Nitrogen (N) is a central mineral nutrient essential for plant development and growth. It is usually scarcely found in soils, so the knowledge of the overall plant N metabolism deserves substantial attention. Polyamines (PAs) are N‐containing low‐molecular‐weight compounds of polycationic nature involved in essential processes all throughout the life of plants whereas nitric oxide (NO) is a gaseous free radical involved in signalling cascades related to many physiological events. PAs and NO share signalling functions and interact with each other in several biological functions, mainly in stress responses. Biosynthesis pathways of PAs and NO are overlapped; PAs induce NO formation, but it is still not completely defined whether PAs act as substrates, cofactors, or signals for promoting NO synthesis and also, which are the mechanisms involved in NO regulation of PAs metabolism. Polyamine levels are of vital importance in the regulation of the network of N‐metabolising pathways in plants, as they are components of the core of the overall N metabolism. In light of the importance of improving the efficiency of N uptake and distribution, it is time to elucidate the intricate relationship among N as a nutrient with PAs and NO as emerging signalling molecules. The close cooperation among these players in the whole N metabolism is an interesting target for the development of biotechnological tools for sustainable agriculture.
Cadmium is one of the most important contaminants and it induces severe plant growth restriction. In this study, we analyzed the metabolic changes associated with root growth restriction caused by cadmium in the early seminal root apex of wheat. Our study included two genotypes: the commercial variety ProINTA Federal (WT) and the PSARK::IPT (IPT) line which exhibit high‐grade yield performance under water deficit. Root tips of seedlings grown for 72 h without or with 10 μM CdCl2 (Cd‐WT and Cd‐IPT) were compared. Root length reduction was more severe in Cd‐WT than Cd‐IPT. Cd decreased superoxide dismutase activity in both lines and increased catalase activity only in the WT. In Cd‐IPT, ascorbate and guaiacol peroxidase activities raised compared to Cd‐WT. The hormonal homeostasis was altered by the metal, with significant decreases in abscisic acid, jasmonic acid, 12‐oxophytodienoic acid, gibberellins GA20, and GA7 levels. Increases in flavonoids and phenylamides were also found. Root growth impairment was not associated with a decrease in expansin (EXP) transcripts. On the contrary, TaEXPB8 expression increased in the WT treated by Cd. Our findings suggest that the line expressing the PSARK::IPT construction increased the homeostatic range to cope with Cd stress, which is visible by a lesser reduction of the root elongation compared to WT plants. The decline of root growth produced by Cd was associated with hormonal imbalance at the root apex level. We hypothesize that activation of phenolic secondary metabolism could enhance antioxidant defenses and contribute to cell wall reinforcement to deal with Cd toxicity.
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