Blue light inhibits stomatal development in soybean isolines containing kaempferol-3-O-2G-glycosyl-gentiobioside (K9), a unique flavonoid glycoside

Plants have developed a finely tuned system to control the balance between assimilation of CO2 and transpiration of water vapour either by varying stomatal density or by adjusting guard cell turgor, which alters the aperture or stoma between adjacent guard cells (i.e. stomatal movement). Considerable knowledge has been gained over the years on stomatal movement (Mansfield, Hetherington & Atkinson 1990; Zeiger 1994; Willmer & Fricker 1996; Assman & Shimazaki 1999), but very little is known about control of stomatal formation and density. Three mutants have been identified with irregular stomatal patterning and development (Zeiger & Stebbins 1972; Yang & Sack 1995), but the genes that result in these phenotypes have not been characterized. The following information about formation of the stomatal apparatus has been established (see recent reviews Chin et al. 1995; Larkin et al. 1997). First, the distribution of stomata over a leaf surface is not random. One hypothesis proposes that inhibitory chemicals generated by a developing stomatal complex block the formation of stomata in adjacent cells (Bünning 1956; Larkin et al. 1997); however, the nature of these chemicals is unknown. Second, the formation of the stomatal apparatus is initiated by one or more asymmetric cell divisions and concluded by a symmetrical division that forms two guard cells. Cell lineage can be traced by following the development of a leaf. Third, stomatal development stops before 60–80% of leaf expansion occurs (Gay & Hurd 1975; Rawson & Craven 1975; Turner & Heichel 1977), but stomatal formation is not synchronous in dicots (Sachs 1979; Larkin et al. 1997).Therefore, stomata at different developmental stages can be found during the early phase of leaf expansion. However, there is a brief time during which stomatal development is most sensitive to environmental change (Schoch et al. 1980). Stomatal density is affected by environmental factors such as light (Willmer & Fricker 1996). Most research has concentrated on light quantity. High light intensity is believed to promote high stomatal density, although this ABSTRACT