Differential metabolic rearrangements in the roots and leaves of Cicer arietinum caused by single or double nitrate and/or phosphate deficiencies

Nitrate (NO₃ ^- ) and phosphate (Pi) deficiencies are the major constraints for chickpea productivity, significantly impacting global food security. However, excessive fertilization is expensive and can also lead to environmental pollution. Therefore, there is an urgent need to develop chickpea cultivars that are able to grow on soils deficient in both NO₃ ^- and Pi. This study focused on the identification of key NO₃ ^- and/or Pi starvation-responsive metabolic pathways in the leaves and roots of chickpea grown under single and double nutrient deficiencies of NO₃ ^- and Pi, in comparison with nutrient-sufficient conditions. A global metabolite analysis revealed organ-specific differences in the metabolic adaptation to nutrient deficiencies. Moreover, we found stronger adaptive responses in the roots and leaves to any single than combined nutrient-deficient stresses. For example, chickpea enhanced the allocation of carbon among nitrogen-rich amino acids (AAs) and increased the production of organic acids in roots under NO₃ ^- deficiency, whereas this adaptive response was not found under double nutrient deficiency. Nitrogen remobilization through the transport of AAs from leaves to roots was greater under NO₃ ^- deficiency than double nutrient deficiency conditions. Glucose-6-phosphate and fructose-6-phosphate accumulated in the roots under single nutrient deficiencies, but not under double nutrient deficiency, and higher glycolytic pathway activities were observed in both roots and leaves under single nutrient deficiency than double nutrient deficiency. Hence, the simultaneous deficiency generated a unique profile of metabolic changes that could not be simply described as the result of the combined deficiencies of the two nutrients.

Metabolite Profiling in Arabidopsisthaliana with Moderately Impaired Photorespiration Reveals Novel Metabolic Links and Compensatory Mechanisms of Photorespiration

Photorespiration is an integral component of plant primary metabolism. Accordingly, it has been often observed that impairing the photorespiratory flux negatively impacts other cellular processes. In this study, the metabolic acclimation of the Arabidopsisthaliana wild type was compared with the hydroxypyruvate reductase 1 (HPR1; hpr1) mutant, displaying only a moderately reduced photorespiratory flux. Plants were analyzed during development and under varying photoperiods with a combination of non-targeted and targeted metabolome analysis, as well as ¹³C- and ¹⁴C-labeling approaches. The results showed that HPR1 deficiency is more critical for photorespiration during the vegetative compared to the regenerative growth phase. A shorter photoperiod seems to slowdown the photorespiratory metabolite conversion mostly at the glycerate kinase and glycine decarboxylase steps compared to long days. It is demonstrated that even a moderate impairment of photorespiration severely reduces the leaf-carbohydrate status and impacts on sulfur metabolism. Isotope labeling approaches revealed an increased CO₂ release from hpr1 leaves, most likely occurring from enhanced non-enzymatic 3-hydroxypyruvate decarboxylation and a higher flux from serine towards ethanolamine through serine decarboxylase. Collectively, the study provides evidence that the moderate hpr1 mutant is an excellent tool to unravel the underlying mechanisms governing the regulation of metabolic linkages of photorespiration with plant primary metabolism.

On the role of the plant mitochondrial thioredoxin system during abiotic stress

Thiol-disulfide redox exchanges are widely distributed modifications of great importance for metabolic regulation in living cells. In general, the formation of disulfide bonds is controlled by thioredoxins (TRXs), ubiquitous proteins with two redox-active cysteine residues separated by a pair of amino acids. While the function of plastidial TRXs has been extensively studied, the role of the mitochondrial TRX system is much less well understood. Recent studies have demonstrated that the mitochondrial TRXs are required for the proper functioning of the major metabolic pathways, including stomatal function and antioxidant metabolism under sub-optimal conditions including drought and salinity. Furthermore, inactivation of mitochondrial TRX system leads to metabolite adjustments of both primary and secondary metabolism following drought episodes in arabidopsis, and makes the plants more resistant to salt stress. Here we discuss the implications of these findings, which clearly open up several research avenues to achieve a full understanding of the redox control of metabolism under environmental constraining conditions.

Photosynthetic and metabolic acclimation to repeated drought events play key roles in drought tolerance in coffee

Over the last decades, most information on the mechanisms underlying tolerance to drought has been gained by considering this stress as a single event that happens just once in the life of a plant, in contrast to what occurs under natural conditions where recurrent drought episodes are the rule. Here we explored mechanisms of drought tolerance in coffee (Coffea canephora) plants from a broader perspective, integrating key aspects of plant physiology and biochemistry. We show that plants exposed to multiple drought events displayed higher photosynthetic rates, which were largely accounted for by biochemical rather than diffusive or hydraulic factors, than those submitted to drought for the first time. Indeed, these plants displayed higher activities of RuBisCO and other enzymes associated with carbon and antioxidant metabolism. Acclimation to multiple drought events involved the expression of trainable genes related to drought tolerance and was also associated with a deep metabolite reprogramming with concordant alterations in central metabolic processes such as respiration and photorespiration. Our results demonstrate that plants exposed to multiple drought cycles can develop a differential acclimation that potentiates their defence mechanisms, allowing them to be kept in an 'alert state' to successfully cope with further drought events.