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The underappreciated role of pods and siliques in seed development

Plants harness energy from sunlight and carbon dioxide through a process called photosynthesis which supports the generation of carbohydrates, proteins and oils stored in seeds – like a corn kernel, a soybean kernel or a grain of rice. Seeds are an essential resource for humans as food, fodder and fuel.

Under the direction of Doug Allen, Ph.D., a USDA-Agricultural Research Service scientist and member of the Danforth Center, a team of scientists led by Danforth Center researcher Somnath Koley, PhD, discovered that pods, sometimes called siliques, which serve as a protective covering around seeds in development, play an underestimated and important role in photosynthesis, promoting seed development and higher grain yield. Their findings challenge the misconception that leaves are solely responsible for capturing light and carbon dioxide in plants. This work was published in the journal, entitled “Metabolic synergy in reproductive tissues for seed development.”

Researchers were inspired to examine the role of siliques in plants after observing their bright green hues and elevated position at the top of the plant. Unlike leaves, many of which begin to fade as the plant grows, siliques are green and have a significant surface area exposed to sunlight during the seed-filling period. Their unique positioning at the top of the plant allows siliques unimpeded access to sunlight, which can fuel the assimilation of carbon dioxide from the atmosphere. Their natural proximity to developing seeds provides a targeted source of carbon for seed development.

“One of the most interesting insights from this study,” noted Dr. Koley, “is the unexplored photosynthetic potential of green siliques and their contribution to plant productivity. » The ability to enhance the photosynthetic capacity of different plant tissues exposed to sunlight could potentially lead to higher seed yields, thereby improving crop productivity, a promising implication for the agricultural industry. Indeed, the results of this study open the door to the exploration of phenomena similar to those of other crops, such as canola, pennycress or soybean, some of which have documented roles in “green” metabolism within the seed itself.

The results support additional temporal synergy between the timing of photosynthetic activity in the silique and the seed filling process. “The temporal development of siliques immediately before the seeds and their proximity provide a targeted, just-in-time delivery system of nutrients to the seeds contained within,” Dr. Allen emphasized, “in the latter part of the life cycle of the plant, when the seeds need nutrients to fill themselves, thus describing an undocumented synergy between tissues. In other words, the siliques fuel growth exactly when and where the seeds need it .

This research was a collaborative effort made possible by the Danforth Center community and its exceptional facilities. Dr. Koley and Dr. Allen recognized the research contributions of the Advanced Bioimaging Laboratory, including co-authors Kirk Czymmek, PhD and Anastasiya Klebanovych, PhD. One idea conceived by Dr. Cyzmmek was to add a fluorescent dye to confirm the transport of substances between the outer wall of the pod and the seed. “Pictures are often worth more than a thousand words in the search for a scientific hypothesis,” Dr. Allen continued, “and the imaging approach provided an early indication that our ideas were reasonable and supported more quantitative experimental efforts .”

Additionally, teams from the Proteomics and Mass Spectrometry Center and the Plant Growth Center were instrumental in the work, and the accomplishments were a direct reflection of effective collaboration between the Danforth Center and USDA -ARS.

Our team’s success reflects the collaborative environment with top-notch scientists at the Danforth Center and USDA-ARS, leveraging state-of-the-art instrumentation, facilities, and know-how that together are rare and that we are lucky to have here.

Doug Allen, Ph.D.

This study “shines a light” on the often overlooked role of pods and siliques in seed development and yield. By recognizing the photosynthetic capacity of the pod, researchers have revealed a new avenue for increasing crop productivity and improving agricultural practices. The Allen lab, with help from an NSF-REU student this summer, is similarly studying silique photosynthesis in a species called pennycress, which, interestingly, has few leaves left by the time seed production and can have equally or more dramatic effects. This and other work in the Allen lab aims to elucidate emergent properties of plant tissues and organs that likely play multiple roles to benefit the plant and are more complicated than overly simplistic textbook descriptions. The synergy of tissues beyond leaves that contribute to seed yield through photosynthesis presents a unique paradigm for the future development of agriculture and crops.

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