Blue and red light effects on stomatal oscillations

Abstract

The response of stomata to red and blue light was investigated using small fibre optics (66µm diameter) to control light levels on a single pair of guard cells without affecting the surrounding tissue. Low intensity red light (50µmolm–2s–1) applied to the entire leaf caused stomata to oscillate continuously for several hours with no apparent decrease in amplitude with time. Adding low intensity blue light (50µmolm–2s–1) caused stomata to stop oscillating, but oscillations resumed when the blue light was removed. Adding the same intensity of red light to an oscillating leaf changed the amplitude of the oscillations but did not stop them. When blue light was added to a single guard cell pair (using a fibre optic) in a red-light-illuminated leaf, the stoma formed by that pair stopped oscillating, but adjacent stomata did not. Red light added to a single guard cell pair did not stop oscillations. Finally, blue light applied through a fibre optic to areas of leaf without stomata caused proximal stomata to stop oscillating, but distal stomata continued to oscillate. The data suggest that blue light affects stomata via direct effects on guard cells as well as by indirect effects on other cells in the leaf.

Atavistic Stomatal Responses to Blue Light in Marsileaceae

“…While oscillations are common in R. diphyllum and not exclusive to any light environment, they are unusually large under blue light and frequently disappeared upon the removal of the blue light. This effect is the opposite of the behavior previously observed in angiosperms, in which blue light inhibited stomatal oscillations in the monocots Musa acuminata (Zait et al, 2017) and Tradescantia pallida (Ballard et al, 2019).…”

“…This hydraulic explanation accounts for most stomatal oscillations, although other causes are possible (Yang et al, 2003). Blue light may inhibit hydraulic oscillations through two distinct mechanisms, one occurring in the guard cells and another based in the surrounding tissue (Ballard et al, 2019). The guard cell mechanism is probably the archetypal blue light response, which may increase the osmotic load in guard cells enough to overcome hydraulic triggers that would otherwise cause stomatal closure.…”

“…This angiosperm stomatal behavior has been explained by attributing oscillations under red light to a hydraulic mismatch between transpiration rate and leaf water supply (Ballard et al, 2019;Zait et al, 2017). A hydraulic mismatch can cause leaf turgor and stomatal conductance to oscillate in opposite phases (Barrs, 1971;Farquhar and Cowan, 1974), particularly if stomatal responses to leaf water status are delayed because they depend on metabolic regulation.…”

“…In R. diphyllum, blue light oscillations were much more common under low fluences (5-40 μmol m -2 s -1 ) than under high fluences (100-300 μmol m -2 s -1 ) of blue light at a constant total light intensity (Figure 3). The absence of oscillations under high fluences of 100 and 300 μmol m -2 s -1 blue light suggests that, as in angiosperms (Ballard et al, 2019;Zait et al, 2017), a high intensity of blue light can generate sufficient osmotic pressure to maintain high guard cell turgor and stomatal aperture even in the presence of other closing signals, such as reduced water availability or even reduced photosynthetic rate. However, the intensity threshold beyond which the blue light signal dominates appears to be higher in Marsileaceae than in angiosperms previously studied (Ballard et al, 2019).…”

“…The blue light stomatal response appears to be ancestral in vascular plants (Doi et al, 2015) and primarily contained within the guard cells (Shimazaki et al, 2007;Suetsugu et al, 2014). Although there is also evidence of a stomatal response to blue light with origins outside of the guard cells, the mechanism underlying this secondary response remains unclear (Ballard et al, 2019). In all lineages, the primary pathway occurring within the guard cells is initiated by blue light perception by phototropins and culminates in guard cell H + -ATPase activation, which hyperpolarizes the plasma membrane and consequently increases guard cell turgor (Doi et al, 2015;Falhof et al, 2016;Kinoshita et al, 2001;Li et al, 2015b;Yamauchi et al, 2016).…”