Metabolism‐induced free radical activity does not contribute significantly to loss of viability in moist‐stored recalcitrant seeds of contrasting species

Abstract

Because recalcitrant seeds are not desiccation-tolerant they must be stored moist. Their limited storage potential presents significant practical problems, but the cause of viability loss is not known. It has been suggested that a stress-induced metabolic imbalance can develop during storage that results in free-radical generation and consequent damage. To investigate this hypothesis, the presence of a stable free radical, lipid peroxidation and representative enzymatic and nonenzymatic protection mechanisms against oxidative attack were monitored in nondormant recalcitrant seeds during moist storage. A comparison was made between seeds of a short-lived subtropical species (Avicennia marina) and two longer-lived temperate species (Quercus robur and Castanea sativa). As a test of the hypothesis, seeds of both temperate species were held under conditions of elevated temperature and oxygen concentration to develop different rates of respiration during storage. The number of normal seedlings produced from seeds of the two temperate species declined during storage, but viability remained high, so effects of ageing were not confounded with an increasing proportion of dead seeds in the population. Under these conditions, lipid peroxidation changed little over the storage period, although there was evidence of accumulation of a stable free radical in Q. robur axes. However, this response was not affected by storage conditions that elevated respiration rates. In the shorter-lived A. marina seeds viability declined soon after the start of storage, but the significant increase in free radicals shown by EPR measurement was only evident when an increasing percentage of the seed population was no longer viable. Changes in the activity of scavenging enzymes and the concentration of antioxidants were time-dependent and not related to respiration rates. Therefore, in the present work, no consistent evidence was found to show that metabolism-induced free-radical activity was a significant contributing factor to pre-mortem deterioration in moist-stored recalcitrant seeds.

Atividade antioxidante e viabilidade de sementes de girassol após estresse hídrico e salino

“…Entretanto, esta regulação pode ser perdida se o estresse for mais severo, aumentando consideravelmente a produção de radicais livres que podem levar a uma cascata de eventos que inicia com a peroxidação de lipídeos, avançando para a degradação de membranas e morte celular (Greggains et al, 2000).…”

Ácido salicílico em sementes de calêndula (Calendula officinalis L.) sob diferentes estresses

“…Radicais livres são formados sob condições de estresse oxidativo bem como pelas reações normais da cadeia de transporte de elétrons, mas que são altamente reguladas Mazhoudi et al, 1997;Greggains et al, 2000), todavia esta regulação pode ser perdida se o estresse for mais severo aumentando consideravelmente a produção de radicais livres que podem levar a uma cascata de evento potentials, induced by mannitol (0; -0.3; -0.6; -0.9 and -1.2MPa) and one with different temperatures (20, 25, 30 e 35ºC).The salicylic acid treatment of 0,025 mM was positive for germination and the germination speed index of Calendula officinalis Marigold seeds under ideal conditions and water stress at the temperature of 35 C.…”

“…Index terms: systemic acquired resistance, water deficit, germination que começando com a peroxidação de lipídeos, avançam para degradação de membranas e para morte celular (Greggains et al, 2000). De acordo com Foyer et al (1997) o aumento nos oxidantes celulares pode levar a super expressão de genes de enzimas de desintoxicação como as superóxido dismutases (SOD) (Giannopolitis e Ries, 1977), catalase (CAT), peroxidase (PRX) e enzimas do ciclo ascorbato-glutationa (Sung e Jeng, 1994;Bailly et al, 1998) como parte de uma estratégia requerida para superar o estresse oxidativo (Foyer et al, 1997).…”

Physiological and cytological aspects of Inga vera subsp. affinis embryos during storage

“…Because recalcitrant seeds are not desiccationtolerant they must be stored moist (Greggains et al, 2000). However, even in moist conditions, their longevity is short, varying from a few weeks to a few months, depending on the species (Roberts and King, 1980a).…”