Document Detail


Functional analysis of corn husk photosynthesis.
MedLine Citation:
PMID:  21511990     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The husk surrounding the ear of corn/maize (Zea mays) has widely spaced veins with a number of interveinal mesophyll (M) cells and has been described as operating a partial C(3) photosynthetic pathway, in contrast to its leaves, which use the C(4) photosynthetic pathway. Here, we characterized photosynthesis in maize husk and leaf by measuring combined gas exchange and carbon isotope discrimination, the oxygen dependence of the CO(2) compensation point, and photosynthetic enzyme activity and localization together with anatomy. The CO(2) assimilation rate in the husk was less than that in the leaves and did not saturate at high CO(2), indicating CO(2) diffusion limitations. However, maximal photosynthetic rates were similar between the leaf and husk when expressed on a chlorophyll basis. The CO(2) compensation points of the husk were high compared with the leaf but did not vary with oxygen concentration. This and the low carbon isotope discrimination measured concurrently with gas exchange in the husk and leaf suggested C(4)-like photosynthesis in the husk. However, both Rubisco activity and the ratio of phosphoenolpyruvate carboxylase to Rubisco activity were reduced in the husk. Immunolocalization studies showed that phosphoenolpyruvate carboxylase is specifically localized in the layer of M cells surrounding the bundle sheath cells, while Rubisco and glycine decarboxylase were enriched in bundle sheath cells but also present in M cells. We conclude that maize husk operates C(4) photosynthesis dispersed around the widely spaced veins (analogous to leaves) in a diffusion-limited manner due to low M surface area exposed to intercellular air space, with the functional role of Rubisco and glycine decarboxylase in distant M yet to be explained.
Authors:
Jasper J L Pengelly; Scott Kwasny; Soumi Bala; John R Evans; Elena V Voznesenskaya; Nuria K Koteyeva; Gerald E Edwards; Robert T Furbank; Susanne von Caemmerer
Publication Detail:
Type:  Journal Article     Date:  2011-04-21
Journal Detail:
Title:  Plant physiology     Volume:  156     ISSN:  1532-2548     ISO Abbreviation:  Plant Physiol.     Publication Date:  2011 Jun 
Date Detail:
Created Date:  2011-06-02     Completed Date:  2011-09-26     Revised Date:  2013-06-30    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  503-13     Citation Subset:  IM    
Affiliation:
Research School of Biology, Australian National University, Canberra, Australian Capital Territory 0200, Australia. jasper.pengelly@anu.edu.au
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MeSH Terms
Descriptor/Qualifier:
Carbon Dioxide / metabolism
Carbon Isotopes
Chlorophyll / metabolism
Photosynthesis / physiology*
Plant Leaves / anatomy & histology,  cytology,  enzymology,  ultrastructure
Plant Proteins / metabolism
Protein Transport
Protein-Serine-Threonine Kinases / metabolism
Ribulose-Bisphosphate Carboxylase / metabolism
Zea mays / anatomy & histology*,  enzymology,  physiology*,  ultrastructure
Chemical
Reg. No./Substance:
0/Carbon Isotopes; 0/Plant Proteins; 124-38-9/Carbon Dioxide; 1406-65-1/Chlorophyll; EC 2.7.1.-/phosphoenolpyruvate carboxylase kinase; EC 2.7.11.1/Protein-Serine-Threonine Kinases; EC 4.1.1.39/Ribulose-Bisphosphate Carboxylase
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