These plants are able to survive because of the compromise their guard cells achieve. Frequently other adaptations such as thick waxy cuticles and leaves which hang down, or are narrow and short, and have reduced exposure to the direst sun are also seen in Australian plants from arid regions. Guard cells, unlike other epidermal cells, possess chloroplasts and are therefore able to perform photosynthesis . In the presence of light, photosynthesis begins in the guard cells and the other photosynthetic cells of the leaf. Water is drawn into the guard cells by osmosis because of the osmotic gradient which develops as the glucose increases.
Guard cells become fully turgid , and because of their specialised structure, they 'bend' apart .
The stomata are open - gas diffusion is possible. That's all very well, if it's early morning and the air is still relatively humid. Water diffuses out of the guard cells in response to the decreasing water content of the air adjacent to them. Guard cells become flaccid . Stomatal pores close .