Effects of a brief cold stress on 2,4-D penetration, migration and metabolism in maize plants
1996
Gauvrit, C. | Heller, R. (Inra, Dijon (France). Lab. de phytopharmacie)
A cold stress (14/4 degrees, light/dark) was applied for 72 hours to maize plants at the 4-leaf stage to mimic meteorological conditions under which 2,4-D had proved phytotoxic towards maize in the field. Treatments with 14C-2,4-D took place 48 h after the start of the cold conditions. The cold stress decreased 2,4-D penetration after 24 h in the first leaf by 60 per cent. Migration of 14C out of the treated leaf was 63 per cent decreased during the cold stress. It resumed nearly to initial rate 48 h after maize plants were returned to normal conditions, and was 36 per cent higher 144 h after. Radioactivity accumulated mainly in young tissues and actively growing leaves but not in nodal roots. During the cold stress, 2,4-D metabolism was blocked in the treated leaf and in the young tissues. When the maize plants were returned to normal conditions, 2,4-D metabolism in the treated leaf resumed at a lower pace (half life was 122 h as compared to 36 h in non-stressed plants). In the young tissues, 2,4-D metabolism had not resumed 48 h after returning to normal conditions. The after-effect of the cold stress on 2,4-D metabolism lasted at least 6 days in the first leaf and at least 2 days in the young tissues. It resulted that 168 h after treatment, 2,4-D per unit dry weight in young tissues was 3 times higher in cold-stressed plants as compared to non stressed plants. The delay between the resumption of 2,4-D migration and the resumption of its metabolism may be responsible for maize sensitivity to 2,4-D under such conditions
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