Metabolite Profile of Xylem Sap in Cotton Seedlings Is Changed by K Deficiency

Abstract

Xylem sap, belonging to the plant apoplast, not only provides plant tissues with inorganic and organic substances but also facilitates communication between the roots and the leaves and coordinates their development. This study investigated the effects of potassium (K) deficiency on the morphology and the physiology of cotton seedlings as well as pH, mineral nutrient contents, and metabolites of xylem sap. In particular, we compared changes in root–shoot communication under low K (LK) and normal K (NK, control) levels. Compared to control, LK stress significantly decreased seedling biomass (leaf, stem, and root dry weight; stem and root length; root surface area and root volume) and the levels of K, Na (sodium), Mg (magnesium), Fe (iron), and Zn (zinc) in xylem sap. A total of 82 metabolites in sap analyzed by high-performance liquid chromatography–tandem mass spectrometry (HPLC–MS/MS) showed significant differences between the two conditions; among these, 38 were up-regulated more than 2-fold, while the others were down-regulated less than 0.5-fold. In particular, several metabolites found in the cell membrane including three cholines (glycerophosphatecholine, 2-hexenylcholine, and caproylcholine) and desglucocoroloside and others such as malondialdehyde, α-amino acids and derivatives, sucrose, and sugar alcohol significantly increased under LK stress, indicating that cell membranes were damaged and protein metabolism was abnormal. It is worth noting that glycerophosphocholine was up-regulated 29-fold under LK stress, indicating that it can be used as an important signal of root–shoot communication. Furthermore, in pathway analyses, 26 metabolites were matched to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways; L-aspartic acid, which was associated with 10 KEGG pathways, was the most involved metabolite. Overall, K deficiency reduced the antioxidant capacity of cotton seedlings and led to a metabolic disorder including elevated levels of primary metabolites and inhibited production of secondary metabolites. This eventually resulted in decreased biomass of cotton seedlings under LK stress. This study lays a solid foundation for further research on targeted metabolites and signal substances in the xylem sap of cotton plants exposed to K deficiency.

Integrated transcriptomic and metabolomic analyses reveal key metabolic pathways in response to potassium deficiency in coconut (Cocos nucifera L.) seedlings

“…This indicates that low-K + stress significantly reduced seedling biomass. In green plants, photosynthesis is an important process that provides the necessary energy sources for metabolism ( Chen et al, 2015 ; Zhang et al., 2020 ). Low-K + stress inhibits the photosynthetic activity of plants, leading to slower metabolism, thus affecting plant growth and development ( Kanai et al., 2011 ; Amanullah.…”

“…Metabolomic analysis is used to detect metabolites in cells or tissues, study the synthesis of all or some metabolites, and elucidate their decomposition or transformation principles ( Hall, 2011 ; Zhang et al., 2020 ). Abiotic stress can lead to metabolic disorders in plants ( Meena et al., 2017 ).…”

“…(2015) studied the metabolic response of tomato leaves and roots to nitrogen (N), phosphorus (P), and K deficiency and found that nutrient deficiency affected plant amino acid metabolism and energy production. Zhang et al. (2020) discovered that α-amino acids and their derivatives, sucrose, and sugar alcohols were significantly increased in cotton seedlings under low-K stress and reflected as damaged cell membranes and abnormal protein metabolism.…”

Utilization of Secondary Metabolites in Cotton Production

“…Nutrient deficiency is another kind of abiotic stress, and Ref. [85] showed that K deficiency reduced the antioxidant capacity of cotton seedlings and resulted in a metabolic disorder characterized by elevated levels of primary metabolites and reduced production of secondary metabolites. The results were from an analysis of xylem sap.…”

Transcriptome Analysis of Sweet Potato Responses To Potassium Deficiency

“…K + is involved in multiple abiotic and biotic stresses [18,19,20]. K + transport participates in abiotic stress responses; the KT/HAK/KUP family genes are differentially responsive to drought and salt stresses [21,22].…”