction are typically coordinated across mesophyll (M) and bundle sheath (BS) cells, respectively. This system consequently requires sufficient light to reach BS to generate enough ATP to allow ribulose-1,5-bisphosphate (RuBP) regeneration in BS. Leaf anatomy influences BS light penetration and therefore constrains C4 cycle functionality.

Deriving C4 photosynthetic parameters from combined gas exchange and chlorophyll fluorescence using an Excel tool: theory and practice.

The higher photosynthetic potential of C4 plants has led to extensive research over the past 50 years, including C4 -dominated natural biomes, crops such as maize, or for evaluating the transfer of C4 traits into C3 lineages. Photosynthetic gas exchange can be measured in air or in a 2% Oxygen mixture using readily available commercial gas exchange and modulated PSII fluorescence systems. Interpretation of these data, however, requires an understanding (or the development) of various modelling approaches, which limit the use by non-specialists.

An Excel tool for deriving key photosynthetic parameters from combined gas exchange and chlorophyll fluorescence: theory and practice.

Combined photosynthetic gas exchange and modulated fluorometres are widely used to evaluate physiological characteristics associated with phenotypic and genotypic variation, whether in response to genetic manipulation or resource limitation in natural vegetation or crops. After describing relatively simple experimental procedures, we present the theoretical background to the derivation of photosynthetic parameters, and provide a freely available Excel-based fitting tool (EFT) that will be of use to specialists and non-specialists alike. We use data acquired in concurrent variable fluorescence-gas exchange experiments, where A/Ci and light-response curves have been measured under ambient and low oxygen.

Esculetin and esculin (esculetin 6-O-glucoside) occur as inclusions and are differentially distributed in the vacuole of palisade cells in Fraxinus ornus leaves: a fluorescence microscopy analysis.

The location of individual coumarins in leaves of Fraxinus ornus acclimated at full solar irradiance was estimated using their specific UV- and fluorescence spectral features. Using a combination of UV-induced fluorescence and blue light-induced fluorescence of tissues stained with diphenylborinic acid 2-amino-ethylester, in wide field or confocal laser scanning microscopy, we were able to visualize the distribution of esculetin and esculetin 6-O-glucoside (esculin) in palisade cells. Coumarins are not uniformly distributed in the cell vacuole, but accumulate mostly in the adaxial portion of palisade cells.

A high throughput gas exchange screen for determining rates of photorespiration or regulation of C4 activity.

Large-scale research programmes seeking to characterize the C4 pathway have a requirement for a simple, high throughput screen that quantifies photorespiratory activity in C3 and C4 model systems. At present, approaches rely on model-fitting to assimilatory responses (A/C i curves, PSII quantum yield) or real-time carbon isotope discrimination, which are complicated and time-consuming. Here we present a method, and the associated theory, to determine the effectiveness of the C4 carboxylation, carbon concentration mechanism (CCM) by assessing the responsiveness of V O/V C, the ratio of RuBisCO oxygenase to carboxylase activity, upon transfer to low O2.

Acclimation of C4 metabolism to low light in mature maize leaves could limit energetic losses during progressive shading in a crop canopy.

C4 plants have a biochemical carbon-concentrating mechanism that increases CO2 concentration around Rubisco in the bundle sheath. Under low light, the activity of the carbon-concentrating mechanism generally decreases, associated with an increase in leakiness (ϕ), the ratio of CO2 retrodiffusing from the bundle sheath relative to C4 carboxylation. This increase in ϕ had been theoretically associated with a decrease in biochemical operating efficiency (expressed as ATP cost of gross assimilation, ATP/GA) under low light and, because a proportion of canopy photosynthesis is carried out by shaded leaves, potential productivity losses at field scale.

The operation of two decarboxylases, transamination, and partitioning of C4 metabolic processes between mesophyll and bundle sheath cells allows light capture to be balanced for the maize C4 pathway.

The C4 photosynthesis carbon-concentrating mechanism in maize (Zea mays) has two CO2 delivery pathways to the bundle sheath (BS; via malate or aspartate), and rates of phosphoglyceric acid reduction, starch synthesis, and phosphoenolpyruvate regeneration also vary between BS and mesophyll (M) cells. The theoretical partitioning of ATP supply between M and BS cells was derived for these metabolic activities from simulated profiles of light penetration across a leaf, with a potential 3-fold difference in the fraction of ATP produced in the BS relative to M (from 0.29 to 0.

Acclimation to low light by C4 maize: implications for bundle sheath leakiness.

C4 plants have a biochemical carbon concentrating mechanism (CCM) that increases CO2 concentration around ribulose bisphosphate carboxylase oxygenase (Rubisco) in the bundle sheath (BS). Under limiting light, the activity of the CCM generally decreases, causing an increase in leakiness, (Φ), the ratio of CO2 retrodiffusing from the BS relative to C4 carboxylation processes. Maize plants were grown under high and low light regimes (respectively HL, 600 versus LL, 100 μE m(-2)  s(-1) ).