Toxic responses of germinating pollen and soybeans to aflatoxins

Abstract

Aflatoxin producing strains of Aspergillus grow on soybeans thereby contaminating the latter through secretion of the toxin. Investigations dealing with either soybean seed germination or intact seedling growth responses to aflatoxin (B1) are lacking. Similarly, a possible interaction of aflatoxins with phosphate in the germination and elongation of both soybeans and pollen as well as roots of the former and tubes of the latter has not been examined. Imbibition of Glycine max, cv. ‘Essex’ seeds for 18 hours in solutions containing 0.38, 2.90, 5.80 or 11.60 μg/ml (AFB1) yielded% germination inhibitions of 5, 20, 40 and 80, respectively. By 36 hours these were 6, 4, 13 and 19 % for the same toxin concentration series. At 140 hours attached root elongation was inhibited 26, 35 and 50 % for 2.90, 5.80 and 11.60 μg/ml AFB1. No effect was noted at 0.38 μg/ml AFB1. Incubation of excised roots in medium containing 3.0 mM KH2PO4 stimulated their elongation 3.2 fold. Addition of 33.28 μg/ml mixed aflatoxins together with KH2PO4 resulted in only a 1.5 fold stimulation. When KH2PO4 was added to a culture medium lacking AFB1, Lilium longiflorum, cv. ‘Ace’ pollen germination was enhanced 50%. Withholding KH2PO2 but supplying AFB1 did not markedly affect germination. However, supplementing the medium with KH2PO4 while simultaneously adding AFB1 did not inhibit germination at 5 and 10 μg/ml but caused 27.3 and 45.1 % declines at 25 and 30 μg/ml. In the absence of KH2PO4 AFB1 stimulated pollen tube elongation 7.5, 14.3, 16.5 and 13.2 % at 5, 10, 15 and 20 μg/ml but 30 μg/ml inhibited it 11.1%. In contrast, tube elongation was suppressed at all AFB1 concentrations (maximum 36.1% at 30 μg/ml) tested upon KH2PO4 addition. Results derived from germinating pollen in medium supplemented with KH2PO4 or NaH2PO4 indicate that the phosphate anion does not preferentially promote aflatoxin-induced inhibition of tube elongation.