The science of the stomata of plants: a continuously growing list of references, abstracts and illustrations, helping researchers to data on publications.
Phototropins are plant-specific light-activated receptor kinases that regulate diverse blue-light-induced responses, and serve to optimize plant growth under various light environments. Phototropins undergo autophosphorylation as an essential step for their signaling and induce a variety of tissue-specific or organ-specific responses, but the divergent mechanisms for these responses are unknown.
It is most likely that the phototropins generate a specific output after the event of autophosphorylation.
In this report, we will review the common steps of phototropin signaling and the numerous interactive proteins of phototropins, which may act as signal transducers for the diverse responses. We also describe the phototropin-mediated signaling process of stomatal guard cells and its crosstalk with abscisic acid signaling.
Blue light (BL) receptor phototropins activate the plasma membrane H+-ATPase in guard cells through phosphorylation of a penultimate threonine and subsequent binding of the 14-3-3 protein to the phosphorylated C-terminus of H+-ATPase, mediating stomatal opening.
To date, detection of the phosphorylation level of the guard cell H+-ATPase has been performed biochemically using guard cell protoplasts (GCPs). However, preparation of GCPs from Arabidopsis for this purpose requires >5,000 rosette leaves and takes >8 h.
Here, we show that BL-induced phosphorylation of guard cell H+-ATPase is detected in the epidermis from a single Arabidopsis rosette leaf via an immunohistochemical method using a specific antibody against the phosphorylated penultimate threonine of H+-ATPase.
BL-induced phosphorylation of the H+-ATPase was detected immunohistochemically in the wild type, but not in a phot1-5 phot2-1 double mutant.
Moreover, we found that physiological concentrations of the phytohormone ABA completely inhibited BL-induced phosphorylation of guard cell H+-ATPase in the epidermis, and that inhibition by ABA in the epidermis is more sensitive than in GCPs.
These results indicate that this immunohistochemical method is very useful for detecting the phosphorylation status of guard cell H+-ATPase. Thus, we applied this technique to ABA-insensitive mutants (abi1-1, abi2-1 andost1-2) and found that ABA had no effect on BL-induced phosphorylation in these mutants.
These results indicate that inhibition of BL-induced phosphorylation of guard cell H+-ATPase by ABA is regulated by ABI1, ABI2 and OST1, which are known to be early ABA signaling components for a wide range of ABA responses in plants.
Figure 6. A possible model for FT/TSF-mediated stomatal opening. The photoperiodic pathway is shown with representative components. The blue light signaling pathway between phototropins and the H+-ATPase is shown with a blue arrow. Arrows and T-bars indicate positive and negative regulation, respectively. Dotted arrows represent input and output of the circadian clock. Gene names in red represent components that were directly analyzed in this study. ELF3 and FT were described previously (Kinoshita et al., 2011). TFs represents transcription factors working downstream of FT and TSF, such as an AP1. Gray lines indicate regulatory mechanisms that are reported in previous works. White arrows show a contribution to stomatal opening, and the thickness of the arrows represents the possible degree of the contribution (for details, see text). – http://www.plantphysiol.org/content/162/3/1529/F6.medium.gif
Abstract
FLOWERINGLOCUS T (FT) is the major regulatory component controlling photoperiodic floral transition. It is expressed in guard cells and affects blue light-induced stomatal opening induced by the blue-light receptor phototropins phot1 and phot2. Roles for other flowering regulators in stomatal opening have yet to be determined.
We show in Arabidopsis (Arabidopsis thaliana) that TWIN SISTER OF FT (TSF), CONSTANS (CO), and GIGANTEA (GI) provide a positive effect on stomatal opening. TSF, which is the closest homolog of FT, was transcribed in guard cells, and light-induced stomatal opening was repressed in tsf-1, a T-DNA insertion mutant of TSF. Overexpression of TSF in a phot1 phot2 mutant background gave a constitutive open-stomata phenotype.
Then, we examined whether CO and GI, which are upstream regulators of FT and TSF in photoperiodic flowering, are involved in stomatal opening. Similar to TSF, light-induced stomatal opening was suppressed in the GI and CO mutants gi-1 and co-1. A constitutive open-stomata phenotype was observed in GI and CO overexpressors with accompanying changes in the transcription of both FT and TSF. In photoperiodic flowering, photoperiod is sensed by photoreceptors such as the cryptochromes cry1 and cry2. We examined stomatal phenotypes in a cry1 cry2 mutant and in CRY2 overexpressors.
Light-induced stomatal opening was suppressed in cry1 cry2, and the transcription of FT and TSF was down-regulated. In contrast, the stomata in CRY2 overexpressors opened even in the dark, and FT and TSF transcription was up-regulated.
We conclude that the photoperiodic flowering components TSF, GI, and CO positively affect stomatal opening.
PLANT STOMATA ENCYCLOPEDIA 
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