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Salinity is an important environmental constraint which strongly reduces crop yield in several areas in the world. Rice (Oryza sativa) is considered as a salt-sensitive species and improvement of salt resistance is a major goal for plant breeders. Some species in the Oryza genus may constitute an interesting source of genes for rice improvement. Comparatively to the classical Asian rice species (Oryza sativa), the African rice Oryza glaberrima is poorly described for its response to salt stress. Our aims were 1-) to identify salt-tolerant varieties of O. glaberrima, 2-) to discriminate between the osmotic and the ionic components of salt stress and 3) to precise the impact of individual ions on salt deleterious impact. Plants were exposed to stress in nutrient solution or in soil culture. Then, a set of parameters related to photosynthesis, mineral nutrition, plant water status, yield, and antioxidative properties were recorded. Our results showed that one accession such as the cultivar TOG5307 was able to maintain a higher net photosynthesis under salt conditions and exhibited a higher level of tolerance to accumulated Na+ ions and a higher capacity for osmotic adjustment comparatively to the salt-sensitive cultivar TOG5949. The salt-resistant cultivar TOG5307 was also less affected by salinity than TOG5949 for yield-related parameters. Na+ ions appeared more toxic than Cl-, although an additive effect was recorded when both ions were simultaneously present in NaCl. The use of non-penetrating osmotic agent PEG demonstrated that osmotic and ionic components of salt stress acted in an additive way in the salt-sensitive cultivar but not in the salt-resistant one where an antagonist action was recorded for several parameters. Data were analyzed in relation to the expression of genes coding for ions transporters., (SC - Sciences) -- UCL, 2021

Environmental stresses such as salinity directly impact crop growth, and by extension, world food supply and societal prosperity. It is estimated that over 800 million hectares of land throughout the world are salt-affected. In arid and semi-arid regions, salt concentration can be close to that in the seawater. Hence, there are intensive efforts to improve plant tolerance to salinity and other environmental stressors. Salicylic acid (SA) is an important signal molecule for modulating plant responses to stress. In the present study, we examined, on multiple plant growth related endpoints, whether SA applied through the rooting medium could mitigate the adverse effects of salinity on tomato (Solanum lycopersicum) cv. Marmande. The latter is a hitherto understudied tomato plant from the above perspective; it is a classic variety that produces the large ribbed tomatoes in the Mediterranean and consumed worldwide. We found salt stress negatively affected the growth of cv. Marmande tomato plants. However, the SA-treated plants had greater shoot and root dry mass, leaf area compared to untreated plants when exposed to salt stress. Application of SA restores photosynthetic rates and photosynthetic pigment levels under salt (NaCl) exposure. Leaf water, osmotic potential, stomatal conductance transpiration rate, and biochemical parameters were also ameliorated in SA-treated plants under saline stress conditions. Overall, these data illustrate that SA increases cv. Marmande tomato growth by improving photosynthesis, regulation and balance of osmotic potential, induction of compatible osmolyte metabolism, and alleviating membrane damage. We suggest salicylic acid might be considered as a potential growth regulator to improve tomato plant salinity stress resistance, in the current era of global climate change.

Background and aims Flooding stress is known to affect root growth and sugar metabolism in plants, but data are crucially missing for Cichorium intybus which stores inulin in its tap root. The aim of the present study was to quantify the impact of recurrent episodes of flooding stress on plant growth, water status, photosynthesis and sugar metabolism in relation to inulin synthesis and accumulation in roots of this species. Methods Plants were cultured for 25 weeks Under controlled environmental conditions on a sand substrate in columns saturated with nutrient solution for periods of 2–3 weeks (starting on week 12) alternating with 7 days non-flooding periods. Plant growth, water status, photosynthesis-related parameters and sugar concentration and metabolism were monitored at regular intervals up to the end of the treatment. Key results Flooding increased the number of leaves but reduced net photosynthesis in relation to stomatal closure and decrease in PSII efficiency. The roots of flooded plants were shorter and larger than those of controls but fresh and dry weight were similar in the two situations. Reducing sugars and organic acids accumulated in the leaves while glucose, fructose, sucrose and 1-kestotriose accumulated in the roots. Sucrose synthase (EC 2.4.1.13) and invertase (EC 3.2.1.26) activities increased in both organs while sucrose-phosphate-synthase activity (EC 2.4.1.14) remained unaffected by flooding. Inulin synthesis was delayed in flooded roots and its mean degree of polymerization (DP) was reduced as a consequence of fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100) inhibition. Conclusions Cichorium intybus is able to cope with intermittent episodes of flooding and modify organ shape without any effect on final weight. Quantity of inulin produced per plant remained unaffected but the quality of inulin (mean DP) decreased as a consequence of flooding.

An increase in mean and extreme summer temperatures is expected as a consequence of climate changes and this might have an impact on plant development in numerous species. Root chicory (Cichorium intybus L.) is a major crop in northern Europe, and it is cultivated as a source of inulin. This polysaccharide is stored in the tap root during the first growing season when the plant grows as a leafy rosette, whereas bolting and flowering occur in the second year after winter vernalisation. The impact of heat stress on plant phenology, water status, photosynthesis-related parameters, and inulin content was studied in the field and under controlled phytotron conditions. In the field, plants of the Crescendo cultivar were cultivated under a closed plastic-panelled greenhouse to investigate heat-stress conditions, while the control plants were shielded with a similar, but open, structure. In the phytotrons, the Crescendo and Fredonia cultivars were exposed to high temperatures (35. °C day/28. °C night) and compared to control conditions (17. °C) over 10 weeks. In the field, heat reduced the root weight, the inulin content of the root and its degree of polymerisation in non-bolting plants. Flowering was observed in 12% of the heat stressed plants during the first growing season in the field. In the phytotron, the heat stress increased the total number of leaves per plant, but reduced the mean leaf area. Photosynthesis efficiency was increased in these plants, whereas osmotic potential was decreased. High temperature was also found to induced flowering of up to 50% of these plants, especially for the Fredonia cultivar. In conclusion, high temperatures induced a reduction in the growth of root chicory, although photosynthesis is not affected. Flowering was also induced, which indicates that high temperatures can partly substitute for the vernalisation requirement for the flowering of root chicory. © 2013 Elsevier GmbH.

A good understanding of the soil water content (SWC) distribution at the field scale is essential to improve the management of water, soil and crops. Recent studies proved that Electrical Resistivity Tomography (ERT) opens interesting perspectives in the determination of the SWC distribution in 3 dimensions (3-D). This study was conducted (i) to check and validate how ERT is able to monitor SWC distribution in a maize field during the late growing season; and (ii) to investigate how maize plants and rainfall affect the dynamics of SWC distribution. Time Domain Reflectometry (TDR) measurements were used to validate ERT-inverted SWC values. Evolution of water mass balance was also calculated to check whether ERT was capable of giving a reliable estimate of soil water stock evolution. It is observed that ERT was able to give the same average SWC as TDR (R2 = 0.98). In addition, ERT gives better estimates of the water stock than TDR thanks to its higher spatial resolution. The high resolution of ERT measurements also allows for the discrimination of SWC heterogeneities. The SWC distribution showed that alternation of maize rows and inter-rows was the main influencing factor of the SWC distribution. The drying patterns were linked to the root profiles, with drier zones under the maize rows. During short periods, with negligible rainfall, the SWC decrease took place mainly in the two upper soil horizons and in the inter-row area. In contrast, rainfall increased the SWC mostly under the maize rows and in the upper soil layer. Nevertheless, the total amount of rainfall during the growing season was not sufficient to modify the SWC patterns induced by the maize rows. During the experimental time, there was hardly any SWC redistribution from maize rows to inter-rows. Yet, lateral redistribution from inter-rows to maize rows induced by potential gradient generates SWC decrease in the inter-row area and in the deeper soil horizons.

Root chicory (Cichorium intybus var. sativum) is a cash crop cultivated for inulin production in Western Europe. This plant can be exposed to severe water stress during the last 3 months of its 6-month growing period. The aim of this study was to quantify the effect of a progressive decline in water availability on plant growth, photosynthesis, and sugar metabolism and to determine its impact on inulin production. Water stress drastically decreased fresh and dry root weight, leaf number, total leaf area, and stomatal conductance. Stressed plants, however, increased their water-use efficiency and leaf soluble sugar concentration, decreased the shoot-to-root ratio and lowered their osmotic potential. Despite a decrease in photosynthetic pigments, the photosynthesis light phase remained unaffected under water stress. Water stress increased sucrose phosphate synthase activity in the leaves but not in the roots. Water stress inhibited sucrose:sucrose 1-fructosyltransferase and fructan:fructan 1 fructosyltransferase after 19 weeks of culture and slightly increased fructan 1-exohydrolase activity. The root inulin concentration, expressed on a dry-weight basis, and the mean degree of polymerization of the inulin chain remained unaffected by water stress. Root chicory displayed resistance to water stress, but that resistance was obtained at the expense of growth, which in turn led to a significant decrease in inulin production.

Root-chicory is a biannual crop cultivated in Western Europe to extract inulin from its tap root. Our aim was to understand the impacts of drier summers and summer floods on its physiology, water uptake and yield. We found that chicory is able to survive to water shortage by reducing its growth and leaf surface. This stress did not damage the plant metabolism. Even if gas exchanges were reduced due to growth reduction and stomatal closure, photosynthesis and sugar production were maintained. The yield was strongly reduced by growth inhibition but the inulin concentration and the length of the chains stayed constant. We followed the water content in the soil thanks to two geophysical techniques: Time Domain Reflectometry and Electrical Resistance Tomography. Using those data and root growth information, we modeled the water uptake. Before the reduction in transpiration, the lack of water in the upper layers was compensated by uptakes in deeper horizons thanks to a passive mechanism called compensation. We found also that the plants reacted actively against drought by sending new lateral roots in the layers where compensation occurred. In case of flooding, it appeared that growth was maintained in waterlogging situations. Contrary to drought, photosynthesis and sugar metabolism were affected by this stress. In terms of yield, the final quantity of inulin produced was not modified by flooding but its quality was reduced. To conclude, this study showed that chicory is able to cope with abiotic stresses thanks to physiological mechanisms and its deep root system which helps the plant to extract water from deep horizons. Nevertheless, drought stress induced yield decrease. On an agronomical point of view and in the conditions we applied, chicory can be qualified as tolerant only to flooding., (AGRO 3) -- UCL, 2012

Chicory (Cichorium intybus L.) is a cash crop culti vated in Western Europe for inulin production. Due to actual and future climate changes, this plant could be exposed to severe water stress at the end of its growing period, leading to a decrease of its yield. The aim of this work was to investigate the chicory root water uptake dynamics and the plant ability to compensate a lack of water in the upper horizons. We performed a controlled experiment with 3 replicates under contrasted irrigation scenarios. We observed that, in case of drought, total root length decreased and root profiles developed deeper. We successfully used a one-dimensional Richards-based model with a stress function and a compensation mechanism (Hydrus 1-D) to inversely characterize the dynamics of the actual sink-term profiles under both irrigation scenarios. We could also use the model to assess the compensation thanks to a weighted stress index that is consistent between replicates. The extracti on profiles evolved differently under water-deficit and controlled situations. The passive compensation mechanism allowed chicory roots under water-limited conditions to take water deeper in the soil, where they had only few lateral roots. We found that, in case of drought, compensation started before the plants had to reduce their transpiration rate. Because the soil kept drying out, compensation was not sufficient anymore, and the plants had to decrease their transpiration some days later. However, chicories maintained their metabolism and continued to transpire and to growth slowly. This allowed them to adapt thanks to an active compensation mechanism, by generating new lateral roots in wetter horizons. This study also showed that there was no unique Feddes stress parameter set able to describe plant behavior under contrasted irrigation conditions or even under different plant development stages.

A good understanding of the soil water content (SWC) distribution at the field scale is essential to improve the management of water, soil and crops. Recent studies proved that electrical resistivity tomography (ERT) opens interesting perspectives in the determination of the SWC distribution in 3 dimensions (3-D). We conducted this study (1) to check and validate the sensitivity of ERT for monitoring SWC distribution in a maize field during the late growing season; and (2) to investigate how maize plants and precipitations affect the dynamics of SWC distribution. We used time domain reflectometry (TDR) measurements to validate ERT-inverted SWC values. We also calculated the evolution of water mass balance to check whether ERT was capable of giving a reliable estimate of soil water stock evolution. We observe that ERT is able to give the same average SWC as TDR (R2 = 0.98). In addition, we showed that ERT give better estimates of the water stock than TDR thanks to its higher spatial resolution. The high resolution of ERT measurements also allows the discrimination of SWC heterogeneities. The SWC distribution shows that alternation of maize rows and inter-rows is the main influencing factor of the SWC distribution. The drying patterns are linked to the root profiles, with drier zones under the maize rows. During small dry periods, the SWC decrease occurs mainly in the two upper soil horizons and in the inter-row area. At the opposite, precipitations increase the SWC mostly under the maize rows and at the upper soil layer. Nevertheless, the total amount of rainfall during the growing season is not sufficient to modify the SWC patterns induced by the maize rows. During the experimental time, the SWC redistribution hardly occurred from maize rows to the inter-rows but lateral redistribution from the inter-row to the maize rows induced by potential gradient generates SWC decrease in the inter-rows area and in the deeper soil horizons.