Light-induced transient ion flux responses from maize leaves and their association with leaf growth and photosynthesis.

Net fluxes of H+, K+ and Ca2+ ions from maize (Zea mays L.) isolated leaf segments were measured non-invasively using ion-selective vibrating microelectrodes (the MIFE technique). Leaf segments were isolated from the blade base, containing actively elongating cells (basal segments), and from non-growing tip regions (tip segments). Ion fluxes were measured in response to bright white light (2600 micromoles m-2 s-1) from either the leaf segments or the underlying mesophyll (after stripping the epidermis). Fluxes measured from the mesophyll showed no significant difference between basal and tip regions. In leaf segments (epidermis attached), light-induced flux kinetics of all ions measured (H+, Ca2+ and K+) were strikingly different between the two regions. It appears that epidermal K+ fluxes are required to drive leaf expansion growth, whereas in the mesophyll light-induced K+ flux changes are likely to play a charge balancing role. Light-stimulated Ca2+ influx was not directly attributable either to leaf photosynthetic performance or to leaf expansion growth. It is concluded that light-induced ion flux changes are associated with both leaf growth and photosynthesis.