Potassium Nitrate Treatment Is Associated with Modulation of Seed Water Uptake, Antioxidative Metabolism and Phytohormone Levels of Pea Seedlings

(1) Background: Seed treatment with potassium nitrate (KNO3) has been associated with dormancy breaking, improved germination and enhanced seedling growth and uniformity in a variety of plant species. However, the KNO3 effect seems to be dependent on plant species and treatment conditions. (2) Methods: We describe the effect of incubation of dry pea seeds with different KNO3 concentration on water uptake kinetic, early seedling growth, antioxidant metabolism and hormone profile in pea seedlings. (3) Results: Low (0.25 mM) KNO3 levels increased seedling water uptake and growth, whereas high (40 mM) levels decreased seedling growth. KNO3 treatment differentially affected the antioxidant defences. Low KNO3 levels maintained the activity of antioxidant enzymes, while high levels reduced the activity of H2O2-scavenging enzymes. KNO3 induced a progressive decline in ascorbate levels and reduced (GSH) and oxidised (GSSG) glutathione. Low KNO3 levels strongly increased GA1 and decreased ABA in both seedlings and cotyledons, resulting in a decline in the ABA/GAs ratio. (4) Conclusions: Pea seed treatment with a low KNO3 level promoted early seedling growth. In this process, an interaction among KNO3, antioxidant defences and ABA/GAs ratio is proposed.

Evaluation of the drought resistance of pea (Pisum sativum L.) from the VIR collection

Background. As a result of global warming, climate change is now taking place, increasing the frequency and duration of droughts. Therefore, the development of new varieties with an increased drought resistance and adaptation to certain environmental conditions is of primary importance. The aim of this work was to modify the express method of drought resistance evaluation in peas at an early stage of plant growth and development, and to apply this method to test 50 accessions from the VIR global collection.Materials and methods. Drought resistance studies involved garden pea accessions of different eco-geographic origin, which had been previously characterized in field tests in conditions of the Krasnodar Territory in 2017-2019. The roll-ups protocol was used for evaluating early drought resistance in the accessions. The stress intensity was modified by varying the concentration of sucrose in the solution used for growing of pea seedlings. To select an appropriate concentration, an osmotic pressure of 0.5 and 0.7 MPa was applied. As a result, the osmotic pressure of 0.5 MPa was chosen. The diagnostic criterion of the method is the radicle length index (RLI), that is, the ratio of the average radicle length of seedlings against a provocative background to the control values.Results. The osmotically active solution led to significant reduction in the radicle length of pea seedlings. The studied accessions exhibited considerable genetic variability for early drought tolerance, the RLI value varied from 0.28 to 0.88. Sources of high drought resistance during the period of seedling growth have been identified. The correlation analysis showed the absence of a reliable relationship between the RLI and the crop structure indicators (correlation coefficients from r = +0.17 to r = -0.24).Conclusion. By using the method of determining the relative drought tolerance at early stages of pea accessions development, one highly resistant (k-9333 from Morocco) and 10 resistant accessions (k-1495, k-9372, k-9401, k-9418, k-9733, k-9909, k-9934, k-9938, k-10072, and k-10116.) have been identified.

Physiological Responses of Young Pea and Barley Seedlings to Plasma-Activated Water

This study demonstrates the indirect effects of non-thermal ambient air plasmas (NTP) on seed germination and plant growth. It investigates the effect of plasma-activated water (PAW) on 3-day-old seedlings of two important farm plants—barley and pea. Applying different types of PAW on pea seedlings exhibited stimulation of amylase activity and had no inhibition of seed germination, total protein concentration or protease activity. Moreover, PAW caused no or only moderate oxidative stress that was in most cases effectively alleviated by antioxidant enzymes and proved by in situ visualization of H2O2 and ˙O2−. In pea seedlings, we observed a faster turn-over from anaerobic to aerobic metabolism proved by inhibition of alcohol dehydrogenase (ADH) activity. Additionally, reactive oxygen/nitrogen species contained in PAW did not affect the DNA integrity. On the other hand, the high level of DNA damage in barley together with the reduced root and shoot length and amylase activity was attributed to the oxidative stress caused by PAW, which was exhibited by the enhanced activity of guaiacol peroxidase or ADH. Our results show the glow discharge PAW at 1 min activation time as the most promising for pea. However, determining the beneficial type of PAW for barley requires further investigation.

Physiological and Biochemical Characterization of the GABA Shunt Pathway in Pea (Pisum sativum L.) Seedlings Under Drought Stress

The physiological and biochemical role of the γ-aminobutyric acid (GABA) shunt pathway in green pea seedlings (Pisum sativum L.) was studied in response to soil water holding capacity levels: 80%, 60%, 40%, 20%, and 10% grown under continuous light at 25 °C for 7 days and 14 days, separately. Characterization of seeds germination pattern, seedlings growth (plant height, fresh and dry weight, and chlorophyll contents), GABA shunt metabolite (GABA, glutamate, and alanine) levels, total protein and carbohydrate levels, and oxidative damage (MDA level) were examined. Data showed a significant effect of drought stress on seed germination, plant growth, GABA shunt metabolites level, total protein and carbohydrate contents, and MDA level. A significant decline in seed germination percentage was recorded at a 20% drought level, which indicated that 20% of soil water holding capacity is the threshold value of water availability for normal germination after 14 days. Seedling fresh weight, dry weight, and plant height were significantly reduced with a positive correlation as water availability was decreased. There was a significant decrease with a positive correlation in Chl a and Chl b contents in response to 7 days and 14 days of drought. GABA shunt metabolites were significantly increased with a negative correlation as water availability decreased. Pea seedlings showed a significant increase in protein content as drought stress was increased. Total carbohydrate levels increased significantly when the amount of water availability decreased. MDA content increased slightly but significantly after 7 days and sharply after 14 days under all water stress levels. The maximum increase in MDA content was observed at 20% and 10% water levels. Overall, the significant increases in GABA, protein and carbohydrate contents were to cope with the physiological impact of drought stress on Pisum sativum L. seedlings by maintaining cellular osmotic adjustment, protecting plants from oxidative stress, balancing carbon and nitrogen (C:N) metabolism, and maintaining cell metabolic homeostasis and cell turgor. The results presented in this study indicated that severe (less than 40% water content of the holding capacity) and long-term drought stress should be avoided during the germination stage to ensure proper seedling growth and metabolism in Pisum sativum L.

Influence of Local Burning on Difference Reflectance Indices Based on 400–700 nm Wavelengths in Leaves of Pea Seedlings

Local damage (e.g., burning) induces a variation potential (VP), which is an important electrical signal in higher plants. A VP propagates into undamaged parts of the plant and influences numerous physiological processes, including photosynthesis. Rapidly increasing plant tolerance to stressors is likely to be a result of the physiological changes. Thus, developing methods of revealing VP-induced physiological changes can be used for the remote sensing of plant systemic responses to local damage. Previously, we showed that burning-induced VP influenced a photochemical reflectance index in pea leaves, but the influence of the electrical signals on other reflectance indices was not investigated. In this study, we performed a complex analysis of the influence of VP induction by local burning on difference reflectance indices based on 400–700 nm wavelengths in leaves of pea seedlings. Heat maps of the significance of local burning-induced changes in the reflectance indices and their correlations with photosynthetic parameters were constructed. Large spectral regions with significant changes in these indices after VP induction were revealed. Most changes were strongly correlated to photosynthetic parameters. Some indices, which can be potentially effective for revealing local burning-induced photosynthetic changes, are separately shown. Our results show that difference reflectance indices based on 400–700 nm wavelengths can potentially be used for the remote sensing of plant systemic responses induced by local damages and subsequent propagation of VPs.

Effect of Pre-Sowing Magnetic Field Treatment on Enzymes and Phytohormones in Pea (Pisum sativum L.) Seeds and Seedlings

The aim of the presented studies was to evaluate the magnetic field (MF) effect on changes in some enzymes and phytohormones that takes place in the process of seed germination and growth of seedlings. Studies were led in the climatic chambers HERAEUS, on Petri dishes during six consecutive days. Pea seeds were divided into three groups from which one was the control (without stimulation) and two were treated with different doses of magnetic field (30 and 85 mT, respectively). Contents of amylolytic enzymes (AE) and phytohormones were determined at seven terms (0; 24; 48; 72; 96; 120 and 144 h) after placing them on the dishes. A favorable effect of seed stimulation with MF was found on the biochemical processes in the germinating seeds and pea seedlings. The size of changes in enzyme concentration was dependent mainly on the advancement of germination process (i.e., on length of time in which the seeds were on the dishes) and the MF treatment. The use of MF also had an effect on the increase in hormone content in the seeds and organs of seedlings, but values from objects treated with different doses did not differ significantly.

Complex Analysis of the Efficiency of Difference Reflectance Indices on the Basis of 400–700 nm Wavelengths for Revealing the Influences of Water Shortage and Heating on Plant Seedlings

A drought, which can be often accompanied by increased temperature, is a key adverse factor for agricultural plants. Remote sensing of early plant changes under water shortage is a prospective way to improve plant cultivation; in particular, the sensing can be based on measurement of difference reflectance indices (RIs). We complexly analyzed the efficiency of RIs based on 400–700 nm wavelengths for revealing the influences of water shortage and short-term heating on plant seedlings. We measured spectra of reflected light in leaves of pea, wheat, and pumpkin under control and stress conditions. All possible RIs in the 400–700 nm range were calculated, significances of differences between experimental and control indices were estimated, and heatmaps of the significances were constructed. It was shown that the water shortage (pea seedlings) changed absolute values of large quantity of calculated RIs. Absolute values of some RIs were significantly changed for 1–5 or 2–5 days of the water shortage; they were strongly correlated to the potential quantum yield of photosystem II and relative water content in leaves. In contrast, the short-term heating (pea, wheat, and pumpkin seedlings) mainly influenced light-induced changes in RIs. Our results show new RIs, which are potentially sensitive to the action of stressors.

Isolation and Characterization of Rhodococcus spp. from Pistachio and Almond Rootstocks and Trees in Tunisia

The purpose of this study was to isolate and identify Rhodococcus spp. strains from almond and pistachio rootstocks and trees in Tunisia. Twenty-eight strains were identified through 16S rDNA and vicA genes amplification and sequencing. Pea bioassay was performed to determine the pathogenicity of the strains. Representative 16S rDNA and vicA sequences of eight strains from pistachio and seven strains from almond were closely related (>98% similarity) to Rhodococcus spp. accessions in GenBank. Phylogenetic analysis based on 16S rDNA sequences revealed that the yellow-colored strains clustered with phytopathogenic Rhodococcusfascians. The red and orange-colored strains were separated into a different group with R. kroppenstedtii and R. corynebacteiroides isolates. Eleven strains affected the pea seedlings’ growth and exhibited different levels of virulence. The number of shoots was significantly higher in seedlings inoculated with four Rhodococcus strains, whereas the other three strains caused up to 80% of plant height reduction and reduced root secondary growth compared to non-inoculated pea seedlings. These strains, most of which are epiphytes from asymptomatic hosts, showed strong pathogenicity during pea bioassay and were established endophytically in pea tissues. Ten att and five fas genes were detected in four strains and may represent a novel model of plant pathogenic Rhodococcus virulence. The results of our survey showed that Rhodococcus is present but not prevalent in all visited orchards of almond and pistachio rootstocks and trees. Our surveys complemented the investments being made on ornamental species in Tunisia and unveiled the presence of undocumented plant-associated Rhodococcus spp. on economically important crops.