A Warmer Arctic Compromises Winter Survival of Habitat-Forming Seaweeds

Continuous winter darkness at a latitude of 79°N was simulated in cultures of four species of Arctic seaweeds at 3 and 8°C. The laminarians Saccharina latissima and Alaria esculenta, and the rhodophytes Phycodrys rubens and Ptilota gunneri were monitored for 4 months in total darkness and after 1 week following light return in early spring, under controlled laboratory conditions. Biomass loss during darkness was enhanced by the high temperature in all species. At 8°C, the two laminarians were unable to resume growth upon re-illumination. Alaria esculenta showed new blade production by the end of the dark period, but only at 3°C. In all species, the photosynthetic ability was sustained, not suspended, during the whole dark period. P. rubens exhibited lower photosynthetic potential at 8°C than at 3°C during the darkness period, but it was able to recover its O2 evolving potential upon re-illumination, as P. gunneri and S. latissima did, but the latter only at 3°C. The reactivation of photosynthesis seemed to involve photosystem II over photosystem I, as 7 d of photoperiod after the prolonged darkness was not enough to fully recover the PAM-related photosynthetic parameters. Only small changes were recorded in the internal chemical composition (total C, total N, carbohydrates, proteins, and lipids), but species-specific differences were observed. Unlike subarctic areas with an operating photoperiod along the year, a warmer polar night might pose a limit to the ability of multi-year seaweeds to occupy the new ice-free illuminated areas of the Arctic coasts, so that newcomers will potentially be restricted to the spring-summer season.

Apple Fruit Growth and Quality Depend on the Position in Tree Canopy

Modern apple orchard systems should guarantee homogeneity of fruit internal and external qualities and fruit maturity parameters. However, when orchards reach productive age, a variation of these parameters takes place and mostly it is related to uneven light distribution within the tree canopy. The aim of the study was to evaluate the canopy position’s effect on fruit internal and external quality parameters. This is the first study where all the main fruit quality and maturation parameters were evaluated on the same trees and were related to the light conditions and photosynthetic parameters. Four fruit positions were tested: top of the apple tree, lower inside part of the canopy, and east and west sides of the apple tree. Fruit quality variability was significant for fruit size, blush, colour indices, total sugar content, dry matter concentration, accumulation of secondary metabolites and radical scavenging activity. Fruit position in the canopy did not affect flesh firmness and fruit maturity parameters such as the starch index, Streif index and respiration rate. At the Lithuanian geographical location (55°60’ N), significantly, the highest fruit quality was achieved at the top of the apple tree. The tendency was established that apple fruits from the west side of the canopy have better fruit quality than from the east side and it could be related to better light conditions at the west side of the tree. Inside the canopy, fruits were distinguished only by the higher accumulation of triterpenic compounds and higher content of malic acid. Light is a main factor of fruit quality variation, thus all orchard management practices, including narrow two-dimensional tree canopies and reflecting ground covers which improve light penetration through the tree canopy, should be applied.

Influence of Pulsed Electric Fields on Photosynthesis in Light/Dark-Acclimated Lettuce

Recent years have seen numerous studies into how applying pulsed high electric fields (PEF) to living organisms induces various stress reactions. Plants produce glucose through photosynthesis and use this as a source of energy for living, yet there are few studies on the photosynthetic response characteristics when PEF is applied to growing plants. In this study, the photosynthetic response when electric fields of 10 to 100 V/mm were applied to light and dark-acclimated leaves of lettuce was measured by combined gas exchange and chlorophyll fluorescence, and the exposure time was kept constant at 500 s. The responses to PEF with regard to the photosynthetic parameters of electron transfer rate (ETR), non-photochemical quenching (NPQ), photosynthetic rate (A), and transpiration rate (E) were recorded during the experiment. Results showed that PEF can cause both the activation and deactivation of photosynthetic activity in lettuce, that there is an optimum value for activation, and that the application of excessive energy leads to inactivation. This study also found that stomata on both active and deactivated lettuce had been open to a greater extent than lettuce to which PEF had not been applied. All the results of statistical significance in this study were p < 0.05 and p < 0.01.

Functional Characterization of an Amaranth Natterin-4-Like-1 Gene in Arabidopsis thaliana

The functional characterization of an Amaranthus hypochondriacus Natterin-4-Like-1 gene (AhN4L-1) coding for an unknown function protein characterized by the presence of an aerolysin-like pore-forming domain in addition to two amaranthin-like agglutinin domains is herewith described. Natterin and nattering-like proteins have been amply described in the animal kingdom. However, the role of nattering-like proteins in plants is practically unknown. The results described in this study, obtained from gene expression data in grain amaranth and from AhN4L-1-overexpressing Arabidopsis thaliana plants indicated that this gene was strongly induced by several biotic and abiotic conditions in grain amaranth, whereas data obtained from the overexpressing Arabidopsis plants further supported the defensive function of this gene, mostly against bacterial and fungal plant pathogens. GUS and GFP AhN4L-1 localization in roots tips, leaf stomata, stamens and pistils also suggested a defensive function in these organs, although its participation in flowering processes, such as self-incompatibility and abscission, is also possible. However, contrary to expectations, the overexpression of this gene negatively affected the vegetative and reproductive growth of the transgenic plants, which also showed no increased tolerance to salinity and water-deficit stress. The latter despite the maintenance of significantly higher chlorophyll levels and photosynthetic parameters under intense salinity stress. These results are discussed in the context of the physiological roles known to be played by related lectins and AB proteins in plants.

Correlation-Based Network Analysis of the Influence of Bemisia tabaci Feeding on Photosynthesis and Foliar Sugar and Starch Composition in Soybean

Bemisia tabaci (MEAM1) represents a species of economic importance in soybean. One of the obstacles to the management of B. tabaci is the quantification of damage by the pest because damage is indirectly inferred through losses in productivity. The objective of this study was to characterize the influence of B. tabaci feeding on soybean by assessing effects on photosynthetic parameters and the sugar and starch content of soybean leaves. The goal was to identify the optimal parameter to directly quantify pest damage on crop yield. Correlation networks were created among data on sugar content (fructose, glucose, and sucrose), starch and photosynthetic parameters (initial fluorescence, performance index on absorption basis, and turn-over number), and the number of nymphs at each of three infestations level (low, medium, and high) during both the vegetative and reproductive stage of the crop. In general, nymphs were more abundant during the vegetative stage. Starch content was strongly correlated with nymph density. A strong positive correlation was observed between fructose and nymph density during the vegetative stage. Among the photosynthetic parameters, the turn-over number N was positively correlated with nymph density at a low-infestation level and negatively correlated with nymphs when they occurred at a high-infestation level. B. tabaci feeding affected the plant’s physiology and its interaction is reflected in part by the relationships among photosynthetic parameters as well as the levels of sugars and starch. This understanding might be useful in developing better monitoring tools for pest management.

Shade stress on maize seedlings biomass production and photosynthetic traits

ABSTRACT: The responses of two maize (Zea mays L.) cultivars, ‘LY336’ (shade tolerant) and ‘LC803’ (shade sensitive), to shade stress in a pot experiment conducted in the 2015 and 2016 growing seasons were investigated. The impact of 50% shade stress treatment on shoot biomass, photosynthetic parameters, chlorophyll fluorescence, and malondialdehyde (MDA) content was evaluated. The shoot biomass of the two maize hybrids was decreased significantly by shade stress treatment, for shade stress 7 d, the LC803 and LY336 were reduced by 56.7% and 44.4% compared with natural light. Chlorophyll fluorescence parameters of LY336 were not significantly affected by shade stress, whereas those of LC803 were significantly affected, the Fo increased under shade stress; however Fm, FV/FM and ΦPSII were decreased under shade stress. Among photosynthetic parameters measured, net photosynthetic rate (Pn), stomatal conductance (Gs), and transpiration rate were significantly decreased compared with natural light, LY336 and LC803 reduction by 28.0%, 22.2%, 57.7% and 35.5%, 18.9%, 62.4%; however, intercellular CO2 concentration (Ci) was significantly increased, for the two cultivars. Under shade stress for different durations (1, 3, 5, 7 d), Pn, Gs, Ci, and MDA content differed significantly between the two cultivars. Results indicated that different maize genotypes showed different responses to shading. Shade-tolerant genotypes are only weakly affected by shade stress.

Reducing the Halotolerance Gap between Sensitive and Resistant Tomato by Spraying Melatonin

Salt stress is one of the primary abiotic stresses that negatively affects agricultural production. Melatonin, as a useful hormone in plants, has been shown to play positive roles in crop improvement to abiotic stress conditions. However, it remains unclear whether spraying melatonin could reduce the halotolerance gap between tomato genotypes with different salt sensitivities. Here, plant growth, H2O2 content, electrolyte leakage, antioxidant system, gas exchange, pigment content, and chloroplast ultrastructure of salt sensitive genotype (SG) and resistant genotype (RG) at CK (control), M (spraying melatonin), S (salt), and SM (spraying melatonin under salt stress) were investigated. The results showed that the weight, height, and stem diameter of the plant at SM from both genotypes significantly increased compared with S. The plant undergoing SM from both genotypes showed significantly decreased H2O2 but increased activity of SOD, APX, GR, and GSH, as well as net photosynthetic rate and Fv/Fm, as compared with S. The ratio between SM and S (SM/S) of SG was significantly higher than that of RG in terms of plant height and stem diameter, whereas antioxidant parameters, H2O2 content, and electrolyte leakage showed no difference between RG and SG in SM/S. The SM/S of SG in terms of photosynthetic parameters and pigment content were significantly higher than that of RG. Chloroplast ultrastructure showed remarkable changes under salt stress, whereas spraying melatonin reduced the destruction of chloroplasts, especially for SG. We concluded that spraying melatonin reduces the halotolerance gap between SG and RG by photosynthesis regulation instead of the antioxidant mechanism. This indicated that the positive roles of melatonin on tomato plants at salt stress depend on the genotype sensitivity.

Differential acclimation responses to irradiance and temperature in two co-occurring seaweed species in Arctic fjords

Arctic fjord systems experience large amplitudes of change in temperature and radiation regime due to climate warming and the related decrease in sea ice. The resultant increase in irradiance entering the water column influences photosynthetic activity of benthic and pelagic primary producers. The subtidal brown alga Desmarestia aculeata and the intertidal red alga Palmaria palmata populate the cold-temperate coasts of the North Atlantic, reaching the polar zone. To evaluate their acclimation potential, we collected both species in Kongsfjorden, Svalbard (78.9°N, 11.9°E), during the Arctic summer and exposed specimens to two different PAR levels (50 and 500 μmol photons m−2 s−1) and temperatures (0, 4 and 8 °C) for 21 days. Photosynthetic parameters and biochemical features (pigment concentration and antioxidants) were assessed. In general, high irradiance was the factor that generated a negative effect for D. aculeata and P. palmata in the photosynthetic parameters of the photosynthesis–irradiance curve and Fv/Fm. The pigment concentration in both species tended to decrease with increasing irradiance. Antioxidant level showed different trends for both species: in D. aculeata, antioxidant potential increased with high irradiance and temperature, while in P. palmata, it only increased with high irradiance. Both species showed responses to the interaction of irradiance and temperature, although D. aculeata was more sensitive to high irradiance than P. palmata. Our study shows how these species, which have similar geographical distribution in the North Atlantic and the Arctic but belong to different taxonomic lineages, have similar strategies of acclimation, although they respond differently to ecophysiological parameters.

The Effects of Fig Tree (Ficus carica L.) Leaf Aqueous Extract on Seed Germination and Seedling Growth of Three Medicinal Plants

Fig tree cultivation land resources are not fully utilized and introducing them into sustainable medicinal agroforestry systems can effectively achieve resource protection and reuse. Laboratory and pot experiments were applied to study the allelopathic effects of fig tree (Ficus carica L.) leaf aqueous extract at five mass concentrations of 8.3, 10.0, 12.5, 16.7, and 25.0 g/L on the morphological and physiological indexes of mint (Mentha haplocalyx Briq.), dandelion (Taraxacum mongolicum Hand.-Mazz.), and woad (Isatis indigotica Fort.). The results showed that mint had the best seed germination rate. The leaf aqueous extract at lower concentrations had a strong promoting effect on the biomass and photosynthetic parameters of mint, dandelion, and woad. With the increase in leaf aqueous extract concentration, the superoxide dismutase, peroxidase, and catalase activity of mint, dandelion, and woad increased initially and then decreased, but the malondialdehyde content increased. The synthetic allelopathic indexes of the three medicinal plants were in the following order: mint >woad >dandelion. Both the low and medium concentration extracts (8.3 g/L-12.5 g/L) showed an obvious promoting effect, while high concentrations exhibited distinct inhibiting effects. In conclusion, mint is the most suitable medicinal plant to be interplanted with fig trees for introduction into medicinal agroforestry systems.

Desiccation-resurrection linked antioxidant machinery of a moss species Campylopus flexuosus (Hedw.) Bird.

Dehydration and rejuvenation during rehydration is the salient feature of certain plants which can withstand drought. The present study was undertaken to justify the tolerance capacity of Campylopus flexuosus, the moss of the Ponmudi belts of Thiruvananthapuram, against dehydration followed by rehydration. Fresh leafy plants of C. flexuosus were hydrated, afterwards dried, and rehydrated under in vitro environment. In the course of loss of water from cells, the relative water content of desiccated thallus was reduced after 4 h with intense inward curling. Upon rehydration, the RWC was regained 85% of its initial water content within hours. The rehydrated thallus showed the normal morphology. Photosynthetic parameters like chlorophyll b (1.01 to 1.56 μg g –1 ), and total carotenoid (0.251 to 0.514 μg g –1 ) increased remarkably in the desiccated state. Superoxide radical (O2 _) content increased (11.4 nmol/g FW), resulting in an oxidative burst during desiccation. Consequently, antioxidant enzymes such as catalase (0.369 U mg protein −1), superoxide dismutase ( 2.68 to 6.02 Units mg−1), peroxidase ( 0.12 μmol min−1 g−1 protein) and glutathione reductase ( 312 Units mg−1 protein) activities were up-regulated in the desiccated thallus to ameliorate oxidative damage. Increased malondialdehyde (1.08 nmol g−1 FW) content during desiccation substantiates membrane damage and loss of its integrity. During desiccation, the osmolytes sucrose and proline (27.6 and 2.57 μmol/g FW respectively) were enhanced to maintain cell structure integrity. After rehydration, biochemical and morphological properties were maintained similar to hydrated conditions. Thus, the study reflects the unique adaptations of the moss to tide over desiccation tolerance.