PLANT PHYSIOLOGY , Vol 102, Issue 1 115-124, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Changes in Lipid Peroxidation and Lipolytic and Free-Radical Scavenging Enzyme Activities during Aging and Sprouting of Potato (Solanum tuberosum) Seed-Tubers
GNM. Kumar and N. R. Knowles
Department of Plant Science, 4-10 Agriculture/Forestry Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2P5
Previous research has shown that cell membranes of potato (Solanum
tuberosum L. cv Russet Burbank) seed-tubers lose integrity between 7 and 26
months of storage (4[deg]C, 95% relative humidity), and this loss coincides
with a significant decrease in growth potential. The age-induced decline in
membrane integrity is apparently due to increased peroxidative damage of
membrane lipids. Malondialdehyde (MDA) and ethane concentrations (sensitive
markers of lipid peroxidation and membrane damage) increased in seed-tuber
tissues with advancing age. Moreover, in vivo ethane production from discs
of cortex tissue from 13- and 25-month-old seed-tubers was 87% greater (on
average) than that from discs from 1-month-old tubers. Calcium suppressed
ethane production from all ages of tissue discs, and the effect was
concentration dependent. Linoleic acid enhanced ethane production from 5-
and 17-month-old tubers by 61 and 228%, respectively, suggesting that older
tissue may contain a higher free-radical (FR) titer and/or lower free
polyunsaturated fatty acid content. In addition, throughout plant
establishment, the internal ethane concentration of older seed-tubers was
54% higher than that of younger seed-tubers. MDA concentration of tuber
tissue declined by about 65% during the initial 7 months of storage and
then increased 267% as tuber age advanced to 30 months. The age-induced
trend in tuber reducing sugar concentration was similar to that of MDA, and
the two were linearly correlated. The age-dependent increase in reducing
sugars may thus reflect peroxidative degeneration of the amyloplast
membrane, leading to increased starch hydrolysis. Compared with 5-month-old
seed tubers, 17- and 29-month-old seed-tubers had significantly higher
levels of lipofuscin-like fluorescent compounds (FCs), which are produced
when MDA reacts with free amino acids. Age-dependent increases in MDA,
ethane, and FCs were not associated with higher activities of phospholipase
and lipoxygenase in tissue from older tubers. In fact, 8-month-old
seed-tubers had significantly higher activities of these enzymes than
20-month-old seed-tubers. However, the activities of superoxide dismutase,
peroxidase, and catalase in 20-month-old tubers were substantially higher
out of storage, and increased at a faster rate during plant establishment,
than in 8-month-old seed-tubers. Collectively, these results suggest that a
gradual build-up of FRs leads to peroxidative damage of membrane lipids
during aging of potato seed-tubers.
