Jigsaw Puzzle: The undersurface of a leaf is tiled with flat cells in a puzzling pattern (outlined in green). This inter-digitating pattern is controlled by antagonistic signaling pathways that make alternating lobes and indentations. Green stomata dot the surface. These are breathing pores, flanked by two kidney shaped guard cells. The red splotches are chloroplasts, that harvest light energy to make plant sugars.
• Blue light/UV-A activates light sensing proteins (phototropins and cryptochromes) which set off a signaling cascade. A proton pump on the cell membrane is activated, making the inside of the cell more negative. This opens voltage-activated potassium channels which let K+ into the guard cells. Water follows the ions (osmosis) and the cells become turgid. This swelling opens the pore. Stomatal opening can be controlled by photosynthesis, drought stress and much more. More images and explanation at: http://goo.gl/5aBFh
Watch: Las estomas – the stomata
The higher magnifications are especially lovely.
Image: Confocal microscopic image of lower surface of Arabidopsis leaf; By D. Page Baluch, Mrinalini Muralidharan and Tsafrir Mor, Arizona State University.