Contribution of PsbS Function and Stomatal Conductance to Foliar Temperature in Higher Plants

Abstract

Natural capacity has evolved in higher plants to absorb and harness excessive light energy. In basic models, the majority of absorbed photon energy is radiated back as fluorescence and heat. For years the proton sensor protein PsbS was considered to play a critical role in non-photochemical quenching (NPQ) of light absorbed by PSII antennae and in its dissipation as heat. However, the significance of PsbS in regulating heat emission from a whole leaf has never been verified before by direct measurement of foliar temperature under changing light intensity. To test its validity, we here investigated the foliar temperature changes on increasing and decreasing light intensity conditions (foliar temperature dynamics) using a high resolution thermal camera and a powerful adjustable light-emitting diode (LED) light source. First, we showed that light-dependent foliar temperature dynamics is correlated with Chl content in leaves of various plant species. Secondly, we compared the foliar temperature dynamics in Arabidopsis thaliana wild type, the PsbS null mutant npq4-1 and a PsbS-overexpressing transgenic line under different transpiration conditions with or without a photosynthesis inhibitor. We found no direct correlations between the NPQ level and the foliar temperature dynamics. Rather, differences in foliar temperature dynamics are primarily affected by stomatal aperture, and rapid foliar temperature increase during irradiation depends on the water status of the leaf. We conclude that PsbS is not directly involved in regulation of foliar temperature dynamics during excessive light energy episodes.

CIA2 and CIA2‐LIKE are required for optimal photosynthesis and stress responses in Arabidopsis thaliana

“…Increased susceptibility to HL and UV‐AB can be a consequence of impaired non‐photochemical quenching (NPQ), which is responsible for the dissipation of excess light energy as heat (Kulasek et al ., 2016; Białasek et al ., 2017). Thus, we monitored NPQ using chlorophyll a fluorescence in Col‐0, cia2–2 , cil‐1 , cil‐2 , cia2–2 cil‐1 and cia2–2 cil‐2 (Figures 6 and S4).…”

“…The redox state of the PQ pool and H 2 O 2 are also involved in high light acclimatory responses (Karpiński et al ., 1999; Mühlenbock et al ., 2008; Gilroy et al ., 2016). Experimentally, it is almost impossible to separate foliar heat shock from high light responses, because exposure to high light for a few seconds significantly warms up Arabidopsis leaves due to the dissipation of energy as heat (Kulasek et al ., 2016). Therefore, it is interesting that CIA2 and CIL antagonistically influence high light and UV‐B acclimation versus thermotolerance in ambient light.…”

Evidence for the Involvement of Electrical, Calcium and ROS Signaling in the Systemic Regulation of Non-Photochemical Quenching and Photosynthesis

“…DCMU binds to the quinone B- (Q B ) binding pocket and blocks the oxidation of quinone A (Q A ) and subsequent reduction of plastoquinone (PQ). It results in a disturbance in F m and F 0 , which leads to strong reduction of NPQ ( Escoubas et al 1995 , Kulasek et al 2016 ). In our experiments, DCMU application also resulted in a strong decrease of NPQ in the leaf area exposed to this inhibitor; however, it did not disturb spreading of Chl fluorescence changes across the treated region ( Fig.…”

Photosystem II 22kDa protein level ‐ a prerequisite for excess light‐inducible memory, cross‐tolerance to UV‐C and regulation of electrical signalling

“…Recently, however, we found no direct correlations between PsbS levels and foliar temperature responses in leaves exposed to strongly increasing and decreasing short (30 s) episodes of excess light. We concluded that PsbS is not directly involved in the regulation of foliar temperature dynamics under variable light conditions, although it still could be indirectly involved in the regulation of stomatal conductance and the transpiration rate and, thus, of foliar temperature (Kulasek, Bernacki, Ciszak, Wito n, & Karpi nski, 2016).…”

“…Recently, however, we found no direct correlations between PsbS levels and foliar temperature responses in leaves exposed to strongly increasing and decreasing short (30 s) episodes of excess light. We concluded that PsbS is not directly involved in the regulation of foliar temperature dynamics under variable light conditions, although it still could be indirectly involved in the regulation of stomatal conductance and the transpiration rate and, thus, of foliar temperature (Kulasek, Bernacki, Ciszak, Witoń, & Karpiński, ). Szechyńska‐Hebda, Kruk, Górecka, Karpińska, and Karpiński () demonstrated that the local and systemic acquired acclimation (SAA) (Karpiński et al, ) – light acclimatory responses induced by episodes of excess light – are regulated by electrical signalling and are required for local and systemic NPQ adjustments (Białasek, Górecka, Mittler, & Karpiński, ).…”