title: Contributions of photosynthetic and non-photosynthetic cell types to leaf respiration in Vicia faba L. and their responses to growth temperature.
abstract: In intact leaves, mitochondrial populations are highly heterogeneous among contrasting cell types; how such contrasting populations respond to sustained changes in the environment remains, however, unclear. Here, we examined respiratory rates, mitochondrial protein composition and response to growth temperature in photosynthetic (mesophyll) and non-photosynthetic (epidermal) cells from fully expanded leaves of warm-developed (WD) and cold-developed (CD) broad bean (Vicia faba L.). Rates of respiration were significantly higher in mesophyll cell protoplasts (MCPs) than epidermal cell protoplasts (ECPs), with both protoplast types exhibiting capacity for cytochrome and alternative oxidase activity. Compared with ECPs, MCPs contained greater relative quantities of porin, suggesting higher mitochondrial surface area in mesophyll cells. Nevertheless, the relative quantities of respiratory proteins (normalized to porin) were similar in MCPs and ECPs, suggesting that ECPs have lower numbers of mitochondria yet similar protein complement to MCP mitochondria (albeit with lower abundance serine hydroxymethyltransferase). Several mitochondrial proteins (both non-photorespiratory and photorespiratory) exhibited an increased abundance in response to cold in both protoplast types. Based on estimates of individual protoplast respiration rates, combined with leaf cell abundance data, epidermal cells make a small but significant (2%) contribution to overall leaf respiration which increases twofold in the cold. Taken together, our data highlight the heterogeneous nature of mitochondrial populations in leaves, both among contrasting cell types and in how those populations respond to growth temperature.
authors.affiliation: ARC Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601, Australia.
authors.forename: Benedict M
authors.identifier: http://orcid.org/0000-0002-4616-2967
authors.initials: BM
authors.lastname: Long
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601, Australia.
authors.forename: Nur H A
authors.initials: NH
authors.lastname: Bahar
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, Division of Plant Sciences, Research School of Biology, Australian National University, Canberra, Australian Capital Territory, 2601, Australia.
authors.forename: Owen K
authors.initials: OK
authors.lastname: Atkin
mesh_terms: D019069:Cell Respiration; D024101:Mitochondrial Proteins / Q000378:metabolism; D010788:Photosynthesis; D059828:Plant Cells / Q000502:physiology*; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D011523:Protoplasts / Q000378:metabolism; D013696:Temperature; D031307:Vicia faba / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*
chemical_list: D024101:Mitochondrial Proteins; D010940:Plant Proteins
keywords: epidermal cells; temperature response