The auxin conjugate indole-3-acetyl-aspartate affects responses to cadmium and salt stress in Pisum sativum L.

Abstract The synthesis of IAA-amino acid conjugates is one of the crucial regulatory mechanisms for the control of auxin activity during physiological and pathophysiological responses. Indole-3-acetyl-aspartate (IAA-Asp) is a low molecular weight amide conjugate that predominates in pea ( Pisum sativum L.) tissues. IAA-Asp acts as an intermediate during the auxin degradation pathway. However, some recent investigations suggest a direct signaling function of this conjugate in various processes. In this study, we examine the effect of 100 μM IAA-Asp alone and in combination with salt stress (160 mM NaCl) or heavy metal stress (250 μM CdCl 2 ) on H 2 O 2 concentration, protein carbonylation as well as catalase and ascorbate (APX) and guaiacol peroxidase (GPX) activities in 7-day-old pea seedlings. As revealed by spectrophotometric analyses, IAA-Asp increased the carbonylated protein level and reduced the H 2 O 2 concentration. Moreover, IAA-aspartate potentiated the effect of both Cd 2+ ions and NaCl on the H 2 O 2 level. The enzymatic activities (catalase and peroxidases) were examined using spectrophotometric and native-PAGE assays. IAA-Asp alone did not affect catalase activity, whereas the two peroxidases were regulated differently. IAA-Asp reduced the APX activity during 48 h cultivation. APX activity was potentiated by IAA-Asp + NaCl after 48 h. Guaiacol peroxidase activity was diminished by all tested compounds. Based on these results, we suggest that IAA-Asp can directly and specifically affect the pea responses to abiotic stress.