Photosystem II Functionality in Barley Responds Dynamically to Changes in Leaf Manganese Status

Area of Science:

• Plant Physiology
• Photosynthesis Research
• Biochemistry

Background:

• A manganese (Mn) cluster in photosystem II's oxygen-evolving complex (OEC) is crucial for water oxidation and photosynthesis.
• Limited knowledge exists on how Mn deficiency impacts PSII functionality and plant adaptation.

Purpose of the Study:

• To investigate the effects of latent Mn deficiency on PSII photochemistry and energy dissipation in two barley genotypes.
• To understand genotypic differences in Mn efficiency related to PSII performance.

Main Methods:

• Measurements of fluorescence induction kinetics (OJIP transients) and non-photochemical quenching (NPQ).
• Analysis of PSII subunit composition.
• Comparison of Mn-efficient and Mn-inefficient barley genotypes.

Main Results:

• Mn deficiency caused severe PSII damage, indicated by reduced quantum yield and new inflection points (K step, D dip) in OJIP transients.
• Plants exhibited decreased NPQ, impaired recovery from photoinhibition, and reduced PsbP/PsbQ subunit abundance.
• Mn-efficient genotypes maintained higher NPQ under mild Mn deficiency, but differences vanished under severe deficiency.

Conclusions:

• Mn deficiency profoundly impacts PSII, affecting water oxidation and energy dissipation.
• NPQ regulation contributes to genotypic differences in Mn efficiency under mild deficiency.
• Severe Mn deficiency leads to a general loss of PSII repair capacity in both genotypes.