Abstract
Blue light (BL) induces stomatal opening through the activation of H+-ATPases with subsequent ion accumulation in guard cells. In most plant species, red light (RL) enhances BL-dependent stomatal opening. This RL effect is attributable to the chloroplasts of guard cell, the only cells in the epidermis possessing this organelle. To clarify the role of chloroplasts in stomatal regulation, we investigated the effects of RL on BL-dependent stomatal opening in isolated epidermis, guard cell protoplasts, and intact leaves of Arabidopsis thaliana. In isolated epidermal tissues and intact leaves, weak BL superimposed on RL enhanced stomatal opening while BL alone was less effective. In guard cell protoplasts, RL enhanced BL-dependent H+-pumping and DCMU, a photosynthetic electron transport inhibitor, eliminated this effect. RL enhanced phosphorylation levels of the H+-ATPase in response to BL, but this RL effect was not suppressed by DCMU. Furthermore, DCMU inhibited both RL-induced and BL-dependent stomatal opening in intact leaves. The photosynthetic rate in leaves correlated positively with BL-dependent stomatal opening in the presence of DCMU. We conclude that guard cell chloroplasts provide ATP and/or reducing equivalents that fuel BL-dependent stomatal opening, and that they indirectly monitor photosynthetic CO2 fixation in mesophyll chloroplasts by absorbing PAR in the epidermis.
Highlights
Light-induced stomatal opening facilitates CO2 uptake for photosynthetic CO2 fixation and drives the transpirational water stream [1,2,3,4]
Red light enhances blue light-dependent stomatal opening via photosynthesis in isolated epidermal tissues To minimize the effect of mesophyll chloroplasts and explore the role of guard cell chloroplasts, effects of red light (RL) on Blue light (BL)-dependent stomatal opening were investigated in isolated epidermal tissues
In the absence of background RL, stomata subtly opened in response to 5 mmol m22 s21 BL, and stomatal aperture became larger as the fluence rate of BL was increased (Figure 1A)
Summary
Light-induced stomatal opening facilitates CO2 uptake for photosynthetic CO2 fixation and drives the transpirational water stream [1,2,3,4]. Blue light (BL) is a signal inducing stomatal opening caused by the swelling of guard cells [1]. The plasma membrane H+-ATPase is activated by phosphorylation of the C-terminal penultimate threonine residue leading to the binding of 14-3-3 proteins, and drives BL-dependent stomatal opening [6,7,8]. Recent molecular genetic analyses in Arabidopsis thaliana identified signal transduction components leading to H+-ATPase activation and stomatal opening. The activated phots phosphorylate the Ser/ Thr protein kinase BLUE LIGHT SIGNALING1 (BLUS1) in a BL-dependent manner [12]. We note that BL inhibits S-type anion channels in guard cells, thereby stimulates stomatal opening in a phototropindependent manner [14]
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