Reduced glutamine synthetase activity plays a role in control of photosynthetic responses to high light in barley leaves

Abstract

a b s t r a c tThe chloroplastic glutamine synthetase (GS, EC 6.3.1.2) activity was previously shown to be the limiting step of photorespiratory pathway. In our experiment, we examined the photosynthetic high-light responses of the GS2-mutant of barley (Hordeum vulgare L.) with reduced GS activity, in comparison to wild type (WT). The biophysical methods based on slow and fast chlorophyll fluorescence induction, P700 absorbance, and gas exchange measurements were employed. Despite the GS2 plants had high basal fluorescence (F 0 ) and low maximum quantum yield (F v /F m ), the CO 2 assimilation rate, the PSII and PSI actual quantum yields were normal. On the other hand, in high light conditions the GS2 had much higher non-photochemical quenching (NPQ), caused both by enhanced capacity of energy-dependent quenching and disconnection of PSII antennae from reaction centers (RC). GS2 leaves also maintained the PSII redox poise (Q A À /Q A total) at very low level; probably this was reason why the observed photoinhibitory damage was not significantly above WT. The analysis of fast chlorophyll fluorescence induction uncovered in GS2 leaves substantially lower RC to antenna ratio (RC/ABS), low PSII/PSI ratio (confirmed by P700 records) as well as low PSII excitonic connectivity.

Low PSI content limits the photoprotection of PSI and PSII in early growth stages of chlorophyll b-deficient wheat mutant lines

“…/ P700 total at graduated light intensities (Fig. 2a, b), which can reliably detect any shift of balance between PSs (Zivcak et al 2013;Brestic et al 2014). While in WT, we can see the symmetrical accumulation of Q À A in PSII Photosynth Res acceptor side and P700 ?…”

Night Light-Adaptation Strategies for Photosynthetic Apparatus in Yellow-Poplar (Liriodendron tulipifera L.) Exposed to Artificial Night Lighting

“…The PSII as the heart of the photosynthetic process is highly sensitive to the environmental stresses. Its activity could be determined with one non-invasive time-resolved fluorescence measurement, which could measure the polyphasic rise with the basic steps of OJIP [43,[48][49][50][51][52][53][54]. Several studies have shown that the chlorophyll a transient has become one of the most popular tools to estimate stress-induced changes in photosynthetic performance.…”

Using the quantum yields of photosystem II and the rate of net photosynthesis to monitor high irradiance and temperature stress in chrysanthemum (Dendranthema grandiflora)

“…non-photochemical quenching of chlorophyll fluorescence) is a feedback regulatory mechanism induced upon exposure to high irradiance exceeding that which may be used at maximum quantum yield by photosystem II (PSII) [20,[22][23][24][25][26]. Previous studies have shown that low irradiance protects the photosynthetic apparatus from the adverse effects of high temperature, while photoinhibition protects against both high irradiance and high temperature stress [7,27,28].…”