Accumulation of calcium in the centre of leaves of coriander (Coriandrum sativum L.) is due to an uncoupling of water and ion transport

Abstract

The aim of this study is to understand the parameters regulating calcium ion distribution in leaves. Accumulation of ions in leaf tissue is in part dependent on import from the xylem. This import via the transpiration stream is more important for ions such as calcium that are xylem but not phloem mobile and cannot therefore be retranslocated. Accumulation of calcium was measured on bulk coriander leaf tissue (Coriandrum sativum L. cv. Lemon) using ion chromatography and calcium uptake was visualized using phosphor-images of 45Ca2+. Leaves of plants grown in hydroponics had elevated calcium in the centre of the leaf compared with the leaf margin, while K+ was distributed homogeneously over the leaf. This calcium was shown to be localised to the mesophyll vacuoles using EDAX. Stomatal density and evapotranspiration (water loss per unit area of leaf) were equal at inner and outer sections of the leaf. Unequal ion distribution but uniformity of water loss suggested that there was a difference in the extent of uncoupling of calcium and water transport between the inner and outer leaf. Since isolated tissue from the inner and outer leaf were able to accumulate similar amounts of calcium, it is proposed that the spatial variation of leaf calcium concentration is due to differential ion delivery to the two regions rather than tissue/cell-specific differences in ion uptake capacity. There was a positive correlation between whole leaf calcium concentration and the difference in calcium concentration between inner and outer leaf tissue. Exposing the plants to increased humidity reduced transpiration and calcium delivery to the leaf and abolished this spatial variation of calcium concentration. Mechanisms of calcium delivery to leaves are discussed. An understanding of calcium delivery and distribution within coriander will inform strategies to reduce the incidence of calcium-related syndromes such as tip-burn and provides a robust model for the transport of ions and other substances in the leaf xylem.

Proteaceae from phosphorus‐impoverished habitats preferentially allocate phosphorus to photosynthetic cells: An adaptation improving phosphorus‐use efficiency

“…We suggest that the ability of specific cells to accumulate large amounts of Ca is primarily driven by a higher expression of Ca 2+ ‐channels and tonoplast Ca 2+ transporters and is less reliant on the movement of water through leaves. This uncoupling of Ca 2+ accumulation from water flow has also been demonstrated in other studies (Atkinson, Ruiz, & Mansfield, ; Kerton et al, ; Storey & Leigh, ). There is a need for further research into the differential expression of these channels and transporters within contrasting cell types, particularly in species such as Lomatia , where Ca accumulates preferentially in distinct layers of what appears to be the one cell type.…”

“…Consequently, Ca is thought to accumulate primarily in cells along this path, such as SM, due to their greater apoplastic [Ca] ([Ca 2+ ] apo ; Gilliham et al, ; Karley, Leigh, & Sanders, ). The accumulation of Ca within SM (in G. avellana and R. montana ) supports this model, as these areas are close to the xylem and typically show greater [Ca 2+ ] apo (Gilliham et al, ; Kerton, Newbury, Hand, & Pritchard, ; White, ). However, for cells to accumulate Ca within their vacuole, they must also express both Ca 2+ ‐permeable ion channels, allowing Ca 2+ to move down an electrochemical potential gradient into the cytosol, and tonoplast‐localized transporters, allowing Ca 2+ uptake against an electrochemical potential gradient (Ca 2+ ‐transporting P‐type‐ATPases and Ca 2+ /H + antiporters), into the vacuole, where it can accumulate to high concentrations (>1,400 μmol g −1 ; Conn et al, ; Mäser et al, ; McAinsh & Pittman, ; Shigaki & Hirschi, ).…”

“…Consequently, Ca is thought to accumulate primarily in cells along this path, such as SM, due to their greater apoplastic [Ca] ([Ca 2+ ] apo ; Gilliham et al, 2011;Karley, Leigh, & Sanders, 2000). Kerton, Newbury, Hand, & Pritchard, 2009;White, 2001 the preferential storage of Ca in these cells . In summary, the movement of water via transpiration is vital for the overall uptake and regulation of Ca in leaves (McLaughlin & Wimmer, 1999), but, on the basis of the patterns of Ca distribution, this is not invariably the primary mechanism underlying cell-specific accumulation of Ca in leaves.…”

Elemental distribution by cryo-micro-PIXE in the zinc and cadmium hyperaccumulator Sedum plumbizincicola grown naturally

“…In the leaf Ca was enriched mainly in the palisade mesophyll and to a lesser extent also in the spongy mesophyll and was depleted in the upper and lower epidermis, while K was enriched in the lower epidermis and spongy mesophyll. The same effect is common in most eudicots studied (Conn and Gilliham 2010) such as Citrus jambhiri (rough lemon) (Storey and Leigh 2004), N. praecox (Vogel-Mikuš et al 2008a) and Coriandrum sativum (coriander) (Kerton et al 2009). …”

Salt stress aggravates boron toxicity symptoms in banana leaves by impairing guttation

“…In contrast, solutes that are actively taken up from the xylem may be found at higher concentrations in the middle of the leaf (Fig. 9; Kerton et al . 2009).…”