No abstract

Phosphorus (P) is one of six essential macronutrients in plants to ensure crop growth and productivity. Plants only acquire phosphorus in the form of inorganic phosphate (Pi) known as orthophosphate, mainly in the form of H2PO4 −. The high demand of Pi in fertilisers for agriculture use contributed to environmental pollution. Therefore, it is important to understand the Pi uptake from the soil and remobilisation within the plant to increase P use efficiency (PUE). In this study, the experiments were undertaken to look at the variation of Pi uptake by Brassica spp. under different soil Pi availability. Two soil Pi concentrations, P1 (0 g L−1) and P4 (0.225 g L−1) were selected to represent the low and high Pi treatment, respectively. B. napus plants grown in compost with both high and low Pi treatments were harvested at four different parts of the plant (leaf, stem, flower, and pod silique and seed) at six different growth stages, namely two-leaf stage, four-leaf stage, flowering stage, first flower opens stage, seed filling stage and maturity stage. The results of free Pi concentration in P4 (0.225 g L−1) were significantly higher than P1 (0 g L−1) (P ≤ 0.01). Remobilisation of Pi determined by total P contents of plants treated with P1 and P4 both showed similar trends, increased P contents up to 50% of plant P at harvest 5 (seed stage), and loss of P at leaf, stem and flower tissues during senescence at maturity stage. Under deficiency, leaf Pi concentration which determined the internal Pi redistribution showed Pi was redistributed from source (mature organs) to sink (developing tissues) Pi tissues. These results provide insights on plant nutrient status and can be used for further investigation for crop optimal production under low Pi availability.

Phosphate (Pi) deficiency in soil is one of the limiting factors to a growing plant due to its slow diffusion and high fixation in the rhizosphere. Brassica rapa plants were grown hydroponically under replete (P+) and deplete (P-) conditions to examine the variations in the expression of Pi responsive genes using real-time quantitative PCR (qPCR). Nine candidate reference genes were selected from the NCBI database. TATA box and SAND were selected as the most suitable reference genes under Pi-replete and Pi-deplete conditions due to their high efficiency and quality. The selected reference genes were validated by analyzing the expression of 14 target Pi responsive genes. The expression analysis of B. rapa root samples under Pi deficiency revealed the variable expression of genes; Bro18-014187 (ALMT1), a gene that is involved in organic acid exudation (OA) in the root system to promote phosphorus use efficiency (PUE) in plants, showed the highest increased (7.6-fold) under Pi-stress. Meanwhile, the expression of genes Bro18-047862 (PAP12), Bro18-038689 (MATE), Bro18-038513 (MMDH1), Bro18-004703 (SUC2), and Bro18-025411 (SUC2) increased with 3.69-fold, 1.9-fold, 1.4-fold, 3.03-fold, and 1.8-fold, respectively. Decreased gene responses were seen in Bro18-009479 (CS4), Bro18-042204 (ALMT1), and Bro18-035630 (MATE), while five other genes Bro18-039999 (PAP12), Bro18-049018 (CS4), Bro18-006954 (ALMT1), Bro18-035465 (MMDH1) and Bro18-013770 (MMDH1) remain unchanged. The whole-genome triplication (WGT) event in B. rapa led to three copies of paralog genes and transcription analysis showed the robust variation in the expression patterns of these paralog genes. Genes involved in signaling, transport, extracellular Pi scavenging, physiological function, and metabolic pathways are among the most highly expressed genes. This research provides a general overview of Pi’s influence on plant growth processes as well as presents particular experimental data on B. rapa responses to Pi deficiency.

This study focused on the efficacy of the fecal matter component from insect-derived frass containing high total crude fibre (TCF) for the effective alleviation of ammonium (NH4+) toxicity in short-term vegetables. Two types of insect-derived frass, bred from different feeding substrates, the black soldier fly (BSF) larvae, Hermetia illucens, known as the BSF frass (BSFF), and the common house cricket (CHC), Acheta domesticus, of both adults and nymphal instars, known as CHC frass (CHCF). The short-term vegetable, Amaranthus tricolor, was chosen as the test crop. A total of 200 A. tricolor vegetable seedlings were tested, with five experimental replicates, each with 10 A. tricolor seedlings set following completely randomized design, each for the different fertilizer treatments, BSFF fertilizer, CHCF fertilizer, NPK 15:15:15 fertilizer as the positive control, and no fertilizer as the negative control, pre-prepared in the form of soil–fertilizer mixtures, applied following the rate of 120 kg N ha−1. Comparatively, BSFF fecal matter component recorded lower rates of decomposition of total organic matter (TOM), total organic carbon (TOC), and organic nitrogen (ON) but with a higher rate of TCF decomposition, contrary to CHCF with higher rates of decomposition of TOM, TOC, ON, and a lower rate of TCF decomposition. Additionally, the rates of ON decomposition to NH4+ and NH4+ uptake were lower for BSFF compared to CHCF. The ratio rates of TOM-TCF (22:31), TOM-ON (22:02), TOC-TCF (30:31), and TOC-ON (30:02) for BSFF recorded the highest difference, compared to CHCF with a lower difference of ratio rates; TOM-TCF (36:21), TOM-ON (36:13), TOC-TCF (38:21), and TOC-ON (38:13). The alleviation of NH4+ toxicity for short-term vegetables with high sensitivity toward excessive NH4+ uptake could only be effectively alleviated with high TCF fecal matter component of the frass, increasing decomposition toward the TCF element and reduced decomposition on the organic N element of the frass’ fecal matter.

In response to Pi deprivation, phosphate 1 (PHO1) is a significant regulator at trans-eQTL hotspots in Brassica rapa. Brassica rapa short-read sequencing data analysis revealed four PHO1 paralog genes, PHO1_A, PHO1_B, PHO1_C, and PHO1_D, placed in tandem with very high sequence similarity. However, based on short-read genomic sequence data, only three transcripts are accessible. Five bacterial artificial chromosomes (BACs) can be sequenced using a long-read sequencer, which improves de novo assembly and identifies structural variants. The PHO1 gene’s quadruplicating tandem positions in the genomic sequence were confirmed by an analysis of long-read data. Transcript analysis identified only three groups of PHO1 paralogs (ortholog AT1G14040 in Arabidopsis), i.e., PHO1_A, PHO1_B, and PHO1_D, expressed in B. rapa leaf tissues under Pi deficiency. PHO1_A, with transcript ID XM_009150437.2, has five different splice variants found. These splice variants’ truncated proteins demonstrated PHO1_A’s function in P control as opposed to protein encoding.