Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Barbara Demmig-Adams

Second Advisor

William W. Adams

Third Advisor

William D. Bowman

Fourth Advisor

Nolan C. Kane

Fifth Advisor

Holly R. Barnard

Abstract

The plant vascular system facilitates the exchange of sugars, water, and other molecules between leaves and the rest of the plant and, therefore, represents a structural interface connecting multiple physiological processes. A role of whole-plant demand for sugar in regulating photosynthesis had been illuminated previously, and long-distance transport of sugar wasn’t thought to limit photosynthetic capacity. However, I investigated possible limitations imposed at the interface of sugar export and water movement within the photosynthesizing leaf. I identified considerable plasticity of foliar minor veins and leaf function under contrasting temperature and light environments as well as significant differences in the degree of this plasticity between natural populations of the model organism Arabidopsis thaliana from Sweden and Italy and between the commonly used Col-0 ecotype and a tocopherol-deficient mutant line of the same genetic background. Growth at cool temperatures resulted in leaves with greater photosynthetic capacity and sugar-exporting infrastructure in all genotypes, with the extent of these responses being greater in the Swedish ecotype relative to the Italian ecotype. Such upregulation presumably counteracts reduced catalytic activities of proteins involved in both photosynthesis and sugar export from leaves, the rate of which must be maintained to avoid foliar sugar accumulation and potential repression of photosynthetic genes. In turn, transpiration, vein density, and water-importing infrastructure were enhanced in the leaves of all genotypes when grown under hot temperatures, with the extent of some responses being more exaggerated in the tocopherol-deficient mutant compared to the Col-0 wild-type. These features were also more exaggerated in the tocopherol-deficient mutant compared to Col-0 in a naturally lit glasshouse with intermittently high temperatures, suggesting that redox networks are integrated with other signaling networks in targeting the foliar vasculature. Growth under high versus low light resulted in leaves with greater photosynthetic capacities and transpiration rates as well as augmented water-importing and sugar-exporting infrastructure, with similar ecotypic variation as that observed in response to growth temperature. These findings demonstrate a critical and novel role for adjustments in leaf vascular architecture in maintaining photosynthetic productivity and whole-plant function across different temperature and light regimes.

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