Improving Photosynthetic Efficiency

Photoinhibition caused by excess sunlight is regarded as a major limiting factor for primary productivity in shallow production ponds under high irradiances [167]. 

---

Zhu, X.G., Long S.P. Ort D.R. (2010). Improving Photosynthetic Efficiency for Greater Yield. Annual Reoiao of Plant Biology, V0I61,0une 2010), pp. 235-261. 

The photosynthetic efficiency mainly depends on the openness of stomata, particularly in C3 crops, while their closure tends to avoid excessive water loss. Abscisic acid (ABA) mediates water loss from the guardian cells of the stomata, which is triggered by a decrease in the water content of the leaf and inhibits leaf expansion. In muskmelon seedlings, ABA could improve the maintenance of the leaf water potential and relative water content, and reduce electrolyte leakage [55]. 

In wheat, the ear weights of both tillers and the main stem were increased, in comparison with untreated controls by brassinolide (BR) sprays (I). In corn, BR treatment had significant influence on the length of the unfertile tip portion of the ear and on the number of vacant kernels. The yield increased compared with untreated controls (2). Little is known of the effect of BR on the ripening of rice plants, and the mode of action of BR on the ripening of rice has not been studied. To increase crop yield, it is necessary to improve the photosynthetic efficiency and promote the translocation of photosynthetic products in the panicles. Therefore, we assessed the ripening of rice, the translocation of photosynthetic products, and plant hormone levels in panicles. 

Photosynthesis typically only captures the energy from about 1% of incident light, leaving ample room for improvement of biomass yields, culture density, and growth rates. Several strategies for increasing photosynthetic efficiency have been employed in algae, as strains with modified photosynthetic apparatuses are quick to make and can be rapidly screened and characterized, at least compared to terrestrial plants. 

Cuaresma M, Janssen M, Vilchez C, et al Horizontal or vertical photobioreactors How to improve microalgae photosynthetic efficiency, Bioresour Technol 102(8) 5129-5137,2011. 

The enzyme Rubisco is a target for genetic manipulation because it catalyses a rate limiting step in photosynthesis- Moreover Rubisco is inefficient in that not only does it have a low catalytic rate but also catalyses a wasteful reaction with oxygen. Consequently researchers hope that by modification of genes for Rubisco the enzyme s characteristics may be improved, leading to a significant increase in photosynthetic efficiency. 

FBPase undergoes a reductive activation by accepting electrons from ferredoxin through the ferredoxin-thioredoxin system, which works as a link between the photosynthetic electron transport and enzyme regulation (7). The existence of non-covalent interactions of FBPase with the chloroplast membrane could improve the efficiency of its reductive light-activation. In this context the strong FBPase-thioredoxin interaction (8), the association between ferredoxin, thioredoxin and ferredoxin-thioredoxin reductase (9), the binding of ferredoxin to thylakoid membranes (10), and the existence of membrane-bound thioredoxins (11) may be relevant. 

Agricultural resources are limited and the buttoning pressures of massive increases in the population of the world drive competition for them by urban and mral sites. Thus, as the stewards of the land are gving way to the encroachment of territory by urban requirements, agriculture is met with the challenge of increasing the efficiency of production with fewer raw materials. Technologies to improve the efficiency of photosynthetic production that have been in-... 

We conclude that treatment of crops with methanol has the potential to improve photosynthetic productivity under a variety of conditions, but it is economically favored under the very hi li t intensities typical of agricultural crops in the sun belt particularly for alternative crops. Methanol is the least expensive of industrially manufactured fixed-carbon nutrient sources for plants. As the mechanism of action of methanol on photosynthesis is elucidated, it is quite likely that other plant treatments will be designed for ever greater efficiencies of U t energy capture. Factoring in the low commodity cost of methanol, however, ensures its utilization in agriculture over a very long future. 

Reduce the size of light-harvesting complexes in photosynthetic bacteria in order to improve hght efficiency (Kars and Gunduz, 2010 HaUenbeck, 2013a Oh et al., 2013). 

In another project in our laboratories, transformation of the tabacco plastid genome has been achieved [20]. Introduction of the gene for improved RuBisCO into the plant will be our next interest. If a Cs plant has Galdieria RuBisCO for its photosynthetic CO2 fixation, the CO2 compensation point of the transformant will decrease from 50 ppm to 20 ppm. The transformant can fix CO2 at a considerable rate photosynthetically at 50 ppm where the ordinary Ca plants cannot adsorb CO2. Thereby, the water-use efficiency of the transformant will be substantially improved. 

---