Impact of pedospheric and atmospheric sulphur nutrition of sulphur metabolism of Allium cepa L., a species with a potential sink capacity for secondary sulphur compounds
2004
Durenkamp, M. | De Kok, L.J.
Onion (Allium cepa L.) was able to use atmospheric H2S as sole sulphur source for growth. The foliarly absorbed H2S was rapidly metabolized into water-soluble, non-protein thiol compounds, including cysteine, and subsequently into other sulphur compounds in the shoots. In H2S-exposed plants, the accumulation of sulphur compounds in the shoots was nearly linear with the concentration (0.15-0.6 microliter l(-1)) and duration of the exposure. Exposure of onion to H2S for up to 1 week did not affect the sulphur content of the roots. Secondary sulphur compounds formed a sink for the foliarly absorbed sulphide, and the sulphur accumulation upon H2S exposure could, for a great part, be ascribed to enhancement of the content of gamma-glutamyl peptides and/or alliins. Furthermore, there was a substantial increase in the sulphate content in the shoots upon H2S exposure. The accumulation of sulphate originated both from the pedosphere and from the oxidation of absorbed atmospheric sulphide, and/or from the degradation of accumulated secondary sulphur compounds. From studies on the interaction between atmospheric and pedospheric sulphur nutrition it was evident that H2S exposure did not result in a down-regulation of the sulphate uptake by the roots.
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