Osmotic Adjustment and Antioxidant System Regulated by Nitrogen Deposition Improve Photosynthetic and Growth Performance and Alleviate Oxidative Damage in Dwarf Bamboo Under Drought Stress

Melatonin imparts tolerance to combined drought and high-temperature stresses in tomato through osmotic adjustment and ABA accumulation

In recent years, environmental stresses viz., drought and high-temperature negatively impacts the tomato growth, yield and quality. The effects of combined drought and high-temperature (HT) stresses during the flowering stage were investigated. The main objective was to assess the effects of foliar spray of melatonin under both individual and combined drought and HT stresses at the flowering stage. Drought stress was imposed by withholding irrigation, whereas HT stress was imposed by exposing the plants to an ambient temperature (AT)+5°C temperature. The drought+HT stress was imposed by exposing the plants to drought first, followed by exposure to AT+5°C temperature. The duration of individual and combined drought or HT stress was 10 days. The results showed that drought+HT stress had a significant negative effect compared with individual drought or HT stress alone. However, spraying 100 µM melatonin on the plants challenged with individual or combined drought and HT stress showed a significant increase in total chlorophyll content [drought: 16%, HT: 14%, and drought+HT: 11%], Fv/Fm [drought: 16%, HT: 15%, and drought+HT: 13%], relative water content [drought: 10%, HT: 2%, and drought+HT: 8%], and proline [drought: 26%, HT: 17%, and drought+HT: 14%] compared with their respective stress control. Additionally, melatonin positively influenced the stomatal and trichome characteristics compared with stress control plants. Also, the osmotic adjustment was found to be significantly increased in the melatonin-sprayed plants, which, in turn, resulted in an increased number of fruits, fruit set percentage, and fruit yield. Moreover, melatonin spray also enhanced the quality of fruits through increased lycopene content, carotenoid content, titratable acidity, and ascorbic acid content, compared with the stress control. Overall, this study highlights the usefulness of melatonin in effectively mitigating the negative effects of drought, HT, and drought+HT stress, thus leading to an increased drought and HT stress tolerance in tomato.

Overexpression of PsAMT1.2 in poplar enhances nitrogen utilization and resistance to drought stress

Ammonium is an important form of inorganic nitrogen, which is essential for plant growth and development, and the uptake of ammonium is mediated by different members of ammonium transporters (AMTs). It is reported that PsAMT1.2 is specially expressed in the root of poplar, and the overexpression of PsAMT1.2 could improve plant growth and the salt tolerance of poplar. However, the role of AMTs in plant drought and low nitrogen (LN) resistance remains unclear. To understand the role of PsAMT1.2 in drought and LN tolerance, the response of PsAMT1.2-overexpression poplar to polyethylene glycol (PEG)-simulated drought stress (5% PEG) under LN (0.001 mM NH4NO3) and moderate nitrogen (0.5 mM NH4NO3) conditions was investigated. The PsAMT1.2-overexpression poplar showed better growth with increased stem increment, net photosynthetic rate, chlorophyll content, root length, root area, average root diameter and root volume under drought and/or LN stress compared with the wild type (WT). Meanwhile, the content of malondialdehyde significantly decreased, and the activities of superoxide dismutase and catalase significantly increased in the roots and leaves of PsAMT1.2-overexpression poplar compared with WT. The content of NH4+ and NO2- in the roots and leaves of PsAMT1.2-overexpression poplar was increased, and nitrogen metabolism-related genes, such as GS1.3, GS2, Fd-GOGAT and NADH-GOGAT, were significantly upregulated in the roots and/or leaves of PsAMT1.2-overexpression poplar compared with WT under drought and LN stress. The result of this study would be helpful for understanding the function of PsAMT1.2 in plant drought and LN tolerance and also provides a new insight into improving the drought and LN tolerance of Populus at the molecular level.

Whole plant response of Pongamia pinnata to drought stress tolerance revealed by morpho-physiological, biochemical and transcriptome analysis

BACKGROUND

Pongamia is considered an important biofuel species worldwide. Drought stress in the early growth stages of Pongamia influences negatively on the germination and seedling development. Due to lack of cultivar stability under drought stress conditions, establishment of successful plantation in drought hit areas becomes a major problem. To address this issue, drought stress response of four Pongamia genotypes was studied at morphological, physio-chemical and transcriptome levels.

METHODS AND RESULTS

Drought stress was levied by limiting water for 15 days on three months old seedlings of four genotypes. A significant effect of water stress was observed on the traits considered. The genotype NRCP25 exhibited superior morpho-physiological, biochemical drought responses. Also, the genotype had higher root length, photosynthetic pigments, higher antioxidant enzymes and solute accumulation compared to other genotypes. In addition, transcript profiling of selected drought responsive candidate genes such as trehalose phosphate synthase 1 (TPS1), abscisic acid responsive elements-binding protein 2 (ABF2-2), heat shock protein 17 (HSP 17 kDa), tonoplast intrinsic protein 1 (TIP 1-2), zinc finger homeodomain protein 2 (ZFP 2), and xyloglucan endotransglucolase 13 (XET 13) showed only up-regulation in NRCP25. Further, the transcriptome responses are in line with key physio-chemical responses exhibited by NRCP25 for drought tolerance.

CONCLUSIONS

As of now, there are no systematic studies on Pongamia drought stress tolerance; therefore this study offers a comprehensive understanding of whole plant drought stress responsiveness of Pongamia. Moreover, the results support important putative trait indices with potential candidate genes for drought tolerance improvement of Pongamia.