Phosphate solubilization potential and phosphatase activity of rhizospheric trichoderma spp

Trichoderma sp., a well known biological control agent against several phytopathogens, was tested for its phosphate (P) solubilizing potential. Fourteen strains of Trichoderma sp. were isolated from the forest tree rhizospheres of pinus, deodar, bamboo, guava and oak on Trichoderma selective medium. The isolates were tested for their in-vitro P-solubilizing potential using National Botanical Research Institute Phosphate (NBRIP) broth containing tricalcium phosphate (TCP) as the sole P source, and compared with a standard culture of T. harzianum. All the cultures were found to solubilize TCP but with varying potential. The isolate DRT-1 showed maximum amount of soluble phosphate (404.07 εg.ml^-1), followed by the standard culture of T. harzianum (386.42 εg.ml^-1) after 96 h of incubation at 30±1⁰C. Extra-cellular acid and alkaline phosphatases of the fungus were induced only in the presence of insoluble phosphorus source (TCP). High extra-cellular alkaline phosphatase activity was recorded for the isolate DRT-1 (14.50 U.ml^-1) followed by the standard culture (13.41 U.ml^-1) at 72h. The cultures showed much lesser acid phosphatase activities. Under glasshouse conditions, Trichoderma sp. inoculation increased chickpea (Cicer arietinum) growth parameters including shoot length, root length, fresh and dry weight of shoot as well as roots, in P-deficient soil containing only bound phosphate (TCP). Shoot weight was increased by 23% and 33% by inoculation with the isolate DRT-1 in the soil amended with 100 and 200 mg TCP kg^-1 soil, respectively, after 60 d of sowing. The study explores high P-solubilizing potential of Trichoderma sp., which can be exploited for the solubilization of fixed phosphates present in the soil, thereby enhancing soil fertility and plant growth.

Improving phosphorus acquisition of white clover (Trifolium repens L.) by transgenic expression of plant-derived phytase and acid phosphatase genes

Phosphate is one of the least available macronutrients restricting crop production in many ecosystems. A phytase gene (MtPHY1) and a purple acid phosphatase gene (MtPAP1), both isolated from the model legume Medicago truncatula, were introduced into white clover (Trifolium repens L.) by Agrobacterium-mediated transformation. The transgenes were driven by the constitutive CaMV35S promoter or the root-specific MtPT1 promoter. Transcripts were detected in roots of the transgenic plants. Phytase or acid phosphatase (APase) activities in root apoplasts of the transgenic plants were increased up to three-fold compared to the wild type control. After the plants were grown 80 days in sand pots supplied with organic phosphorus (Po) as the sole P source, dry weights of shoot tissues of the best performing transgenic plants almost doubled that of the control and were comparable to the counterparts supplied with inorganic phosphorus (Pi). Relative biomass production of the transgenics under Po treatment was over 90% and 80% of that from the Pi treatment when the plants were grown in hydroponics (40 days) and sand pots (80 days), respectively. In contrast, biomass of the wild type controls under Po treatment was only about 50% of the Pi treatment in either hydroponic cultures or sand pots. In addition, shoot P concentrations of the transgenic plants were significantly increased compared to the control. Transgenic plants accumulated much higher amounts of total P (up to 2.6-fold after 80 days of growth) than the control in Po supplied sand pots. The results showed that transgenic expression of MtPHY1 or MtPAP1 in white clover plants increased their abilities of utilizing organic phosphorus in response to P deficiency.

The effects of nickel, calcium and magnesium on the acid phosphatase activity of two Alyssum species

Root Surface acid phosphatase activity was assessed in seedlings of two species of Alyssum, one endemic to Tuscan serpentines (Alyssum bertolonii Desv.) and the other of wide occurrence (Alyssum saxatile L.), cultivated in solutions to which various concentrations of Ni²⁺ , Ca²⁺ and Mg²⁺ were added. Treatments were applied in two factorial experiments of type 2ⁿ . A concentration of 0.01 mM Ni²⁺ markedly stimulated phosphatase activity in A. bertolonii, but slightly decreased it in A. saxatile. Increased Ca²⁺ concentration stimulated enzyme activity in both species, hut in A. bertolonii the highest activity was obtained with low Ca²⁺ concentrations, whilst the opposite occured in A. saxatile. A. bertolonii instead required high Mg²⁺ concentrations to increase phosphatase activity significantly. The same concentrations were toxic to A. saxatile. In the serpentine species, favourable conditions for the increase of phosphatase activity were induced by a high Mg²⁺ /Ca²⁺ ratio, which also favoured dry mass production. Therefore it is possible that the increase of phosphatase activity might be an aspect of plant adaptation to serpentines.

Purification and characterization of acid phosphatase in aleurone particles of rice grains

The major acid phosphatase (EC 3.1.3.2) associated with aleurone particles of rice grains (Oryza sativa L. Japonica cv. Koshihikari) was purified to homogeneous state by polyacrylamide gel electrophoresis. Its molecular weight was 72,000 when determined by gel filtration and 68,000 when found by polyacrylamide gradient gel electrophoresis in the presence of sodium dodecyl sulfate and β-mercaptoethanol. The purified enzyme had a violet color and an absorption peak at 530 nm. Triton X-100 and lysolecithin stabilized the purified enzyme. The optimum pH for hydrolysis of p-nitrophenyl phosphate was 4.8. The enzyme hydrolyzed all inositol phosphates, several other phosphomonoesters and pyrophosphate. However, α,β-glycerol phosphate, glucose-6-phosphate, adenosine monophosphate and inosine monophosphate were not hydrolyzed. The Km for myo-inositol hexaphosphate was 0.43 mm, which was the lowest among myo-inositol phosphates. The Km value increased as the number of phosphate linkages on myo-inositol decreased. No correlation between the maximum initial velocity (Vmax) and Km was observed. Among the myo-inositol phosphates, the Vmax for myo-inositol triphosphate was the highest. The Km for p-nitrophenyl phosphate was 1.74 mm and that for ATP was 5.26 mm. l-Tartrate, orthophosphate, molybdate and arsenate were competitive inhibitors, and F(-) was a noncompetitive inhibitor. Ag(+), Zn(2+), Hg(2+), Cu(2+) and Fe(2+) were inhibitory and the enzyme was also inactivated by preincubation with EDTA.