Introduction
Starch-sugar hypothesis was the basic concept of stomatal physiology in
the early 20th century. This theory was brought up by Kohl in 1895. When
the plant receives light, photosynthesis occurs, the amount of
CO2 in the cell decreases, the pH of the guard cell
increases. At high pH, starch phosphorylase, which decomposes starch
into sucrose, is activated, increasing the osmotic pressure of the guard
cell. On the contrary, it was considered that the photosynthesis did not
occur in the dark-treated leaves, resulting in an increase of
CO2 concentration. As a result, at low pH, the starch
does not decompose into sucrose and the stomata close. It is now known
that in the distribution of carbon, carbon assimilated by photosynthesis
during the day is used for starch synthesis of chloroplasts or
transported to the cytoplasm for sucrose synthesis.
Therefore, the initial starch-sugar theory is not perfect, but it is
still a partially accepted theory that it was understood as a sucrose as
the main osmotic material that opens stomata.
In 1943, Imamura isolated epidermis from the mesophyll cells and
cultured epidermal strips in a high concentration of KCl solution. And
then, he observed an increase of K+ concentration in
the guard cell. Experimented in the same way as Imamura, in 1976, Hsiao
announced that the accumulation of K+ occurs when
stomata open. From this point on, many stomatal researchers began to see
K+ as the main osmotic material for stomata opening.
In 1996, when stomata were opened, a paper was published stating that up
to 800mM of K+ was accumulated in the guard cell
(Talbott et al . 1996). Even today, many scientists understand
that stomatal opening is caused by K+. Environmental
factors, such as light and CO2 concentration, trigger
events, which may result in stomatal opening. However, currently still,
how these signals are sensed and how they are transduced into driving
osmotic materials, which control stomatal movements, are not fully
understood. Some of the stomatal researchers actually measured the
K+ concentration of the guard cell to see if it needed
so much potassium for the stomatal opening (Travis & Mansfield 1977,
Bowling 1987, DeSilva et al . 1996). When the K+concentration of the guard cell was measured, the total concentration of
K+ ions presents in the cytoplasm, apoplast, and
vacuole was 100~150 mM, and most K+was known to exist in the apoplast (50~75 mM).
The above results showed that the concentration of K+for stomatal opening was not higher than expected. In this confused
state, the osmotic material needed for stomatal opening was considered
to be sucrose, as in early theory (Outlaw 1989, Reckmann et al .
1990, Gautier et al . 1991, Poffenroth et al . 1992, Outlaw
1996, Lu et al . 1997, Asai et al . 2000, Outlaw & De
Vleighere 2001, Lawson et al . 2002, 2003, von Caemmerer et
al . 2004, Outlaw 2003, Kang et al . 2007).
Currently, according to stomatal researchers, K+ or
sucrose is believed to be the main osmotic material, so two types of
theories are compatible. Of course, for stomatal opening, most stomatal
researchers recognize that Cl- and
malte2- are necessary in addition to
K+ and sucrose. It has been found that
K+ and sucrose can act similarly for stomatal opening
(Tallman & Zeiger 1988). They reported that stomata were opened by
k+ in the early morning and sucrose acts as an osmotic
material in the afternoon. Zeaxanthin and phototropins (pho1 andpho2 ), blue light photoreceptors for stomatal openings, have been
identified. Blue light has been shown to promote regulatory 14-3-3
protein, as the activity of PM (plasma membrane)
H+-ATPase by IAA is mediated by regulatory 14-3-3
protein (Eigo & Kinoshita 2018). However, despite the discovery of a
mechanism for stomatal opening by blue light, stomata are also opened by
red and white light. The size of the stomatal apertures caused by white
light was about 18μm in Commelina communis , but increased by
about 6μm stomatal aperture by single blue light and stomatal aperture
of about 7.3 μm by red light (Schwarz & Zeiger 1984, Lee & Bowling
1992). The stomatal aperture by blue light was estimated to be the sum
of the stomatal opening by chlorophyll and carotenoid and the stomatal
opening mediated by blue light photoreceptors. Indeed, experiments with
stomatal aperture measurements associated with blue light receptors have
been described by Talbott et al . (2003) is the only one. After
the blue light receptors-deficient mutant plants were made inArabidopsis thaliana , the stomatal opening by blue light was
observed. In wild type, stomatal opening increased by about 0.7 μm when
treated with blue light, but stomatal opening of the npq1 mutant was
suppressed by about 0.3 μm. The photo1 /photo2 mutant had a
rather increased stomatal opening of about 0.3 μm. In the experiment
using the blue photoreceptor mutation, the wild type increased about 0.4
μm compared to the photo1 /photo2 mutant. SEM (The standard
errors of the mean) of about 20 stomatal apertures repeated twice in theCommelina communis was ± 0.89 μm (Lee & Bowling 1992).
Therefore, it is difficult to see that the effect of the distinct blue
light receptor appeared in Talbott et al ’. (2003)’s experiment.
Recently, stomatal researchers who studied stomata in relation to blue
light photo-receptors were difficult to find, but review papers were
available (Inoue & kinoshita 2017, Matthews et al . 2020).
Therefore, in this paper, the environmental characteristics of ion and
sucrose transport between the guard cell cytoplasm and vacuole are
examined, and attempts are made to clarify the opinions on stomatal
opening by blue light.