Microalgae from Nordic collections demonstrate biostimulant effect by enhancing plant growth and photosynthetic performance.

We investigated the biostimulant potential of six microalgal species from Nordic collections extracted with two different procedures: thermal hydrolysis with a weak solution of sulfuric acid accompanied by ultrasonication and bead-milling with aqueous extraction followed by centrifugation. To this aim, we designed a phenotyping pipeline consisting of a root growth assay in the model plant Arabidopsis thaliana, complemented with greenhouse experiments to evaluate lettuce yield (Lactuca sativa L. cv. Finstar) and photosynthetic performance. The best-performing hydrolyzed extracts stimulated Arabidopsis root elongation by 8%-13% and lettuce yield by 12%-15%. The in situ measured photosynthetic performance of lettuce was upregulated in the efficient extracts: PSII quantum yield increased by 26%-34%, and thylakoid proton flux increase was in the range of 34%-60%. In contrast, aqueous extracts acquired by bead-milling showed high dependence on biomass concentration in the extract and an overall plant growth enhancement was not attained in any of the applied dosages. Our results indicate that hydrolysis of the biomass can be a decisive factor for rendering effective plant biostimulants from microalgae.

The different patterns of post-heat stress responses in wheat genotypes: the role of the transthylakoid proton gradient in efficient recovery of leaf photosynthetic capacity.

The frequency and severity of heat waves are expected to increase in the near future, with a significant impact on physiological functions and yield of crop plants. In this study, we assessed the residual post-heat stress effects on photosynthetic responses of six diverse winter wheat (Triticum sp.) genotypes, differing in country of origin, taxonomy and ploidy (tetraploids vs. hexaploids). After 5 days of elevated temperatures (up to 38 °C), the photosynthetic parameters recorded on the first day of recovery (R1) as well as after the next 4-5 days of the recovery (R2) were compared to those of the control plants (C) grown under moderate temperatures. Based on the values of CO2 assimilation rate (A) and the maximum rates of carboxylation (VCmax) in R1, we identified that the hexaploid (HEX) and tetraploid (TET) species clearly differed in the strength of their response to heat stress. Next, the analyses of gas exchange, simultaneous measurements of PSI and PSII photochemistry and the measurements of electrochromic bandshift (ECS) have consistently shown that photosynthetic and photoprotective functions in leaves of TET genotypes were almost fully recovered in R2, whereas the recovery of photosynthetic and photoprotective functions in the HEX group in R2 was still rather low. A poor recovery was associated with an overly reduced acceptor side of photosystem I as well as high values of the electric membrane potential (Δψ component of the proton motive force, pmf) in the chloroplast. On the other hand, a good recovery of photosynthetic capacity and photoprotective functions was clearly associated with an enhanced ΔpH component of the pmf, thus demonstrating a key role of efficient regulation of proton transport to ensure buildup of the transthylakoid proton gradient needed for photosynthesis restoration after high-temperature episodes.

Transient Heat Waves May Affect the Photosynthetic Capacity of Susceptible Wheat Genotypes Due to Insufficient Photosystem I Photoprotection.

We assessed the photosynthetic responses of eight wheat varieties in conditions of a simulated heat wave in a transparent plastic tunnel for one week. We found that high temperatures (up to 38 °C at midday and above 20 °C at night) had a negative effect on the photosynthetic functions of the plants and provided differentiation of genotypes through sensitivity to heat. Measurements of gas exchange showed that the simulated heat wave led to a 40% decrease in photosynthetic activity on average in comparison to the control, with an unequal recovery of individual genotypes after a release from stress. Our results indicate that the ability to recover after heat stress was associated with an efficient regulation of linear electron transport and the prevention of over-reduction in the acceptor side of photosystem I.

Genomic and Phenomic Screens for Flower Related RING Type Ubiquitin E3 Ligases in Arabidopsis.

Flowering time control integrates endogenous as well as environmental signals to promote flower development. The pathways and molecular networks involved are complex and integrate many modes of signal transduction. In plants ubiquitin mediated protein degradation pathway has been proposed to be as important mode of signaling as phosphorylation and transcription. To systematically study the role of ubiquitin signaling in the molecular regulation of flowering we have taken a genomic approach to identify flower related Ubiquitin Proteasome System components. As a large and versatile gene family the RING type ubiquitin E3 ligases were chosen as targets of the genomic screen. The complete list of Arabidopsis RING E3 ligases were retrieved and verified in the Arabidopsis genome v11 and their differential expression was used for their categorization into flower organs or developmental stages. Known regulators of flowering time or floral organ development were identified in these categories through literature search and representative mutants for each category were purchased for functional characterization by growth and morphological phenotyping. To this end, a workflow was developed for high throughput phenotypic screening of growth, morphology and flowering of nearly a thousand Arabidopsis plants in one experimental round.