Stress metabolism. IX. Effect of salt stress on trigonelline accumulation in tomato

Abstract

The presence of quaternary ammonium compounds (QAC) and their accumulation in tomato (Lycopersicon esculentum Mill.) cv. Duke in response to different modes for causing NaCl stress were studied. Pre-germinated tomato seeds were grown in sand culture and 25-d-old seedlings were subjected to abrupt, progressive or prolonged salt stress using NaCl at various osmotic potentials. Plant water status was measured using psychrometry and quaternary ammonium compounds were visualized using thin-layer chromatography and then confirmed and quantified using nuclear magnetic resonance spectrometry. Leaf water potential and osmotic potential declined depending on the osmotic potential of the rooting medium and the mode of stress imposition. A greater decline in osmotic potential compared with the total water potential led to turgor maintenance in plants under progressive or prolonged NaCl stress. The QAC, trigonelline and choline were identified in tomato. Trigonelline, but not choline, accumulated rapidly in response to abrupt, progressive or prolonged NaCl stress. The threshold external water potential (Ψext.) for trigonelline accumulation was -0.565 MPa. Trigonelline accumulation correlated with changes in ΨL (r = -0.92***), ΨS (r = -0.94***) and ΨP (r = 0.85***). Trigonelline contributed only -0.035 MPa to the osmotic adjustment, suggesting that its role may also lie in areas other than osmoregulation.