Malic acid secretion

Abstract: Hyoscyamus albus is a well-known source of the tropane alkaloids, hyoscyamine and scopolamine, which are biosynthesized in the roots. To assess the major biochemical adaptations that occur in the roots of this plant in response to iron deficiency, we used a small-scale proteomic approach in which 100 mg of root tips were treated with and without Fe, respectively, for 5 days. Two-dimensional mini gels showed that 48 spots were differentially accumulated between the two conditions of Fe availability and a further 36 proteins were identified from these spots using MALDI-QIT-TOF mass spectrometry. The proteins that showed elevated levels in the roots lacking Fe were found to be associated variously with carbohydrate metabolism, cell differentiation, secondary metabolism and oxidative defense. Most of the proteins involved in carbohydrate metabolism were increased in abundance, but mitochondrial NAD-dependent malate dehydrogenase was decreased, possibly resulting in malate secretion. Otherwise, all the proteins showing diminished levels in the roots were identified as either Fe-containing or ATP-requiring. For example, a significant decrease was observed in the levels of hyoscyamine 6beta-hydroxylase (H6H), which requires Fe and is involved in the conversion of hyoscyamine to scopolamine. To investigate the effects of Fe deficiency on alkaloid biosynthesis, gene expression studies were undertaken both for H6H and for another Fe-dependent protein, Cyp80F1, which is involved in the final stage of hyoscyamine biosynthesis. In addition, tropane alkaloid contents were determined. Reduced gene expression was observed in the case of both of these proteins and was accompanied by a decrease in the content of both hyoscyamine and scopolamine. Finally, we have discussed energetic and Fe-conservation strategies that might be adopted by the roots of H. albus to maintain iron homeostasis under Fe-limiting conditions.

Abstract: Leaves of chickpea (Cicer urietinum L.) secrete malic acid hut the significance of this secretion is not known. Our studies have confirmed that secretion of malic acid was mostly confined to the day time. PEP carboxylase activity and the secretion of malic acid are associated with the presence of glands on the surface of leaves and fruit wall. PEP carboxylase activity increased while malic acid secretion and MDH activity decreased in water stressed plants. The secretion of malic acid did not influence the reflectance properties of the crop canopy thereby discounting the possibility of reducing radiation load. It is suggested that the significance of malic acid secretion in chickpea should be considered in relation to insect pests which are very few on this plant.

Abstract: The invention discloses a malic acid transporter gene GmALMT1 and an application thereof. The nucleotide sequence of the malic acid transporter gene GmALMT1 is shown as SEQ ID NO.1. An amino acid sequence of an encoded protein is shown as SEQ ID NO.2. The GmALMT1 gene provided by the invention can be used for regulating soybean root tip malic acid secretion.

Abstract: There are significant differences of organic acid secretion among species that with different Al-tolerant levels under Al stress.Organic acid is produced during the tricarboxylic acid cycle pathway.However,the relationship between organic acid secretion differences and organic acid metabolism are still needed to be identified.This experiment was performed by two wheat(Tritium aestivum L.) cultivars,ET8(Al-resistant) and ES8(Al-sensitive).Effects of Al on endogenous malic acid content,activities of phosphoenolpyruvate carboxylase(PEPC),citrate synthase(CS) and malate dehydrogenase(MDH) were studied.Results were as fellows: the contents of endogenous malic acid were not affected by Al(0,25,50,and 100(mol-L-1),and there were no differences between ET8 and ES8 when they received same treatment.The endogenous malic acid contents were(0.48±0.01),(0.46±0.03),(0.57±0.02),(0.52±0.02) nmol-root apex-1 and(0.45±0.02),(0.51±0.09),(0.51±0.1),(0.54±0.04) nmol-root apex-1,respectively of ET8 and ES8.Compared with Al free treatment,activities of PEPC were increased significantly under Al(50 or 100(mol-L-1) treatment,but not CS or MDH.The activities of PEPC(or CS,MDH) of ET8 and ES8 were close to each other under the same treatment.In conclusion,the malic acid secretion differences of different Al-tolerant wheat were independent on the endogenous malic acid content and the organic acid metabolism.