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Abstract

A pot experiment confirmed that pigeonpea could efficiently utilize various sources of phosphorus (P) (aluminium phosphate, iron phosphate and apatite), irrespective of genotype. A qualitative assay method for iron (Fe)-P solubilizing activity showed that root exudates collected from P-deficient pigeonpea contained Fe-P solubilizing substances and that they were released mainly from root tips. Citric, malic, malonic, succinic and piscidic acids were identified in root exudates. Citric and piscidic acids release from roots was increased by low-P treatment in all the genotypes tested. The release rates of citric and piscidic acids were affected by the P concentration of shoots rather than that of roots. The pigeonpea roots released approximately 5-100 times more piscidic acid than citric acid depending on P stress status, plant age and genotype. When organic acids were added to Alfisols, citric acid was most capable of mobilizing P from the soil, followed by piscidic acid and malic acid. No correlation was found between genotypic variability in the release rates of citric and piscidic acids from the roots under low-P treatment at hydroponic culture and in the growth and P uptake of plants on Alfisols. Although citric and piscidic acids released from pigeonpea roots may play a partial role in solubilizing unavailable insoluble P in soils, the releases were thought to be an unsatisfactory strategy for explaining genotypic variation in low P availability of pigeonpea.

Effects of crop rotation and fallow residue management on maize growth, yield and soil carbon in a savannah-forest transition zone of Ghana

“…In some studies, increased soil P availability under pigeon pea was attributed to the efficient solubilization and uptake of P from bound sources (e.g. Fe-P) by root exudates (Ae et al 1990;Ishikawa et al 2002) but this aspect was not investigated in the present study.…”

Relationships between jasmonates and auxin in regulation of some physiological processes in higher plants

“…JA-Me inducible expression of the promoter of a potato gene for cathepsin D inhibitor in tobacco cell line BY-2 was higher in cells cultured in medium containing BAP than in cells cultured in medium containing 2,4-D, and the repression by 2,4-D was largely released by the addition of aphidicolin an inhibitor of DNA synthesis. These results suggest that JA-Me inducible expression is repressed during active cell divisions (Ishikawa et al 1994b). …”

Metabolic alterations provide insights into Stylosanthes roots responding to phosphorus deficiency

“…The quantity and type of organic acids by roots highly depended on the plant species, genotypes and growth conditions and so on. According to published literature, under low P stress, the organic acids released into rhizosphere was mainly citrate and malate by white lupin cluster roots [2], piscidic acid by pigeonpea (Cajanus cajan) roots [61], malate and oxalate by soybean roots [62], citrate by Stylosanthes roots [38]. In the study, malate participating in the tricarboxylic acid (TCA) cycle was observed markedly reduced accumulation in stylo roots, as well as its derivative 2-Isopropylmalate.…”