Effect of environmental factors on the biosynthesis of the neuro-excitatory amino acid ß-ODAP (ß-N-oxalyl-L-α,ß-diaminopropionic acid) in callus tissue of Lathyrus sativus.

Habituated callus tissues derived from leaf explants of Lathyrus sativus L. (grass pea) were cultured under different environmental conditions such as drought, salinity and deficiency or oversupply of micronutrients. The biosynthesis of the neuro-excitatory ß-ODAP (ß-N-oxalyl-L-α,ß-diaminopropionic acid) was induced by feeding the precursor BIA, (ß-isoxazolin-5-on-2-yl)-alanine, to those calli habituated under different stress conditions. Conversion of BIA into ß-ODAP was reduced by Zn(2+) at different levels of Fe(2+) supplements while excess of Fe(2+) enhanced it at different Zn(2+) levels in the media. The biosynthesis of ß-ODAP was increased by both oversupply and deficiency of Mn(2+) manganese while B(3+) as well as Co(2+) increased it significantly by oversupply. Al(3+) enhanced the conversion of BIA into ß-ODAP significantly in a concentration-dependent way. Cu(2+) also reduced the formation of ß-ODAP when increased in the media. Mo(6+) had no apparent effect. NaCl decreased the conversion of BIA into ß-ODAP proportionately with the increase in salinity. ß-ODAP was increased with increasing mannitol concentration till -0.23MPa while at this osmotic potential created with PEG-20,000 the formation of ß-ODAP is completely inhibited in low toxin calli. These experiments demonstrate the importance of environmental factors, especially micronutrients and salinity, on the biosynthesis of ß-ODAP.

Participation of chlorobiumquinone in the transplasma membrane electron transport system of Leishmania donovani promastigote: effect of near-ultraviolet light on the redox reaction of plasma membrane.

The respiratory quinone composition of the parasitic protozoa Leishmania donovani promastigote was investigated. 1'-oxomenaquinone-7, a chlorobiumquinone was found to be the major isoprenoid quinone. Substantial level of ubiquinone-9 was also present. Isolation and identification of the quinone from the purified plasma membrane yielded mainly 1'-oxomenaquinone-7 and ubiquinone-9; menaquinone was not detected. Membrane bound 1'-oxomenaquinone-7 could be destroyed by near-ultraviolet irradiation, with a concomitant loss or stimulation of plasma membrane electron transport activities. The abilities of different quinones to restore alpha-lipoic acid and ferricyanide reductase activity in near UV-irradiated cell preparations were compared. The order was; conjugate of chlorobiumquinone and sphingosine base approximately conjugate of 2-methyl-3-(1'-oxooctadecyl)-1,4-napthoquinone and octadecylamine >> chlorobiumquinone approximately 2-methyl-3-(1'-oxooctadecyl)-1,4-napthoquinone > menaquinone-4 approximately ubiquinone-10. After irradiation with near-UV light, transmembrane alpha-lipoic acid reduction was inhibited, while transmembrane ferricyanide reduction was stimulated. The result obtained indicates that chlorobiumquinone mediates the plasma membrane electron transport between cytosolic reductant and oxygen as well as alpha-lipoic acid. UV-inactivation of chlorobiumquinone shuts down the plasma membrane oxygen uptake and diverts the electron flux towards ferricyanide reduction via ubiquinone-9. Chlorobiumquinone is the only example of a polyisoprenoid quinone containing a side chain carbonyl group from photosynthetic green-sulphur bacteria. Recent work has revealed numerous genes of trypanosomatid sharing common ancestry with plants and/or bacteria. These observations pose some fascinating questions about the evolutionary biology of this important group of parasitic protozoa.