Manipulating chloroplast size does not increase photosynthetic efficiency

In a study recently published in the scientific journal New Phytologist, researchers from the project "Understanding Increased Photosynthetic Efficiency" (RIPE) questioned the effectiveness of manipulating the size of chloroplasts - the organelles responsible for photosynthesis in plant cells - - as a strategy to increase the photosynthetic efficiency of crops.

The research team, led by Professor Katarzyna Glowacka of the University of Nebraska-Lincoln, found that changes in chloroplast size had relatively small effects on photosynthesis.

"Chloroplast size affects photosynthetic efficiency in several ways," Glowacka said. "However, our results suggest that manipulating chloroplast size is unlikely to be a profitable strategy for improving photosynthetic efficiency."

Chloroplasts are vital to plant life as they are where light energy is absorbed by chlorophyll and used to transform carbon dioxide into carbohydrates, feeding the plant's organic constituents. Glowacka's team explored whether altering chloroplast size could be a viable approach to improving photosynthetic performance, using a variety of techniques from confocal microscopy to field tests.

Stephen Long, director of the RIPE project and holder of the Ikenberry University Chair in Crop Sciences and Plant Biology at the Illinois Carl R. Woese Institute for Genomic Biology, commented: "There are many reasons why chloroplast size may affect photosynthetic efficiency. However, our experiments have shown that manipulating chloroplast size does not appear to improve productivity under field conditions."

The results of this can direct future research in the field of photosynthetic efficiency. Glowacka, who is also a former postdoctoral researcher in Long's lab, concluded, "This research allows us to narrow down the many possibilities and focus efforts where it will have the greatest impact."

The summary of the article, in free translation into Portuguese, is as follows:

"Improving photosynthetic efficiency has recently emerged as a promising way to sustainably increase agricultural production. Although chloroplast size can affect photosynthetic efficiency in several ways, our goal was to explore whether manipulating chloroplast size could be a viable approach to improve photosynthetic performance.

Various strains of tobacco (Nicotiana tabacum) with contrasting chloroplast sizes were generated by manipulating chloroplast division genes to evaluate photosynthetic performance under constant and fluctuating light. A selection of lines were included in a field trial to explore productivity.

Lines with increased chloroplasts showed lower performance in most of the traits measured. Lines with smaller and more numerous chloroplasts showed similar efficiency to wild-type (WT) tobacco. Chloroplast size only weakly affected light absorption and light profiles within the leaf. Increasing chloroplast size decreased mesophyll conductance (gm), but decreasing chloroplast size did not increase gm. Increasing chloroplast size reduced chloroplast movements and increased non-photochemical quenching. Chloroplast smaller than WT was shown to be no better than WT in terms of photosynthetic efficiency and productivity under field conditions.

The results indicate that manipulations of chloroplast size are unlikely to lead to greater photosynthetic efficiency or growth."