Strategies to Apply Water-Deficit Stress: Similarities and Disparities at the Whole Plant Metabolism Level in Medicago truncatula

Abstract

Water-deficit stresses such as drought and salinity are the most important factors limiting crop productivity. Hence, understanding the plant responses to these stresses is key for the improvement of their tolerance and yield. In this study M. truncatula plants were subjected to 250 mM NaCl as well as reduced irrigation (No-W) and 250 g/L polyethylene glycol (PEG)-6000 to induce salinity and drought stress, respectively, provoking a drop to −1.7 MPa in leaf water potential. The whole plant physiology and metabolism was explored by characterizing the stress responses at root, phloem sap and leaf organ level. PEG treatment led to some typical responses of plants to drought stress, but in addition to PEG uptake, an important impairment of nutrient uptake and a different regulation of carbon metabolism could be observed compared to No-W plants. No-W plants showed an important redistribution of antioxidants and assimilates to the root tissue, with a distinctive increase in root proline degradation and alkaline invertase activity. On the contrary, salinity provoked an increase in leaf starch and isocitrate dehydrogenase activity, suggesting key roles in the plant response to this stress. Overall, results suggest higher protection of salt-stressed shoots and non-irrigated roots through different mechanisms, including the regulation of proline and carbon metabolism, while discarding PEG as safe mimicker of drought. This raises the need to understand the effect at the whole plant level of the different strategies employed to apply water-deficit stress.

Melatonin improves drought stress tolerance of pepper (Capsicum annuum) plants via upregulating nitrogen metabolism

“…The accumulation and synthesis of soluble compounds, such as amino acids, particularly proline and soluble sugars, control osmoregulation during drought (Casta ñeda and González 2021). The results of current study showed that both free amino acid and proline concentrations increased in response to drought, which is in agreement with prior research conducted by Du et al (2020b) and Cao et al (2022). This finding supports the notion that increased accumulation of free amino acids and proline is a common response of plants to water deficit conditions.…”

“…The activities of nitrogen metabolism-related enzymes significantly increased when exogenous melatonin (MT) was applied to pepper plants under drought conditions in this study. These findings are consistent with previous research, which has shown that exogenous MT can help to maintain a consistent level of nitrogen assimilation by upregulating significant enzyme activities and offsetting the negative effects of drought on these essential enzyme activities in nitrogen metabolism + (Cao et al 2022). Inorganic N forms such as NH 4 and NO 3…”

“…Drought-induced physiological abnormalities unavoidably influence the synthesis, breakdown and metabolism of nitrogenous substances (Cao et al 2022). Overall, this may result in a shortage of the substrate needed by enzymes involved in nitrogen metabolism, which could explain why those enzyme activities declined in this study under drought conditions.…”

“…Drought stress dramatically lowers the soil water potential, which prevents the delivery of nitrogen (N) to the root surface, slows down root growth and significantly limits the available surface area of the root for nutrient absorption (Wang et al 2019;Cao et al 2022). Also, metabolic abnormalities brought about by a water shortage in the plant influence the synthesis, breakdown and metabolism of nitrogenous substances in plants (Ozturk et al 2021).…”

Evaluation of the Morpho-Physiological, Biochemical and Molecular Responses of Contrasting Medicago truncatula Lines under Water Deficit Stress

“…Hence, the identification of these compounds provides a promising connecting link that could bridge the gap between genotype and morpho-physiological traits. As osmotic regulating substances, soluble sugars and soluble protein content are considered as important indicators of the physiological status of plants related to drought tolerance [17,18]. Genes regulating the levels of osmoprotectants are highly stress-responsive and were among the first stressinducible transcripts reported in the literature [19].…”