Conclusion
Plant photosynthesis is the primary producer on earth, making it an
essential energy source for the survival of all living things, including
humans. In addition, many metabolisms of plants are associated with
photosynthesis, including plant growth and morphogenesis, stomatal
opening, photorespiration, energy production, enzyme activity, ions
transport and cell wall synthesis. It is assumed that the photosynthesis
products, inorganic ions and hormones, are very likely to be transported
between the guard cells and the mesophyll cells. Chloroplasts in
mesophyll cells have evolved optimally for photosynthesis for hundreds
of millions of years. However, chloroplasts in guard cells have evolved
to be less optimized for photosynthesis. This may be seen as a reduction
in the role of chloroplasts in the guard cell or a decrease in
photosynthetic activity. There were much lacks of understanding of guard
cell apoplast when explaining the stomatal opening mechanism. The guard
cell vacuole is normally maintained at pH 5~5.5. It is
regulated by the high activities of V-H+-ATPase and
H+-PPase in apoplast. Due to the activity of
V-H+-ATPase and H+-PPase in the
guard cell vacuole, vacuole has a high positive charges by
H+, so the transport of K+ into
vacuole through the inward vacuolar K+ channels can be
limited. Tonoplast has outward-K+-channels/FV,
outward-TPK/VK-channels and TPC1/SV channels that release vacuole
K+ into the cytoplasm. These channels are responsible
for balancing the positive charges as well as the K+concentration in the vacuole. Sucrose-H+ antiporters
transport sucrose to vacuole relatively easily. The above results
support that sucrose is clearly the main osmotic material for stomatal
opening.