Endogenous ureides are employed as a carbon source in Arabidopsis plants exposed to carbon starvation conditions.

Ureides, the degraded products of purine catabolism in Arabidopsis, have been shown to act as antioxidant and nitrogen sources. Herein we elucidate purine degraded metabolites as a carbon source using the Arabidopsis Atxdh1, Ataln, and Ataah knockout (KO) mutants vis-à-vis wild-type (WT) plants. Plants were grown under short-day conditions on agar plates containing half-strength MS medium with or without 1% sucrose. Notably, the absence of sucrose led to diminished biomass accumulation in both shoot and root tissues of the Atxdh1, Ataln, and Ataah mutants, while no such effect was observed in WT plants. Moreover, the application of sucrose resulted in a reduction of purine degradation metabolite levels, specifically xanthine and allantoin, predominantly within the roots of WT plants. Remarkably, an increase in proteins associated with the purine degradation pathway was observed in WT plants in the presence of sucrose. Lower glyoxylate levels in the roots but not in the shoot of the Atxdh1 mutant in comparison to WT, were observed under sucrose limitation, and improved by sucrose application in root, indicating that purine degradation provided glyoxylate in the root. Furthermore, the deficit of purine-degraded metabolites in the roots of mutants subjected to carbon starvation was partially mitigated through allantoin application. Collectively, these findings signify that under conditions of sucrose limitation and short-day growth, purines are primarily remobilized within the root system to augment the availability of ureides, serving as an additional carbon (as well as nitrogen) source to support plant growth.

Determination of ROS Generated by Arabidopsis Xanthine Dehydrogenase1 (AtXDH1) Using Nitroblue Tetrazolium (NBT) and 3,3'-Diaminobenzidine (DAP).

Plants generate reactive oxygen species (ROS) during different metabolic processes, which play an essential role in coordinating growth and response. ROS levels are sensitive to environmental stresses and are often used as a marker for stress in plants. While various methods can detect ROS changes, histochemical staining with nitroblue tetrazolium (NBT) and 3,3'-diaminobenzidine (DAB) is a popular method, though it has faced criticism. This staining method is advantageous as it enables both the quantification and localization of ROS and the identification of the enzymatic origin of ROS in plants, cellular compartments, or gels. In this protocol, we describe the use of NBT and DAP staining to detect ROS generation under different stresses such as nitrogen starvation, wounding, or UV-C. Additionally, we describe the use of NBT staining for detecting enzymatic generation of ROS in native and native SDS PAGE gels. Our protocol also outlines the separation and comparison of the origin of ROS generated by xanthine dehydrogenase1 (XDH1) using different substrates.