Function of the ascorbate-glutathione cycle in aged sunflower seeds

Abstract

duvilla, C. J. 1996. Functioti of the ascorbate-glutathione cycle in aged sunflower seeds. -Physiol, Plant. 96: 543-550,The function of the ascorbate-glutathione (AsA/GSH) cycle was analyzed in seeds of sunflower (Helianthus annuus L. cv. Peredovik) subjected to accelerated ageing at 43°C and 75% relative humidity for 1 to 11 days. The study was performed using dry seeds and seeds hydrated by imbibition in distilled water for 4 h at 25°C. Lipid peroxidation was also determined by measuring the malondialdehyde (MDA) level. As the ageing period increased, a progi'essive loss of seed viability became increasingly evident. Even though high levels of MDA were detected, the MDA level did not change during accelerated ageing, suggesting that lipid peroxidation might occur to some extent, the study of the ascorbate/glutathione {.4sA/GSH) cycle revealed that the GSH system is the major detoxifying mechanism in both dry and imbibed sunflower seeds. The GSH system is mainly located in the embryo, and its protective role is mediated by reactions that consume the GSH pool and, thereby, minimize the increase of the oxidized form (GSSG). Seed imbibition activates cellular metabolism and allows some antioxidant enzymes like glutathione reductase (EC 1.6.4.2) to^ act upon toxic agents. These reactions provide a reducing status, so that repair of damage becomes possible. However, prolonged ageing conditions (II days) restilt in an irreversible damage, as evidenced by tlie appem'ance of dead seeds when the germination period ended. Multiple regression analysis revealed the effectiveness of the GSH system in aged seeds, especially upon imbibition and until the AsA/GSH cycle became completely functional.

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

“…For example, a decline in total glutathione has previously been reported in stressed recalcitrant seeds of Aesculus hippocastanum and Acer pseudoplatanus (Hendry et al, 1996) and ageing in sunflower seeds led to a decrease in viability and total glutathione (De Paula et al, 1996). This, coupled to the apparent absence of glutathione in short-lived A. marina, suggests that further study of glutathione in other species might be worthwhile.…”

Free Radicals and Antioxidant System in Seed Biology

“…The antioxidant ascorbate system reported to play an important role in embryogenesis and cell growth [41,85]. Ascorbate content proposed to inluence cell growth by modulating the expression of genes involved in hormonal signaling pathways [96].…”

“…Glutathione an important water-soluble antioxidant and is synthesized from the amino acids glycine, glutamate, and cysteine, which directly scavenges ROS such as lipid peroxides, and also plays a vital role in xenobiotic detoxiication [85][86][87][88]. Research suggests that glutathione and vitamin C work interactively to quench free radicals and that they have a sparing efect upon each other [85][86][87]. Glutathione peroxidases (GPX) may also catalyze the reduction of H 2 O 2 and hydroperoxides [85][86][87][88].…”

“…Research suggests that glutathione and vitamin C work interactively to quench free radicals and that they have a sparing efect upon each other [85][86][87]. Glutathione peroxidases (GPX) may also catalyze the reduction of H 2 O 2 and hydroperoxides [85][86][87][88]. Polyphenol oxidase (PPO), the function of this antioxidant system is to scavenge the toxic radicals produced during oxidative stress and thus help the plants to survive through such conditions.…”

“…These enzymes also participate in the regeneration of the powerful antioxidants such as reduced glutathione (GSH), ascorbic acid (vitamin C), and α-tocopherol (vitamin E) (Figure 1). Glutathione an important water-soluble antioxidant and is synthesized from the amino acids glycine, glutamate, and cysteine, which directly scavenges ROS such as lipid peroxides, and also plays a vital role in xenobiotic detoxiication [85][86][87][88]. Research suggests that glutathione and vitamin C work interactively to quench free radicals and that they have a sparing efect upon each other [85][86][87].…”