Changes in stomatal behaviour in the calcicole Leontodon hispidus due to the disruption by ozone of the regulation of apoplastic Ca2+ by trichomes

Abstract

Regulation of the concentration of Ca2+ in the apoplast of plants is essential in order to allow Ca(2+)-dependent processes, such as Ca(2+)-mediated signal transduction in stomatal guard cells, to function correctly. This is particularly important for plants growing with high levels of Ca2+ in the rhizosphere. Recently, we have shown that in two calcicoles, Leontodon hispidus L. and Centaurea scabiosa L., trichomes play a key role in this regulatory process. Ozone is known to have a marked effect on plant Ca2+ homeostasis. Therefore, we have examined the effect of this pollutant on the regulation by trichomes of apoplastic Ca2+ in the calcicole L. hispidus. Treatment with 100 nl l-1 ozone resulted in a reduction in stomatal conductance of approximately 25% in plants grown with 15 mM Ca2+ in the rhizosphere. Analysis of total Ca2+ levels revealed that these changes in stomatal behaviour reflect a decrease in the ability of trichomes to sequester Ca2+. The amount of Ca2+ present in the trichome tip cell was reduced by approximately 38%. This was accompanied by an increase in the levels of Ca2+ in the guard cells and other tissues of the leaf. These data suggest that ozone has a detrimental effect on the ability of trichomes to regulate the concentration of apoplastic Ca2+ in L. hispidus, resulting in altered stomatal behaviour, and hence gaseous exchange, possibly due to the disruption of guard-cell Ca(2+)-mediated signal transduction. This has important implications for the growth and survival of plants growing in Ca(2+)-rich soils.

Transcriptome analysis approaches for the isolation of trichome-specific genes from the medicinal plant Cistus creticus subsp. creticus

“…Metallothionein genes have also been found to be predominantly expressed in the trichomes of other plant species and are believed to be involved in heavy metal homeostasis by sequestration of excess metal ions in the trichome's body (Foley and Singh 1994;Garcia-Hernandez et al 1998). Glandular trichomes are known to accumulate and secrete various elements to the leaf surface (Broadhurst et al 2004;Choi et al 2001;De Silva et al 2001;Kamiya et al 2006;Kupper et al 2000Kupper et al , 2001Lavid et al 2001;Salt et al 1995). These observations are consistent with a putative detoxification role of trichomes and this could be the case for C. creticus trichomes as well.…”

“…Calcium is often used as a secondary messenger molecule in response to various environmental conditions (Plieth 2005). More precisely, unbound cytoplasmic calcium levels are of great importance for signal transduction pathways related to photosynthesis, stomatal opening and closure and plant responses to water deficit (De Silva et al 2001). Trichomes as epidermal appendages are hypothesized to have a putative role in stomatal homeostasis (Martin and Glover 2007).…”

Chronic exposure to increasing background ozone impairs stomatal functioning in grassland species

“…We postulate that the signalling pathways involved in stomatal functioning were disrupted or overloaded in the leaves that had developed under long‐term exposure to elevated background ozone. In previous laboratory studies, Ca 2+ ‐mediated signal transduction pathways were thought to have been disrupted in L. hispidus (De Silva et al , 2001); this may have been occurring in the L. hispidus and possibly the D. glomerata used in the current study. The loss in response to ABA was comparable with that in aging wheat leaves (Atkinson et al , 1989) which may indicate that, although young green and apparently healthy, the L. hispidus leaves were undergoing premature aging.…”

Calcium signalling in stomatal responses to pollutants

“…(1994) have reported a decrease in stomatal conductance in Norway spruce ( Picea abies ) exposed to ozone which correlates with a marked increase in the calcium content of guard cells. In a more recent study, De Silva et al . (2001) have shown a similar decrease in stomatal conductance associated with an increase in the guard cell calcium content in the calcicole Leontodon hispidus in response to 100 ppb ozone.…”