Plant Nanobionics : From Localized Carbon Capture to Precision Molecular Delivery

• Photosynthesis is an evolutionary marvel that not only sustains plant life but also profoundly shaped the climatic conditions necessary for the development of other advanced forms of life and the ecosystems we know today. During photosynthesis, plants harness the energy of light to convert carbon dioxide (CO2), one of the main greenhouse gases, into sugars for the growth of both themselves and organisms that consume plants, and oxygen that sustains life on Earth. As we face the challenges of a rapidly changing climate and growing global population, understanding and enhancing the functions of plants such as photosynthesis and drought tolerance is of major importance.With advances in materials science over the years, an increasing number of nanotechnologies harnessing the unique properties of materials with sizes in the nanometer range (<100 nm) are emerging, holding promise to revolutionize various sectors, including agriculture and plant biology. At the intersection of materials science and plant biology, the field of plant nanobionics emerges as a transformative discipline pioneering a novel approach to integrating nanomaterials directly into plant systems. Departing from traditional genetic modification, this interdisciplinary field seeks to create bio-hybrid systems to enhance plants’ natural functions such as photosynthesis or introduce entirely new capabilities such as environmental sensing, monitoring, or even light emission.Various strategies exist in plant nanobionics, including the use of carbon nanotubes, silica nanoparticles, liposomes, or even quantum dots. The use of polymers, which consist of long chains of molecules with repeating units, has also been particularly intriguing for nanotechnological and nanobionic approaches due to their versatile and tunable properties.The primary focus of this thesis was to increase the diffusion rate of atmospheric CO2 in the leaves of tobacco plants using polymeric nanoparticles. The nanoparticles are engineered to directly capture CO2 from the atmosphere and are able to cross various plant cell membranes to deliver it to the photosynthetic reaction centers. The initial carboxylation reaction of photosynthesis, where atmospheric CO2 is converted into sugar precursors (3-phosphoglyceric acid or 3-PGA) with the help of the enzyme RuBisCO, is often considered the limiting step of the photosynthetic process. The poor affinity of RuBisCO to CO2 coupled with the limited diffusion of CO2 to the reaction sites is responsible for a considerable reduction in the potential photosynthetic efficiency of plants.With that in mind, we designed nanoparticles based on polyethyleneimine, a polymer able to capture atmospheric CO2 and cross cellular membranes, and modified it with chitosan, a biocompatible polymer, to design nanoparticles that we further labeled with fluorescein isothiocyanate (FITC) for fluorescent observation purposes. We studied their ability to self-integrate into plant cells and the plant chloroplasts, where the photosynthetic reaction occurs, without causing harm to the cells or the plants in general. We further evaluated the capacity of the nanoparticles to integrate into plant cells in culture and demonstrated that the nanoparticles have a natural affinity for the cells and self-integrate in the cells, crossing the cell wall, after 3 days. The nanoparticles also had no negative impact on the capacity of the cells to keep growing and dividing. We also demonstrated the nanoparticles' ability to still capture atmospheric CO2 when integrated into plant leaves and, in vitro, to redistribute it to RuBisCO enhancing the production of 3-PGA by 20%. Since the entry of the nanoparticles into plant leaves requires forced infiltration using a syringe infiltration method, we also studied the impact of the method itself on the plants' natural capacity to uptake CO2 and perform photosynthesis. We found there was a temporary impact of the infiltration process on the leaves’ natural CO2 uptake that also resulted in a reduction of their natural photosynthetic abilities. This will enable future studies to reliably quantify the impact of the nanoparticles on plant processes. We also used an organic electronic ion pump as a precision delivery method to study the impact of various biomolecules, such as malic and abscisic acid, on the plants' natural regulation of carbon dioxide uptake through the leaf pores known as stomata.Our work elucidates the various mechanisms at play when infiltrating nanoparticles or delivering biomolecules into plant leaves and plant cells in culture. We demonstrated a proof-of-concept use of phytocompatible nanoparticles in vivo, paving the way for a nanomaterials-based CO2-concentrating mechanism in plants that can potentially increase plants’ photosynthetic efficiency and overall CO2 storage.

Ämnesord

NATURVETENSKAP  -- Biologi -- Biokemi och molekylärbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Biochemistry and Molecular Biology (hsv//eng)

Nyckelord

Plant nanobionics

Nanoparticles

Chitosan-modified polyethyleneimine

Infiltration

CO2 capture

Photosynthesis

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