Photosynthetic phenotyping requires quick characterization of dynamic traits when measuring large plant numbers in a fluctuating environment. Here, we evaluated the light-induced fluorescence transient (LIFT) method for its capacity to yield rapidly fluorometric parameters from 0.6 m distance. The close approximation of LIFT to conventional chlorophyll fluorescence (ChlF) parameters is shown under controlled conditions in spinach leaves and isolated thylakoids when electron transport was impaired by anoxic conditions or chemical inhibitors. The ChlF rise from minimum fluorescence ( F o ) to maximum fluorescence induced by fast repetition rate ( F m−FRR ) flashes was dominated by reduction of the primary electron acceptor in photosystem II (Q A ). The subsequent reoxidation of Q A − was quantified using the relaxation of ChlF in 0.65 ms ( F r1 ) and 120 ms ( F r2 ) phases. Reoxidation efficiency of Q A − ( F r1 / F v , where F v = F m−FRR − F o ) decreased when electron transport was impaired, while quantum efficiency of photosystem II ( F v / F m ) showed often no significant effect. ChlF relaxations of the LIFT were similar to an independent other method. Under increasing light intensities, F r2 ′/ F q ′ (where F r2 ′ and F q ′ represent F r2 and F v in the light-adapted state, respectively) was hardly affected, whereas the operating efficiency of photosystem II ( F q ′/ F m ′) decreased due to non-photochemical quenching. F m−FRR was significantly lower than the ChlF maximum induced by multiple turnover ( F m−MT ) flashes. However, the resulting F v / F m and F q ′/ F m ′ from both flashes were highly correlated. The LIFT method complements F v / F m with information about efficiency of electron transport. Measurements in situ and from a distance facilitate application in high-throughput and automated phenotyping. Electronic supplementary material The online version of this article (10.1007/s11120-018-0594-9) contains supplementary m...

The adaptive response of Sorghum bicolor landraces from Egypt to drought stress and following recovery was analyzed using two-dimensional difference gel electrophoresis, 2D-DIGE. Physiological measurements and proteome alterations of accession number 11434, drought tolerant, and accession number 11431, drought sensitive, were compared to their relative control values after drought stress and following recovery. Differentially expressed proteins were analysed by Matrix assisted laser desorption ionisation time-of-flight mass spectrometry, MALDI-TOF-MS. Alterations in protein contents related to the energy balance, metabolism (sensu Mewes et al. 1997), and chaperons were the most apparent features to elucidate the differences between the drought tolerant and sensitive accessions. Further alterations in the levels of proteins related to transcription and protein synthesis are discussed.

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The impact of (long-term) drought acclimation and (short-term) heat stress and their combination on fast chlorophyll fluorescence induction curves (OJIP) and grain yield was tested using pot-grown plants of wild barley (Hordeum spontaneum) originating from Northern Egypt. Concerning agronomic traits, the main effect of drought was decreased biomass accumulation and grain yield, while heat specifically affected floral development. The treatments caused specific inhibitions of photosystem II (PSII) functionality. While heat stressed plants showed a reduction of maximum quantum efficiency of PSII (φP0), an indication of effects on oxygen evolving complex (OEC) functionality, and the connectivity of PSII units, these features were entirely missing in drought acclimated plants. Drought caused a reduction of the Performance Index (PIabs) and of the relative amplitude of the IP-phase of the OJIP induction curve (ΔVIP). Individuals suffering from a combination of drought and heat showed a better ability to recover photosynthetic electron transport after the relief of stress in comparison to heat stressed plants. However, this improved capacity to recover was not accompanied by an increased grain yield. Thus, we conclude that chlorophyll fluorescence measurements provide valuable physiological data; however, their use in agronomic studies for the prediction of agronomic traits should be done with some precaution.

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Low temperature is one of the most important environmental factors that affect global survival of humans and animals and equally importantly the distribution of plants and crop productivity. Survival of metazoan cells under cold stress requires regulation of the sensor-kinase Target Of Rapamycin (TOR). TOR controls growth of eukaryotic cells by adjusting anabolic and catabolic metabolism. Previous studies identified the Thyroid Adenoma Associated (THADA) gene as the major effect locus by positive selection in the evolution of modern human adapted to cold. Here we investigate the role of THADA in TOR signaling and cold acclimation of plants. We applied BLAST searches and homology modeling to identify the AtTHADA (AT3G55160) in Arabidopsis thaliana as the highly probable orthologue protein. Reverse genetics approaches were combined with immunological detection of TOR activity and metabolite profiling to address the role of the TOR and THADA for growth regulation and cold acclimation. Depletion of the AtTHADA gene caused complete or partial loss of full-length mRNA, respectively, and significant retardation of growth under non-stressed conditions. Furthermore, depletion of AtTHADA caused hypersensitivity towards low-temperatures. Atthada displayed a lowered energy charge. This went along with decreased TOR activity, which offers a molecular explanation for the slow growth phenotype of Atthada. Finally, we used TOR RNAi lines to identify the de-regulation of TOR activity as one determinant for sensitivity towards low-temperatures. Taken together our results provide evidence for a conserved function of THADA in cold acclimation of eukaryotes and suggest that cold acclimation in plants requires regulation of TOR.

This article is protected by copyright. All rights reserved • Solar-induced fluorescence (SIF) is highly relevant in mapping photosynthesis from remotesensing platforms. This requires linking SIF to photosynthesis and understanding the role of non-photochemical quenching (NPQ) mechanisms under field conditions. Hence, active and passive fluorescence were measured in Arabidopsis thaliana with altered NPQ in outdoor conditions. • Plants had mutations in either violaxanthin de-epoxidase (npq1) or PsbS protein (npq4), resulting in reduced NPQ capacity. Parallel measurements of NPQ, photosystem II efficiency, SIF and spectral reflectance (ρ) were conducted diurnally on one sunny summer day and two consecutive days during a simulated cold spell. • Results showed that both npq mutants had higher levels of SIF compared to wild type. Changes in reflectance were related to changes in the violaxanthin-antheraxanthin-zeaxanthin cycle and not to PsbS-mediated conformational changes. When plants were exposed to cold temperatures, rapid onset of photoinhibition strongly quenched SIF in all lines. • Using well-characterized npq mutants of Arabidopsis, we could show for the first time the quantitative link between SIF, photosynthetic efficiency, NPQ components and leaf reflectance. We discuss the functional potential and limitations of SIF and reflectance measurements for estimating photosynthetic efficiency and NPQ in the field.

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