Search Results (2)

Gene expression and phytohormone contents were measured in response to elevating ascorbate in the absence of other confounding stimuli such as high light and abiotic stresses. Young Arabidopsis plants were treated with 25 mM solutions of l-galactose pathway intermediates l-galactose (l-gal) or l-galactono-1,4-lactone (l-galL), as well as L-ascorbic acid (AsA), with 25 mM glucose used as control. Feeding increased rosette AsA 2- to 4-fold but there was little change in AsA biosynthetic gene transcripts. Of the ascorbate recycling genes, only Dehydroascorbate reductase 1 expression was increased. Some known regulatory genes displayed increased expression and included ANAC019, ANAC072, ATHB12, ZAT10 and ZAT12. Investigation of the ANAC019/ANAC072/ATHB12 gene regulatory network revealed a high proportion of ABA regulated genes. Measurement of a subset of jasmonate, ABA, auxin (IAA) and salicylic acid compounds revealed consistent increases in ABA (up to 4.2-fold) and phaseic acid (PA; up to 5-fold), and less consistently certain jasmonates, IAA, but no change in salicylic acid levels. Increased ABA is likely due to increased transcripts for the ABA biosynthetic gene NCED3. There were also smaller increases in transcripts for transcription factors ATHB7, ERD1, and ABF3. These results provide insights into how increasing AsA content can mediate increased abiotic stress tolerance. Full article

Continuous light (CL) or a predominant nitrogen supply as ammonium (NH₄⁺) can induce leaf chlorosis and inhibit plant growth. The similarity in injuries caused by CL and NH₄⁺ suggests involvement of overlapping mechanisms in plant responses to these conditions; however, these mechanisms are poorly understood. We addressed this topic by conducting full factorial experiments with tomato plants to investigate the effects of NO₃⁻ or NH₄⁺ supply under diurnal light (DL) or CL. We used plants at ages of 26 and 15 days after sowing to initiate the treatments, and we modulated the intensity of the stress induced by CL and an exclusive NH₄⁺ supply from mild to strong. Under DL, we also studied the effect of nitrogen (N) deficiency and mixed application of NO₃⁻ and NH₄⁺. Under strong stress, CL and exclusive NH₄⁺ supply synergistically inhibited plant growth and reduced chlorophyll content. Under mild stress, when no synergetic effect between CL and NH₄⁺ was apparent on plant growth and chlorophyll content, we found a synergetic effect of CL and NH₄⁺ on the accumulation of several plant stress hormones, with an especially strong effect for jasmonic acid (JA) and 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, in xylem sap. This modulation of the hormonal composition suggests a potential role for these plant hormones in plant growth responses to the combined application of CL and NH₄⁺. No synergetic effect was observed between CL and NH₄⁺ for the accumulation of soluble carbohydrates or of mineral ions, indicating that these plant traits are less sensitive than the modulation of hormonal composition in xylem sap to the combined CL and NH₄⁺ application. Under diurnal light, NH₄⁺ did not affect the hormonal composition of xylem sap; however, N deficiency strongly increased the concentrations of phaseic acid (PA), JA, and salicylic acid (SA), indicating that decreased N concentration rather than the presence of NO₃⁻ or NH₄⁺ in the nutrient solution drives the hormone composition of the xylem sap. In conclusion, N deficiency or a combined application of CL and NH₄⁺ induced the accumulation of JA in xylem sap. This accumulation, in combination with other plant hormones, defines the specific plant response to stress conditions. Full article