Terrestrial plants have waxy cuticles on their leaves and stems that prevent water loss but also interfere with gas exchange. To deal with this problem, plants have developed pores in the epidermis called stomata. A stoma is made up of two symmetrically opposite specialized cells: guard cells that can contract and swell, closing or opening the pore. These pores absorb CO2 for photosynthesis and lose water to cool the plant. The density of stomata and the movement of guard cells are controlled by the network of various hormones and environmental factors. Stomata formation in Arabidopsis thaliana involves at least one asymmetric division and a single symmetric division in a specialized epidermal cell line (Daszkowska et al., 2009; Le et al., 2014). Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay Although stomatal density can vary between different plant species, stomatal spacing is stable and causes stomata to be separated from each other by at least one intervening cell (one cell spacing rule). Numerous signaling components have been implicated in this process (Table 1), (Rychel et al., 2010; Serna et al., 2011; Shimada et al., 2011). These include a small secreted peptide, a subtilisin-like protease, a transmembrane receptor-like protein, a family of receptor-like kinases, and several genes of a mitogen-activated protein kinase (MAP kinase) cascade, five transcription factors which are fundamental to them. (Lai et al., 2005; Ohashi-Ito and Bergmann, 2006; MacAlister et al., 2007; Pillitteri et al., 2007; Wang et al., 2007). Loss of function of many of these components shows an increase in stomatal density and loss of epidermal division patterns, which ultimately results in a breakdown of a cell's spacing rule and the production of adjacent stomata. It is believed that if stomata form adjacent, they cannot function efficiently. On the other hand, overexpression or gain of function in some components reduces stomatal production, indicating that these signaling components inhibit entry into the stomatal lineage. The identification of several patterning mutants revealed a core group of signaling molecules that include a protease, a leucine-rich repeat receptor like kinase (LRRRLK), an LRR receptor-like protein, MAP kinase components, and small secreted peptide-rich of cysteine. involved in the regulation of stomatal development (Pillitteri et al., 2008). Please note: this is just an example. Get a customized document from our expert writers now. Get a Custom Essay Stomatal density of young leaves can vary in response to environmental cues, but the controls of such stomatal development have not been fully elucidated. In recent years, molecular genetic approaches have been used in the model plant Arabidopsis for the identification of genes involved in stomatal development. Once extracellular signaling is recognized by cell surface receptors, the mitogen-activated protein kinase (MAPK) cascade within the cell is activated, thereby regulating transcription factors that promote stomatal development (Shimada et al., 2011). This review summarizes recent advances in research work on hormonal regulation and crosstalk during stomatal development with advances in understanding negative and positive influence in stomatal developmental events.