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Normalization of 11C-autoradiographic images for semi-quantitative analysis of woody tissue photosynthesis

Mincke, J., Hubeau, M., Cortyn, J., Brans, B., Vanhove, C., Vandenberghe, S., Steppe, K.
Acta horticulturae 2018 no.1222 pp. 35-42
branches, carbon dioxide, drought, global carbon budget, image analysis, leaves, mortality, photosynthesis, radioactivity, transpiration, trees, xylem
To understand plant survival and mortality during drought it is important to gain better insights into the different mechanisms contributing to both the carbon budget and the hydraulic functioning of plants. However, the role of internally transported carbon dioxide (CO2) in xylem together with related woody tissue photosynthesis is often neglected. Trees contain large amounts of CO2 (often between 3 and 10%, and sometimes exceeding 20%), which is substantially higher than the atmospheric CO2 concentration (c. 0.04%). It is known that a portion of this locally respired CO2 escapes to the atmosphere during transport and that photosynthetic active cells in woody tissues or leaves can fix another portion. A new approach for direct visualization of woody tissue (stem) photosynthesis is presented in this study and using a radioactive 11C-tracer and autoradiographic imaging. To allow semi-quantitative comparison of woody tissue photosynthesis between different branches, a normalization method is required. We developed such a normalization technique by taking into account: (i) the radioactivity at the start of the experiment; (ii) the labeling time; (iii) the start and (iv) duration of exposure of the branch to the autoradiographic phosphor screen. In addition to these time-related parameters, we also accounted for total transpiration during the labeling experiment.