Heat stress affects a broad spectrum of cellular components and metabolism. The objectives of this study were to investigate the behavior of Photosystem II (PSII) in tall fescue (Festuca arundinacea Schreb) with various thermotolerance capacities and to broaden our comprehension about the relationship between thermotolerance and PSII function. Heat-tolerant and heat-sensitive accessions were incubated at 24 °C (control) and 46 °C (heat stress) for 5 h. The fluorescence transient curves (OJIP curves), slow Chl fluorescence kinetic, and light response curve were employed to study the behavior of PSII subjected to heat stress. After heat stress, performance index for energy conservation from photons absorbed by PSII antenna until the reduction of PSI acceptors (PITotal), the value of electrons produced per photon (a), and the maximal rate of electron transport (ETRmax) of heat-tolerant accessions were lower than those of heat-sensitive accessions. Relatively lower reactive oxygen species (ROS) contents were detected in heat-tolerant accessions. Simultaneously, there was a significant decline in the quantum yield of photochemical energy conversion in PS II (Y(II)), probability that a PSII Chl molecule functions as reaction center (γRC), and the increase of quantum yield for non-regulated non-photochemical energy loss (Y(NO)) in heat-tolerant accessions. Moreover, a significant inverse correlation between heat tolerance indexes (HTI) and Y(II) was observed. Therefore, maintaining a lower photochemical activity in heat-tolerant accessions could be a crucial strategy to improve their thermotolerance. This finding could be attributed to the structural difference in the reaction center, and for heat-tolerant accessions, it could simultaneously limit energy input into linear electron transport, and dissipate more energy through non-regulated non-photochemical energy loss processes.

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Agrobacterium rhizogenes causes hairy root growth on a large number of plant species. It does so by transferring specific DNA fragments (T-DNA) from its root-inducing plasmid (pRi) into plant cells. Expression of T-DNA genes leads to abnormal root growth and production of specific metabolites (opines) which are taken up by the bacterium and used for its growth. Recent work has shown that several Nicotiana, Linaria, and Ipomoea species contain T-DNA genes from A. rhizogenes in their genomes. Plants carrying such T-DNAs (called cellular T-DNA or cT-DNA) can be considered as natural transformants. In the Nicotiana genus, seven different T-DNAs are found originating from different Agrobacterium strains, and in the Tomentosae section no <4 successive insertion events took place. In several cases cT-DNA genes were found to be expressed. In some Nicotiana tabacum cultivars the opine synthesis gene TB-mas2′ is expressed in the roots. These cultivars were found to produce opines. Here we review what is known about natural Agrobacterium transformants, develop a theoretical framework to analyze this unusual phenomenon, and provide some outlines for further research.

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An interesting ecological and evolutionary puzzle arises from the observations of male-biased sex ratios in genus Populus, whereas in the taxonomically related Salix, females are generally more dominant. In the present study, we combined results from a field investigation into the sex ratios of the Salicaceous species along an altitudinal gradient on Gongga Mountain, and a pot experiment by monitoring growth and energy utilization properties to elucidate the mechanisms governing sexual dimorphism. At middle altitudes 2000 and 2300 m, the sex ratios were consistent with a 1:1 equilibrium in sympatric Populus purdomii and Salix magnifica. However, at the lower and higher ends of the altitudinal gradient, skewed sex ratios were observed. For example, the male:female ratios were 1.33 and 2.36 in P. purdomii at 1700 and 2600 m respectively; for S. magnifica the ratio was 0.62 at 2600 m. At 2300 m, the pot-grown seedlings of both species exhibited the highest biomass accumulation and total leaf area, simultaneously with the balanced sex ratios in the field. At 3300 m, the specific leaf area in male P. purdomii was 23.9% higher than that of females, which may be the morphological cause for the observed 19.3% higher nitrogen allocation to Rubisco, and 20.6% lower allocation to cell walls. As such, male P. purdomii showed a 32.9% higher foliar photosynthetic capacity, concomitant with a 12.0% lower construction cost. These properties resulted in higher photosynthetic nitrogen- and energy-use efficiencies, and shorter payback time (24.4 vs 40.1 days), the time span that a leaf must photosynthesize to amortize the carbon investment. Our results thus suggested that male P. purdomii evolved a quicker energy-return strategy. Consequently, these superior energy gain-cost related traits and the higher total leaf area contributed to the higher growth rate and tolerance in stress-prone environments, which might, in part, shed new light on the male-biased sex ratios in Populus. However, no significant sexual difference was observed in S. magnifica for all the above parameters, thereby implying that the female-biased sex ratios in Salix cannot be explained in terms of the energy-use properties studied here.

Stable isotope-assisted metabolomics (SIAM) enables global tracking of isotopic labels in nontargeted metabolomics in living organisms. However, its application in tracking transformation products (TPs, as metabolites of contaminants) of environmental contaminants is still a challenge due to limits in methodology, unmatured algorithms, and the high cost of 13 Clabeled contaminants. Therefore, we developed a 2 H-SIAM pipeline coupled with a highly flexible algorithm 2 H-SIAM(1.0) (https://github.com/kechen1984/2H-SIAM), facilitating tracking TPs of contaminants in the environmental matrix. A detailed discussion illustrates the theory, behavior, and prospect of 2 H-SIAM. We demonstrate that the proposed 2 H-SIAM pipeline has unique advantages over 13 C-SIAM, for example, cost-effective 2 Hlabeled contaminants, easy synthesis of 2 H-labeled emerging contaminants, and providing more structural information. A pyrene soil degradation study further confirmed its high performance. It efficiently discarded 99% of noise signals and extracted 52 features from the nontargeted high resolution mass spectrometry (HRMS) data. Among them, 13 features were annotated as TPs of pyrene with identification confidence from Level 2a to Level 5, and 5 TPs were reported for the first time. In conclusion, the proposed 2 H-SIAM pipeline is powerful in tracking potential TPs of environmental contaminants with unique advantages.

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