Physiological and Transcriptomic Analysis Reveals the Responses and Difference to High Temperature and Humidity Stress in Two Melon Genotypes

Due to the frequent occurrence of continuous high temperatures and heavy rain in summer, extremely high-temperature and high-humidity environments occur, which seriously harms crop growth. High temperature and humidity (HTH) stress have become the main environmental factors of combined stress in summer. The responses of morphological indexes, physiological and biochemical indexes, gas exchange parameters, and chlorophyll fluorescence parameters were measured and combined with chloroplast ultrastructure and transcriptome sequencing to analyze the reasons for the difference in tolerance to HTH stress in HTH-sensitive ‘JIN TAI LANG’ and HTH-tolerant ‘JIN DI’ varieties. The results showed that with the extension of stress time, the superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) activities of the two melon varieties increased rapidly, the leaf water content increased, and the tolerant varieties showed stronger antioxidant capacity. Among the sensitive cultivars, Pn, Fv/Fm, photosystem II, and photosystem I chlorophyll fluorescence parameters were severely inhibited and decreased rapidly with the extension of stress time, while the HTH-tolerant cultivars slightly decreased. The cell membrane and chloroplast damage in sensitive cultivars were more severe, and Lhca1, Lhca3, and Lhca4 proteins in photosystem II and Lhcb1-Lhcb6 proteins in photosystem I were inhibited compared with those in the tolerant cultivar. These conclusions may be the main reason for the different tolerances of the two cultivars. These findings will provide new insights into the response of other crops to HTH stress and also provide a basis for future research on the mechanism of HTH resistance in melon.

Canopy Solar-Induced Chlorophyll Fluorescence and Its Link to Transpiration in a Temperate Evergreen Needleleaf Forest during the Fall Transition

Northern hemisphere evergreen needleleaf forest (ENF) contributes a significant fraction of global water exchange but regional transpiration (T) observation in ENF ecosystems is still challenging. Traditional remote sensing techniques and terrestrial biosphere models reproduce the transpiration seasonality with difficulty, and with large uncertainties. Solar-induced chlorophyll fluorescence (SIF) emission from vegetation correlates to photosynthesis at multiple spatial and temporal scales. However, how SIF links to transpiration of evergreen forest during seasonal transition is unclear. Here, we explored the relationship between canopy SIF and T retrieved from ground observation towers in ENF. We also examined the role of meteorological and soil factors on the relationship between SIF and T. A slow decrease of SIF and T with a fast reduction in photosynthetically active radiation (PAR), air temperature, vapor pressure deficit (VPD), soil temperature and soil water content (SWC) were found in the ENF during the fall transition. The correlation between SIF and T at hourly and daily scales varied significantly among different months (Pearson correlation coefficient = 0.29–0.68, p < 0.01). SIF and T were significantly linearly correlated at hourly (R2 = 0.53, p < 0.001) and daily (R2 = 0.67, p < 0.001) timescales in the October. Air temperature and PAR were the major moderating factors for the relationship between SIF and T in the fall transition. Soil water content (SWC) influenced the SIF-T relationship at an hourly scale. Soil temperature and VPD’s effect on the SIF-T relationship was evident at a daily scale. This study can help extend the possibility of constraining ecosystem T by SIF at an unprecedented spatiotemporal resolution during season transitions.

APPLICATION OF OJIP CHLOROPHYLL FLUORESCENCE TRANSIENT ANALYSIS TO STUDY THE POSTHARVEST CHANGES IN PHOTOSINTHETIC APPARATUS IN CUT FOLIAGE SPECIES

Chlorophyll fluorescence (ChlF) is a non-invasive technique that can be potentially used in postharvest research to gain useful information on early responses to postharvest stresses. This study was conducted to validate the application of ChlF transient analysis in determining the postharvest changes in photosynthetic apparatus in three ornamental foliage species, i.e., Cordyline fruticosa ‘Willy’s Gold’ and ‘Rubra’, Dracaena sanderiana ‘White’, and Nephrolepis exaltata. Salicylic acid (100 and 300 mg·L−1), glucose (10 g·L−1), and their combinations were used as holding solutions with control treatment (distilled water) at room temperature (25±2°C). Vase life was evaluated using OJIP analysis. OJIP parameters, i.e., specific energy fluxes per reaction center (ABS/RC, TR/RC, ET/RC, and DI/RC), flux ratios (maximum quantum yield of primary photochemistry-φPo), electron transport efficiency (ψo), and quantum yield of electron transport (φEo), and performance index (PI) were recorded every other day, using a fluorometer (FluorPen 100). Leaf chlorophyll contents of all species and anthocyanin contents of two cordyline cultivars were determined. Data were subjected to ANOVA in a completely randomized design. Mean separation was done by DMRT (p ≤ 0.05). Clear variations in ChlF were observed in every foliage species with the time. OJIP analysis showed species-depended variations. The higher ABS/RC and DI/RC were recorded for D. sanderiana and N. exaltata compared to the PI of those species. At the end of the experiment, the chlorophyll contents were decreased, while anthocyanin contents were increased. Consequently, chlorophyll fluorescence changes in photosynthetic apparatus can be used for the prediction of the postharvest stresses and longevity of cut foliage.

On the impact of canopy model complexity on simulated carbon, water, and solar-induced chlorophyll fluorescence fluxes

Lack of direct carbon, water, and energy flux observations at global scales makes it difficult to calibrate land surface models (LSMs). The increasing number of remote-sensing-based products provide an alternative way to verify or constrain land models given their global coverage and satisfactory spatial and temporal resolutions. However, these products and LSMs often differ in their assumptions and model setups, for example, the canopy model complexity. The disagreements hamper the fusion of global-scale datasets with LSMs. To evaluate how much the canopy complexity affects predicted canopy fluxes, we simulated and compared the carbon, water, and solar-induced chlorophyll fluorescence (SIF) fluxes using five different canopy complexity setups from a one-layered canopy to a multi-layered canopy with leaf angular distributions. We modeled the canopy fluxes using the recently developed land model by the Climate Modeling Alliance, CliMA Land. Our model results suggested that (1) when using the same model inputs, model-predicted carbon, water, and SIF fluxes were all higher for simpler canopy setups; (2) when accounting for vertical photosynthetic capacity heterogeneity, differences between canopy complexity levels increased compared to the scenario of a uniform canopy; and (3) SIF fluxes modeled with different canopy complexity levels changed with sun-sensor geometry. Given the different modeled canopy fluxes with different canopy complexities, we recommend (1) not misusing parameters inverted with different canopy complexities or assumptions to avoid biases in model outputs and (2) using a complex canopy model with angular distribution and a hyperspectral radiation transfer scheme when linking land processes to remotely sensed spectra.

Effect of Up-Converting Luminescent Nanoparticles with Increased Quantum Yield Incorporated into the Fluoropolymer Matrix on Solanum lycopersicum Growth

The influence of light conversion induced by glasses coated with up-converting luminescent nanoparticles on Solanum lycopersicum cultivation was studied. Nanoparticles of Sr0.46Ba0.50Yb0.02Er0.02F2.04 solid solution were used as the up-converting luminophore. These nanoparticles were able to transform IR radiation into visible light (λem = 660 nm with minor peaks at 545 nm and 525 nm). By applying the “variable” chlorophyll fluorescence (ΔF), it was shown that the cultivation of tomatoes under the photoconversion glasses stimulated changes in the rate of plant adaptation to ultraviolet radiation. The restoration time of values of effective quantum yield of photosystem II photochemical reactions and photochemical quenching of chlorophyll fluorescence (reflecting disappearance of imbalance between photosynthetic electron transport and the utilization of NADPH) was reduced from three weeks to three days in the case of control and photoconversion films, respectively. As a result, plants grown under photoconversion glass had an increased leaf number (12.5%), total leaf area (33%), stem length (35%) and chlorophyll content in the leaves (two-fold). It is assumed that an increase in the proportion of red light in the growing spectrum has a positive effect on photosynthetic activity and plant growth.

Interplay between LHCSR proteins and state transitions governs the NPQ response in intact cells of Chlamydomonas during light fluctuations.

Photosynthetic organisms use sunlight as the primary energy source to fix CO2. However, in the environment, light energy fluctuates rapidly and often exceeds saturating levels for periods ranging from seconds to hours, which can lead to detrimental effects for cells. Safe dissipation of excess light energy occurs primarily by non-photochemical quenching (NPQ) processes. In the model green microalga Chlamydomonas reinhardtii, photoprotective NPQ is mostly mediated by pH-sensing light-harvesting complex stress-related (LHCSR) proteins and the redistribution of light-harvesting antenna proteins between the photosystems (state transition). Although each component underlying NPQ has been documented, their relative contributions to the dynamic functioning of NPQ under fluctuating light conditions remains unknown. Here, by monitoring NPQ throughout multiple high light-dark cycles with fluctuation periods ranging from 1 to 10 minutes, we show that the dynamics of NPQ depend on the frequency of light fluctuations. Mutants impaired in the accumulation of LHCSRs (npq4, lhcsr1, and npq4lhcsr1) showed significantly less quenching during illumination, demonstrating that LHCSR proteins are responsible for the majority of NPQ during repetitive exposure to high light fluctuations. Activation of NPQ was also observed during the dark phases of light fluctuations, and this was exacerbated in mutants lacking LHCSRs. By analyzing 77K chlorophyll fluorescence spectra and chlorophyll fluorescence lifetimes and yields in a mutant impaired in state transition, we show that this phenomenon arises from state transition. Finally, we quantified the contributions of LHCSRs and state transition to the overall NPQ amplitude and dynamics for all light periods tested and compared those with cell growth under various periods of fluctuating light. These results highlight the dynamic functioning of photoprotection under light fluctuations and open a new way to systematically characterize the photosynthetic response to an ever-changing light environment.