2.3. Soil and plant sampling
To study the influence of life stage on pesticide uptake and LPO,
a destructive harvest was performed at 15 (first period) and 60 days
(second period) after germination (appearance of the first true
leaves). Two or three plants were harvested per pot and period.
Roots, stems and leaves obtained from each pot were pooled and
analyzed as a single sample. Plant subsamples were immediately
frozen and maintained at 80 C until analysis.
Within each pot, three separated soil fractions were defined
according to White (2001) in relation to the influence exerted by
the plant root. Bulk soil (BS) that had no contact with plant roots
was taken from the top of individual planted pots. The near-root
soil (NRS) was operationally defined as the soil that was under
root influence. The NRS settled within the volume occupied by the
roots. The rhizosphere soil (Ri) was defined as the soil that
remained attached to the roots and required mechanical removal.
The Ri was obtained by washing the roots with distilled water and a
centrifugation of water-Ri solution at 840 g for 10 min at room
temperature (this procedure was selected to preserve fine roots
during rhizosphere extraction). Additionally, soil samples from Un
soils were obtained at 15 and 60 days. Soil samples were maintained
frozen (80 C) until analysis.
2.4. Dehydrogenase activity determination
Soil dehydrogenase activity (DHA) analysis was used to assess
the microbiological activity in the soil samples (Wu and Brookes,
2005), differing in their proximity to roots (BS and NRS), from
plants grown on endosulfan-polluted soils. One gram of each soil
sample was incubated, in triplicate, for 24 h at 25 C, in darkness,
with 0.2 mL of 0.4% 2-p-iodophenyl-3 p-nitrophenyl-5 tetrazolium
chloride (INT) as a substrate. The iodonitrotetrazolium formazan
(INTF) formed was measured spectrophotometrically a
2.3. Soil and plant samplingTo study the influence of life stage on pesticide uptake and LPO,a destructive harvest was performed at 15 (first period) and 60 days(second period) after germination (appearance of the first trueleaves). Two or three plants were harvested per pot and period.Roots, stems and leaves obtained from each pot were pooled andanalyzed as a single sample. Plant subsamples were immediatelyfrozen and maintained at 80 C until analysis.Within each pot, three separated soil fractions were definedaccording to White (2001) in relation to the influence exerted bythe plant root. Bulk soil (BS) that had no contact with plant rootswas taken from the top of individual planted pots. The near-rootsoil (NRS) was operationally defined as the soil that was underroot influence. The NRS settled within the volume occupied by theroots. The rhizosphere soil (Ri) was defined as the soil thatremained attached to the roots and required mechanical removal.The Ri was obtained by washing the roots with distilled water and acentrifugation of water-Ri solution at 840 g for 10 min at roomtemperature (this procedure was selected to preserve fine rootsduring rhizosphere extraction). Additionally, soil samples from Unsoils were obtained at 15 and 60 days. Soil samples were maintainedfrozen (80 C) until analysis.2.4. Dehydrogenase activity determinationSoil dehydrogenase activity (DHA) analysis was used to assessthe microbiological activity in the soil samples (Wu and Brookes,2005), differing in their proximity to roots (BS and NRS), fromplants grown on endosulfan-polluted soils. One gram of each soilsample was incubated, in triplicate, for 24 h at 25 C, in darkness,with 0.2 mL of 0.4% 2-p-iodophenyl-3 p-nitrophenyl-5 tetrazoliumchloride (INT) as a substrate. The iodonitrotetrazolium formazan(INTF) formed was measured spectrophotometrically a
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