Organ-Level Analysis of Idioblast Patterning in Egeria densa Planch. Leaves

Abstract

Leaf tissues of plants usually contain several types of idioblasts, defined as specialized cells whose shape and contents differ from the surrounding homogeneous cells. The spatial patterning of idioblasts, particularly of trichomes and guard cells, across the leaf epidermis has received considerable attention as it offers a useful biological model for studying the intercellular regulation of cell fate and patterning. Excretory idioblasts in the leaves of the aquatic monocotyledonous plant Egeria densa produced light blue autofluorescence when irradiated with ultraviolet light. The use of epifluorescence microscopy to detect this autofluorescence provided a simple and convenient method for detecting excretory idioblasts and allowed tracking of those cells across the leaf surfaces, enabling quantitative measurement of the clustering and spacing patterns of idioblasts at the whole leaf level. Occurrence of idioblasts was coordinated along the proximal–distal, medial–lateral, and adaxial–abaxial axes, producing a recognizable consensus spatial pattern of idioblast formation among fully expanded leaves. Idioblast clusters, which comprised up to nine cells aligned along the proximal–distal axis, showed no positional bias or regularity in idioblast-forming areas when compared with singlet idioblasts. Up to 75% of idioblasts existed as clusters on every leaf side examined. The idioblast-forming areas varied between leaves, implying phenotypic plasticity. Furthermore, in young expanding leaves, autofluorescence was occasionally detected in a single giant vesicle or else in one or more small vesicles, which eventually grew to occupy a large portion of the idioblast volume as a central vacuole. Differentiation of vacuoles by accumulating the fluorescence substance might be an integral part of idioblast differentiation. Red autofluorescence from chloroplasts was not detected in idioblasts of young expanding leaves, suggesting idioblast differentiation involves an arrest in chloroplast development at a very early stage, rather than transdifferentiation of chloroplast-containing epidermal cells.

Metabolic Noise and Distinct Subpopulations Observed by Single Cell LAESI Mass Spectrometry of Plant Cells in situ

“…Here, we demonstrated the direct analysis of idioblasts interspersed among epidermal cells in E. densa leaf tissues. Idioblasts can be identified based on their autofluorescence in the UV range ( Hara et al, 2015 ). The visualization of these cells for our study was based on imaging the autofluorescence of chlorophyll a ( Krause and Weis, 1991 ).…”

“…However, these cells occur in significantly lower numbers than epidermal cells in plant tissues. Assuming a leaf surface area of ∼43.5 ± 15 mm 2 , the estimated numbers of adaxial epidermal cells and idioblasts are ∼7700 and 214, respectively ( Hara et al, 2015 ). This means a 2.8% frequency for the idioblasts resulting in a 36-time dilution of the analytical signal for them in a bulk sample.…”

Structural basis for C4 photosynthesis without Kranz anatomy in leaves of the submerged freshwater plant Ottelia alismoides

“…Mature leaves of O. alismoides have two types of photosynthetic cell, epidermal and mesophyll. In contrast, leaves from three other species of Hydrocharitaceae, H. verticillata, E. densa and Elodea callitrichoides, only have two layers of epidermal cells and no mesophyll cells (Falk and Sitte, 1963;Pendland, 1979;Hara et al, 2015). As a consequence, the leaf thickness of O. alismoides, especially in the leaves grown at high CO2, at 196 µm, is much greater than the median (95 µm) for submerged leaves from a range of freshwater macrophytes (Maberly and Gontero, 2018) and greater than E. callitrichoides and E. densa estimated from published images to be about 65 µm.…”

“…1 in Falk and Sitte (1963) is correct since the adaxial and abaxial layers are not specifically labelled. Similarly, in E. densa, the transverse sectional area of the upper epidermal cells is about five-times larger than that of the lower epidermal cells (Hara et al, 2015). The functional significance of these differences is currently unknown but they could be linked to the use of bicarbonate involving different processes in upper and lower cell layers (Steemann Nielsen, 1947;Prins and Elzenga, 1989).…”

Observation of Colorless Idioblasts in <i>Egeria densa</i> Leaves by Conventional Ultraviolet-Excitation Fluorescence Microscopy

“…In a recent study, we revealed the differentiation pattern of chloroplast-deficient idioblast cells of E. densa leaves (Hara et al 2015). Egeria idioblasts are visually transparent among the surrounding chloroplast-abundant epidermal cells but have drawn little attention since their description by Hans Solereder a century ago (1913; cited in our paper).…”