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NERC E4 “When, and to what extent, do shaded saplings and forest-floor herbs salvage carbon from their cell-wall polysaccharides?”

  • Full or part time
    Prof S C Fry
  • Application Deadline
    Thursday, January 09, 2020
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Interested individuals must follow the "how to apply" link on the Geosciences E4 Doctoral Training Partnership web page: http://www.ed.ac.uk/e4-dtp/how-to-apply

Summary
Saplings and forest-floor herbs may be carbon-deficient owing to shading. They salvage C from starch prior to leaf abscission. But when/where do they also salvage C from structural polysaccharides, their major organic resource?

Project background
Carbon (C)-starved plants salvage C reserves, e.g. from stored starch. This project explores the emerging idea [2,3] that structural polysaccharides e.g. hemicelluloses [1] are also mobilised during severe C starvation and the released sugars used for respiration and biosynthesis. Hemicelluloses are often ~25% of a plant’s dry weight, and the biosphere’s 2nd most abundant organic material. Thus, C-salvaging from leaf hemicellulose prior to abscission can appreciably augment a starved plant’s C status and impact the global C cycle.

Ecologically relevant instances of C starvation are
* Deciduous saplings in an existing forest.
* Herbs (e.g. wood anemones) on the forest floor, where there is only transiently (in spring) enough light. Such herbs should salvage maximal leaf C for underground storage.
* Herbivore-attacked plants, left with insufficient foliage.

The project will provide solid new data on hemicellulose mobilisation in starved plants’ mature leaves, and discover when, where and to what extent this occurs. We will also test whether cellulose and pectin are salvaged.

The project will make an important new contribution to plant ecophysiology.

Research questions
To what extent do the leaves of young deciduous trees and forest-floor herbs carry out the reported hemicellulose mobilisation prior to abscission?

Is the mobilisation of foliar starch and hemicellulose greater in carbon-starved trees and herbs (e.g. heavily shaded or partially defoliated)?

Which particular hemicelluloses are most subject to mobilisation (xyloglucan, xylan, mannan)?

Are other leaf structural polysaccharides (cellulose, pectin) also appreciably mobilised in carbon-starved trees and herbs?

What is the fate (translocation/metabolism) of monosaccharides released from foliar hemicelluloses?

Methodology
Year 1: Growing deciduous saplings (oak, beech) and forest-floor herbs (bluebell, wood anemone) under standard glasshouse conditions. Tracking saplings in natural habitats. Checking for disease-free status.Monitoring changes in their foliar dry weight during senescence and at abscission. Learning the techniques of polysaccharide analysis to quantify foliar hemicelluloses (xyloglucans, xylans and mannans separately), pectin, cellulose and starch. Recording this quantification in leaves during senescence and after abscission.

Year 2: Repeating the polysaccharide quantification in leaves of heavily shaded and partially defoliated (versus control) plants. The senescing leaves will be harvested at timed intervals during summer (woodland herbs) and during autumn (saplings), freeze-dried, and analysed for polysaccharides when time permits.

Year 3: Determining the major monosaccharides lost from hemicelluloses during senescence (chromatography and colorimetric analysis). Exploring the fate (translocation and metabolism) of these monosaccharides by use of radioisotopic tracers.
Training

Learning the techniques of starch and cell-wall polysaccharide fractionation and their quantification.

Learning the techniques of identifying and quantifying the monosaccharide residues of hemicelluloses.

Participating in the University’s radiation protection course.

Taking responsibility for housekeeping of a selection of the laboratory’s communal equipment.

Participating in appropriate advanced undergraduate classes to plug any gaps in the student’s repertoire (e.g. Evolution and Ecology of Plants 3, Plant Growth and Development 4, Project Skills in Plant Science 4).

Presenting research group seminars (3 per year) and posters at international meetings.

Attending weekly one-to-one meetings with Prof. Fry to troubleshoot and discuss plans.

Requirements
Applicants should have or expect to obtain a First or Upper Second class Hons degree in a discipline such as plant science, ecology or ‘wet’ biochemistry. A strong interest in plant ecophysiology or biochemical ecology is paramount. Specific skills related to polysaccharide analysis are not required and will be taught during the PhD project.

Funding Notes

This project is eligible for the E4 Doctoral Training Partnership. The E4 projects are currently available for full NERC studentship funding which is competitive by interview AND AVAILABLE ONLY TO UK citizens and to EU citizens who have worked or studied in the UK for the previous 3 years.

For application details see View Website
Further details here - View Website

References

[1] Fry SC (2017) Plant Cell Wall Polymers. Pp 59–88 in Biofuels and Bioenergy edited by J. Love, J.A. Bryant and C. Butler. Wiley–Blackwell, Oxford (ISBN-10: 1118350561; ISBN-13: 978-1118350560).

[2] Hoch G (2007) Cell wall hemicelluloses as mobile carbon stores in non-reproductive plant tissues. Functional Ecology 21: 823–834.

[3] Weber R, Schwedener A, Schmid S, Lambert S, Wiley E, Landhäusser H, Hoch G (2018) Living on next to nothing: tree seedlings can survive weeks with very low carbohydrate concentrations. New Phytologist 218: 107–118.

[4] Oland K (1963) Changes in the content of dry matter and major nutrient elements of apple foliage during senescence and abscission. Physiologia Plantarum 16: 682–694. https://doi.org/10.1111/j.1399-3054.1963.tb08346.x

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