Oxidative metabolism and the physiological age of seed potatoes are affected by increased α-linolenate content

doi:10.1034/j.1399-3054.2002.1160206.x

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Wiley InterScience

Physiologia Plantarum

Volume 116 Issue 2, Pages 172 - 185

Published Online: 30 Sep 2002

Published on behalf of the Scandinavian Society for Plant Physiology

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Oxidative metabolism and the physiological age of seed potatoes are affected by increased α-linolenate content

Vladimir Zabrouskov ^a , G.N. Mohan Kumar ^a , James P. Spychalla ^b,1 and N. Richard Knowles ^a, *

^a Department of Horticulture and Landscape Architecture, PO Box 646414, Washington State University, Pullman, WA 99164-6414, USA
^b Institute of Biological Chemistry, Washington State University, Pullman, WA 99164-6340, USA ^† Present address: James Spychalla Farms Inc., N3974 Hwy. 52, Antigo, WI 54409, USA

* Corresponding author, e-mail: rknowles@wsu.edu

ABSTRACT

The effects of high α-linolenate content on lipid peroxidation, oxidative stress and loss of plant growth potential during ageing of potato (Solanum tuberosum L.) seed-tubers was examined. Endoplasmic reticulum (FAD₃) and plastidal (FAD₇) 18:2 fatty acid desaturases were upregulated in potato (cv. Desiree), resulting in a 2-fold average increase in mol percentage 18:3 in the total lipid fraction across all transgenic clones. In double-transformed (FAD₃₊₇) tubers, high α-linolenate phenotype effected accelerated ageing, resulting in growth responses characteristic of older seed-tubers. Although respiration rates of wild-type (WT) and FAD₃₊₇ tubers were equal at 7 months of storage, rates had increased by 23% and 50% in WT and FAD₃₊₇ tubers, respectively, by 19 months of storage. Electrolyte leakage of tissue from 19-month-old FAD₃₊₇ tubers was significantly greater than that from WT tubers of the same age, indicating that the high α-linolenate phenotype was detrimental to membrane integrity during long-term storage. On average, indices of lipid peroxidation (malondialdehyde, ethane, C-6 aldehydes) were higher in older FAD₃₊₇ tubers, relative to WT tubers. Activities of glucose-6-phosphate dehydrogenase, peroxidase, glutathione reductase, ascorbate peroxidase and monodehydroascorbate reductase increased in tubers with advancing age and were higher, on average, in FAD₃₊₇ tubers. Dehydroascorbate reductase activity decreased with age, with no difference between transgenic and WT lines. Collectively, these results indicate that FAD₃₊₇ tubers underwent a higher degree of oxidative stress during ageing. The age-induced increase in respiration of FAD₃₊₇ tubers was at least partly a response to fuel increased free radical scavenging through the ascorbate-glutathione antioxidant pathway. By affecting the susceptibility of lipids to peroxidation, the degree of fatty acid unsaturation influenced the development of oxidative stress and the overall rate at which growth potential was lost from seed-tubers during ageing. Thus, oxidative stress plays an integral role in modulating the ageing process to affect growth potential from potato seed-tubers.