Interesting Photosynthesis Research in 2022

Photosynthesis is crucial for crop yield improvement, forest management, and environmental protection. Increasingly research on photosynthesis is cross-disciplinary. Some studies combine photosynthesis with fields wide apart, like cancer cures, plastic degradation, or computers. Read further about the most striking photosynthesis research emerging last year, 2022. 

1. Photosynthesis for cancer cure?

Figure 1: Jiang et al. 2022. (Image credits: https://doi.org/10.1016/j.biomaterials.2022.121561)

Cell death/ Apoptosis dysregulation makes melanoma resistant. Therefore search is on for oncological treatments that activate cell death. One means is to provide an oxygen-rich or hyperoxic environment. However, since finding such a source is difficult, there are very few studies on the impact of giving a continuous supply of oxygen (O2) to tumors. 

In one attempt to supply controllable O2 to check melanoma, Jiang et al. 2022 developed nano-enabled photosynthetic microcapsules (PMCs) and introduced them into the tumors. Algal microbes are a significant source of O2 on earth, so Jiang et al. 2022 wanted to exploit photosynthesis to get a stable oxygen supply in melanoma.

Alginate microcapsules of cyanobacteria and upconversion nanoparticles were developed. The nano-enabled photosynthesis provided a micro oxygen factory controlled externally by (Near Infrared) NIR-II laser irradiation to create a hyperoxia microenvironment in melanoma tumors. 

These PMCs and X-rays triggered lipid peroxidation and ferroptosis in melanoma cells, see Figure 1. In addition, the combined treatment inhibited tumor metastases/ secondary growth leading to a higher survival rate of melanoma-bearing mice. The scientists consider that nano-enabled photosynthesis could be explored further as a potential oncological treatment.

2. Photosynthesis to power microprocessors

Figure 2: The new photosynthetic battery for microprocessor and its performance, Bombelli et al. 2022. (Image credits: https://doi.org/10.1039/d2ee00233g) 

Microbial photosynthesis can also provide eco-friendly energy generation solutions. Internet of Things or IoT units has increased to billions and are expected to reach a trillion soon. Though each IoT unit needs small amounts of energy, the cumulative demand from this modern technology makes it necessary to find additional portable energy sources.

The batteries that harvest and store solar energy are made of unsustainable materials like rare earth, making their production expensive. Moreover, end-of-life solar panels are also hazardous wastes that are challenging to manage.

To solve these problems,  Bombelli et al. have tried to develop an alternate photovoltaic energy harvester system. Their system uses photosynthetic microbes on an aluminum anode capable of powering standard microprocessors used in IoT, namely the 

Arm Cortex M0+, see Figure 2. The trial successfully ran the microprocessor for six months under ambient light in a domestic environment. The new bio-photovoltaic system is made of common, inexpensive materials, most of which are recyclable.

3. Artificial photosynthesis for solar panels

Among all the technologies to harvest solar energy, the most attractive is using photosynthesis of hydrogen peroxide (H2O2), a liquid fuel whose production can become cost-effective. H2O2 is produced during photosynthesis in plant cells. The process is replicated in artificial photosynthesis to produce H2O2 from water and O2, and in the process, convert solar energy into chemical energy.

Most studies use organic polymers in the process, which have the disadvantage of being susceptible to oxidants. Therefore, Liu et al. 2022, used an inorganic MO-doped faceted BiVO4 system as photocatalysts.

The scientists achieved high H2O2 photosynthesis efficiency with the new system compared to other inorganic photocatalysts. The apparent quantum yield was 1.2 percent, and the solar-to-chemical conversion was 0.29 percent at the full spectrum and 5.8 percent at 420 nm. In addition, spectroscopic studies show that catalyst spatial placement and electronic structures make it possible to use inorganic particulate photocatalysts for efficient artificial photosynthesis of H2O2.

4. Hybrid inorganic–biological photosynthesis system for food production

Figure 3: “(a) CO2 electrolysis uses electricity (generated by photovoltaics) to convert CO2 and H2O into O2 and acetate. This process was optimized to produce an effluent output ideal for supporting the growth of food-producing organisms. (b) Chlamydomonas, Saccharomyces, mushroom-producing fungi, and various vascular crop plants were grown using the electrolyzer-produced effluent. (c) The organisms grown using the electrolyzer-produced effluent serve as food or food products. This system is capable of making food independent of photosynthesis, using CO2, H2O, and solar energy” Hann et al., 2022. ( Image credits: https://www.nature.com/articles/s43016-022-00530-x)

Artificial photosynthesis could also provide a means to capture using solar energy from photovoltaics to produce food. Hann et al. 2022 developed a hybrid inorganic-biological system to grow food. 

They created a two-step CO2 electrolyzer to produce concentrated acetate with 57 percent carbon selectivity. The acetate produced can be used as a source of carbon and energy for the heterotropic cultivation of mushrooms, yeast, and photosynthetic green alga and as input for lettuce, rice, tomato, green pea, cowpea, canola, pepper, tobacco, and Arabidopsis (A. thaliana), see Figure 3.

The nine crop plants, externally supplied with carbon from the acetate, incorporated it into their metabolic pathways to increase their biomass. As a result, connecting existing photovoltaic systems to controlled environment cultivation would be able to grow four times more than biological photosynthesis.    

5. Plastic photosynthesis

Figure 4: “Differences and relations between plastics photodegradation and photosynthesis,” Chu et al. 2022. (Image credits: https://doi.org/10.1002/aenm.202200435)

Photosynthesis offers a method to recycle plastic waste compared to conventional methods like gasification or pyrolysis, which need high temperature and energy, or even photocatalysis, which uses low-temperature pressure and light (see Figure 4 for comparison).

Chu et al. 2022 show how photosynthesis conducted in oxygen-free environments using irradiated semiconductors can selectively turn plastic waste into valuable products by breaking down the C-C and C-H bonds in the plastic polymers. The remaining electrons produced by light reduce protons to give hydrogen. Photosynthesis can produce high-value fuels, chemicals, and materials.   

These methods can provide green alternatives to reduce waste and produce secondary materials that can be used in a circular plastic economy, eliminating the negative environmental impact of new plastic production and waste.

6. Phosphorus constraints to photosynthesis in global forests 

Tropical forests fix more carbon annually than any other terrestrial ecosystem. It is well-known that phosphorus limitations affect carbon uptake in tropical and subtropical regions. However, scientists are unsure this is the standard relationship between phosphorus and photosynthesis. 

Ellsworth et al. 2022 show that photosynthesis and related processes depend on leaf nitrogen and phosphorus levels. The latter has similar effects on photosynthesis across four continents. Based on these results, the scientists incorporated the impact of phosphorus 

limitations into the ORCHIDEE-CNP model and found that it reduced photosynthesis by 36 percent globally. For the first time, phosphorus effects have been integrated into global terrestrial C models.

7. Photosynthesis occurs in the far-red range.

At present, photosynthetically active radiation is between 400 to 700 nm. However, scientists have long been aware that there also exist interactions between far-red photons and shorter-wavelength photons. However, this interaction has yet to be studied in natural sunlight conditions.

Zehn et al. 2022, removed photons above 700 nm with a filter to quantify their effects on photosynthesis in many species under full sun, medium light, and shade to study the contribution of far-red photons on photosynthesis.

They found that the far-red (701 to 750 nm) range from sunlight was also used during photosynthesis, especially when the leaves were in the shade. In the shade, far-red light makes up over 50% of the incident light between 400 to 750 nm. In C3 and C4 plants, far-red light contributes to 25-50 percent of leaf gross photosynthesis in the shade, and 10-14 percent of leaf gross photosynthesis, when plants are in the understory or deep shade.

Therefore, it is vital to include photosynthesis due to far-red light to accurately measure the photosynthesis at the scale of the leaf, canopy, and ecosystems. This can improve our understanding of crop and ecosystem productivity.

8. Impact of microplastics on photosynthesis in Cucurbita pepo

Figure 5: Graphical representation of the experiment, Colzi et al. 2022. (Image credits: https://doi.org/10.1016/j.jhazmat.2021.127238)

Cucurbita pepo plants were grown in pots with soils contaminated by increasing amounts of microplastics of four types- polyethylene terephthalate (PET), polypropylene (PP), polyvinylchloride (PVC), and polyethylene (PE). Plant biometry and photosynthetic parameters checked the effect of microplastic toxicity on the plants.

Colzi et al. 2022 show that all four plastics types reduced root and shoot growth, see Figure 5. Different reactions depended on the plastic type, concentrations, and parameters tested, such as leaf size, photosynthetic efficiency, and chlorophyll content. PVC was the most toxic, and PE the least. PVC reduced leaf lamina, plant iron, and photosynthetic performance more than the other three microplastics. 

Based on the results of C. pepo, scientists are concerned that widespread microplastic pollution could influence food yield and lead to economic loss. Moreover, there is a risk of microplastic transfer in the food chain. 

9. Atmospheric dryness can reduce photosynthesis. 

Soil water content (SWC) and atmospheric dryness or vapor pressure deficit (VPD) can both reduce the gross primary production (GPP) of terrestrial systems. They both reduce stomatal conductance to reduce hydraulic transfer from soil to plants. However, it has been challenging to separate the effect of the two correlated factors, SWC and VPD, on productivity.

Fu et al. 2022, used global eddy-covariance to show that a fall in SWC doesn’t always decrease GPP. GPP declines only if SWC is below a threshold and can increase when very high SWC decreases. In contrast, any increase in VPD across the SWC range will reduce GPP. The maximum photosynthetic assimilation rate decreases as VPD increases but increases when SWC reduces from a high SWC.

Also, canopy conductance declines as VPD increases and SWC decreases in drier soils.

Earth System Models underestimate VPD’s negative effects on GPP, and the trend can continue in future predictions of VPD effects.

10. Effect of pollution and temperature increase on Nitella microcarpa photosynthesis 

The Charales are freshwater algae, primary producers in aquatic ecosystems, that can increase habitat heterogeneity and water transparency. In addition, herbicide pollution and rise in temperature due to climate change are potential stressors. Boas and Branco 2022 studied the effect of these factors on the photosynthesis of the algae  Nitella microcarpa var. wrightii. 

They measured the effects after a seven days exposure to different concentrations of herbicide tebuthiuron (0.05, 0.6, and 1.2 mg L−1) and two global warming scenarios described by the Intergovernmental Panel on Climate Change in RCP 4.5 and RCP 8.5.

The chlorophyll-a fluorescence measurements showed a significant difference in the treatments. Tebuthiuron levels of 0.6 mg L−1 and significantly negatively affected all fluorescence parameters and reduced electron transport rate (ETR) at all concentrations. Temperature rise in the RCP 8.5 scenario strengthened the herbicide effects by reducing the plant’s ability to withstand stress. 

The scientists concluded that the herbicides affected the N. microcarpa, negatively influencing their ability to fix carbon, which could lower the aquatic ecosystem’s primary productivity.

Measuring Photosynthesis

Modern methods of analyzing photosynthesis and its efficiency are imperative to meet the needs of the new research. Portable, rapid, and accurate devices like the CI-340 Handheld Photosynthesis System, manufactured by CID BioScience Inc, have been successfully used by scientists for several years. The CI-340 can take measurements of photosynthesis, stomatal conductance, transpiration, and chlorophyll fluorescence to help in a variety of research studies to address the environmental challenges confronting us.  

Sources

Bombelli, P., Savanth, A., Scarampi, A., et al. (2022). Powering a microprocessor by photosynthesis. Energy & Environmental Science, 15(6), 2529–2536. https://doi.org/10.1039/d2ee00233g 

Chu, S., Zhang, B., Zhao, X., et al. (2022). Photocatalytic conversion of plastic waste: From photodegradation to photosynthesis. Advanced Energy Materials, 12(22), 2200435. https://doi.org/10.1002/aenm.202200435

Colzi, I., Renna, L., Bianchi, E., et al. (2022). Impact of microplastics on growth, photosynthesis and essential elements in Cucurbita pepo l. Journal of Hazardous Materials, 423, 127238. https://doi.org/10.1016/j.jhazmat.2021.127238

Ellsworth, D. S., Crous, K. Y., De Kauwe, M. G., et al. (2022). Convergence in phosphorus constraints to photosynthesis in forests around the world. Nature Communications, 13(1). https://doi.org/10.1038/s41467-022-32545-0

Fu, Z., Ciais, P., Prentice, I.C. et al. (2022). Atmospheric dryness reduces photosynthesis along a large range of soil water deficits. Nat Commun 13, 989. https://doi.org/10.1038/s41467-022-28652-7

Hann, E.C., Overa, S., Harland-Dunaway, M. et al. (2022). A hybrid inorganic–biological artificial photosynthesis system for energy-efficient food production. Nat Food 3, 461–471 https://doi.org/10.1038/s43016-022-00530-x

Jiang, J., Wang, W., Zheng, H., Chen, X., Liu, X., Xie, Q., Cai, X., Zhang, Z., & Li, R. (2022). Nano-enabled photosynthesis in tumours to activate lipid peroxidation for overcoming cancer resistances. Biomaterials, 285, 121561. https://doi.org/10.1016/j.biomaterials.2022.121561

Liu, T., Pan, Z., Vequizo, J. J., et al. (2022). Overall photosynthesis of H2O2 by an inorganic semiconductor. Nature Communications, 13(1). https://doi.org/10.1038/s41467-022-28686-x

Xie, Y., Khoo, K. S., Chew, K. W., et al. (2022). Advancement of renewable energy technologies via artificial and microalgae photosynthesis. Bioresource Technology, 363, 127830. https://doi.org/10.1016/j.biortech.2022.127830

Vilas Boas, L. K., & Branco, C. C. (2022). Effect of Tebuthiuron and temperature increase related to climate change on the photosynthesis of Nitella microcarpa var. Wrightii (Charophyceae). Journal of Applied Phycology, 34(3), 1721–1729. https://doi.org/10.1007/s10811-022-02750-x

Yang, S., Zhao, Y., Qin, X., et al. (2022). New insights into the role of melatonin in photosynthesis. Journal of Experimental Botany, 73(17), 5918–5927. https://doi.org/10.1093/jxb/erac230

Zahra, N., Al Hinai, M. S., Hafeez, M. B., et al. (2022). Regulation of photosynthesis under salt stress and associated tolerance mechanisms. Plant Physiology and Biochemistry, 178, 55–69. https://doi.org/10.1016/j.plaphy.2022.03.003

Zhen, S., van Iersel, M. W., & Bugbee, B. (2022). Photosynthesis in Sun and shade: The surprising importance of far‐red photons. New Phytologist, 236(2), 538–546. https://doi.org/10.1111/nph.18375