Overexpression of the barley aquaporin HvPIP2;1 increases internal CO(2) conductance and CO(2) assimilation in the leaves of transgenic rice plants

The internal conductance for CO(2) diffusion (g(i)) and CO(2) assimilation rate were measured and the related anatomical characteristics were investigated in transgenic rice leaves that overexpressed barley aquaporin HvPIP2;1. This study was performed to test the hypothesis that aquaporin facilitates CO(2) diffusion within leaves. The g(i) value was estimated for intact leaves by concurrent measurements of gas exchange and carbon isotope ratio. The leaves of the transgenic rice plants that expressed the highest levels of Aq-anti-HvPIP2;1 showed a 40% increase in g(i) as compared to g(i) in the leaves of wild-type rice plants. The increase in g(i) was accompanied by a 14% increase in CO(2) assimilation rate and a 27% increase in stomatal conductance (g(s)). The transgenic plants that had low levels of Aq-anti-HvPIP2;1 showed decreases in g(i) and CO(2) assimilation rate. In the plants with high levels of Aq-anti-HvPIP2;1, mesophyll cell size decreased and the cell walls of the epidermis and mesophyll cells thickened, indicating that the leaves had become xeromorphic. Although such anatomical changes could partially offset the increase in g(i) by the aquaporin, the increase in aquaporin content overcame such adverse effects.     

A high-performance system of multiple gas-exchange chambers with a laser spectrometer to estimate leaf photosynthesis,stomatal conductance,and mesophyll conductance

Journal of Plant Research - Direct measurements of ecophysiological processes such as leaf photosynthesis are often hampered due to the excessive time required for gas-exchange measurements and the...     

Seasonal changes in needle water content and needle ABA concentration of Japanese red pine, Pinus densiflora, in declining forests on Mt. Gokurakuji, Hiroshima prefecture, Japan

To evaluate the effects of air pollution on the decline of Pinus densiflora forests, various research has been conducted around Mt. Gokurakuji (34° 23N, 132° 19E, 693 m a.s.l.) north of the Seto Inland Sea, west Japan. To investigate the mechanisms responsible for decreases in photosynthesis (Pn) and stomatal conductance (gl), ¹³C of needles and seasonal changes in the water content (WC) and abscisic acid concentration (ABA) of needles were measured in various stands. The ¹³C values were less negative in declining stands and younger needles. ABA and WC were not correlated with each other. WC decreased consistently with needle age while the ABA showed a minimum in August and a smaller content in older needles. Monthly precipitation and the daily maximum vapor pressure were not correlated with ABA and WC. In declining stands, WC and ABA tended to be higher and lower, respectively, than in nondeclining stands. These results suggest that the trees in declining stands received less water stress than those in nondeclining stands and the differences in gl and ¹³C are not caused by the difference in water stress. The possibilities of the effects of air pollution and the infection of pine-wood nematode on the physiological decline on the pine needles are discussed.     

How plants grow under gravity conditions besides 1 g: perspectives from hypergravity and space experiments that employ bryophytes as a model organism

Plant Molecular Biology - Plants have evolved and grown under the selection pressure of gravitational force at 1 g on Earth. In response to this selection pressure, plants have acquired...     

Irradiance and phenotype: comparative eco-development of sun and shade leaves in relation to photosynthetic CO2 diffusion

The subject of this paper, sun leaves are thicker and show higher photosynthetic rates than the shade leaves, is approached in two ways. The first seeks to answer the question: why are sun leaves thicker than shade leaves? To do this, CO2 diffusion within a leaf is examined first. Because affinity of Rubisco for CO2 is low, the carboxylation of ribulose 1,5-bisphosphate is competitively inhibited by O2, and the oxygenation of ribulose 1,5-bisphosphate leads to energy-consuming photorespiration, it is essential for C3 plants to maintain the CO2 concentration in the chloroplast as high as possible. Since the internal conductance for CO2 diffusion from the intercellular space to the chloroplast stroma is finite and relatively small, C3 leaves should have sufficient mesophyll surfaces occupied by chloroplasts to secure the area for CO2 dissolution and transport. This explains why sun leaves are thicker. The second approach is mechanistic or 'how-oriented'. Mechanisms are discussed as to how sun leaves become thicker than shade leaves, in particular, the long-distance signal transduction from mature leaves to leaf primordia inducing the periclinal division of the palisade tissue cells. To increase the mesophyll surface area, the leaf can either be thicker or have smaller cells. Issues of cell size are discussed to understand plasticity in leaf thickness.     

Effects of internal conductance on the temperature dependence of the photosynthetic rate in spinach leaves from contrasting growth temperatures

The photosynthetic rate may be strongly limited by internal conductance from the intercellular airspace to the chloroplast stroma (g(i)). However, the effects of growth and leaf temperature on g(i) are still unclarified. In this work, we determined the temperature dependence of g(i) in spinach leaves grown at 30/25 degrees C (high temperature; HT) and 15/10 degrees C (low temperature; LT), using the concurrent measurements of the gas exchange rate and stable carbon isotope ratio. Moreover, we quantified the effects of g(i) on the temperature dependence of the photosynthetic rate. We measured g(i) and the photosynthetic rate at a CO(2) concentration of 360 microl l(-1) under saturating light (A(360)) at different leaf temperatures. The optimum temperature for A(360) was 28.5 degrees C in HT leaves and 22.9 degrees C in LT leaves. The optimum temperatures for g(i) were almost similar to those of A(360) in both HT and LT leaves. There was a strong linear relationship between A(360) and g(i). The photosynthetic rates predicted from the C(3) photosynthesis model taking account of g(i) agreed well with A(360) in both HT and LT leaves. The temperature coefficients (Q(10)) of g(i) between 10 and 20 degrees C were 2.0 and 1.8 in HT and LT leaves, respectively. This suggests that g(i) was determined not only by physical diffusion but by processes facilitated by protein(s). The limitation of the photosynthetic rate imposed by g(i) increased with leaf temperature and was greater than the limitation of the stomatal conductance at any temperature, in both HT and LT leaves. This study suggests that g(i) substantially limits the photosynthetic rate, especially at higher temperatures.     

Variations in the foliar δ13C and C3/C4 species richness in the Japanese flora of Poaceae among climates and habitat types under human activity

For 383 Poaceae species harvested over the Japanese islands and stored as herbarium specimens along several decades, we determined C₃ and C₄ types of photosynthesis from leaf stable carbon isotope ratio (δ¹³C). Then, we sought the relationships between C₄ species richness and climatic factors or habitat types. Except for the two Panicum species (P. lanuginosum and P. scoparium) having the possibility of C₃–C₄ intermediate, 227 and 154 species were classified into C₃ and C₄. The C₄ species richness increased from northern to southern islands in Japan, positively correlated with mean annual air temperature. Greater C₄ species richness in the seashore habitats, and smaller C₄ species richness in the shaded, wet and highland habitats would be related to the photosynthetic responses to local environmental factors such as irradiance level and temperature regime. No difference of leaf δ-value of C₃ Poaceae was obtained between the habitats with different soil water availability, suggesting the less importance of soil water availability on leaf water-use efficiency in C₃ Poaceae species in Japan having humid climate. Additionally, possible effects of human activity around the harvested time or site on leaf δ-value were estimated, because the habitat includes the sites with high human activity. Leaf δ-value was decreased with sampling year, and it was higher in the densely inhabited district for both C₃ and C₄. They are probably due to a historical decrease in the atmospheric δ-value via increasing human activity, and high gas emission at the districts of high human density.     

The photosynthetic response of tobacco plants overexpressing ice plant aquaporin McMIPB to a soil water deficit and high vapor pressure deficit

We investigated the photosynthetic capacity and plant growth of tobacco plants overexpressing ice plant (Mesembryanthemum crystallinum L.) aquaporin McMIPB under (1) a well-watered growth condition, (2) a well-watered and temporal higher vapor pressure deficit (VPD) condition, and (3) a soil water deficit growth condition to investigate the effect of McMIPB on photosynthetic responses under moderate soil and atmospheric humidity and water deficit conditions. Transgenic plants showed a significantly higher photosynthesis rate (by 48 %), higher mesophyll conductance (by 52 %), and enhanced growth under the well-watered growth condition than those of control plants. Decreases in the photosynthesis rate and stomatal conductance from ambient to higher VPD were slightly higher in transgenic plants than those in control plants. When plants were grown under the soil water deficit condition, decreases in the photosynthesis rate and stomatal conductance were less significant in transgenic plants than those in control plants. McMIPB is likely to work as a CO₂ transporter, as well as control the regulation of stomata to water deficits.     

The feasibility of age-specific travel restrictions during influenza pandemics

Background

Epidemiological studies have shown that imposing travel restrictions to prevent or delay an influenza pandemic may not be feasible. To delay an epidemic substantially, an extremely high proportion of trips (~99%) would have to be restricted in a homogeneously mixing population. Influenza is, however, strongly influenced by age-dependent transmission dynamics, and the effectiveness of age-specific travel restrictions, such as the selective restriction of travel by children, has yet to be examined.

Methods

A simple stochastic model was developed to describe the importation of infectious cases into a population and to model local chains of transmission seeded by imported cases. The probability of a local epidemic, and the time period until a major epidemic takes off, were used as outcome measures, and travel restriction policies in which children or adults were preferentially restricted were compared to age-blind restriction policies using an age-dependent next generation matrix parameterized for influenza H1N1-2009.

Results

Restricting children from travelling would yield greater reductions to the short-term risk of the epidemic being established locally than other policy options considered, and potentially could delay an epidemic for a few weeks. However, given a scenario with a total of 500 imported cases over a period of a few months, a substantial reduction in the probability of an epidemic in this time period is possible only if the transmission potential were low and assortativity (i.e. the proportion of contacts within-group) were unrealistically high. In all other scenarios considered, age-structured travel restrictions would not prevent an epidemic and would not delay the epidemic for longer than a few weeks.

Conclusions

Selectively restricting children from traveling overseas during a pandemic may potentially delay its arrival for a few weeks, depending on the characteristics of the pandemic strain, but could have less of an impact on the economy compared to restricting adult travelers. However, as long as adults have at least a moderate potential to trigger an epidemic, selectively restricting the higher risk group (children) may not be a practical option to delay the arrival of an epidemic substantially.