The Metabolite Pathway between Bundle Sheath and Mesophyll: Quantification of Plasmodesmata in Leaves of C3 and C4 Monocots.
C4 photosynthesis is characterized by a CO2-concentrating mechanism between mesophyll (M) and bundle sheath (BS) cells of leaves. This generates high metabolic fluxes between these cells, through interconnecting plasmodesmata (PD). Quantification of these symplastic fluxes for modeling studies requires accurate quantification of PD, which has proven difficult using transmission electron microscopy. Our new quantitative technique combines scanning electron microscopy and 3D immunolocalization in intact leaf tissues to compare PD density on cell interfaces in leaves of C3 (rice [Oryza sativa] and wheat [Triticum aestivum]) and C4 (maize [Zea mays] and Setaria viridis) monocot species. Scanning electron microscopy quantification of PD density revealed that C4 species had approximately twice the number of PD per pitfield area compared with their C3 counterparts. 3D immunolocalization of callose at pitfields using confocal microscopy showed that pitfield area per M-BS interface area was 5 times greater in C4 species. Thus, the two C4 species had up to nine times more PD per M-BS interface area (S. viridis, 9.3 PD µm(-2); maize, 7.5 PD µm(-2); rice 1.0 PD µm(-2); wheat, 2.6 PD µm(-2)). Using these anatomical data and measured photosynthetic rates in these C4 species, we have now calculated symplastic C4 acid flux per PD across the M-BS interface. These quantitative data are essential for modeling studies and gene discovery strategies needed to introduce aspects of C4 photosynthesis to C3 crops.
ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Canberra 2601, Australia International Rice Research Institute, Laguna 4030, Philippines.
Florence R
0000-0002-7352-3852
FR
Danila
International Rice Research Institute, Laguna 4030, Philippines University of Sheffield, Sheffield S10 2TN, United Kingdom.
William Paul
WP
Quick
CSIRO Agriculture, Canberra 2601, Australia.
Rosemary G
0000-0002-7618-3814
RG
White
ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Canberra 2601, Australia CSIRO Agriculture, Canberra 2601, Australia robert.furbank@anu.edu.au.
Robert T
0000-0001-8700-6613
RT
Furbank
ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Canberra 2601, Australia.
Susanne
0000-0002-8366-2071
S
von Caemmerer
D018556:Crops, Agricultural / Q000378:metabolism / Q000648:ultrastructure; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D058503:Mesophyll Cells / Q000378:metabolism* / Q000648:ultrastructure; D012275:Oryza / Q000378:metabolism / Q000648:ultrastructure; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000378:metabolism* / Q000648:ultrastructure; D058526:Plant Vascular Bundle / Q000378:metabolism / Q000648:ultrastructure; D031425:Plasmodesmata / Q000378:metabolism* / Q000648:ultrastructure; D014908:Triticum / Q000378:metabolism / Q000648:ultrastructure; D003313:Zea mays / Q000378:metabolism / Q000648:ultrastructure