Screening of ‘King’ Mandarin Hybrids as Tolerant Citrus Rootstocks to Flooding Stress

This work compares the tolerance to long-term anoxia conditions (35 days) of five new citrus ‘King’ mandarin (Citrus nobilis L. Lour) × Poncirus trifoliata ((L.) Raf.) hybrids (named 0501XX) and Carrizo citrange (CC, Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), the widely used citrus rootstock in Spain. Growth parameters, chlorophyll concentration, gas exchange and fluorescence parameters, water relations in leaves, abscisic acid (ABA) concentration, and PIP1 and PIP2 gene expressions were assessed. With a waterlogging treatment, the root system biomass of most hybrids went down, and the chlorophyll a and b concentrations substantially dropped. The net CO2 assimilation rates (An) and stomatal conductance (gs) lowered significantly due to flooding, and the transpiration rate (E) closely paralleled the changes in gs. The leaf water and osmotic potentials significantly increased in most 0501 hybrids. As a trend, flooding stress lowered the ABA concentration in roots from most hybrids, but increased in the leaves of CC, 05019 and 050110. Under the control treatment (Ct) conditions, most 0501 hybrids showed higher PIP1 and PIP2 expressions than the control rootstock CC, but were impaired due to the flooding conditions in 05019 and 050110. From this study, we conclude that 0501 genotypes develop some adaptive responses in plants against flooding stress such as (1) stomata closure to prevent water loss likely mediated by ABA levels, and (2) enhanced water and osmotic potentials and the downregulation of those genes regulating aquaporin channels to maintain water relations in plants. Although these traits seemed especially relevant in hybrids 050110 and 050125, further experiments must be done to determine their behavior under field conditions, particularly their influence on commercial varieties and their suitability as flooding-tolerant hybrids for replacing CC, one of the main genotypes that is widely used as a citrus rootstock in Spain, under these conditions.

Physiological quality of seeds and growth of seedlings of chickpea under salt stress

Salt stress is a condition that causes physiological changes in several species, the identifying cultivars tolerant to such conditions is essential to high salinity environments. The objective was to evaluate the physiological quality of seeds of chickpea cultivars to salt stress during germination and seedling growth. Two cultivars (‘BRS Cícero’ and ‘BRS Aleppo’) and five osmotic potentials simulated with sodium chloride solutions (0.0; -0.2; -0.4; -0.6 and -0.8 MPa), were evaluated by the test of germination speed index, mean germination time, epicotyl and primary root length, epicotyl and primary root fresh mass, epicotyl and the primary root dry mass of the seeds were evaluated. Significant interactions were found for all variables, indicating that there are cultivars with specific performance for a particular salt condition, and the simulated salt stress conditions negatively affected germination and seedling growth. Osmotic potentials of less than -0.4 MPa are harmful to the germination and growth of chickpea seedlings. The ‘BRS Cícero’ seeds showed a higher salt tolerance than ‘BRS Aleppo’. The cultivar BRS Aleppo has a longer epicotyl length compared to 'BRS Cícero' when subjected to the same conditions of salt stress.

​Antioxidant Responses of Ricebean [Vigna umbellata (Thunb.) Ohwi and Ohashi] Seedling under Iso-osmotic Potential of Salinity and Drought Stress

Background: Salinity and drought are the major abiotic stresses and both can cause osmotic imbalances. Drought stress directly results in osmotic stress whereas salinity problem firstly disrupts the water balance and eventually induces ion toxicity which results in cyto-toxicity, metabolic impairment, nutrient imbalance and finally poor crop growth and yield. The co-ordinated up-regulation or constitutive expression of antioxidative system in plants is the main defense in plant against these stresses and thus the present experiment was undertaken to study the antioxidant responses under drought and salinity stress at seedling stage in ricebean (Bidhan 1). Methods: For studying the effect of iso-osmotic potential of salinity and drought stress solutions of NaCl and PEG 6000 with -0.2 MPa (50mM NaCl and 10% PEG), -0.4 MPa (100 mM NaCl and 12% PEG) and -0.8 MPa (200mM NaCl and 18% PEG) osmotic potential were used. The experiment was done in the laboratory of Department Plant Physiology, Bidhan Chandra Krishi Viswavidyalaya (BCKV), Mohanpur, Nadia and West Bengal in the year 2017-18 and 2018-19. Result: Under moderate to high intensity of osmotic stresses the leaf proline content decreased. The mild and medium stress treatments induced much higher activity of GPOX and APX in the leaf which then decreased somewhat as the intensity of stress increased. The experiment showed that drought stress was found to produce more drastic effects on seedling growth in ricebean as compared to the salinity stress at iso-osmotic potentials.

Direct evidence for dynamics of cell heterogeneity in watercored apples: turgor-associated metabolic modifications and within-fruit water potential gradient unveiled by single-cell analyses

Watercore is a physiological disorder in apple (Malus × domestica Borkh.) fruits that appears as water-soaked tissues adjacent to the vascular core, although there is little information on what exactly occurs at cell level in the watercored apples, particularly from the viewpoint of cell water relations. By combining picolitre pressure-probe electrospray-ionization mass spectrometry (picoPPESI-MS) with freezing point osmometry and vapor pressure osmometry, changes in cell water status and metabolisms were spatially assayed in the same fruit. In the watercored fruit, total soluble solid was lower in the watercore region than the normal outer parenchyma region, but there was no spatial difference in the osmotic potentials determined with freezing point osmometry. Importantly, a disagreement between the osmotic potentials determined with two methods has been observed in the watercore region, indicating the presence of significant volatile compounds in the cellular fluids collected. In the watercored fruit, cell turgor varied across flesh, and a steeper water potential gradient has been established from the normal outer parenchyma region to the watercore region, retaining the potential to transport water to the watercore region. Site-specific analysis using picoPPESI-MS revealed that together with a reduction in turgor, remarkable metabolic modifications through fermentation have occurred at the border, inducing greater production of watercore-related volatile compounds, such as alcohols and esters, compared with other regions. Because alcohols including ethanol have low reflection coefficients, it is very likely that these molecules would have rapidly penetrated membranes to accumulate in apoplast to fill. In addition to the water potential gradient detected here, this would physically contribute to the appearance with high tissue transparency and changes in colour differences. Therefore, it is concluded that these spatial changes in cell water relations are closely associated with watercore symptoms as well as with metabolic alterations.

Seed priming improves Salvia hispanica L. seed performance under salt stress

Salvia hispanica L. is an alternative crop cultivated by farmers who want to diversify their production. However, this species is sensitive to salinity, which affects its germination negatively. Seed priming with different attenuators is a technique with potential to mitigate the effects of salt stress. Thus, the objective of this study was to evaluate the effect of seed priming with the use of different attenuators on the germination, growth, and organic solute accumulation of S. hispanica seedlings under salt stress. The experimental design was completely randomized, with treatments distributed in a 4 × 5 factorial scheme, corresponding to four seed priming treatments and five osmotic potentials, with four replicates of 50 seeds in each treatment. The seed treatments consisted of presoaking seeds for 4h in salicylic acid, gibberellic acid, and distilled water and the control treatment, which did not involve soaking. These seeds were germinated at osmotic potentials of 0.0, -0.1, -0.2, -0.3, and -0.4 MPa, using NaCl as an osmotic agent to simulate the different salinity levels. Among all the treatments implemented, S. hispanica seed priming with salicylic acid was the most efficient in mitigating the salt stress effects.

Physiological performance of common bean seeds of the black commercial group under saline stress

Saline stress is a condition that causes changes in physiological performance in several species and even in cultivars of the same species. Thus, this studyaimed to evaluate the physiological performance of black bean cultivars to salt stress. A completely randomized experimental design was used in a factorial scheme with two cultivars (Mataço and BRS Paisano) and five osmotic potentials simulated with sodium chloride solutions (control = 0.0; -0.2; -0.4; -0.6 and -0.8 MPa), in four replications of 50 seeds per treatment. The variables related to germination, first germination count, germination speed index, and shoot length were evaluated. There were significant interactions (p <0.05) for all variables analyzed. In general, it is concluded that the physiological performance of the seeds of black bean cultivars is affected under simulated saline stress by NaCl solution with an osmotic potential below -0.2 MPa.

The plant water pump: why water flows uphill of water potential gradients in a root hydraulic anatomy model

&lt;p&gt;Guttation is the exudation of xylem sap from vascular plant leaves. This process is particularly interesting because in its configuration root water uptake occurs against the hydrostatic pressure driving force. Hence, it emphasizes the contribution of another driving force that lifts water in plants: the osmotic potential gradient.&lt;/p&gt;&lt;p&gt;The current paradigm of root water uptake explains that, due to the endodermal apoplastic barrier, water flows across root radius from the same principles as through selective membranes: driven by the total water potential gradient. This theory relies on the idea that during guttation, osmolites loaded in xylem vessels decrease xylem total water potential, making it more negative than the total soil water potential, and generating water inflow by osmosis as in an osmometer.&lt;/p&gt;&lt;p&gt;However, this theory fails at explaining experiments in which guttation occurs without sufficient solute loading in root xylem of maize (Enns et al., 1998; Enns et al., 2000) and arrowleaf saltbush (Bai et al., 2007) among others; studies concluding that experimental observations &amp;#8220;could not be explained with the current theories in plant physiology&amp;#8221;. Such flow rates towards combined increasing pressure potentials and increasing osmotic potentials between separate apoplastic compartments would necessitate an effective root radial conductivity that is negative; a mind bender.&lt;/p&gt;&lt;p&gt;What piece of hydraulic network would make it possible for water to flow against the total water potential driving force?&lt;/p&gt;&lt;p&gt;We implemented Steudle&amp;#8217;s composite water transport model in the explicit root cross-section anatomical hydraulic network MECHA (Couvreur et al., 2018). All apoplastic, transmembrane and symplastic pathways are interconnected in the network. The results show that while root radial conductivity is particularly sensitive to cell membrane permeability, the combination of conductive plasmodesmata and increased dilution of protoplast osmotic potentials inwards is a key to explain root water flow towards increasing total potentials. A triple cell theory is suggested as new paradigm of root radial flow.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Bai X-F, Zhu J-J, Zhang P, Wang Y-H, Yang L-Q, Zhang L (2007) Na+ and Water Uptake in Relation to the Radial Reflection Coefficient of Root in Arrowleaf Saltbush Under Salt Stress. Journal of Integrative Plant Biology 49: 1334-1340&lt;/p&gt;&lt;p&gt;Couvreur V, Faget M, Lobet G, Javaux M, Chaumont F, Draye X (2018) Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots. Plant Physiology 178: 1689-1703&lt;/p&gt;&lt;p&gt;Enns LC, Canny MJ, McCully ME (2000) An investigation of the role of solutes in the xylem sap and in the xylem parenchyma as the source of root pressure. Protoplasma 211: 183-197&lt;/p&gt;&lt;p&gt;Enns LC, McCully ME, Canny MJ (1998) Solute concentrations in xylem sap along vessels of maize primary roots at high root pressure. J. Exp. Bot. 49: 1539-1544&lt;/p&gt;

No fitness cost associated with Asn-2041-Ile mutation in winter wild oat (Avena ludoviciana) seed germination under various environmental conditions

Knowledge about the fitness cost imposed by herbicide resistance in weeds is instrumental in devising integrated management methods. The present study investigated the germination response of ACCase-resistant (R) and susceptible (S) winter wild oat under different environmental conditions. The DNA of the plants was sequenced after being extracted and purified. The segregated F2 seeds were subjected to various temperatures, water potentials, NaCl concentrations, different pHs, darkness conditions, and burial depths. The results of the sequencing indicated that Ile-2041-Asn mutation is responsible for the evolution of resistance in the studied winter wild oat plants. The seeds were able to germinate over a wide range of temperatures, osmotic potentials, NaCl concentrations, and pHs. Germination percentage of R and S seeds under dark and light conditions was similar and ranged from 86.3 to 88.3%. The highest emergence percentage for both R and S plants was obtained in 0, 1, and 2 cm depths and ranged from 66.6 to 70.3%. In overall, no differences were observed in the germination response between the R and S winter wild oat plants under all studied conditions. No fitness cost at seed level indicates that control of R winter wild oats is more difficult, and it is essential to adopt crop and herbicide rotation to delay the further evolution of resistance.

Seed germination and performance of sunflower seedlings submitted to produced water

ABSTRACT The use of produced water becomes an option in the irrigation of non-food crops with potential for biofuel production. However, its effects on different stages of plant development and mainly on seed germination should be known. The study was conducted to evaluate the performance of sunflower seedlings subjected to different types of produced water. An experimental design in a factorial scheme was adopted to evaluate 3 cultivars (Catissol 01, Embrapa 122 and IAC Iaramã) and 6 types of water (distilled water - control, public-supply water, water resulting from the water and oil separation process - WOS, filtration in sand filter - SAF, filtration in sand + charcoal filter - SCF, and filtration in sand + osmosis filter - SOF). In addition, the substrate was moistened with polyethylene glycol (PEG) solutions, simulating the osmotic potentials of the evaluated waters, and a sensitivity test was conducted with lettuce seeds under conditions similar to those adopted for sunflower. The cv. Catissol showed higher percentages of germination and vigor of seedlings, regardless of the water used. There was a trend of reduction in germination and vigor of seedlings with the use of produced water treated with the WOS, SAF and SCF systems. All water potentials simulated by PEG solutions reduced the germination and vigor of lettuce seeds, and the effect was more pronounced for the WOS system. SOF was the only one capable of making the produced water non-toxic to sunflower seeds and lettuce seedlings.

Effects of drought stress on germination and seedling growth of different field pea varieties

Germination and seedling growth of seven genotypes of field pea (Pisum sativum L.) were studied in PEG-6000 solution having osmotic potentials -0.1 and -0.2 MPa. A study was undertaken to evaluate the influence of different osmotic potentials (MPa) on seed germination percentage (GP) and mean germination time (MGT). Results show that the percentage of germination decreased with a decrease in osmotic potential, while mean germination time increased. Variety Javor is much more sensitive than the other varieties at all levels of osmotic stress. By contrast, the lowest sensitivity of germination and MGT was found in varieties Mraz and Trezor. Seed germination tests at -0.1 to -0.2 MPa have the potential to be used as tests in field pea. Osmotic stress exposure and its duration significantly affected the growth of seedlings (shoot and root) and the accumulation of biomass, while its effect was more prominent on the growth of the shoot than on root growth, which was also confirmed by the root tolerance index.