Rubisco evolution in C4 eudicots: an analysis of Amaranthaceae sensu lato

BACKGROUND Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyses the key reaction in the photosynthetic assimilation of CO₂. In C₄ plants CO₂ is supplied to Rubisco by an auxiliary CO₂-concentrating pathway that helps to maximize the carboxylase activity of the enzyme while suppressing its oxygenase activity. As a consequence, C₄ Rubisco exhibits a higher maximum velocity but lower substrate specificity compared with the C₃ enzyme. Specific amino-acids in Rubisco are associated with C₄ photosynthesis in monocots, but it is not known whether selection has acted on Rubisco in a similar way in eudicots. METHODOLOGY/PRINCIPAL FINDINGS We investigated Rubisco evolution in Amaranthaceae sensu lato (including Chenopodiaceae), the third-largest family of C₄ plants, using phylogeny-based maximum likelihood and Bayesian methods to detect Darwinian selection on the chloroplast rbcL gene in a sample of 179 species. Two Rubisco residues, 281 and 309, were found to be under positive selection in C₄ Amaranthaceae with multiple parallel replacements of alanine by serine at position 281 and methionine by isoleucine at position 309. Remarkably, both amino-acids have been detected in other C₄ plant groups, such as C₄ monocots, illustrating a striking parallelism in molecular evolution. CONCLUSIONS/SIGNIFICANCE Our findings illustrate how simple genetic changes can contribute to the evolution of photosynthesis and strengthen the hypothesis that parallel amino-acid replacements are associated with adaptive changes in Rubisco.This research was funded by NERC (http://www.nerc.ac.uk/; grant number NE/H007741/1)

Observable effects caused by vacuum pair creation in the field of high-power optical lasers

We consider the possibility of an experimental proof of vacuum e+e- pair creation in the focus of two counter-propagating optical laser beams with an intensity of the order of 10^20 - 10^22 W/cm^2. Our approach is based on the collisionless kinetic equation for the distribution function of the e+e- pairs with the source term for particle production. As a possible experimental signal of vacuum pair production we consider the refraction of a high-frequency probe laser beam by the produced e+e- plasma to be observed by an interference filter. The generation of higher harmonics of the laser frequency in the self-consistent electric field is also investigated.Comment: 7 pages, 7 figures; typos corrected, Eq.(16) corrected, reference adde

The numerical simulation of utilizer of soil heat and heat receiver in joint operation

The numerical model of the joint work of borehole heat exchanger and evaporator of the heat pump is developed. The design of the evaporator is shelltube heat exchanger with segmental baffles with a boiling in the U-shaped tubes. The design of ground heat exchanger is heat exchanger with two U-shaped tubes, which are arranged in a vertical borehole. The effect on the system temperature of soil, the multiplicity of circulation in the evaporator heat exchanger, the filler of borehole is modeled by the developed model

Method of calculation and analysis of joint operation of circuit loop of ground heat exchangers and heat pump

The method of heat calculation of the joint work of borehole heat exchangers and heat pump circuits in quasi-stationary regime is developed. The effect of the heat pump efficiency of heat exchangers design values, refrigerant superheating in evaporator, temperatures of heat source and heat consumer were analyzed on the base of the developed method

Influence of ground heat source parameters and consumer on characteristics of geothermal heat pump system

Features of heat supply system based on the use of ground are investigated with the help of the method of numerical simulation. The variables are the parameters characterizing the heat source and the consumer: the average temperature ofthe soil, the area and the radiative properties of the surface heating panels, air temperature of heated space. It was found that the maximum energy efficiency of the system is achieved by using a low-temperature floor heating system