The Activity of Nodules of the Supernodulating Mutant Mtsunn Is not Limited by Photosynthesis under Optimal Growth Conditions

Legumes match the nodule number to the N demand of the plant. When a mutation in the regulatory mechanism deprives the plant of that ability, an excessive number of nodules are formed. These mutants show low productivity in the fields, mainly due to the high carbon burden caused through the necessity to supply numerous nodules. The objective of this study was to clarify whether through optimal conditions for growth and CO₂ assimilation a higher nodule activity of a supernodulating mutant of Medicago truncatula (M. truncatula) can be induced. Several experimental approaches reveal that under the conditions of our experiments, the nitrogen fixation of the supernodulating mutant, designated as sunn (super numeric nodules), was not limited by photosynthesis. Higher specific nitrogen fixation activity could not be induced through short- or long-term increases in CO₂ assimilation around shoots. Furthermore, a whole plant P depletion induced a decline in nitrogen fixation, however this decline did not occur significantly earlier in sunn plants, nor was it more intense compared to the wild-type. However, a distinctly different pattern of nitrogen fixation during the day/night cycles of the experiment indicates that the control of N₂ fixing activity of the large number of nodules is an additional problem for the productivity of supernodulating mutants.     

Changes in Photosynthesis Could Provide Important Insight into the Interaction between Wheat and Fungal Pathogens

Photosynthesis is a universal process for plant survival, and immune defense is also a key process in adapting to the growth environment. Various studies have indicated that these two processes are interconnected in a complex network. Photosynthesis can influence signaling pathways and provide both materials and energy for immune defense, while the immune defense process can also have feedback effects on photosynthesis. Pathogen infection inevitably leads to changes in photosynthesis parameters, including Pn, Gs, and Ci; biochemical materials such as SOD and CAT; signaling molecules such as H₂O₂ and hormones; and the expression of genes involved in photosynthesis. Some researchers have found that changes in photosynthesis activity are related to the resistance level of the host, the duration after infection, and the infection position (photosynthetic source or sink). Interactions between wheat and the main fungal pathogens, such as Puccinia striiformis, Blumeria graminis, and Fusarium graminearum, constitute an ideal study system to elucidate the relationship between changes in host photosynthesis and resistance levels, based on the accessibility of methods for artificially controlling infection and detecting changes in photosynthesis, the presence of multiple pathogens infecting different positions, and the abundance of host materials with various resistance levels. This review is written only from the perspective of plant pathologists, and after providing an overview of the available data, we generally found that changes in photosynthesis in the early stage of pathogen infection could be a causal factor influencing acquired resistance, while those in the late stage could be the result of resistance formation.     

Antenna Protein Clustering In Vitro Unveiled by Fluorescence Correlation Spectroscopy

Antenna protein aggregation is one of the principal mechanisms considered effective in protecting phototrophs against high light damage. Commonly, it is induced, in vitro, by decreasing detergent concentration and pH of a solution of purified antennas; the resulting reduction in fluorescence emission is considered to be representative of non-photochemical quenching in vivo. However, little is known about the actual size and organization of antenna particles formed by this means, and hence the physiological relevance of this experimental approach is questionable. Here, a quasi-single molecule method, fluorescence correlation spectroscopy (FCS), was applied during in vitro quenching of LHCII trimers from higher plants for a parallel estimation of particle size, fluorescence, and antenna cluster homogeneity in a single measurement. FCS revealed that, below detergent critical micelle concentration, low pH promoted the formation of large protein oligomers of sizes up to micrometers, and therefore is apparently incompatible with thylakoid membranes. In contrast, LHCII clusters formed at high pH were smaller and homogenous, and yet still capable of efficient quenching. The results altogether set the physiological validity limits of in vitro quenching experiments. Our data also support the idea that the small, moderately quenching LHCII oligomers found at high pH could be relevant with respect to non-photochemical quenching in vivo.     

嫁接对薄皮甜瓜光合特性、产量与含糖量的影响

试验选用玉美人薄皮甜瓜(Cucum is m eloL.)作接穗,以圣砧1号白籽南瓜为砧木进行嫁接,以自根苗为对照,主要研究嫁接对薄皮甜瓜光合特性、产量及含糖量的影响。结果表明:嫁接明显地增加了薄皮甜瓜的总叶面积,嫁接植株茎蔓生长明显快于自根植株。各个时期嫁接植株各个器官干物重均高于自根植株。但嫁接对薄皮甜瓜叶片中叶绿素的含量影响不大,并且对植株生长发育各时期的功能叶片的净光合速率、蒸腾速率、气孔导度及胞间CO2浓度影响不明显。因此,嫁接主要是通过扩大植株的总叶面积来提高植株的光合速率的。另外,嫁接的增产效果显著,其平均单瓜重和单位面积产量均高于对照。嫁接薄皮甜瓜果实的内壁糖度和中心糖度均低于对照。     

Thioflavin T‐Amyloid Hybrid Nanostructure for Biocatalytic Photosynthesis

Amyloidogenic peptides can self‐assemble into highly ordered nanostructures consisting of cross β‐sheet‐rich networks that exhibit unique physicochemical properties and high stability. Light‐harvesting amyloid nanofibrils are constructed by employing insulin as a building block and thioflavin T (ThT) as a amyloid‐specific photosensitizer. The ability of the self‐assembled amyloid scaffold to accommodate and align ThT in high density on its surface allows for efficient energy transfer from the chromophores to the catalytic units in a similar way to natural photosystems. Insulin nanofibrils significantly enhance the photoactivity of ThT by inhibiting nonradiative conformational relaxation around the central C? C bonds and narrowing the distance between ThT molecules that are bound to the β‐sheet‐rich amyloid structure. It is demonstrated that the ThT‐amyloid hybrid nanostructure is suitable for biocatalytic solar‐to‐chemical conversion by integrating the light‐harvesting amyloid module (for nicotinamide cofactor regeneration) with a redox biocatalytic module (for enzymatic reduction).     

环境因素对番茄单叶净光合速率的影响

论述了环境与番茄净光合速率间的关系及番茄净光合速率的日变化规律，在日光温室番茄光饱和点和补偿点范围内的光 光合曲线呈直角双曲线型，光饱和点为１３６１．４９μｍｏｌ·ｓ－１·ｍ－２，光补偿点为３７．０５μｍｏｌ·ｓ－１·ｍ－２，最大净光速率为１７．７０ｍｇＣＯ２·ｄｍ－２·ｈ－１。番茄在７～５０℃之间均有净光合，其温度 光合曲线呈抛物线型，且光合作用适宜温度范围为２４～３４℃，最适温度为２６～３２℃。光照度在１０２３．７５μｍｏｌ·ｓ－１·ｍ－２时，ＣＯ２饱和点为１９２５μＬ·Ｌ－１；光照度在５２６．５μｍｏｌ·ｓ－１·ｍ－２时，ＣＯ２饱和点为１７１８μＬ·Ｌ－１；光照度在３１２μｍｏｌ·ｓ－１·ｍ－２时，ＣＯ２饱和点为１７２１μＬ·Ｌ－１，但ＣＯ２补偿点为５７．１～７１．７μＬ·Ｌ－１，不同光照度间差异不大。番茄净光合速率日变化呈双峰曲线，但中午时的“午体现象”不明显。在正常的生产条件下，ＣＯ２浓度乃是经常的限制因子。因此，生产上人工施用ＣＯ２对提高番茄产量具有重要意义。     

From CO2 to Electricity: Photosynthesis-Based Functionally Cooperating Mini-Generator

Recently, the global warming and climate changes have aroused focus of attentions. Hence, there is an increased demand to capture, utilize, and sequestrate the greenhouse gas, i.e., carbon dioxide (CO₂), for promising applications. Functionally cooperating mini-generators are a kind of self-propelled smart devices that can harvest environmental energy and convert it to electricity through Faraday's law. But traditional mini-generators are based on an energy-consuming process appealing for energy consumption from high-grade state to low-grade one. Herein, a mini-generator based on photosynthesis with CO₂ as the fuel is designed. The generator can convert the internal energy of O₂ bubbles produced by photosynthesis to electricity. This is an energy conversion from the lowest energy state to the applicable energy. Based on the high-efficiency photosynthesis of hydrophyte, spontaneously water-dissolved CO₂ can afford to induce regularly cycled surfacing-diving motion, and the induced electrical output can simultaneously actuate multiple electronic components. Owing to the weather sensitivity of the photosynthesis, the system can be used to monitor weather through reading the changes of output electrical signals. By integrating the artificial smart device with natural plants, this research will promote the applications of miniaturized devices toward green development.     

Modelling biological processes by using a probabilistic P system software

In this paper we present a probabilistic P system simulator that implements the evolution-communication model proposed in (Cavaliere, 2003) enriched with some probabilistic parameters inspired by the cell biology.After describing the software and its working, we compare the mathematical model used with the biological reality of the cell. Then, we present some mathematical and biological applications showing how one can use this software to simulate simple but interesting biological phenomena, related to respiration and photosynthesis processes in some bacteria.     

On the Edge of Dispensability,the Chloroplast ndh Genes

The polypeptides encoded by the chloroplast ndh genes and some nuclear genes form the thylakoid NADH dehydrogenase (Ndh) complex, homologous to the mitochondrial complex I. Except for Charophyceae (algae related to higher plants) and a few Prasinophyceae, all eukaryotic algae lack ndh genes. Among vascular plants, the ndh genes are absent in epiphytic and in some species scattered among different genera, families, and orders. The recent identification of many plants lacking plastid ndh genes allows comparison on phylogenetic trees and functional investigations of the ndh genes. The ndh genes protect Angiosperms under various terrestrial stresses, maintaining efficient photosynthesis. On the edge of dispensability, ndh genes provide a test for the natural selection of photosynthesis-related genes in evolution. Variable evolutionary environments place Angiosperms without ndh genes at risk of extinction and, probably, most extant ones may have lost ndh genes recently. Therefore, they are evolutionary endpoints in phylogenetic trees. The low number of sequenced plastid DNA and the long lifespan of some Gymnosperms lacking ndh genes challenge models about the role of ndh genes protecting against stress and promoting leaf senescence. Additional DNA sequencing in Gymnosperms and investigations into the molecular mechanisms of their response to stress will provide a unified model of the evolutionary and functional consequences of the lack of ndh genes.