Doctoral defence: Ingmar Tulva "Causes and consequences of stomatal density in relation to atmospheric humidity"

On 23 October at 15:15, Ingmar Tulva will defend his doctoral thesis "Causes and consequences of stomatal density in relation to atmospheric humidity" for obtaining the degree of Doctor of Philosophy (Environmental Engineering)

Supervisior:
Associate Professor Hanna Hõrak, University of Tartu

Opponent:
Professor Tracy Lawson, University of Illinois, USA

Summary: This thesis studies plants’ stomata, primarily their density relations with air humidity. Stomata are microscopic closeable holes in the plant leaf, through which the plant lets in air to photosynthesizing cells, while trying trying to keep water loss under control. Stomatal permeability to air is determined by their openness (which can change in minutes) and their density (fixed during development).

One of our study strategies was simultaneous genetic manipulation of density and openness of stomata, lookinf for an optimal combination depending on the environment. We showed that such combining is freely possible, but the overabundance of stomata puts a burden on the plant in its early growth, universally slowing down growth. We also demonstrated that this growth disorder is not a direct consequence of water loss, because plant lines which struggle to close their stomata did not show a similar loss.

Stomata are in many plant species exclusively located on the underside of the leaf. However, there are many species with stomata on the upper leaf side as well. A lot is known about the genetic mechanisms that drive the development of stomata, but nothing of it conclusively explains the differences between leaf sides, let alone the complete lack of them in some species. With our research, we moved a few steps closer to the solution, systematically showing which genes that control stomatal development affect the leaf sides differently. We also dug into the relationship between stomatal density and size, showing how the general "more means smaller" relation applies between similar plants, but disappears when genetic brakes are removed from stomatal development.

In these studies, we dealt with Arabidopsis, which, while economically unimportant, is an easy-tohandle plant species and the common first step for physiological and genetic studies. Our research group is busily verifying these results on crops, looking for ways to put the gained knowledge into practical use in agriculture.