Chapter 29 Stomata

You Must Know Mechanisms by which plant cells communicate with other cells.

Stomata: Major Pathways for Water Loss About 95% of the water a plant loses escapes through stomata. Guard cell

Radially oriented cellulose microfibrils Cell wall Vacuole Guard cell Figure 29.19a Guard cells turgid/Stoma open Guard cells flaccid/Stoma closed (a) Changes in guard cell shape and stomatal opening and closing (surface view)

KK H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Guard cells turgid/Stoma open (b) Role of potassium ions (K  ) in stomatal opening and closing H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O Guard cells flaccid/Stoma closed CYTOPLASM EXTRACELLULAR FLUID Proton pump Hydrogen ion (a) H  and membrane potential HH HH HH HH HH HH HH HH

Stimuli for Stomatal Opening and Closing Generally, stomata open during the day and close at night to minimize water loss. Stomatal opening at dawn is triggered by – Light – CO 2 depletion – An internal “clock” in guard cells All eukaryotic organisms have internal clocks; circadian rhythms are 24-hour cycles