Changes in the Elemental and Metabolite Profile of Wheat Phloem Sap during Grain Filling Indicate a Dynamic between Plant Maturity and Time of Day

Abstract

The long distance transport of Fe and Zn in the phloem sap of wheat (Triticum aestivum L.) is the key route for seed supply, due to wheat having a xylem discontinuity. To date, our knowledge is limited on Fe and Zn homeostasis in the phloem sap during the reproductive and grain filling stages. With the use of aphid stylectomy to collect samples of phloem sap, we explored maturity and morning versus afternoon (within-day) changes in nutrient and metabolite profiles. Phloem exudate was collected from a wheat breeding line, SAMNYT16, at three times during the grain filling period and at both midday and mid-afternoon. There were significant changes in the concentration of Mg, K, Fe and Zn during the course of grain loading and there were also significant within-day differences for Fe and K concentrations in the phloem exudate during the early phases of grain development. We found that, for K and Fe, there was an increase of 1.1- and 1.4-fold, respectively, for samples taken prior to midday to those from mid-afternoon. There was also a significant decrease in K, Fe and Zn phloem sap concentration of 1.5-, 1.4- and 1.1-fold, respectively, from the start of peak grain loading to the end of grain loading. Of the 79 metabolites detected within samples of phloem exudate, 43 had significant maturity differences and 38 had significant within-day variability. Glutamine was found to increase by 3.3–5.9-fold from midday to mid-afternoon and citric acid was found to decrease by 1.6-fold from the start of grain loading to the end of grain loading. These two metabolites are of interest as they can complex metal ions and may play a role in long distance transport of metal ions. The work presented here gives further insight into the complex composition of the phloem sap and variability that can occur during the day and also with increasing maturity.

Further Understanding of Metabolic Processes for Crop Improvement – An Integrated Approach with Reference to Deprived and Developed Countries

“…To achieve the goals of increasing yield, protein content and desired protein composition knowledge from the crops has been obtained and being obtained and exploited by employing various tools and methodologies Viz; whole genome sequencing, genotyping, association mapping, genome editing, antisense technology, site directed mutagenesis, RNA silencing, bioinformatic tools, GWAS (Genome wide association studies), determining the number of copies of genes for different storage fractions, selective amplification of nutritionally rich genes, expression of heterologous genes, marker assisted selection (MAS), transcriptional and post-transcriptional regulation, translational and post transcriptional regulation and posttranslational modifications, hormonal regulation, regulation by small, micro RNA's, transcription factors, nitrate/ amino acid/amides/ ureide transporters /permeases, transcriptomics, proteomics, metabolomics, phenomics, transgenic technology, CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)-Cas (CRISPR-associated proteins) technology, high-throughput sequencing, etc [3,12,13,20,24,43,46,50,61,64,71,82,89,94,98].…”

“…Organic acids particularly malate; minerals particularly potassium; a few proteins and peptides are also transported in phloem. Apparently phloem transported metabolites in addition to being used as a source of nutrients maybe involved in signaling and regulation of metabolism [4,7,11,23,28,33,36,38,39,43,52,56,70,75,81].…”

“…This will indicate the relative proportions of direct contributions of soil nitrogen versus nitrogen mobilized into the seed as a result of already stored protein degradation in senescing leaves. This depends primarily on how active roots are even at the stage of seed development [7,9,16,23,33,36,40,43,47,54,56,60,67,69,75,76,81,82,83,87,97].…”

“…As hormones except ethylene have been implicated in embryonic and endosperm cell division and enlargement and maturity, why not an empirical approach of spraying different permutations and combinations of hormones during seed development phase on different parts of the plant? [5,19,40,43,76,96]…”

“…NTP's can also arise from the degradation of DNA in nucleus, mitochondria and chloroplasts of senescing leaves and other sources transporting nutrients like stems etc. Search and study of nucleotide transporters is useful [7,33,36,43,56,70,75].…”