Outline7 marksChallenge
A researcher investigated the effect of water stress on stomatal aperture in leaves of a shrub species. Plants were either kept well-watered or subjected to water stress by withholding water. The table shows mean stomatal aperture (µm) measured at midday over several days.
| Day | Well-watered plants (µm) | Water-stressed plants (µm) |
|---|---|---|
| 1 | 10.2 | 10.1 |
| 2 | 10.0 | 7.8 |
| 3 | 10.1 | 4.2 |
| 4 | 10.0 | 1.5 |
Outline the mechanism by which water stress leads to stomatal closure, including the roles of abscisic acid (ABA) and calcium ions as a second messenger.