Scott McAdam, Assistant Professor
Botany and Plant Pathology 
Purdue University

Topic: Why did the ancestor of seed plants evolve a stomatal response to the hormone abscisic acid?

Abstract: 
Plants restrict excessive water loss during drought by closing stomata.  Extensive work on model angiosperms indicates that the hormone abscisic acid (ABA) is critical for closing stomata during drought.  We have recently found that this hormonal stomatal response evolved in the common ancestor of seed plants.  In the earliest diverging lineages of vascular plants, the lycophytes and ferns, stomatal closure during drought is driven by a simple, passive-hydraulic mechanism, whereby guard cell turgor is linked to leaf turgor.  Why did the common ancestor of seed plants evolve an elaborate stomatal response to a hormone that mimics an energetically inexpensive, ancestral stomatal control mechanism, observed today in lycophytes and ferns?  Recent experiments on conifers, particularly during drought, has yielded some very exciting results that may answer this question and potentially provide a physiological explanation for why seed plants dominate seasonally dry environments.

Host Lab: Holbrook