Effect of molybdenum supply on growth and distribution of molybdenum in black gram

The effects of seven levels of molybdenum (Mo) supply on growth, distribution and redistribution of Mo in black gram cv. Regur on a Mo deficient acid soil were examined in a glasshouse experiment. Seed of Mo concentration 17 4 Mg Mo/g dry matter was used. At the three lowest Mo rates, plants showed N deficiency symptoms typically induced by low Mo supply in legumes. Nitrogen deficiency symptoms depressed whole shoot dry matter. Increasing the Mo supply increased Mo concentrations in all plant parts. In the leaf blades of plants at all growth stages, the increases were smaller over the three lowest rates of Mo supply: further increases in the Mo supply markedly increased the concentrations of Mo in all leaves, particularly in the recently matured leafblades (YFELb and YFEL-1 b). In addition, in petioles, the concentrations of Mo exceeded those in the blades which they supported at all levels of Mo supply. In Mo-adequate plants, the concentrations of Mo were higher in the stems than in the petioles and higher in the -petioles than in the blades. Molybdenum concentrations in the nodules were higher than in the above ground plant parts except at the high levels of Mo supply where the concentrations in the basal stem exceeded those in the nodules. The mobility of Mo in the phloem appeared to vary with plant parts and the Mo supply. For example, in Mo-adequate plants, there was no net loss of Mo

Diagnosis and prognosis of molybdenum deficiency in black gram (Vigna mungo L. Hepper) by plant analysis

Diagnosis and prognosis of molybdenum (Mo) deficiencies in black gram crops by plant analysis is difficult because Mo standards have not been set and tested in the field. Therefore, critical Mo concentrations, for the diagnosis of Mo deficiency at early flowering and for diagnosis and prognosis at pod filling in black gram, were determined in two glasshouse experiments by examining the relationship of Mo concentrations in young leaves and nodules to shoot nitrogen content or seed dry matter in plants treated with seven levels of Mo supply on a Mo-deficient sandy loam. In severely Mo-deficient plants, shoot dry matter (DM) and shoot nitrogen (N) content were depressed. Molybdenum concentrations in plant parts increased with increasing Mo supply and were closely related to shoot N content. shoot DM, and seed DM. Critical Mo concentrations for diagnosis of hi0 deficiency were obtained from the relationship between N content and &lo concentrations in leaves and nodules. and for prognosis of Mo deficiency were obtained from the relationship between seed yield and Mo concentrations in plant parts. Critical Mo concentrations were much higher in nodules than in leaves, and among young leaf blades, they increased with decreasing leaf age. For diagnosis of Mo deficiency, blades of the leaf immediately older than the youngest fully expanded leaf (YFEL+lb) and nodules are recommended plant parts. Their respective critical concentrations were 22 and 9600 ng Mo/g DM at flowering, and 22 and 3378 ng Mo/g DM at initial pod set. Molybdenum concentrations in the YFEL+lb and nodules at podding were also related to seed production at maturity. Recommended critical h10 concentrations in the YFELflb and nodules at initial pod set for the prognosis of IbIo deficiency for seed DM were 18 and 3000 ng Mo/g DM respectively

Distribution and redistribution of molybdenum in black gram (Vigna mungo L. Hepper) in relation to molybdenum supply

The effect of seven rates of molybdenum (Mo) supply on the distribution and redistribution of Mo in Vigna mungo (black gram) cv. Regur on a Mo-deficient sandy loam was examined from flower bud appearance to pod set in one experiment and during pod filling to maturity in another. At the three lowest Mo supply rates, N deficiency symptoms typical of Mo deficiency appeared, and shoot dry matter and shoot nitrogen content were depressed. Increasing Mo supply increased Mo concentrations in all plant parts but the response varied with Mo supply and with plant part. In leaf blades and petioles, Mo concentrations increased slightly when the Mo supply increased from severely deficient to deficient levels but further increases in Mo supply markedly increased the Mo concentrations, particularly in immature and recently matured leaves. In petioles, Mo concentrations generally exceeded those in the blades which they supported at all levels of Mo supply. At Mo rates greater than that required for maximum growth, Mo concentrations in basal stem segments exceeded those in petioles. Molybdenum concentrations in nodules exceeded those in above ground plant parts except at the highest level of Mo supply where the concentrations in basal stem segments exceeded those in nodules. In Mo-adequate plants, Mo contents in the trifoliolate leaves decreased with time suggesting that Mo was readily remobilized. By contrast, in stem segments at all levels of Mo supply, and in trifoliolate leaves in Mo-deficient plants, Mo contents remained constant or increased with time suggesting that Mo was not remobilized in all plant parts or at all levels of Mo supply. Thus, the results suggest that in black gram Mo was variably mobile, being phloem immobile at low Mo supply, but phloem-mobile in all plant parts with the possible exception of stem segments at adequate Mo supply. The relevance of these results for the development of plant tests for Mo deficiency diagnosis is discussed

Effects of low molybdenum seed on nodule initiation, development and N2 fixation in black gram (Vigna mungo L.)

In legumes, both increases and decreases in nodule number in response to Mo deficiency have been reported, but reasons for the different responses have not been proposed. The present study examined nodule initiation and development in black gram seedlings using two levels of seed Mo to induce Mo deficiency. In the first 11 days after inoculation, low levels of Mo in seed had no effect on nodule initiation or the number of nodules. At 13 days after inoculation, low Mo in seed depressed bacteroid concentration, leghaemoglobin concentration, nodule number and nodule fresh weight. Acetylene reduction activity was delayed by 2 days in plants grown from low Mo seed. We suggest that the delay in N2 fixation in plants grown from low Mo seed was due to slower incorporation of Mo of soil origin into nitrogenase. We further suggest that restricted supply of essential metabolites to the nodules on plants from low Mo seed resulted in the slower maturation of early initiated nodules and the repression of formation of new nodules

Effect of molybdenum and inorganic nitrogen on molybdenum redistribution in black gram (Vigna mungoL. Hepper) with particular reference to seed fill

Seeds used to plant a crop may contain sufficient molybdenum (Mo) to prevent subsequent Mo deficiency in the crop even when they are sown on Mo deficient soils. However, little is known about either the sources of the Mo acquired by the seed, or the timing of its redistribution during seed development. A glasshouse experiment was set up to examine the effect of Mo supply and nitrogen source on the redistribution of Mo within black gram, from full flowering to seed maturity. Treatments comprised two sources of N (symbiotic N2fixation, NH4NO3), two levels of Mo supply [nil (−Mo), 0.64 mg Mo kg−1soil (+Mo)] and four harvests (full flowering, early pod setting, late pod filling and seed maturity). The redistribution of Mo in black gram was examined by determining changes over time in the content of Mo in plant parts at each growth stage. Molybdenum supply and the plant growth stage strongly affected the redistribution of Mo to the seed. In −Mo plants reliant on symbiotic N2fixation, Mo redistributed from roots, stems and leaves was the only source of Mo for reproductive development since, from full flowering until maturity, there was no net increase in whole plant Mo. For pod and early seed development, the roots were the major source of Mo in −Mo plants. After late pod filling, nodules replaced roots as the major source of Mo for seed fill in −Mo plants. By contrast, for +Mo plants reliant on symbiotic N2fixation, Mo taken up from the soil after full flowering could have supplied nearly 50% of the seed Mo. The major sources of Mo for seed filling in +Mo plants were middle stem leaves during early podding, and middle stems and pod walls from late podding. Supplying NH4NO3to plants from sowing had little effect on Mo distribution or redistribution in +Mo black gram plants. However, in −Mo plants it accelerated the loss of Mo from middle stems and their leaves compared to nodulated plants

The importance of sampling immature leaves for the diagnosis of boron deficiency in oilseed rape (Brassica napus cv. Eureka)

Plant analysis can diagnose boron (B) deficiency when the standards used have been properly developed by establishing that a close relationship exists between B concentration in a plant part and its physiological function. The purpose of the present study was to demonstrate the importance of choosing the growing immature leaves for B deficiency diagnosis and for establishing critical B concentrations for the diagnosis of B deficiency in oilseed rape (Brassica napus). In Experiment 1, the plants were subject to seven levels of B supply using programmed nutrient addition, for the estimation of critical B concentrations in plant parts for shoot growth. In Experiment 2, the plants were treated with two levels of B supply in solution: 10 (+B) and 0 (-B) uM B, for the estimation of functional B requirements for leaf elongation. The results showed that critical B concentrations varied amongst the plant parts sampled and decreased with leaf age. As B taken up by roots is largely phloem-immobile, B concentrations in mature leaves are physiologically irrelevant to plant B status at the time of sampling, giving rise to a significant over- or underestimation of the B requirement for plant growth. By contrast, a growing, immature leaf, in this case the youngest open leaf (YOL), was the most reliable plant part for B deficiency diagnosis. Critical B concentrations developed from both methods were comparable-i.e. 10–14 mg B kg–1 dry matter in the YOL at vegetative growth stages up to stem elongation