Oxidative Stress Results in Increased Sinks for Metabolic Energy during Aging and Sprouting of Potato Seed-Tubers

Abstract

Glutathione-mediated free-radical-scavenging and plasma membrane ATPase activities increase as sinks for metabolic energy with advancing tuber age. Plasma membrane ATPase activity from 19-month-old tubers was 77% higher than that from 7-month-old tubers throughout sprouting. The higher activity was not attended by an increase in the amount of ATPase per unit plasma membrane protein.Concentrations of oxidized (CSSC) and reduced glutathione more than doubled as tuber age advanced from 6 to 30 months, but the proportion of GSSG to total glutathione remained constant with age. l h e activity of glutathione transferase, an enzyme that catabolizes lipidhydroperoxides, increased by 44 and 205% on a fresh weight and protein basis, respectively, as tubers aged from 6 to 30 months. Glutathione reductase activity also increased with advancing age, by 90% on a fresh weight basis and 305% on a protein basis. Older tubers had more glutathione reductase per unit of soluble and mitochondrial protein. The age-induced increase in cytosolic glutathione transferase activity was likely due to increased availability of lipid-hydroperoxides and/or a positive effector. Synthesis of glutathione requires ATP, and the increased reduction of CSSC resulting from catalysis of lipidhydroperoxides is NADPH-dependent. Thus, increased plasma membrane ATPase and glutathione-mediated free-radical-scavenging activities likely constitute substantial sinks for ATP in older tubers prior to and during sprouting. lncreased oxidative stress and loss in membrane integrity are central features of aging that undoubtedly contribute to the enhanced respiration of sprouting older tubers.Potato (Solanum tuberosum L.) seed-tubers provide a model system for studies of the metabolic processes associated with aging of plant tissues in general and vegetative propagules in particular. Russet Burbank seed-tubers maintain their viability for about 3 years in cold storage (4"C, 95% RH); however, vigor and growth potential of tuber meristems depend on age. As tubers advance in age beyond about 7 months, apical dominance and plant vigor gradually decline, resulting in the production of many shoots per tuber, each with low specific leaf area and sparse root systems (Mikitzel and Knowles, 1990; Kumar and Knowles, 1993a). Paradoxically, older tubers have substantially higher rates of fully coupled, Cyt-mediated respiration than younger tubers at similar stages of sprout development (Kumar and Knowles, 1996). This greater ATP production by sprouting older tubers is required to '

Decreased ascorbic acid levels and brown core development in pears (Pyrus communis L. cv. Conference)

“…Potential ATP sinks during aging are ATPases in the plasmalemma that become leaky with advanced age. Older tubers respire with a faster rate to achieve the same AEC (Kumar and Knowles 1996a,b). In the case of pears stored in CA, respiration cannot be accelerated due to the limiting oxygen concentration in the storage room.…”

“…Longer stored tubers have a substantially higher respiration rate during the initial stage of sprouting, compared to younger tubers (Kumar and Knowles 1996a), which is required to equal the higher ATP consumption of older tubers. Since increased free‐radical‐mediated peroxidation of fatty acids occurs during tuber aging, glutathione‐mediated free‐radical scavenging is sumpposed to be an ATP sink (Kumar and Knowles 1996b). The ascorbate‐glutathione cycle, which is important in the defence against hydrogen peroxide and free radicals, is present in plant mitochondria and peroxisomes.…”

Age-induced loss of wound-healing ability in potato tubers is partly regulated by ABA

“…The blot was developed with alkaline phosphatase-conjugated goat secondary antibody to rabbit and visualized by incubating in NaHCO 3 buVer (100 mM, pH 9.8) containing 1 mM MgCl 2 , 5.2 M 5-bromo-4-chloro-indolyl-phosphate and 9.2 M nitroblue tetrazolium (Kumar and Knowles 1996).…”

Impact of selenium enrichment on seed potato tubers

“…Moreover, respiration rate of seed tuber depends on how far sprouting has progressed Knowles 1989a, Kumar andKnowles 1996). During prolonged storage, increased peroxidative damage to the amyloplast membrane Knowles 1989, Kumar andKnowles 1993) and enhanced membrane permeability lead to senescent sweetening of potato tubers (Spychalla and Desborough 1990).…”