Germination of Pisum sativum L. Seeds Is Associated with the Alternative Respiratory Pathway

SIMPLE SUMMARY: Germination is a complex process that begins with rapid water uptake and a marked increase in oxygen consumption rate from initiation of aerobic respiration. The mitochondrial electron transport chain (ETC) in plants is a critical cellular respiratory system that has two different pathways: the cytochrome oxidase (COX) pathway and the alternative oxidase (AOX) pathway. The AOX enzyme plays a crucial role in energy production as well as in stress response. An AOX gene family study in Pisum sativum revealed three AOX genes (PsAOX). Transcript accumulation analysis revealed the involvement of all three PsAOX members in pea seed germination, albeit with high genotype variation. Calorespirometry was used to monitor metabolic changes during a germination trial using inhibitors of both respiratory pathways and proved to be useful for distinguishing differing respiratory activity in different cultivars. This study offers valuable insights into the AOX family composition in P. sativum, as well as their role during seed germination. ABSTRACT: The alternative oxidase (AOX) is a ubiquinol oxidase with a crucial role in the mitochondrial alternative respiratory pathway, which is associated with various processes in plants. In this study, the activity of AOX in pea seed germination was determined in two pea cultivars, ‘Maravilha d’América’ (MA) and ‘Torta de Quebrar’ (TQ), during a germination trial using cytochrome oxidase (COX) and AOX inhibitors [rotenone (RT) and salicylic hydroxamic acid (SHAM), respectively]. Calorespirometry was used to assess respiratory changes during germination. In both cultivars, SHAM had a greater inhibitory effect on germination than RT, demonstrating the involvement of AOX in germination. Although calorespirometry did not provide direct information on the involvement of the alternative pathway in seed germination, this methodology was valuable for distinguishing cultivars. To gain deeper insights into the role of AOX in seed germination, the AOX gene family was characterized, and the gene expression pattern was evaluated. Three PsAOX members were identified—PsAOX1, PsAOX2a and PsAOX2b—and their expression revealed a marked genotype effect. This study emphasizes the importance of AOX in seed germination, contributing to the understanding of the role of the alternative respiratory pathway in plants.