The Green Revolution has resulted in major improvements in crop productivity, but left photosynthesis largely unimproved. Despite ample variation of photosynthetic performance in crops and their wild relatives, the photosynthetic capacity of elite breeding lines remains well below its theoretical maximum. As yield is often the primary selective trait, current plant breeding approaches result in photosynthetic trade-offs that prevent positive selection for photosynthetic performance itself. Currently, genetic variation for photosynthetic performance is seldomly validated at the genetic level, and as a result these photosynthetic trade-offs remain poorly understood. Here we reveal the physiological nature of a photosynthetic trade-off caused by the NAD(P)H dehydrogenase (NDH) complex. The use of an Arabidopsis thaliana cybrid panel revealed how a natural allele of the chloroplastic gene NAD(P)H-QUINONE OXIDOREDUCTASE SUBUNIT 6 - a subunit of the NDH complex - results in a faster recovery of photosystem II efficiency after a transition from high to low irradiances. This improvement is due to a reduction in NDH activity. Under low-light conditions this reduction in NDH activity has a neutral effect on biomass, while under highly fluctuating light conditions, including high irradiances, more NDH activity is favoured. This shows that while allelic variation in one gene can have beneficial effects on one aspect of photosynthesis, it can, depending on environmental conditions, have negative effects on other aspects of photosynthesis. As environmental conditions are hardly ever stable in agricultural systems, understanding photosynthetic trade-offs allows us to explore shifting photosynthetic performance closer to the theoretical maximum.

In nature, light is never constant, while in the controlled environments used for vertical farming, in vitro propagation, or plant production for scientific research, light intensity is often kept constant during the photoperiod. To investigate the effects on plant growth of varying irradiance during the photoperiod, we grew Arabidopsis thaliana under three irradiance profiles: a square-wave profile, a parabolic profile with gradually increasing and subsequently decreasing irradiance, and a regime comprised of rapid fluctuations in irradiance. The daily integral of irradiance was the same for all three treatments. Leaf area, plant growth rate, and biomass at time of harvest were compared. Plants grown under the parabolic profile had the highest growth rate and biomass. This could be explained by a higher average light-use efficiency for carbon dioxide fixation. Furthermore, we compared the growth of wild type plants with that of the PsbS-deficient mutant npq4. PsbS triggers the fast non-photochemical quenching process (qE) that protects PSII from photodamage during sudden increases in irradiance. Based mainly on field and greenhouse experiments, the current consensus is that npq4 mutants grow more slowly in fluctuating light. However, our data show that this is not the case for several forms of fluctuating light conditions under otherwise identical controlled-climate room conditions.

Simazine is an herbicide that is able to contaminate surface waters, ground waters, and milk/dairy products, thus posing concerns in both environmental health and food safety. A yeast-based bioprobe was utilized to detect simazine in spiked real samples of livestock drinking water and raw cow’s milk. Yeast aerobic respiration was taken as short-term toxicological endpoint. We carried out comparative measures of yeast oxygen consumption between simazine-spiked samples and blank samples. Percentage interference (%ρ) on yeast aerobic respiration was calculated through the comparison of aerobic respiration of simazine-exposed and non-exposed yeast cells. The method was optimized for raw cow’s milk samples by using boric acid as fungistatic agent in order to avoid cellular proliferation. Overall, the results have shown that simazine can be detected up to concentrations five times below the EU legal concentration limits for drinking water (0.02 ppb) and cow’s milk (2 ppb) (%ρ values of 18.53% and 20.43% respectively; %RSD ≤ 15%). Dose-effect relationships of simazine were assessed. The findings of the bioassays match reasonably well with known mechanisms of toxicity and intracellular detoxification in yeast. A correlation between fat content in milk samples and analytical performance of the bioprobe was established. Results suggest the involvement of a matrix effect, presumably due to lipid sequestration of simazine. The yeast-based bioprobe has proved to be sensitive and suitable for the detection of simazine in real samples in concentrations of interest.