Diurnal Response of Photosystem I to Fluctuating Light Is Affected by Stomatal Conductance.

Ting-Yu Li,Wei Huang,Shi-Bao Zhang,Qi Shi,Ming Yue,Hu Sun

doi:10.3390/cells10113128

Abstract

Upon a sudden transition from low to high light, electrons transported from photosystem II (PSII) to PSI should be rapidly consumed by downstream sinks to avoid the over-reduction of PSI. However, the over-reduction of PSI under fluctuating light might be accelerated if primary metabolism is restricted by low stomatal conductance. To test this hypothesis, we measured the effect of diurnal changes in stomatal conductance on photosynthetic regulation under fluctuating light in tomato (Solanum lycopersicum) and common mulberry (Morus alba). Under conditions of high stomatal conductance, we observed PSI over-reduction within the first 10 s after transition from low to high light. Lower stomatal conductance limited the activity of the Calvin–Benson–Bassham cycle and aggravated PSI over-reduction within 10 s after the light transition. We also observed PSI over-reduction after transition from low to high light for 30 s at the low stomatal conductance typical of the late afternoon, indicating that low stomatal conductance extends the period of PSI over-reduction under fluctuating light. Therefore, diurnal changes in stomatal conductance significantly affect the PSI redox state under fluctuating light. Moreover, our analysis revealed an unexpected inhibition of cyclic electron flow by the severe over-reduction of PSI seen at low stomatal conductance. In conclusion, stomatal conductance can have a large effect on thylakoid reactions under fluctuating light.

Highlights

Fluctuating light (FL) is the typical light condition under natural field conditions [1]
The stomatal conductance at 18:00 was much lower than that at 15:00 (Figure 1A), which was accompanied by a decrease in maximum photosystem II (PSII) electron flow (ETRIImax) under FL (Figure 1B)
Y(NA) decreased to its lowest value starting 30 s after the light transition at 15:00, but remained high at 18:00. These results indicated that the PSI redox state under FL changed during diurnal photosynthesis

Summary

Introduction

Fluctuating light (FL) is the typical light condition under natural field conditions [1]. ATP and NADPH produced by linear electron flow cannot be immediately consumed by the primary metabolism. Such imbalance between light and dark reactions leads to the accumulation of electrons in PSI, which manifests as PSI over-reduction [5,6,7]. Under such conditions, the transfer of electrons from PSI electron carriers to oxygen (O2) increases, producing reactive oxygen species (ROS) [8]. Owing to the important role of PSI in the operation of photosynthetic electron transport, PSI photoinhibition significantly suppresses CO2 assimilation, photoprotection, and plant growth [13,14,15,16]

Methods

Results

Conclusion