Exploring the Involvement of the Alternative Respiratory Pathway in Pisum sativum L. Seed Germination

Abstract

Organic agriculture, recognized as a more sustainable agricultural system, strongly depends on the use of highly resilient genotypes. Seed resilience, with increased tolerance to germination that provide vigorous seedlings under environmental stresses, currently represents one of the most important agronomical traits. Seed germination involves the activation of several metabolic pathways, including cellular respiration. Alternative oxidase (AOX), a key enzyme in the alternative respiratory pathway, plays a crucial role in regulating cell reprogramming by controlling metabolic transitions related to the cellular redox state and the variable carbon balance. The involvement of the alternative respiratory pathway during germination was explored by analysis of PsAOX gene/protein expression. Seeds of four Pisum sativum L. cultivars (‘Respect-1′, ‘S134′, ‘G78′, and ‘S91′) were imbibed in sterile tap water for 16 h and metabolic parameters were measured by calorespirometry (heat and CO2 emission rates) in a multi-cell differential scanning calorimeter in isothermal mode at 25 °C. The involvement of PsAOX was evaluated by transcript quantification (PsAOX1, PsAOX2a, and PsAOX2b) through RT-qPCR, and by analyzing PsAOX expression through Western blot. The results demonstrate that cv. ‘S91′, characterized by a low germination rate, exhibited the lowest metabolic heat and CO2 emission rate. However, contrary to expectations, PsAOX transcript accumulation and PsAOX protein expression were significantly higher for ‘S91′ than for the other cultivars. These results indicate that higher levels of PsAOX (transcript and protein) could be linked to lower metabolic rates for embryo growth when seed germination is compromised.