Hormonal and environmental signals guiding stomatal development

Abstract

Stomata are pores on plant epidermis that facilitate gas exchange and water evaporation between plants and the environment. Given the central role of stomata in photosynthesis and water-use efficiency, two vital events for plant growth, stomatal development is tightly controlled by a diverse range of signals. A family of peptide hormones regulates stomatal patterning and differentiation. In addition, plant hormones as well as numerous environmental cues influence the decision of whether to make stomata or not in distinct and complex manners. In this review, we summarize recent findings that reveal the mechanism of these three groups of signals in controlling stomatal formation, and discuss how these signals are integrated into the core stomatal development pathway.

Fig. 1.

Summary of the effects that diverse range of signals have on stomatal development. a A cartoon showing stomatal cell-lineage transitions from a protodermal cell, a meristemoid mother cell (MMC), meristemoids undergoing asymmetric amplifying divisions and producing stomatal-lineage ground cells (SLGCs), and a guard mother cell (GMC) to a stoma with paired guard cells (GCs). A protodermal cell could differentiate into a pavement cell, and SLGCs could become pavement cells. Cartoons are modified from Han and Torii [11]. b An Arabidopsis seedling with stomata highlighted in green is in the center. Signals that negatively regulate stomatal development are shown on the left, indicated with red arrows. Signals that promote stomatal formation are shown on the right, indicated with green arrows. The black and yellow boxes indicate darkness (or signals that inhibit stomatal development) and light (or signals that promote stomatal development), respectively. When a signal is deficient, a minus sign is put in front of it. Top left: cotyledon epidermis with pavement cell only. Middle left: cotyledon epidermis with arrested meristemoids. Bottom left: hypocotyl epidermis with pavement cell only. Top right: cotyledon epidermis with clustered stomata. Middle right: cotyledon epidermis with high stomatal density. Bottom right: hypocotyl epidermis with clustered stomata. Confocal microscopy images of the cotyledon and hypocotyl epidermis of wild-type and various mutant seedlings were taken using a Leica SP5 WLL and false colored using Adobe Photoshop CS6

Fig. 2.

How hormonal and environmental cues are integrated into the core stomatal developmental pathway. Components involved in the same pathway are grouped with the same color. The experimentally confirmed steps are shown as solid lines, and the steps that are uncertain are shown as broken lines. An arrow indicates a positive regulation, while a ‘T’ indicates negative regulation