Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Genetics, Development and Cell Biology


Molecular, Cellular, a nd Developmental Biology

First Advisor

Nick Lauter


Plants utilize sophisticated mechanisms and morphologies to mitigate stress. The epidermis, a single-cell boundary layer to the external environment, offers protection against stresses and is comprised of diverse specialized cell-types. In grasses, bulliform cells, which are highly vacuolated and positioned in the adaxial leaf epidermis, are utilized to mitigate drought stress by mechanically mediating the leaf rolling response, thereby reducing transpirational water losses. Considering that leaf rolling intensity directly relates to plant water status, other plant features that enhance water capture and utilization may also influence the leaf rolling response. As such, the structure-function relationships between bulliform cells, leaf rolling, and drought-stress mitigation is complex and not well understood, especially in diverse collections of germplasm used in today's crop breeding programs. To elucidate these relationships, phenomic and genomic analyses were undertaken on bulliform cell architectures, leaf rolling, and a variety of morphological traits on a diverse panel of maize inbred lines. Surprisingly, leaf width had the greatest effect on leaf rolling propensity. However, genetic and physiological evidence indicated that reductions in bulliform cell size under drought are also distinctly associated to leaf rolling.

In addition to mitigating drought stress, epidermal cells sense environmental conditions and accordingly regulate responses and metabolite secretions. Due to their extraordinary lengths and dense nutrient contents, maize's stigmatic silks are quite affected by water deficits, pathogens, and pests. These vulnerabilities are particularly high following emergence from husk-leaves that protectively encase the ear. To examine molecular responses elicited after silk emergence into the external environment, gene expression was assayed across five contiguous silk sections that span both husk-encased and emerged portions of silks. The examined expression patterns revealed dramatic activation of a diverse set of stress pathways, including defense hormone signaling, cellular secretion pathways, and defense metabolite biosynthesis in emerged silks, providing intriguing molecular insights into the abiotic and biotic stress responses employed by this tissue.

In conclusion, these results advance our current understanding of the mechanisms and morphologies utilized by the epidermis to mitigate stress.


Copyright Owner

Colton McNinch



File Format


File Size

171 pages

Available for download on Thursday, June 16, 2022