RIMSULFURON UPTAKE, TRANSLOCATION, METABOLISM AND

Research was conducted to determine the role in selectivity

of uptake, translocation, metabolism and ALS (acetolactate

synthase) activity of rimsulfuron in two maize (

Zea mays

L.) hybrids (‘Cargill 2127’, tolerant, and ‘Pioneer 3897’,

sensitive) grown at temperatures of 14°C and 21°C. Forty

eight hours after treatment (HAT), uptake of rimsulfuron

was 40% and 67% in ‘Pioneer 3897’, and 26% and 43%

in ‘Cargill 2127’ at 14°C and 21°C, respectively. Neither

total translocation nor allocation of rimsulfuron in various

organs differed greatly between the hybrids. Translocation

of

14C-rimsulfuron was greater at 21°C (53%) than at 14°C

(23%), 48 HAT. In ‘Pioneer 3897’ over 65% and 30% of

the total

14C-activity present in plant extracts was recovered

as the parent compound within 24 HAT, at 14°C and

21°C, respectively. However, in ‘Cargill 2127’ detoxification

of rimsulfuron was not affected by temperature, and

27% of the

14C-total activity was recovered as the parent

compound. Crude ALS extracts from ‘Pioneer 3897’ and

‘Cargill 2127’ maize seedlings were treated with various

doses (0.001, 0.005, 0.01, 0.1 and 1.0

μM) of rimsulfuron.

Based on ALS specific activity, I

50 values differed sligthly

between the two hybrids (I

50 ‘Pioneer 3897’ = 0.091 μM

and I

50 ‘Cargill 2127’ = 0.142 μM). These results suggest

that the mechanism of rimsulfuron tolerance in maize

could be mainly explained by differential herbicide uptake

and detoxification, with translocation and ALS sensitivity

having little effect on differential tolerance of these maize

hybrids to rimsulfuron. On the other hand, the greater

uptake and translocation of rimsulfuron at 21°C, compared

to 14°C, could explain the observed herbicide injury in

maize at high temperatures under field conditions.