![carbon stored as organic acid cam carbon stored as organic acid cam](https://blog.ucbmsh.org/wp-content/uploads/2021/05/Fig.-1.-Showing-CAM-Pathway.-Fig.-2.-Crassulaceae.png)
The column recoveries ranged from 100 to 104%. Cr-oxalate, Cr-malate, Cr-citrate, Cr-aconitate and Cr-quinate complexes and Cr-nitrate (pH 6.5) were chromatographically separated from Cr(VI) by applying linear gradient elution from 100% water to 100% NH4Cl at a flow rate of 1.5 ml min−1 in 10 min.
![carbon stored as organic acid cam carbon stored as organic acid cam](https://www.frontiersin.org/files/Articles/205704/fpls-07-01042-HTML/image_m/fpls-07-01042-g002.jpg)
To optimize the analytical procedure, Cr complexes were first synthesized from Cr-nitrate with the addition of an excess of ligand (90☌). Organic acids play a role in plants in providing redox equilibrium, supporting ionic gradients on membranes, and acidification of the extracellular medium.Ī new analytical procedure for the speciation of chromium (Cr) in plants by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was developed using a strong anion-exchange Mono Q column for the separation of the Cr species. Malonate is accumulated at high concentrations in legume plants. Glyoxylate, a product of either glycolate oxidase or isocitrate lyase, can be converted to oxalate. Trans-aconitate is formed from citrate or cis-aconitate, accumulation of hydroxycitrate can be linked to metabolism of 2-oxoglutarate, while 4-hydroxy-2-oxoglutarate can be formed from pyruvate and glyoxylate. They form the additional pools of fixed carbon and stabilize the TCA cycle. The secondary reactions, associated with the central metabolic pathways, in particularly with the TCA cycle, result in accumulation of other organic acids that are derived from the intermediates of the cycle. However, the intensity of reactions linked to the conversion of these compounds can cause preferential accumulation of other organic acids, e.g., fumarate or isocitrate, in higher concentrations than malate and citrate. This results in malate and citrate frequently being the most accumulated acids in plants. When redox level in the cell increases, e.g., in conditions of active photosynthesis, the tricarboxylic acid (TCA) cycle in mitochondria is transformed to a partial cycle supplying citrate for the synthesis of 2-oxoglutarate and glutamate (citrate valve), while malate is accumulated and participates in the redox balance in different cell compartments (via malate valve). Organic acids are synthesized in plants as a result of the incomplete oxidation of photosynthetic products and represent the stored pools of fixed carbon accumulated due to different transient times of conversion of carbon compounds in metabolic pathways.