ABA Regulation of Stomatal Movement - Abscisic Acid: Metabolism, Transport and Signaling - page 280

major regulators of CO 2 responses, impairs CO 2 -induced stomatal closure, but
retains ABA-induced stomatal closure and blue light-induced stomatal opening in
Arabidopsis (Hashimoto et al. 2006 ; Hu et al. 2010 ). Therefore, the regulatory net-
works of stomatal movement for different phytohormones and environmental stimuli
are not completely independent from each other. They share some key components
and crosstalk through these shared components. Guard cells can perceive and inte-
grate different stimulating signals together (Merilo et al. 2014 ), and regulate the sto-
mata pores precisely to ensure an optimal gas exchange. The elucidation of ABA
signaling network in guard cells not only facilitates our understanding about ABA-
induced stomatal movement, but also will potentially help us to understand how
other signals involves in stomatal movement.
Drought stress induces ABA production, and ABA closes stomata as a signal of
drought stress. Almost 30 years ago, the fantastic experiment of dividing the roots
of maize between two containers, in which soil was dry in one container, but well-
watered in another, resulted in partial closure of stomata and reduced water loss
while the plant could grow normally (Blackman and Davies 1985 ). This technique
was called partial root drying (PRD), which shed a light into the mind of plant sci-
entists, and made them to believe that it is possible to reduce water loss significantly
without disrupting the normal growth of plants, especially the yield of crops by engi-
neering. Considering the short of fresh water globally, saving fresh water in plant
growth, including crops, is meaningful for the survival and development of human
society. Numerous ABA signaling researchers from different countries dedicate their
energy to unravel the ABA signaling network in stomata for decades, their goals
are to understand the signaling network and use the knowledge and techniques they
develop to reduce the water loss and improve the resistant ability of plants against
environmental stresses. In the last two to three decades, huge advances were made in
this research field. This chapter will mainly focus on ABA signaling in stomata.
15.2 Stomata Development
Guard cells are derived from epidermal stem cells. Protodermal cells differentiate
into meristemoid mother cells (MMCs), from which two daughter cells in different
sizes are derived by asymmetrical cell division. The smaller one (meristemoids)
has stem cell-like capabilities and is generally engaged for further asymmetric cell
division. The larger one is called guard mother cell (GMC) and divides symmetri-
cally to yield two guard cells, which surround a pore to form a stomata. Stomata
stem cells persist mounting in epidermis until all cells complete differentiation.
Stomata are separated by at least one epidermis pavement cell, and this pattern is
being kept through the whole period of plant development. Stomata development
and the formation of correct pattern require an appropriate timing and orientation
of asymmetric and symmetric cell divisions, cell fate selection, and cell-cell com-
munication, which is possibly mainly through small peptide molecules to ensure a
correct cell positioning. This process is regulated and influenced by a number of