CHANGES IN LIPID-PEROXIDATION AND LIPOLYTIC AND FREE-RADICAL SCAVENGING ENZYME-ACTIVITIES DURING AGING AND SPROUTING OF POTATO (SOLANUM-TUBEROSUM) SEED-TUBERS
Gnm. Kumar et Nr. Knowles, CHANGES IN LIPID-PEROXIDATION AND LIPOLYTIC AND FREE-RADICAL SCAVENGING ENZYME-ACTIVITIES DURING AGING AND SPROUTING OF POTATO (SOLANUM-TUBEROSUM) SEED-TUBERS, Plant physiology, 102(1), 1993, pp. 115-124
Previous research has shown that cell membranes of potato (Solanum tub
erosum L. cv Russet Burbank) seed-tubers lose integrity between 7 and
26 months of storage (4-degrees-C, 95% relative humidity), and this lo
ss coincides with a significant decrease in growth potential. The age-
induced decline in membrane integrity is apparently due to increased p
eroxidative damage of membrane lipids. Malondialdehyde (MDA) and ethan
e 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 dis
cs 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 tube
rs by 61 and 228%, respectively, suggesting that older tissue may cont
ain 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 declin
ed by about 65% during the initial 7 months of storage and then increa
sed 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 me
mbrane, leading to increased starch hydrolysis. Compared with 5-month-
old seed tubers, 17- and 29-month-old seed-tubers had significantly hi
gher levels of lipofuscin-like fluorescent compounds (FCs), which are
produced when MDA reacts with free amino acids. Age-dependent increase
s in MDA, ethane, and FCs were not associated with higher activities o
f 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 supe
roxide dismutase, peroxidase, and catalase in 20-month-old tubers were
substantially higher out of storage, and increased at a faster rate d
uring plant establishment, than in 8-month-old seed-tubers. Collective
ly, these results suggest that a gradual build-up of FRs leads to pero
xidative damage of membrane lipids during aging of potato seed-tubers.