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ARS Home » Midwest Area » Urbana, Illinois » Global Change and Photosynthesis Research » Research » Publications at this Location » Publication #342867
Title: Is phloem loading a driver of plant photosynthetic responses to elevated atmospheric [CO2]? 

Author
item LEMMONIER, PAULINE - Oak Ridge Institute For Science And Education (ORISE)
item QUEBEDEAUX, JENNIFER - University Of Illinois
item BISHOP, KRISTEN - University Of Illinois
item BUSH, DANIEL - Colorado State University
item LEAKEY, ANDREW - University Of Illinois
item Ainsworth, Elizabeth - Lisa

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/14/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: A better understanding of the interactions between photosynthesis, photoassimilate translocation and sink activity is necessary to improve crop productivity. Rising atmospheric [CO2] is perturbing source-sink balance in a manner not experienced by crops during the history of their cultivation, so needs to be addressed to adapt crops to future growing conditions. This project employs two approaches to investigate the importance of phloem loading in the plant photosynthetic responses to elevated [CO2]. First, we postulated that species with different phloem loading strategies can be differentially adapted to high mesophyll sucrose concentrations, and may have fundamentally different photosynthetic responses to growth at elevated [CO2]. Over three field seasons, six species with either apoplastic loading, passive loading, or polymer-trapping were grown at ambient and elevated [CO2] at the Soybean Free Air Concentration Enrichment (SoyFACE) facility. Instantaneous light-saturated photosynthesis, photosynthetic capacity as well as leaf carbohydrate contents were measured throughout the growing seasons and compared between the different species. The results from these experiments indicated that in contrast to our hypothesis, there was little difference in photosynthetic response to elevated [CO2] among these species. However, phylogenetically controlled comparative analysis may be required to fully reject the hypothesis. Second, we hypothesized that plants could have insufficient sugar export capacity from the photosynthetic source to sink tissues under conditions of high carbon availability. This is suggested by feedback inhibition of photosynthetic capacity in plants grown at elevated [CO2]. To overcome this potential limitation, soybean, an apoplastic loading species, was transformed to overexpress a proton/sucrose symporter in the companion cells in the leaf phloem. Photosynthesis, transgene expression, sucrose transport activity, and carbohydrate content in leaves and pods were assessed during preliminary experiments conducted at SoyFACE in 2016. In 2017, we will test how increasing sucrose transport capacity in soybean impacts the seed yield response to elevated [CO2].