Growth & Development

Spatial arrangement of stomata in Michelia

The spatial pattern of stomata is mainly caused by small-scale epidermal competition.

In hierarchically reticulate venation patterns, smaller orders of veins form areoles in which stomata are located. Shi et al. aimed to quantify the spatial relationship among stomata at the areole level.

Previous studies have shown that stomatal density is negatively correlated with stomatal size, so that a lower stomatal density corresponds to a larger stomatal size. On average, the number of stomata within an areole is observed to be positively related to the areole size for many plant groups. Although prior studies have shown a negative correlation between the lamina surface area occupied by vascular bundle sheaths and stomatal density, the spatial relationship between stomata has not been extensively examined.

Positions of the sections sampled for analysis of stomatal distributions (left panel) and an image of a representative chemically cleared leaf showing the venation pattern (right panel) of the warm temperate evergreen tree M. cavaleriei var. platypetala. Source Shi et al. 2021.

For each of 12 leaves of Michelia cavaleriei var. platypetala, the scientists assumed that stomatal characteristics were symmetrical on either side of the midrib, and divided the leaf surface on one side of the midrib into six layers equidistantly spaced along the apical–basal axis. They then further divided each layer into three positions equidistantly spaced from midrib to leaf margin, resulting in a total of 18 sampling locations. In addition, for 60 leaves, they sampled three positions from midrib to margin within only the widest layer of the leaf. Stomatal density and mean nearest neighbour distance (MNND) were calculated for each section. A replicated spatial point pattern approach quantified stomatal spatial relationships at different distances (0–300 μm).

The botanists observed a tendency towards regular arrangement (inhibition as opposed to attraction or clustering) between stomatal centres at distances <100 μm. Spatial inhibition might be caused by the one-cell-spacing rule, resulting in more regular arrangement of stomata, and it was found to exist at distances up to ~100 μm. This work implies that leaf hydraulic architecture, consisting of both vascular and mesophyll properties, is sufficient to prevent important spatial variability in water supply at the areole level.

RESEARCH ARTICLE

Shi, P., Jiao, Y., Diggle, P.J., Turner, R., Wang, R., Niinemets, Ü., 2021. Spatial distribution characteristics of stomata at the areole level in Michelia cavaleriei var. platypetala (Magnoliaceae). Annals of Botany. https://doi.org/10.1093/aob/mcab106

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