Physiological and biochemical response to drought stress in the leaves of Aegiceras corniculatum and Kandelia obovata

In vitro response of sugarcane (Saccharum spp. Hybrid) plantlets to flooding stress

Flooding caused by climate change puts the productivity of sugarcane cultivation at risk. The objective of this study was to evaluate the effect of in vitro flooding stress on sugarcane plantlets. Sugarcane plantlets were grown in test tubes containing Murashige and Skoog semi-solid medium without growth regulators as a control treatment and two stress levels using a double layer with sterile distilled water to simulate hypoxia and anoxia. After 15 d of culture, the number of new shoots, plantlet height, number of leaves, number of roots, root length, stomatal density, percentage of closed stomata and percentage of dry matter were evaluated. In addition, biochemical variables such as chlorophylls, carotenoids, phosphoenolpyruvate (PEP), Rubisco, total proteins (TP), proline (Pr), glycine-betaine (GB), phenols, antioxidant capacity and lipid peroxidation were determined in all treatments. Results showed a higher number of new shoots, leaves and percentage of closed stomata in the flooded plantlets, while plantlet height, number of roots, stomatal density, and dry matter were higher in the control treatment. Regarding, chlorophyll, carotenoid, PEP and Rubisco contents decreased in the flooded treatments, while TP and phenol contents were higher in the partially submerged treatment. Antioxidant capacity and lipid peroxidation increased in the fully submerged treatment. Pr and GB contents did not show changes in any of the evaluated treatments. Stress induced by excess water in a double layer in vitro is an alternative method to determining physiological and biochemical mechanisms of tolerance to hypoxia and anoxia caused by flooding for breeding programs in sugarcane.

Enhancement of drought tolerance in Arabidopsis plants induced by sulfur dioxide

Sulfur dioxide (SO₂) is a common air pollutant that has multiple effects on plants. In the present study, the improvement of drought tolerance in Arabidopsis plants by SO₂ fumigation was investigated. The results showed that pre-exposure to 30 mg/m³ SO₂ for 72 h could reduce water loss, stomatal conductance (Gs) and the transpiration rate (Tr) but increased the net photosynthetic rate (Pn), water use efficiency (iWUE) and photosynthetic pigment contents under drought conditions. The activities of superoxide dismutase (SOD) and peroxidase (POD) were significantly increased, while the contents of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) were decreased in SO₂-pretreated Arabidopsis plants under drought stress. Additionally, the activity of o-acetylserine(thio)lyase (OASTL) and the content of cysteine (Cys), the rate-limiting enzyme and the first organic product of sulfur assimilation, were significantly increased in drought-stressed plants after SO₂ pretreatment, along with increases in other thiol-containing compounds, such as glutathione (GSH) and nonprotein thiol (NPT). Meanwhile, SO₂ pre-exposure induced a higher level of proline accumulation, with increased activity of proline synthase P5CS and decreased activity of proline dehydrogenase ProDH. Consistent with the changes in enzyme activity, their corresponding gene expression patterns were different after SO₂ treatment. Overall, the enhanced drought tolerance afforded by SO₂ might be related to the improvement of plant photosynthesis, antioxidant defense, sulfur assimilation and osmotic adjustment. These findings provide new insights into the role of SO₂ in plant adaptation to environmental stress.

Ammonia–Nitrate Mixture Dominated by NH4+–N Promoted Growth, Photosynthesis and Nutrient Accumulation in Pecan (Carya illinoinensis)

Although ammonia–nitrogen (NH4+–N) and nitrate–nitrogen (NO3−–N) are the two main forms of N absorbed and utilized by plants, the preferences of plants for these forms are still unclear. In this study, we analyzed the growth, photosynthesis, and nutrients of pecan under different NH4+:NO3− ratios (0/0, 0/100, 25/75, 50/50, 75/25, 100/0) by indoor aerosol incubation. The results showed that additions of different N forms promoted the growth and development of pecan seedlings. When NO3−–N was used as the sole N source, it significantly promoted the ground diameter growth of pecan and increased the leaf pigment content and photosynthetic rate. The NH4+:NO3− ratio of 75:25 and NH4+–N as the sole N source significantly increased the soluble sugars in stems and roots, starch in leaves, stems and roots, soluble protein in leaves and stems, and soluble phenols in stems and roots. Additionally, the NH4+:NO3− ratio of 75:25 increased plant height, leaf number, root soluble protein, and leaf soluble phenol contents. In conclusion, regarding the physiological aspects of pecan growth, pecans are more inclined to use NH4+–N. Considering that the NH4+–N as the only N source may lead to nutrient imbalance or even toxicity, the NH4+:NO3− ratio of 75:25 was most favorable for the growth and development of pecan seedlings.

Comparative Transcriptome Analysis of Two Aegilops tauschii with Contrasting Drought Tolerance by RNA-Seq

As the diploid progenitor of common wheat, Aegilops tauschii is considered to be a valuable resistance source to various biotic and abiotic stresses. However, little has been reported concerning the molecular mechanism of drought tolerance in Ae. tauschii. In this work, the drought tolerance of 155 Ae. tauschii accessions was firstly screened on the basis of their coleoptile lengths under simulated drought stress. Subsequently, two accessions (XJ002 and XJ098) with contrasting coleoptile lengths were selected and intensively analyzed on rate of water loss (RWL) as well as physiological characters, confirming the difference in drought tolerance at the seedling stage. Further, RNA-seq was utilized for global transcriptome profiling of the two accessions seedling leaves under drought stress conditions. A total of 6969 differentially expressed genes (DEGs) associated with drought tolerance were identified, and their functional annotations demonstrated that the stress response was mediated by pathways involving alpha-linolenic acid metabolism, starch and sucrose metabolism, peroxisome, mitogen-activated protein kinase (MAPK) signaling, carbon fixation in photosynthetic organisms, and glycerophospholipid metabolism. In addition, DEGs with obvious differences between the two accessions were intensively analyzed, indicating that the expression level of DEGs was basically in alignment with the physiological changes of Ae. tauschii under drought stress. The results not only shed fundamental light on the regulatory process of drought tolerance in Ae. tauschii, but also provide a new gene resource for improving the drought tolerance of common wheat.

The complete chloroplast genome of a mangrove Kandelia obovata Sheue, Liu & Yong

Kandelia obovata is a widely distributed species of mangrove in Eastern Asia. In this study, the complete chloroplast genome sequence of K. obovata was assembled and characterised from high-throughput sequencing data. The chloroplast genome was 168,244 bp in length, consisting of large single-copy (LSC) and small single-copy (SSC) regions of 94,869 bp and 20,088 bp, respectively, which were separated by a pair of 26,618 bp inverted repeat (IR) regions. The genome is predicted to contain 129 genes, including 84 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. The overall GC content of the genome is 34.6%. A phylogenetic tree reconstructed by 15 chloroplast genomes reveals that K. obovata is mostly related to Rhizophora stylosa.

Pseudomonas monteilii PN1: a great potential P-nitrophenol degrader with plant growth promoting traits under drought and saline-alkali stresses

OBJECTIVES

To evaluate Pseudomonas monteilii strain PN1 for the removal efficiency of P-nitrophenol (PNP) in soils and its growth promotion of maize (Zea mays L.) seedlings under drought and saline-alkali stress.

RESULTS

PN1 can survive in soils contaminated with PNP dosage between 90 and 155 mg/kg and considerably improved the removal PNP efficiency in soils. Drought and saline-alkali stress reduced maize seedling growth (root length, shoot height and dry or fresh weight) and improved the antioxidant enzyme activities and malondialdehyde (MDA) and proline (PRO) contents. However, maize seedlings treated with PN1 remarkably promoted their growth compared with the control. The reduction in antioxidant enzyme activities and MDA and PRO contents was significant. This result may be correlated to the increased tolerance of maize seedlings to drought and saline-alkali stress.

CONCLUSIONS

Application of P. monteilii PN1 can be an extremely useful approach for the development of bioinoculants in improving plant tolerance to several abiotic stresses and removing PNP in soils to ensure secure crop production.