Induced in vitro adaptation for salt tolerance in date palm (Phoenix dactylifera L.) cultivar Khalas

Effect of potassium chloride-induced salt stress on bacoside A biosynthesis in Bacopa monnieri (L.) grown under in vitro and in vivo conditions: a comparative study

Bacopa monnieri L. is a highly acclaimed plant species for its diverse pharmaceutical properties and is mostly found in the Indian subcontinent. In this study, the effects of salt (KCl) stress on plant height, biomass, chlorophyll content, and antioxidant enzyme activities of Bacopa monnieri in both in vitro and in vivo conditions were investigated. A significant increase of up to 1.8 folds and 1.3 folds in bacoside-A content at 100 mM KCl was recorded in both in vivo and in vitro grown plants, respectively. Higher salinity (> 100 mM KCl) stress exerted a negative effect on plant height and plant biomass, whereas at levels ≤ 100 KCl, substantial improvement in terms of plant height (PH) and biomass (PB) was recorded in both in vivo (up to 1.6-fold and 1.8-fold high) and in vitro (up to 1.9-fold and 1.7-fold high) conditions. Total chlorophyll content and antioxidant enzyme (CAT, POD) activities were also maximum at 100 mM KCl. However, at higher KCl levels (200 mM), no significant increase in any of the morphophysiological parameters was recorded. Therefore, 100 mM KCl was identified as the optimum salt concentration for enhancing bacoside A content, plant growth, and physiological properties in terms of antioxidant enzyme activity and chlorophyll content in B. monnieri.

Harnessing rhizospheric core microbiomes from arid regions for enhancing date palm resilience to climate change effects

Date palm cultivation has thrived in the Gulf Cooperation Council region since ancient times, where it represents a vital sector in agricultural and socio-economic development. However, climate change conditions prevailing for decades in this area, next to rarefication of rain, hot temperatures, intense evapotranspiration, rise of sea level, salinization of groundwater, and intensification of cultivation, contributed to increase salinity in the soil as well as in irrigation water and to seriously threaten date palm cultivation sustainability. There are also growing concerns about soil erosion and its repercussions on date palm oases. While several reviews have reported on solutions to sustain date productivity, including genetic selection of suitable cultivars for the local harsh environmental conditions and the implementation of efficient management practices, no systematic review of the desertic plants' below-ground microbial communities and their potential contributions to date palm adaptation to climate change has been reported yet. Indeed, desert microorganisms are expected to address critical agricultural challenges and economic issues. Therefore, the primary objectives of the present critical review are to (1) analyze and synthesize current knowledge and scientific advances on desert plant-associated microorganisms, (2) review and summarize the impacts of their application on date palm, and (3) identify possible gaps and suggest relevant guidance for desert plant microbes' inoculation approach to sustain date palm cultivation within the Gulf Cooperation Council in general and in Qatar in particular.

Biochar and nano biochar: Enhancing salt resilience in plants and soil while mitigating greenhouse gas emissions: A comprehensive review

Salinity stress poses a significant challenge to agriculture, impacting soil health, plant growth and contributing to greenhouse gas (GHG) emissions. In response to these intertwined challenges, the use of biochar and its nanoscale counterpart, nano-biochar, has gained increasing attention. This comprehensive review explores the heterogeneous role of biochar and nano-biochar in enhancing salt resilience in plants and soil while concurrently mitigating GHG emissions. The review discusses the effects of these amendments on soil physicochemical properties, improved water and nutrient uptake, reduced oxidative damage, enhanced growth and the alternation of soil microbial communities, enhance soil fertility and resilience. Furthermore, it examines their impact on plant growth, ion homeostasis, osmotic adjustment and plant stress tolerance, promoting plant development under salinity stress conditions. Emphasis is placed on the potential of biochar and nano-biochar to influence soil microbial activities, leading to altered emissions of GHG emissions, particularly nitrous oxide(N2O) and methane(CH4), contributing to climate change mitigation. The comprehensive synthesis of current research findings in this review provides insights into the multifunctional applications of biochar and nano-biochar, highlighting their potential to address salinity stress in agriculture and their role in sustainable soil and environmental management. Moreover, it identifies areas for further investigation, aiming to enhance our understanding of the intricate interplay between biochar, nano-biochar, soil, plants, and greenhouse gas emissions.

In vitro and in vivo screening for the identification of salt-tolerant sugarcane (Saccharum officinarum L.) clones: molecular, biochemical, and physiological responses to salt stress

Sugarcane is a glycophyte whose growth and yield can be negatively affected by salt stress. As the arable lands with potential saline soils expand annually, the increase of salt-tolerance in sugarcane cultivars is highly desired. We, herein, employed in vitro and in vivo conditions in order to screen sugarcane plants for salt tolerance at the cellular and at the whole plant levels. Calli of sugarcane cv. Khon Kaen 3 (KK3) were selected after culturing in selective media containing various NaCl concentrations, and regenerated plants were then reselected after culturing in selective media containing higher NaCl concentrations. The surviving plants were finally selected after an exposure to 254 mM NaCl under greenhouse conditions. A total of 11 sugarcane plants survived the selection process. Four plants that exhibited tolerance to the four different salt concentrations applied during the aforementioned screening process were then selected for the undertaking of further molecular, biochemical, and physiological studies. The construction of a dendrogram has revealed that the most salt-tolerant plant was characterized by the lowest genetic similarity to the original cultivar. The relative expression levels of six genes (i.e., SoDREB, SoNHX1, SoSOS1, SoHKT, SoBADH, and SoMIPS) were found to be significantly higher in the salt-tolerance clones than those measured in the original plant. The measured proline levels, the glycine betaine content, the relative water content, the SPAD unit, the contents of chlorophyll a and b, as well as the K⁺/Na⁺ ratios of the salt-tolerant clones were also found to be significantly higher than those of the original plant.When the salt-tolerant clones were grown in a low saline soil, they exhibited a higher Brix percentage than that of the original cultivar.

Artificial neural network modeling for deciphering the in vitro induced salt stress tolerance in chickpea (Cicer arietinum L)

Salt stress is one of the most critical abiotic stresses having significant contribution in global agriculture production. Chickpea is sensitive to salt stress at various growth stages and a better knowledge of salt tolerance in chickpea would enable breeding of salt tolerant varieties. During present investigation, in vitro screening of desi chickpea by continuous exposure of seeds to NaCl-containing medium was performed. NaCl was applied in the MS medium at the rate of 6.25, 12.50, 25, 50, 75, 100, and 125 mM. Different germination indices and growth indices of roots and shoots were recorded. Mean germination (%) of roots and shoots ranged from 52.08 to 100%, and 41.67-100%, respectively. The mean germination time (MGT) of roots and shoots ranged from 2.40 to 4.78 d and 3.23-7.05 d. The coefficient of variation of the germination time (CVt) was recorded as 20.91-53.43% for roots, and 14.53-44.17% for shoots. The mean germination rate (MR) of roots was better than shoots. The uncertainty (U) values were tabulated as 0.43-1.59 (roots) and 0.92-2.33 (shoots). The synchronization index (Z) reflected the negative impact of elevated salinity levels on both root and shoot emergence. Application of NaCl exerted a negative impact on all growth indices compared to control and decreased gradually with elevated NaCl concentration. Results on salt tolerance index (STI) also revealed the reduced STI with elevated NaCl concentration and STI of roots was less than shoot. Elemental analysis revealed more Na and Cl accumulation with respective elevated NaCl concentrations. The In vitro growth parameters and STI values validated and predicted by multilayer perceptron (MLP) model revealed the relatively high R 2 values of all growth indices and STI. Findings of this study will be helpful to broaden the understanding about the salinity tolerance level of desi chickpea seeds under in vitro conditions using various germination indices and seedling growth indices.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01282-z.

Insight into Membrane Stability and Physiological Responses of Selected Salt-Tolerant and Salt-Sensitive Cell Lines of Troyer Citrange (Citrus sinensis [L.] x Citrus trifoliata [L.] Raf.) under Salt Stress

The aim of this study was to evaluate the membrane integrity and some physiological responses of rootstock citrus calli under exposure to different concentrations of NaCl. Selected salt-tolerant cell lines were compared with salt-sensitive calli of Troyer’s citrange (Citrus sinensis [L.] x Citrus trifoliata [L.] Raf.) (TC) with respect to growth, water content, Na+, K+ and Cl− ion content as well as cell membrane stability under exposure to different NaCl concentrations. The results show that the stressed sensitive lines have a consistently high ion efflux. The values recorded for these sensitive calli are 3 to 6 times higher than those of the tolerant calli. Thus, only selected halotolerant calli were able to maintain the integrity of their membranes under salt stress conditions. In the sensitive calli, NaCl always induces a slowing down of growth even from 4 g L−1, and the reduction in the relative growth rate is higher than 50% and reaches more than 90% for the three culture durations at 8 g L−1 NaCl. For the salt-tolerant selected lines, the relative growth rate seems to be slightly slowed down until the second month of culture but becomes equal to that of the control at the third month, whether at 4 or 8 g L−1 NaCl. At the end of the third month, the relative growth rate of the selected calli is 100% at 8 g L−1 NaCl. The water content is twice as high in the selected tolerant calli as in the sensitive ones after three months of salt treatment at 8 g L−1 NaCl. After long-term culture, the halotolerant calli absorbed similar or even higher amounts of Na+ and Cl− than the salt-sensitive lines. However, by the 3rd month, the recorded accumulation rate dropped in the unselected but continued to increase in the tolerant calli (4-fold higher at 12 g L−1 NaCl than the control). Furthermore, exposure of both types of calli (salt-sensitive and salt-tolerant) to equal concentrations of NaCl resulted in greater loss of K+ by the NaCl-sensitive lines. However, for tolerant lines, K+ uptake is not affected at 4 g L−1 NaCl and the decrease in tissue content is less than 25% at 8 g L−1 NaCl. From this observation, it can be concluded that growth and the ability to retain high levels of internal K+ are correlated.

Analyzing the Spatial Correspondence between Different Date Fruit Cultivars and Farms’ Cultivated Areas, Case Study: Al-Ahsa Oasis, Kingdom of Saudi Arabia

Diversity in date palm (DP) cultivars plays a crucial role in the agroecosystems of several countries, such as the Kingdom of Saudi Arabia (KSA). This study aims to map and analyze the spatial distribution of the most grown DP cultivars (Khlas, Ruziz, and Shishi) in the Al-Ahsa oasis in the KSA and to highlight their spatial correlation with the corresponding cultivated patches within farms. Descriptive and spatial data on 288 farms were analyzed using GIS, data curation, cross-TAB statistics, clustering maps, and spatial autocorrelation techniques. The obtained results revealed that most of the oasis’s DP farms are within a cultivated area of <500 m2. The larger cultivated areas are mostly in the oasis’s northern and central subregions, agreeing with the spatial distribution of trees. In total, 56.9% of the studied farms grew the cultivars together within the least rank (<500 m2) of cultivated area, having the greatest tendency for DP cultivation. Khlas was the most dominant cultivar being the least absent from cultivation with 3.1% compared to Ruziz (31.9%) and Shishi (37.8%). The spatial distribution of DP plantations in the oasis was also consistent with the spatial variation in soils and irrigation water salinity, necessitating the need for special agricultural extension programs. In conclusion, these outcomes indicate that this study is essential for DP sustainability, growers, authorities, and policy makers.

Oxidative damage, antioxidant mechanism and gene expression in tomato responding to salinity stress under in vitro conditions and application of iron and zinc oxide nanoparticles on callus induction and plant regeneration

BACKGROUND

Salinity is one of the most challenging abiotic stresses restricting the growth of plants. In vitro screening will increase the efficiency and speed of salinity tolerant genotypes identifications. The response of four tomato cultivars under salinity was analyzed in vitro to evaluate the seedlings growth, biochemical, and gene expression responses as well as the effect of nano zinc and iron on callus induction and plant regeneration.

RESULTS

The results showed that an increase in salinity stress in the medium decreased the germination percentage, fresh and dry weight of shoot, root length, chlorophyll a, b and carotenoids content, K and Ca content, and on the other hand, Na content was increased. MDA content ('Nora', 'PS-10', 'Peto' and 'Roma': 1.71, 1.78, 1.66 and 2.16 folds, respectively), electrolyte leakage ('PS-10': 33.33%; 'Roma': 56.33%), were increased with salinity of 100 mM compared to control. Proline content was increased in 50 mM NaCl (10.8 fold). The most activity of antioxidant enzymes including CAT, SOD, APX, GPX, and GR was observed in the 'PS-10' cultivar, and the lowest activity of these enzymes was observed in 'Roma' under salinity stress. The AsA and GSH were decreased and DHA and GSSG were increased with the increased intensity of salinity. The relative expression of SOD, APX, and GR genes varied in different cultivars at different salinity concentrations. The most percentage of callus induction was observed with applying iron oxide nanoparticles, and the most regeneration rate was recorded using zinc oxide nanoparticles.

CONCLUSION

The results showed that salt-tolerant cultivars such as 'PS-10' with better osmotic adjustment, are suitable candidates for the future production and breeding programs. The use of nutrient nanoparticles under salinity stress for different tomato cultivars increased their performance.

Agronomical, Physiological and Biochemical Characterization of In Vitro Selected Eggplant Somaclonal Variants under NaCl Stress

Previously, an efficient regeneration protocol was established and applied to regenerate plants from calli lines that could grow on eggplant leaf explants after a stepwise in vitro selection for tolerance to salt stress. Plants were regenerated from calli lines that could tolerate up to 120 mM NaCl. For further in vitro and in vivo evaluation, four plants with a higher number of leaves and longer roots were selected from the 32 plants tested in vitro. The aim of this study was to confirm the stability of salt tolerance in the progeny of these four mutants ('R18', 'R19', 'R23' and 'R30'). After three years of in vivo culture, we evaluated the impact of NaCl stress on agronomic, physiological and biochemical parameters compared to the parental control ('P'). The regenerated and control plants were assessed under in vitro and in vivo conditions and were subjected to 0, 40, 80 and 160 mM of NaCl. Our results show significant variation in salinity tolerance among regenerated and control plants, indicating the superiority of four regenerants ('R18', 'R19', 'R23' and 'R30') when compared to the parental line ('P'). In vitro germination kinetics and young seedling growth divided the lines into a sensitive and a tolerant group. 'P' tolerate only moderate salt stress, up to 40 mM NaCl, while the tolerance level of 'R18', 'R19', 'R23' and 'R30' was up to 80 mM NaCl. The quantum yield of PSII (ΦPSII) declined significantly in 'P' under salt stress. The photochemical quenching was reduced while nonphotochemical quenching rose in 'P' under salt stress. Interestingly, the regenerants ('R18', 'R19', 'R23' and 'R30') exhibited high apparent salt tolerance by maintaining quite stable Chl fluorescence parameters. Rising NaCl concentration led to a substantial increase in foliar proline, malondialdehyde and soluble carbohydrates accumulation in 'P'. On the contrary, 'R18', 'R19', 'R23' and 'R30' exhibited a decline in soluble carbohydrates and a significant enhancement in starch under salinity conditions. The water status reflected by midday leaf water potential (ψl) and leaf osmotic potential (ψπ) was significantly affected in 'P' and was maintained a stable level in 'R18', 'R19', 'R23' and 'R30' under salt stress. The increase in foliar Na+ and Cl- content was more accentuated in parental plants than in regenerated plants. The leaf K+, Ca2+ and Mg2+ content reduction was more aggravated under salt stress in 'P'. Under increased salt concentration, 'R18', 'R19', 'R23' and 'R30' associate lower foliar Na+ content with a higher plant tolerance index (PTI), thus maintaining a normal growth, while foliar Na+ accumulation was more pronounced in 'P', revealing their failure in maintaining normal growth under salinity stress. 'R18', 'R19', 'R23' and 'R30' showed an obvious salt tolerance by maintaining significantly high chlorophyll content. In 'R18', 'R19', 'R23' and 'R30', the enzyme scavenging machinery was more performant in the roots compared to the leaves. Salt stress led to a significant augmentation of catalase, ascorbate peroxidase and guaiacol peroxidase activities in the roots of 'R18', 'R19', 'R23' and 'R30'. In contrast, enzyme activities were less enhanced in 'P', indicating lower efficiency to cope with oxidative stress than in 'R18', 'R19', 'R23' and 'R30'. ACC deaminase activity was significantly higher in 'R18', 'R19', 'R23' and 'R30' than in 'P'. The present study suggests that regenerated plants 'R18', 'R19', 'R23' and 'R30' showed an evident stability in tolerating salinity, which shows their potential to be adopted as interesting selected mutants, providing the desired salt tolerance trait in eggplant.

Obtaining Salt Stress-Tolerant Eggplant Somaclonal Variants from In Vitro Selection

An efficient regeneration protocol was applied to regenerate shoots on salt stress-tolerant calli lines of aubergine (Solanum melongena). These NaCl-tolerant cell lines were obtained by two different methods. On the one hand, the developed callus tissue was transferred to a medium with a continuous salt content of 40, 80, 120, or 160 mM NaCl. On the other hand, the callus tissue was subjected to a stepwise increasing salinity to 160 mM NaCl every 30 days. With the second method, calli which could be selected were characterized by compact growth, a greenish color, and absence of necrotic zones. When grown on salt-free medium again, NaCl-tolerant calli showed a decline in relative growth rate and water content in comparison to the control line. This was more obvious in the 120 mM NaCl-tolerant callus. Lipid peroxidase activity increased in 40 and 80 mM NaCl-tolerant calli; yet did not increase further in 120 mM-tolerant callus. An increase in ascorbic acid content was observed in 80 and 120 mM NaCl-tolerant calli compared to the 40 mM NaCl-tolerant lines, in which ascorbic acid content was twice that of the control. All NaCl-tolerant lines showed significantly higher superoxide dismutase (SOD) (208-305-370 µmol min-1 mg-1 FW) and catalase (CAT) (136-211-238 µmol min-1 mg-1 FW) activities compared to control plants (231 and 126 µmol min-1 mg-1 FW). Plants were regenerated on the calli lines that could tolerate up to 120 mM NaCl. From the 32 plants tested in vitro, ten plants with a higher number of leaves and root length could be selected for further evaluation in the field. Their high salt tolerance was evident by their more elevated fresh and dry weight, their more increased relative water content, and a higher number and weight of fruits compared to the wild-type parental control. The presented work shows that somaclonal variation can be efficiently used to develop salt-tolerant mutants.

Plant Group II LEA Proteins: Intrinsically Disordered Structure for Multiple Functions in Response to Environmental Stresses

In response to various environmental stresses, plants have evolved a wide range of defense mechanisms, resulting in the overexpression of a series of stress-responsive genes. Among them, there is certain set of genes that encode for intrinsically disordered proteins (IDPs) that repair and protect the plants from damage caused by environmental stresses. Group II LEA (late embryogenesis abundant) proteins compose the most abundant and characterized group of IDPs; they accumulate in the late stages of seed development and are expressed in response to dehydration, salinity, low temperature, or abscisic acid (ABA) treatment. The physiological and biochemical characterization of group II LEA proteins has been carried out in a number of investigations because of their vital roles in protecting the integrity of biomolecules by preventing the crystallization of cellular components prior to multiple stresses. This review describes the distribution, structural architecture, and genomic diversification of group II LEA proteins, with some recent investigations on their regulation and molecular expression under various abiotic stresses. Novel aspects of group II LEA proteins in Phoenix dactylifera and in orthodox seeds are also presented. Genome-wide association studies (GWAS) indicated a ubiquitous distribution and expression of group II LEA genes in different plant cells. In vitro experimental evidence from biochemical assays has suggested that group II LEA proteins perform heterogenous functions in response to extreme stresses. Various investigations have indicated the participation of group II LEA proteins in the plant stress tolerance mechanism, spotlighting the molecular aspects of group II LEA genes and their potential role in biotechnological strategies to increase plants' survival in adverse environments.