Apple Nitrogen Research Articles

A peptide encoding gene MdCLE8 regulates lateral root development in apple

Nitrogen is not only an essential nutrient for plant, but also an important signal molecule to integrate and regulate gene expression, metabolism and growth. Plant peptides are considered as a new type of hormone, and play an important regulatory role in plant growth and development. However, little is known about the co-regulation network between nitrogen and peptide hormones in plant. Here we identified an apple MdCLE8 gene, which encodes a putative peptide, induced by nitrogen deficiency in apple. Ectopic expression of MdCLE8 inhibited lateral root formation in Arabidopsis under nitrogen deficiency. Similarly, overexpression of MdCLE8 inhibited lateral root development in apple adventitious roots, and this inhibition was amplified under nitrogen deficiency treatment. Further studies showed that MdCLE8 may inhibit the expression of several key genes during lateral root emergence stage in Arabidopsis, thereby inhibiting the emergence of lateral root from root cortex cells. Collectively, our study not only broadened the gene regulatory network under the influence of nitrogen in apple, but also expanded the function of CLE peptide hormones in apple.

Depth-wise distribution of different forms of nitrogen in apple growing soils of Pulwama district of Kashmir Valley

Depth-wise distribution of different fractions of nitrogen in some selective sites (soil depths) of district Pulwama of Kashmir valley was studied. In all the soil profiles nitrogen fractions (forms) decreased with increase in depth except the fixed NH 4 -N which increased with decreased depth. Organic nitrogen showed high significant positive correlations with total nitrogen (r=0.987***), organic nitrogen decreased with depth while the fixed NH 4 -N increased and these two fraction were also showed highly significant correlation with each other (r=0.645***).

CO2 assimilation in relation to nitrogen in apple leaves

SummaryBench-grafted Fuji/M.26 apple (Malus domestica Borkh.) trees were fertigated for 45 d with different nitrogen concentrations in modified Hoagland's solutions. A wide range of leaf N content was noted in recently fully expanded leaves (from 0.9–4.4 g m–2). Apparent quantum efficiency for CO2 assimilation was relatively constant except for a slight decrease at the lower end of the leaf N range. The light saturation point for CO2 assimilation increased with increasing leaf N. Curvilinear relationships were found between leaf N and 1) light-saturated CO2 assimilation at ambient CO2 2) the initial slope of the response of CO2 assimilation to intercellular CO2 concentration, and 3) CO2-saturated photosynthesis. All three initially increased linearly with increasing leaf N, then reached a plateau at a leaf N content of approximately 3 g m–2. The relationship between leaf N and stomatal conductance was similar to that of CO2 assimilation with leaf N. Calculated intercellular CO2 concentration, however, tended to decrease with increases in leaf N, indicating that stomatal conductance did not limit photosynthesis in leaves with low N content. Light-saturated CO2 assimilation, expressed on a leaf N basis, decreased with increasing leaf N. A curvilinear relationship existed between leaf N content and photosynthetic capacity in apple leaves. Photosynthetic N use efficiency decreased with increasing leaf N content.

Light Absorption and Partitioning in Response to Nitrogen in Apple Leaves

Bench-grafted Fuji/M26 apple trees were fertigated with different concentrations of nitrogen by using a modified Hoagland solution for 6 weeks, resulting in a range of leaf N from 1.0 to 4.3 g·m–2. Over this range, leaf absorptance increased curvilinearly from 75% to 92.5%. Under high light conditions (1500 (mol·m–2·s–1), the amount of absorbed light in excess of that required to saturate CO2 assimilation decreased with increasing leaf N. Chlorophyll fluorescence measurements revealed that the maximum photosystem II (PSII) efficiency of dark-adapted leaves was relatively constant over the leaf N range except for a slight drop at the lower end. As leaf N increased, non-photochemical quenching under high light declined and there was a corresponding increase in the efficiency with which the absorbed photons were delivered to open PSII centers. Photochemical quenching coefficient decreased significantly at the lower end of the leaf N range. Actual PSII efficiency increased curvilinearly with increasing leaf N, and was highly correlated with light-saturated CO2 assimilation. The fraction of absorbed light potentially used for free radical formation was estimated to be about 10% regardless of the leaf N status. It was concluded that increased thermal dissipation protected leaves from photo-oxidation as leaf N declined.

Phloem Translocation of Storage Nitrogen in Apple

AbstractMobilization of nitrogenous compounds during the spring was studied in ringed isolated shoot sections (bearing one intact bud each) from Golden Delicious apple trees and in intact stem‐ringed apple rootstocks M VII. The changes in total, protein and soluble nitrogen and soluble amino acids and amides were followed in the bark of the shoot sections for 3 weeks during leafing‐out and in the shoot and stem bark of the rootstocks for 6 weeks starting at bud‐break.Ringing prevented nitrogen movement from below the ring both in the shoot sections and in the rootstocks almost completely, thus demonstrating the importance of the phloem as translocation pathway for stored nitrogenous compounds, even over longer distances.Asparagine and arginine were the major soluble amino compounds throughout. The values of the asparagine/arginine quotient in the various tissues suggest that when the distance between points of nitrogen supply and demand is short asparagine is translocated preferentially, but that at increasing distance this preference shifts to arginine.