We investigate the major physiological innovations that allowed plants to survive on land and colonize increasingly arid environments.

We make use of ecological and evolutionary diversity to answer fundamental questions related to the roles of stomatal regulation, abscisic acid, and xylem physiology in driving land plant tolerance to water deficit.


Stomatal regulation


Stoma on live leaf of Senecio minimus 

Stomata are turgor-operated valves that respond to a variety of environmental and endogenous signals. These responses regulate the crucial trade-off between carbon assimilation and water loss that limits photosynthesis in nearly all terrestrial plants. The sensitivity of stomatal responses varies across land plants, exhibiting both ecological and phylogenetic trends. In the McAdam Lab, we seek to understand how stomatal regulation has evolved over the past 410 million years.

Abscisic acid


Chemical structure of abscisic acid 

Abscisic acid (ABA) is a plant hormone that is synthesized when cells lose turgor. In seed plants, it plays a critical role in closing stomata under conditions of water stress. At the same time, ABA initiates drought responses in other systems, facilitating a coordinated physiological reaction. ABA also performs unrelated functions ranging from sex determination in fern gametophytes to the initiation of leaf senescence. Our group is pursuing several projects focused on the evolution of ABA's diverse functions.

Xylem physiology


Xylem of Phellodendron amurense

Xylem, the tissue responsible for transporting water and dissolved nutrients, appeared early in the history of land plants and (with phloem) serves as the defining characteristic of all vascular plants. However, vascular plants show dramatic differences in the amount, arrangement, and architecture of their xylem. We are investigating the nature of these differences and their effects on hydraulic conductivity, water use efficiency, and drought tolerance.