Effects of aflatoxin B₁ on in vitro cultures ofNicotiana tabacum var. Samsun

Abstract

Calli ofNicotiana tabacum (tobacco) were treated with two dose ranges of aflatoxin B₁ (0.1–2.0 µg ml⁻¹ - low does; 5–25 µg ml⁻¹ aflatoxin B₁). The ability of calli to recover following 3 weeks of toxin exposure was also investigated. The I₅₀ (50% inhibition) value for fresh mass accumulation was approximately 2 µg ml⁻¹ AFB₁. Fresh mass accumulation was significantly lower than the control value from 0.5 µg ml⁻¹ AFB₁. Following 3 weeks growth without a toxin source, the growth of calli up to and including 10 µg ml⁻¹ AFB₁, was significantly greater than control calli, indicating reversibility of the toxic effects. With increasing toxin concentration, chlorophyll content of callus was inhibited from 0.5 µg ml⁻¹. Transfer to a toxin-free medium resulted in a degree of recovery (up to 0.5 µg ml⁻¹). In the dose range 5–25 µg ml⁻¹, the levels of chlorophyll were drastically reduced, with no recovery following AFB₁ removal. Electron microscopy revealed a disruption of chloroplast structure as an early deteriorative event in AFB₁ exposure of callus cells. Protein levels were less sensitive, with inhibition manifested only in the high dose range. Shoot development occurred at all concentrations, but was significantly inhibited from 5 µg ml⁻¹ AFB₁. Recovery following toxin removal was minimal at these higher AFB₁ concentrations. The number of necrotic calli increased progressively from 5 µg ml⁻¹ as toxin levels increased.