Biochemical and ultrastructural changes associated with chilling injury in soybean seeds during imbibition.
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Date
1996
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Abstract
Biochemical and ultrastructural changes associated with chilling injury (CI) in
soybean seeds imbibed at 5°C and 25°C were investigated. Soybean seed
germination appeared to be affected by chilling temperatures and initial seed
moisture content. Seeds with higher moisture contents exhibited 85% germination,
while low moisture content seeds had a 32% germination.
Leakage rates were greater in chilled seeds, indicating that membrane integrity in
the tissues was impaired at chilling. The low rates of potassium ion leakage between
6 and 24 hours of imbibition compared to the high peroxide levels observed during
this period led to the suggestion that lipid peroxidation was a better marker of CI
than leakage.
Transient changes in lipid hydroperoxide levels were observed in chilled and non-chilled
seeds and axes. However, in axes, the increase in lipid hydroperoxides after
12 hours of imbibition at chilling temperatures was associated with an 18% decline
in linoleic acid levels of total lipid fraction. Similarly, a 10% decline was observed in
the polar lipid fraction. These results suggest that the capacity of seeds to control
lipid peroxidation may be an important component in CI and that a consequence of
peroxidation is likely to be a loss of fatty acid unsaturation.
Sugar levels were not affected by chilling and non-chilling temperatures and no
relationship could be established with CI.
Antioxidant defense enzymes (catalase and superoxide dismutase) were expressed
at chilling and non-chilling temperatures and increases were observed after 24 hours of imbibition which showed an apparent correlation with increases to lipid
hydroperoxide levels. Enzyme levels decreased after 48 hours of imbibition at a time
which coincided with the decline observed in the peroxide levels. Overall, no
marked differences were observed in chilled and non-chilled cells at the
ultrastructural level, except that vacuolar reserve mobilization was markedly
impeded.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
Keywords
Seeds--Deterioration., Seeds--Viability., Seeds--Physiology., Germination., Plants, Effect of stress on., Theses--Botany.