PHOTOSYNTHETICA

Photosynthetica 2021, 59(SI):409-421 | DOI: 10.32615/ps.2021.023

The love-hate relationship between chlorophyll a and water in PSII affects fluorescence products

C.R. GUADAGNO¹, D.P. BEVERLY^{1, 2}, B.E. EWERS^{1, 3}

¹ University of Wyoming, Department of Botany, Laramie, Wyoming, U.S.A.

² University of Wyoming, Water Resources/Environmental Science and Engineering, Laramie, Wyoming, U.S.A.

³ University of Wyoming, Program in Ecology, Laramie, Wyoming, U.S.A.

Chlorophyll a (Chl a) has an asymmetrical molecular organization, which dictates its orientation and the location of the pigment in the mature photosynthetic apparatus. Although Chl a fluorescence (ChlF) is widely accepted as a proxy for plant photosynthetic performance under countless stress conditions and across species, a mechanistic understanding of this causality is missing. Since water plays a much greater role than solvent for the photosynthetic machinery, elucidating its influence on Chl a may explain the reliable reflection of plant stress response in the ChlF signal. We examine the effect of hydration from well-watered to lethal drought on ChlF imagery results across morphologically diverse species to begin testing the impact of molecular scale hydration of Chl a on ChlF. Our results support a conceptual model where water is an integral part of the photosystems' structure and directly influences Chl a behavior leading to changes in the energy partitioning and ultimately in ChlF.

Additional key words: chlorophyll a fluorescence; drought; leaf water content; molecular water; mortality; photosystem II.

Received: December 21, 2020; Revised: March 13, 2021; Accepted: March 31, 2021; Prepublished online: May 25, 2021; Published: July 23, 2021  Show citation