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Micronutrients are essential for plants. Their growth, productivity and reproduction are directly influenced by the supply of micronutrients. Currently, there are eight trace elements considered to be essential for higher plants: Fe, Zn, Mn, Cu, Ni, B, Mo, and Cl. Possibly, other essential elements could be discovered because of recent advances in nutrient solution culture techniques and in the commercial availability of highly sensitive analytical instrumentation for elemental analysis.
S. No. | Micronutrient | Year of Discovery | Ionic Form of Intake | Normal Value (ppm) | Deficient Value (ppm) | Toxic Value (ppm) |
---|---|---|---|---|---|---|
1 | Boron (B) | Warington (1937) | H2BO3, H2BO3−, HBO32−, BO33− | 10–20 | 5–10 | 50–200 |
2 | Chlorine (Cl) | Broyer et al. (1954) | Cl− | 100–500 | Less than 100 | 500–1000 |
3 | Copper (Cu) | Lipman and Mackinney (Sachs 1931) | Cu2+ | 5–30 | 2–5 | 100–200 |
4 | Iron (Fe) | Sachs (1860) | Fe2+, Fe3+ | 100–500 | Less than 50 | More than 500 |
5 | Manganese (Mn) | Mchargue (1922) | Mn2+ | 20–300 | 15–20 | 300–500 |
6 | Molybdenum (Mo) | Arnon and Stout (1939) | MoO42− | 0.1–2.0 | 0.03–0.15 | More than 100 |
7 | Zinc (Zn) | Sommer and Lipman (1926) | Zn2+ | 27–150 | 10–20 | 100–400 |
S.No. | Micronutrients | Representative Constituents/Proteins | Functions | Symptoms of Deficiency | Probable Cause of Deficiency & Method of Correction | References |
---|---|---|---|---|---|---|
1 | Zinc (Zn) | Cu–Zn superoxide, Peptide deformylase, enzyme carbonic anhydrase (CA), α-Mannosidase, Matrix metalloproteinase alcoholic dehydrogenase, and superoxide dismutase (SOD) |
role in nitrogen metabolism and photosynthesis, controls the concentration of auxin in plants, increases seed viability and seedling vigor, protection against abiotic and biotic stresses | Reduced vigor, chlorotic leaves, white streaks parallel to leaf blade, slow growth, restricted RNA and protein synthesis | Low Zn in soil, high soil pH—lower soil pH, apply foliar spray or add Zn to soil. | [8][9][10][11][12][13][14][15][16] |
2 | Copper (Cu) | Plastocyanin Cu-Znsuperoxide, Ascorbate, Cu-metallothionein, biosynthesis oxidase, Mo-cofactor, dismutase, polyphenol or catechol oxidase, tyrosinase, laccase, Cytochrome-C oxidase, Ethylene receptor ascorbic oxidase and Polyphenol oxidase | saves plants from diseases, improves the fertility of male flower, concerned with the oxidation of iron in plants | Leaf tips dries, break down and dies, ragged leaves, reduced growth | Low soil Cu, high organic matter—apply foliar spray or add Cu to soil | [17][18][19][20][21][22][23][24][25][26] |
3 | Iron (Fe) | Aconitase, dismutase, Xanthine dehydrogenase, Ferredoxin, porphyrin NADH, Succinate, Leg hemoglobin, heme and heme enzymes peroxidase oxidase, dehydrogenase, Nitrate reductase oxidoreductases, Thioredoxin reductase, Cytochrome P450, Aldehyde oxidase, Catalase, Nitrite reductase, Lipoxygenase, Alternative oxidase, Fe-superoxide Ferritin and other functional metallic proteins |
Present in haemoglobin of the leguminous root nodules, leg-haemoglobin and is involved in nitrogen fixation as a constituent of ferredoxin | Interveinal, creamy chlorosis on apical leaves, stunted shoots, reduced yield | Waterlogged soil, over fertilized, excess of elements like Mn—spraying plant with iron rich fertilizer, chelated iron powder or blood meal directly to the soil | [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] |
4 | Manganese (Mn) | Malic enzyme, Mn-superoxide, amidohydrolase, primary component of water-splitting enzyme related to photosystem II, PEP carboxylase, Allantoate, Iso-citrate lyase, dismutase PEP-carboxykinase | Involved in tricarboxylic acid cycle in oxidation and reduction reactions, activates several enzymes such as oxidoreductases, hydrolases and lyase, also autocatalyzes isocitrate dehydrogenase, malic dehydrogenase, glycocyaminase and D-alanyl synthase. | Reduced quality and yield, stunted plants, intervenial chlorosis in leaves, yellow cast in deficient areas. Death of basal leaves, decreased cold hardiness, growth of lateral roots stopped, inhibition of nitrate metabolism. | Low soil Mn, high soil pH due to over liming—lower soil pH, apply foliar spray or add Mn to soil | [47][48][49][50][51][52] |
5 | Boron (B) | Rhamnogalacturonan II | increases cell wall thickness and flower production, as well as retention, pollen tube elongation and germination, along with seed and fruit development. It also helps in the translocation of photosynthates. It inhibits IAA oxidation and gives drought tolerance to crops | Thick and leathery old leaves, shoot tip death, rosette leaves with short internodes, excess branching, short, twisted and/or ruptured petioles, vegetables with hollow heart, small and deformed/no fruits with cork spots chlorosis, stubby roots, inhibited nitrogen metabolism. | Low soil B especially on sandy soils or light textured soils—apply foliar spray or add B to soil | [53][54][55][56] |
6 | Molybdenum (Mo) | nitrogenase, sulphite oxidase, nitrate reductase Aldehyde oxidase and xanthine oxidase/dehydrogenase | aids in the synthesis of ascorbic acid, formation of pollens and anthers, acts as a remedy to excessive copper, manganese and zinc | stunted growth with twisted stems, leaves turning pale green, necrotic area in leaves along the mid rib between veins and along leaf edges | Low soil pH, low Mo content in soil—inoculate seed with Mo, apply foliar spray or add Mo to soil | [33][34][57][58] |
7 | Chlorine (Cl) | Oxygen-evolving complex Seismonastic movement | activates enzymes that are involved in starch utilization which affects germination and energy transfer. Inmoisture-stress conditions chlorine helps in the movement of water into cells and maintenance of that water. Chlorine also controls the opening and closing of stomata on leaf surfaces | stunted/restricted growth, stubby roots, interveinal chlorosis, non-succulent tissue, wilting | Low soil Cl especially in soils subjected to leaching—apply Cl containing fertilizer | [55][59] |
S. No. | Micronutrients | Type | Symptoms of Excess Usage | References |
---|---|---|---|---|
1 | Zinc (Zn) | Metal | Inhibited root growth, young leaf chlorosis, interveinal mild chlorosis in young leaves starting from base and spread towards apex followed by reddish brown coloration, rolling of leaves | [61] |
2 | Copper (Cu) | Metal | Reduced vigor, inhibited root growth/root damage, older leaves develop orange or pink coloration followed by severe rolling of leaf margins due to loss in turgidity | |
3 | Iron (Fe) | Metal | Reduced yield, bronzing and stippling of leaves, and, in some plants, acid is secreted from the roots | |
4 | Manganese (Mn) | Metal | Tissue injury, leaf sheath and lower parts of stem in cereal normally consist of minute brown spots, legumes develop brown or purple spots over leaf margin, deficiency symptoms of other nutrients | |
5 | Boron (B) | Metalloid | Toxicity results in dark brown speckles or necrosis on the edge of older leaves, cupped and wrinkled young leaves | |
6 | Molybdenum (Mo) | Metal | Leaf malformation, tints of golden yellow or blue color in leaves | |
7 | Chlorine (Cl) | Non metal | Death of leaf margin, leaves are reduced in size and number, have bronze or yellow coloration with brown or scorched leaf margins. |
Metal | Plant Species | Plant Part | Extraction Method | Protein Name | Function | Regulation | References |
---|---|---|---|---|---|---|---|
Boron (B) | Citrus grandis | Root | iTRAQ | Alcohol dehydrogenase 1 | Energy metabolism | Down | [62] |
Serine/arginine- rich 22 | Nucleic acid metabolic process | Down | |||||
Clathrin light chain protein | Cellular cytoskeleton and transport | Up | |||||
Peroxiredoxin IIF | Cellular response to stress | Down | |||||
Phospholipase C2 | Signal transduction | Down | |||||
Arabidopsis thaliana | Leaf | 2-DE, LC-MS/MS | Rubisco activase | Photosynthesis | Up | [63] | |
Actin 7 | Metabolism | Down | |||||
Fructose-bisphosphate aldolase | Energy metabolism | Up | |||||
Glycolate oxidase | Photosynthesis | Down | |||||
Coppe (Cu) | Sorghum bicolor | Leaf | 2-DE, MALDI-TOF MS | Thymidine kinase | Protein translation and synthesis | Down | [64] |
Thaumatin-like protein | Stress and defense | Up | |||||
Maturase K | Growth and development | Down | |||||
Alcohol dehydrogenase | Oxidation– reduction process | Up | |||||
Oryza sativa | Root | 2-DE, MALDI-TOF MS | Putative peroxidase | Anti-oxidation and detoxification | Up | [65] | |
Putative cold shock protein-1 | Transcriptional regulation | Up | |||||
Putative elongationfactor EF-2 | Protein synthesis | Down | |||||
Glutamine synthetase shoot isozyme | Amino acid synthesis | Down | |||||
Allium cepa | Root | 2-DE, MALDI-TOF MS | Glutaredoxin | Defense | Up | [66] | |
Ran-binding protein 1 | Protein synthesis | Down | |||||
Cinnamoyl-Co-A-reductase 1 | Cell wall synthesis | Down | |||||
Proliferation-associated 2 g4 | Cell cycle and DNA replication | Up | |||||
Iron (Fe) | Arabidopsis thaliana | Root | Itraq, LC-MS | Oxidoreductase | Hormone metabolism | Up | [67] |
WAKL4, WAK- like receptor- like kinase | Signaling | Up | |||||
FRO3, ferric chelate reductase 3 | Metal handling | Up | |||||
SAPX, Stromal ascorbate peroxidase | Redox | Down | |||||
IRT3, Iron regulated transporter3 | transport | Down | |||||
Zea may | Root | LC-MS/MS | Aquaporin PIP2-2 | Transport proteins | Down | [68] | |
Gibberellin receptor GID1L2 | Signaling proteins | Down | |||||
Aldolase | Metabolism | Up | |||||
Actin-2 | Cytoskeleton | Down | |||||
Callreticulin 2 | Protein folding | Up | |||||
Cucumis sativus | Root | 2-DE, ESI-LC-MS | Phosphoglycerate kinase | Glycolysis | Up | [69] | |
Malate dehydrogenase | Carbohydrate-related metabolism | Up | |||||
Alanine aminotransferase | Nitrogen-related metabolism | Up | |||||
Xylan 1,4-beta-xylosidase | Metabolism of sucrose | Down | |||||
Manganese (Mn) | Citrus grandis | Root | 2-DE, MALDI-TOF MS, LTQ-ESI-MS/MS | Acetohydroxyacid isomeroreductase | Protein metabolism | Down | [70] |
Maturase K | Nucleic acid metabolism | Up | |||||
Alcohol dehydrogenase | Carbohydrate metabolism | Up | |||||
Iron- sUperoxide dismutase | Stress response | Down | |||||
Valosin- containing protein | Cell transport | Down | |||||
Zinc (Zn) | Lactuca sativa | Leaf | LC-MS/MS, MALDI-TOF | MPBQ/MSBQ transferase | Photosynthesis | Up | [71] |
Cytosolic fructose-1,6-bisphosphate | Energy metabolism | Up | |||||
Putative cellulose synthase | Cell wall metabolism | Down | |||||
Phenylalanine ammonia-lyase | Phenylpropanoids biosynthesis | Down |
Metals | Plant Species | Tissue | Method of Identification | Gene | Functions | Regulation | References |
---|---|---|---|---|---|---|---|
Boron (B) | Arabidopsis thaliana | Root | qRT-PCR | SHB1/HY1 | B-tolerance | Up | [72] |
Oryza sativa | Root | Microarray, qRT-PCR | LOC_Os08g30740 | ABC transporter | Down | [73] | |
LOC_Os10g30156 | Starch synthase | Down | |||||
LOC_Os10g30080 | Xylosyltransferase | Down | |||||
Citrus sinensis | Leaf | Illumina sequencing, qRT-PCR | Ciclev10017846m | Ubiquitin-protein ligase activity | Down | [74] | |
Ciclev 10012377m | Transcription factor | Up | |||||
Ciclev 10009779 m | Blue copper protein | Up | |||||
Zinc (Zn) | Arabidopsis thaliana | Whole plant | qRT-PCR | PDR8 | Phytochelatin synthesis | Up | [75] |
ABCCI | Metabolism | Down | |||||
Iron (Fe) | Citrus sinensis | Whole plant | qRT-PCR | Cs3g19420 | Ethylene-responsive transcription factor | Up | [76] |
Cs4g12540 | Ethylene synthesis | Down | |||||
Cs9g02930 | Flavone synthase | Down | |||||
Arabidopsis thaliana | Root | qRT-PCR | FRO2 | Iron homeostasis | Up | [77] | |
Manganese (Mn) | Arabidopsis thaliana | Root | qRT-PCR and RNA sequencing | AT5G05960 | Bifunctional inhibitor | Down | [78] |
AT4G39940 | Glucosinolate | Up | |||||
AT1G15820 | metabolism Photosynthesis | Up | |||||
Citrus sinensis | Leaf | cDNA-AFLP and qRT-PCR | TDF #065-1 | Energy metabolism | Up | [79] | |
TDF #073-1 | Cell transport | Down | |||||
TDF #103-2 | Stress responses | Down | |||||
Copper (Cu) | Arabidopsis thaliana | Whole plant | qRT-PCR | OsLAC10 | Laccase activity | Up | [80] |
AtLAC11 | Lignin biosynthesis | Up | |||||
Oryza sativa | Whole plant | Western blotting, qRT-PCR | OsHMA4 | Copper accumulation | Down | [74] |