Mobilisation of nutrients and transport via the xylem sap in a shrub (Ligustrum ovalifolium) during spring growth: N and C compounds and interactions

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W-N-P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W-N applications, regardless of P inputs. Moderate-to-highest W-N-P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N-P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N-P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W-N-P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year-1, N and P at 110 and 45 kg ha-1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

Application of capillary electrophoretic methods for the analysis of plant phloem and xylem saps composition: A review

Plant vascular tissue is essential for the exchange of water, nutrients, metabolic products, and signals among distant organs in cormophytes. The compositions of phloem and xylem saps are highly dependent on many internal and external factors, and thus their analysis provides a valuable insight into plant physiology, growth, and development as well as nutrition status or presence of biotic or abiotic stresses. Capillary electrophoresis characterized by highly efficient separations and minuscule sample requirements represents a suitable analytical technique for this purpose because the sap constitutes a complex mixture with generally minimal availability. This review aims at providing a comprehensive overview of published capillary electrophoretic methods for the analysis of primary components present in the phloem and xylem saps of higher plants.

Asparagine and sugars are both required to sustain secondary axis elongation after bud outgrowth in Rosa hybrida

Nitrogen is required for optimal plant growth, especially in young organs such as secondary axes (axes II) after axillary bud outgrowth. Several studies have shown an increase of nitrogen concentration in xylem sap concomitantly with bud outgrowth, but the relation between nitrogen, sugars and plant hormones in axis II still remains unclear. We investigated in Rosa hybrida the involvement of nitrogen nutrition in axis II elongation in relation with sugars and cytokinins using ¹⁵N-labeled nitrate and sugars, amino acids and cytokinin quantifications. Besides, we measured the effect of the exogenous supply of these compounds on axis II elongation using in vitro excised bud culture. We demonstrated that nitrogen in the axis II comes mainly from new root uptake after decapitation. Asparagine, which concentration increases in sap exudates and tissues during axis II elongation, was the sole amino acid able to sustain an efficient elongation in vitro when supplied in combination with sucrose.

Supplying nitrate before bud break induces pronounced changes in nitrogen nutrition and growth of young poplars

Tree nutrient research concentrated on endogenous C and N remobilisation in spring has neglected to acknowledge the possibilities of significant effects of N uptake before bud break, especially on the quality of regrowth and N reserve remobilisation. To investigate this subject, experimental studies were performed on young poplars (Populus tremula×Populus alba, clone INRA 717-1B4) grown with a controlled nutrient supply: (i) without N, 'control'; (ii) N supplied throughout the course of the experiment, 'N-supply'; and (iii) N supplied only before bud break, 'N-pulse'. Results confirm the hypothesis that poplar scions can significantly take up nitrate before bud break, amounting to ~34% of the total N stored the previous year. After bud break, emerging leaves restart the sap flow, which increased nitrate uptake to support the regrowth. N-pulse and N-supply treatments were found to have significant effects shortly after a growth period, i.e. by increasing N content of all tissues (e.g. 37 and 81% in new shoots respectively), leaf area (18 and 29%) and specific leaf area (20 and 35%). Therefore, results confirm the hypothesis that early N supply plays a significant role in the N status and N remobilisation involved in the spring regrowth of young trees.

Magnesium nutrition on accumulation and transport of amino acids in tea plants

BACKGROUND

Free amino acids in young tea shoots are important chemical constituents, remarkably influencing the quality of green teas. Nutrient solution, soil pot and field experiments were conducted to investigate the effect of magnesium nutritional status on accumulation and transport of free amino acids in tea plants (Camellia sinensis (L.) O. Kuntze).

RESULTS

A sufficient supply of Mg in nutrient solution increased biomass production and concentrations of free amino acids, notably theanine in young shoots and roots, without affecting total N in the leaves, absorption rates of inorganic N and glutamine synthetase activity. Amino acids in xylem saps and phloem exudates or total sugars in phloem exudates of tea plants from pot and field experiments showed their highest levels in bud breaking and shoot extension in early spring (March and early April). Application of Mg increased the amounts of amino acids and total sugars in the xylem saps and phloem exudates.

CONCLUSION

Adequate supply of Mg nutrient promoted the synthesis of theanine in roots and its accumulation in the young shoots of tea plants. Magnesium nutritional status was an important factor influencing the mobility of amino acids and sugars via xylem and phloem especially when N and C reserves remobilized to support spring growth of young shoots.

Nitrogen partitioning in orchard-grown Macadamia integrifolia

Nut yield is highly variable in commercial macadamia production, and to ensure that nitrogen (N) supply does not limit yield, high rates of N fertilizer are generally applied. To elucidate N source and sink relations in mature Macadamia integrifolia Maiden et Betche trees, we traced (15)N label after injection into individual branches and, after soil application, analysed xylem sap and examined the effects of hedging on tree N relations. Xylem sap N and sugar composition and concentration changed in relation to phenology and tree management. Canopy position did not affect xylem sap N concentration but sampling date had a significant effect. Hedging in spring was associated with a rapid and dramatic reduction of the concentration of xylem sap N until the following autumn, but unhedged trees were not available to unequivocally assess the significance of the results. Following (15)N-branch injection in winter, most (15)N label was incorporated into flushing leaves and into bark. After (15)N injection in spring, flushing leaves and flowers were most strongly (15)N-labelled. In late spring, (15)N label was equally incorporated by developing nuts that were retained or later abscised. Soil (15)N application in summer resulted in (15)N-labelling of outer and mid-canopy leaves. In the following spring, (15)N label was translocated to flushing leaves, flowers and developing nuts. The results indicate that outer and mid-canopy leaves are the main N sink for soil-derived N during the vegetative phase and a N source for developing tissues during the reproductive phase. Our study provides evidence that N supply to developing nuts is not a primary cause for nut abscission, supporting the notion that high N fertilizer application rates do not improve nut retention. We propose that current orchard design and hedging practices should be reviewed in context of the role of outer canopy leaves as a source of N for reproductive tissues.

Carbohydrate uptake from xylem vessels and its distribution among stem tissues and buds in walnut (Juglans regia L.)

Bud break pattern is a key determinant of tree architecture. The mechanisms leading to the precedence of certain buds over the others are not yet fully explained, but the availability of soluble sugars may play a significant role, especially those in the xylem sap at the onset of the growing period. Here, we measured carbon availability in the different tissues (bud, xylem and bark). To assess the capacity of buds to use the xylem sap carbohydrates, the fluxes between xylem vessels and parenchyma cells, bark and buds of walnut (Juglans regia cv 'Franquette') were measured during the rest period until bud break. This uptake capacity varies according to the temperature, the sugar and the position on the branch of the fragment studied. Between December and March, in xylem tissues, the active component of sucrose uptake was predominant compared with diffusion (90% of the total uptake), whereas the active component accounted for more moderate amounts in buds (50% of the uptake). The active uptake of hexoses took place belatedly (April) in xylem. The flow rates between xylem vessels and buds increased 1 month before bud break and reached 2000 microg sucrose h(-)(1) g DW(-)(1). Fluxes seemed to depend on bud position on the branch. However, this study strongly suggests that they were mainly dependent on the sink strength of the buds and on the sink competition between bud, xylem parenchyma and bark.

Exogenous ammonium inhibits petal pigmentation and expansion in Gerbera hybrida

Petal pigmentation is the most important aspect in natural flower coloration. In the present study, the inhibition of petal pigmentation by exogenous ammonium was investigated. Ray floret petals detached from inflorescences of Gerbera hybrida (Shenzhen No. 5) were cultured in vitro on media supplied with different forms of nitrogen and its assimilated compounds. The expression of a set of genes involved in anthocyanin biosynthesis and regulation was determined by Northern blotting assay. It was found that ammonium (NH4+), not nitrate (NO3-), in millimolar concentrations inhibited anthocyanin accumulation. The expressions of Gerbera chalcone synthase 1 (GCHS1), Gerbera chalcone synthase 2 (GCHS2) and Gerbera dihydroflavonol-4-reductase (GDFR) decreased, while six other related genes showed no significant changes after NH4+ treatment. Further studies on NH4+ function indicated that glutamine (Gln) acted as a downstream factor of NH4+ to suppress petal pigmentation. Both exogenous Gln and NH4+ were found to inhibit anthocyanin accumulation in the petals, and the application of Gln was also found to inhibit the expressions of GCHS1, GCHS2 and GDFR. The application of NH4+ also resulted in an increase in the activity of Gerbera glutamine synthetase (EC 6.3.1.2) along with a rapid increase of Gln content. When methionine sulfoximine, an inhibitor of glutamine synthetase (GS), was added, it was found to block the NH4+-induced inhibition of pigmentation. From these experiments, we conclude that the NH4+-induced suppression of petal pigmentation is not because of NH4+ toxicity, and the inhibition of pigmentation caused by the addition of exogenous NH4+ is the result of its assimilation into Gln.