Triacontanol: a potent plant growth regulator in agriculture

Abstract

Triacontanol (TRIA) is a natural plant growth regulator found in epicuticular waxes. It is used to enhance the crop production in millions of hectares, particularly in Asia. Quite a number of researchers have reported the TRIA-mediated improvement in growth, yield, photosynthesis, protein synthesis, uptake of water and nutrients, nitrogen-fixation, enzymes activities and contents of free amino acids, reducing sugars, soluble protein, and active constituents of essential oil in various crops. Expectedly, TRIA enhances the physiological efficiency of the cells and, thus, exploits the genetic potential of plant to a large extent. In fact, TRIA increased free amino acids, reducing sugars, and soluble protein of rice (Oryza sativa L.) and maize (Zea mays L.) within 5 min. TRIA elicited the appearance of L(+)-adenosine within 1 min in the roots of plants, the shoots of which were sprayed with nanomolar concentrations of TRIA. TRIA and octacosanol (OCTA), the primary alcohols, are ubiquitous in the environment. OCTA was reported to inhibit the activity of TRIA in the seedlings of rice (Oryza sativa L.) at equimolar concentrations; and both TRIA and OCTA elicited a second messenger, known as OCTAM and triacontanol second messenger (TRIM), respectively. TRIA rapidly increases the ratio of L(+)- to D(–)-adenosine, probably at the tonoplast. However, it is to be resolved as to how TRIA elicits L(+)-adenosine and what is the source of L(+)-adenosine in plants. Based on known metabolic processes, de novo synthesis of L(+)-adenosine is unlikely, because of the rapidity of the response. TRIA-mediated increase in dry matter production could influence the inter-relationship between primary and secondary metabolism, leading to increased biosynthesis of secondary products. Various studies present strong evidences that application of TRIA applied either to the root medium or to leaves enhanced the growth and yield of vegetables and other crops, including agronomic and horticultural crops as well as medicinal and aromatic crop plants under normal and adverse conditions. However, further investigations are required to elucidate the possible role of TRIA on plant growth regulation, physiological activities and secondary metabolite biosynthesis regarding medicinal and aromatic plants subjected to abiotic stress. The present review covers the pivotal role of TRIA in plant growth and development, its mode of action and its significance in improving the crop productivity and quality of agricultural crops.     

Rapid elicitation of second messengers by nanomolar doses of triacontanol and octacosanol

Triacontanol (TRIA) increases the dry weight and alters the metabolism of rice (Oryza sativa L.) seedlings within 10 min of application to either the shoots or roots. This activity is prevented if octacosanol (OCTA, C₂₈ primary alcohol) is applied with the TRIA on the roots or shoots. Triacontanol activity is also stopped if the OCTA is applied at least 1 min before the TRIA on the opposite part of the seedling.Triacontanol rapidly elicits a second messenger that moves rapidly throughout the plant resulting in stimulation of growth (dry-weight increase) and water uptake. Octacosanol also produces a second messenger that inhibits TRIA activity. We have named the putative secondary messengers elicited by TRIA and OCTA, TRIM and OCTAM, respectively. The water-soluble TRIM extracted from plants treated with TRIA increases the growth of rice seedlings about 50% more than extracts from untreated plants, within 24 h of application. Both OCTAM and OCTA inhibit the activity of TRIA but not of TRIM.The TRIA messenger was isolated from rice roots within 1 min of a foliar application of TRIA. The TRIM elicited by TRIA will pass through a 4-mm column of water connecting cut rice shoots with their roots and can also be recovered from water in which cut stems of TRIA-treated plants have been immersed. Triacontanol applied to oat (Avena sativa L.) or tomato (Lycopersicon esculentum Mill.) shoots connected to rice roots by a 4-mm water column also results in the appearance of TRIM in rice roots.Abbreviations OCTA octacosanol - OCTAM second messenger elicited by OCTA - TAS tallow alkyl sulfate - TRIA triacontanol - TRIM second messenger elicited by TRIA Michigan Agricultural Experiment Station Journal Article No. 12001     

Rapid Growth and Apparent Total Nitrogen Increases in Rice and Corn Plants following Applications of Triacontanol

Triacontanol (TRIA) increased fresh and dry weight and total reducible nitrogen (total N) of rice (Oryza sativa L.) seedlings within 40 minutes. Increases in total N in the supernatants from homogenates of corn (Zea mays L.) and rice leaves treated with TRIA for one minute before grinding occurred within 30 and 80 minutes, respectively. The source for the increase was investigated utilizing atmospheric substitution and enrichment and depletion studies with ¹⁵N. The increase in total N in seedlings was shown to be independent of method of N analysis and the presence of nitrate in the plants. Automated Kjeldahl determinations showing apparent increases in N composition due to TRIA were shown to be correlated with hand Kjeldahl, elemental analysis, and chemiluminescent analysis in three independent laboratories. TRIA did not alter the nitrate uptake or endogenous levels of nitrate in corn and rice seedlings. Enrichment experiments revealed that the total N increases in rice seedlings, in vivo, and in supernatants of corn leaf homogenates, in vitro, are not due to atmospheric N₂. TRIA increased the soluble N pools of the plants, specifically the free amino acid and soluble protein fractions. No differences in depletion or enrichment of ¹⁵N incorporated into soluble and insoluble N fractions of rice seedlings could be detected on an atom per cent ¹⁵N basis. The apparent short-term total N increases cannot be explained by current knowledge of major N assimilation pathways. TRIA may stimulate a change in the chemical composition of the seedlings, resulting in interference with standard methods of N analysis.     

Triacontanol and Its Second Messenger 9-beta-l(+)-Adenosine as Plant Growth Substances

Triacontanol (TRIA), a common constituent of plant waxes, was first shown in 1977 to be an active growth substance which at nanomolar concentrations increased the growth and yield of crops. TRIA is used to increase crop yields on millions of hectares, particularly in Asia. Many investigators have shown that it affects several basic metabolic processes including photosynthesis, nutrient uptake, and enzyme activity. However, the initial site of action has not been elucidated. TRIA rapidly elicits a second messenger (TRIM) in rice (Oryza sativa L.), which at nanomolar concentrations causes plants to respond in a manner similar to TRIA. TRIM has been identified as 9-β-l(+)-adenosine (9H-purin-6-amine, 9-β-l-ribofuranosyl). During the process of isolating and identifying 9-β-l(+)-adenosine, it was shown that this enantiomer, which previously has not been reported as occurring in nature, made up about 1% of the total adenosine pool in roots from untreated rice seedlings.     

Biochemical and photochemical changes in response to triacontanol in rice (Oryza sativa L.)

Triacontanol (TRIA) increased the contents of total chlorophyll (Chl), Chl a and Chl b by 25.1%, 26.1% and 22.4% respectively 4 h after treatment in rice seedlings. The minimal fluorescence (F₀), the maximal fluorescence (Fm) and Fv/Fm were also higher in TRIA-treated plants. In actinic light, other Chl fluorescence parameters were measured at different photon flux densities (PFD) to construct light response curves of the quantum yield of PSII electron transport (_PSII), light response curves of photochemical quenching (qp), and light response curves of non-photochemical quenching (qN), respectively. The _PSII and qp declined with the increasing PFD with a higher level present in TRIA-treated plants. The qN increased with the increasing PFD with a lower level present in TRIA-treated plants. Two-dimensional gel electrophoresis indicated a protein expression difference between TRIA-treated materials and the controls at the total-soluble-protein level. Rubisco was 30% higher in TRIA-treated plants than in controls. The quantity of other proteins was unchanged in response to TRIA. These data provide biochemical and photochemical evidence for the effects of TRIA on photosynthesis.     

实时荧光定量PCR检测RSV胁迫下抗病、感病水稻中与脱落酸相关基因的差异表达

采用实时荧光定量PCR方法测定了水稻条纹病毒(Rice stripe virus,RSV)胁迫下抗性不同品种水稻中与脱落酸相关基因的mRNA转录水平变化.结果表明:感病品种武育梗3号中WGPI、OsGASA2、Polcalcin、OsCBIA、Myb和OsCIPK15基因表达水平均上调,上调比率分别为4.96、5.17、2.01、5.17、12.04和7.84.而抗病品系KT 95-418中,OsGASA2和OsCIPK15基因表达水平下调,下调比率分别为1/5.40和1/2.08;Polcalcin和Myb基因表达水平上调,上调比率分别为4.20和3.86;WGPI和OsCBIA表达量变化不明显.这些结果表明,RSV胁迫能诱导脱落酸相关基因表达量的变化,并且在抗病、感病水稻品种中的表达特征不同,从而提示植物激素脱落酸可能调控了RSV胁迫条件下相关基因的表达.     

生物有机肥对盐碱地水稻叶片的影响转录组分析

改良修复盐碱地对保障粮食安全和守护耕地红线具有重要意义,种植水稻配施生物有机肥是修复改良盐碱地的一项有效措施。基于生物有机肥肥料效应,测定水稻灌浆期农艺性状,开展叶片转录组测序,通过基因本体(GO)和京都基因与基因组百科全书(KEGG)数据库分析差异基因的生物学功能和代谢通路,以期揭示生物有机肥对盐碱地水稻的潜在促生机制。试验共设置4个处理,生物有机肥+化肥(T1)、生物有机肥灭活+化肥(T2)、化肥(T3)和空白对照(T4),结果表明,施用生物有机肥能够显著提高水稻叶面积和叶绿素、植株分蘖数和干物质量(P<0.05);T2vsT1、T3vsT1、T4vsT1、T4vsT3差异基因数量分别为6593、4796、6976和1866条,生物有机肥配施化肥引起差异基因表达数量最高,其次为灭活生物有机肥,单施化肥最小;GO分析显示,生物有机肥主要影响水稻叶片肽和酰胺的生物合成与代谢、翻译过程、细胞器及细胞器膜等,化肥对水稻叶片生物学过程影响的差异基因无显著富集(P>0.05);KEGG分析表明,施用生物有机肥差异显著基因主要富集在核糖体和能量代谢相关途径,核糖体相关基因差异表达较多...     

Specificity of 1-triacontanol as a plant growth stimulator and inhibition of its effect by other long-chain compounds

The effect of several analogs of 1-triacontanol (TRIA), differing in C-chain length (16–32), the position of the hydroxyl group and the terminal functional group, were tested alone and in combination with TRIA on the growth of rice (Oryza sativa L.), maize (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seedlings. Applied alone, none of the compounds caused an increase in growth; thus, chain length (30 C) and presence and position (terminal) of the hydroxyl group appear to be specific for the growth-promoting activity of TRIA. When applied simultaneously with TRIA, all analogs inhibited the response to the latter in all three test plants, whether applied in the nutrient solution, as foliar spray or by seed soaking. 1-Octacosanol inhibited the response of rice seedlings to 2.3 x 10^-8 M TRIA at concentrations as low as 2.4 x 10^-12 M. Thus preparations of TRIA and application equipment must be free from trace amounts of other long-chain compounds if they are to be used to increase plant growth.Abbreviation TRIA 1-triacontanol     

激活蛋白处理水稻引发基因差异表达的研究

利用抑制性消减杂交技术(Suppression Subtractive Hybridization,SSH)成功构建了植物激活蛋白处理水稻与非处理组水稻中差异表达的消减cDNA文库。从文库中一共筛选到1756个克隆,通过反向Northern杂交,从中得到264个有效克隆并测序,利用BLAST在GenBank数据库进行序列相似性比对分析,获得28个上升表达差异基因。通过分析这些基因与植物的光合作用、营养物质的运输代谢等多种植物的生理生化功能相关。本研究为揭示激活蛋白的作用机理奠定基础。     

A rice serine carboxypeptidase-like gene OsBISCPL1 is involved in regulation of defense responses against biotic and oxidative stress

Serine carboxypeptidase-like proteins (SCPLs) comprise a large family of protein hydrolyzing enzymes that play roles in multiple cellular processes. During the course of study aimed at elucidating the molecular basis of induced immunity in rice, a gene, OsBISCPL1, encoding a putative SCPL, was isolated and identified. OsBISCPL1 contains a conserved peptidase S10 domain, serine active site and a signal peptide at N-terminus. OsBISCPL1 is expressed ubiquitously in rice, including roots, stems, leaves and spikes. Expression of OsBISCPL1 in leaves was significantly up-regulated after treatments with benzothiadiazole, salicylic acid, jasmonic acid and 1-amino cyclopropane-1-carboxylic acid, and also up-regulated in incompatible interactions between rice and the blast fungus, Magnaporthe grisea. Transgenic Arabidopsis plants with constitutive expression of OsBISCPL1 were generated and disease resistance assays indicated that the OsBISCPL1-overexpressing plants showed an enhanced disease resistance against Pseudomonas syringae pv. tomato and Alternaria brassicicola. Expression levels of defense-related genes, e.g. PR1, PR2, PR5 and PDF1.2, were constitutively up-regulated in transgenic plants as compared with those in wild-type plants. Furthermore, the OsBISCPL1-overexpressing plants also showed an increased tolerance to oxidative stress and up-regulated expression of oxidative stress-related genes. The results suggest that the OsBISCPL1 may be involved in regulation of defense responses against pathogen infection and oxidative stress.     

Triacontanol as a dynamic growth regulator for plants under diverse environmental conditions

Triacontanol (TRIA) being an endogenous plant growth regulator facilitates numerous plant metabolic activities leading to better growth and development. Moreover, TRIA plays essential roles in alleviating the stress-accrued alterations in crop plants via modulating the activation of the stress tolerance mechanisms. The present article critically focuses on the role of exogenously applied TRIA in morpho-physiology and biochemistry of plants for example, in terms of growth, photosynthesis, enzymatic activity, biofuel synthesis, yield and quality under normal and stressful conditions. This article also enlightens the mode of action of TRIA and its interaction with other phytohormones in regulating the physio-biochemical processes in counteracting the stress-induced damages in plants.

     

Cytosolic APX knockdown rice plants sustain photosynthesis by regulation of protein expression related to photochemistry,Calvin cycle and photorespiration

The biochemical mechanisms underlying the involvement of cytosolic ascorbate peroxidases (cAPXs) in photosynthesis are still unknown. In this study, rice plants doubly silenced in these genes (APX1/2) were exposed to moderate light (ML) and high light (HL) to assess the role of cAPXs in photosynthetic efficiency. APX1/2 mutants that were exposed to ML overexpressed seven and five proteins involved in photochemical activity and photorespiration, respectively. These plants also increased the pheophytin and chlorophyll levels, but the amount of five proteins that are important for Calvin cycle did not change. These responses in mutants were associated with Rubisco carboxylation rate, photosystem II (PSII) activity and potential photosynthesis, which were similar to non‐transformed plants. The upregulation of photochemical proteins may be part of a compensatory mechanism for APX1/2 deficiency but apparently the finer‐control for photosynthesis efficiency is dependent on Calvin cycle proteins. Conversely, under HL the mutants employed a different strategy, triggering downregulation of proteins related to photochemical activity, Calvin cycle and decreasing the levels of photosynthetic pigments. These changes were associated to strong impairment in PSII activity and Rubisco carboxylation. The upregulation of some photorespiratory proteins was maintained under that stressful condition and this response may have contributed to photoprotection in rice plants deficient in cAPXs. The data reveal that the two cAPXs are not essential for photosynthesis in rice or, alternatively, the deficient plants are able to trigger compensatory mechanisms to photosynthetic acclimation under ML and HL conditions. These mechanisms involve differential regulation in protein expression related to photochemistry, Calvin cycle and photorespiration.     

Overexpression of the Qc-SNARE gene OsSYP71 enhances tolerance to oxidative stress and resistance to rice blast in rice (Oryza sativa L.)

OsSYP71 is an oxidative stress and rice blast response gene that encodes a Qc-SNARE protein in rice. Qc-SNARE proteins belong to the superfamily of SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors), which function as important components of the vesicle trafficking machinery in eukaryotic cells. In this paper, 12 Qc-SNARE genes were isolated from rice, and expression patterns of 9 genes were detected in various tissues and in seedlings challenged with oxidative stresses and inoculated with rice blast. The expression of OsSYP71 was clearly up-regulated under these stresses. Overexpression of OsSYP71 in rice showed more tolerance to oxidative stress and resistance to rice blast than wild-type plants. These results indicate that Qc-SNAREs play an important role in rice response to environmental stresses, and OsSYP71 is useful in engineering crop plants with enhanced tolerance to oxidative stress and resistance to rice blast.     

Characterization of the Ferredoxin-Gogat gene (OsGog2 clone) expression in rice

Ferredoxin-dependent glutamate synthase (Fd-Gogat; EC 1.4.7.1) in leaf and root plastids is the last enzyme involved in the pathway of nitrate assimilation in higher plants. Arabidopsis thaliana expresses two different genes: the first, light regulated, specific of green tissues and the second expressed in other tissues. In this work, we investigated whether in our clone, OsGog2 AC Y12595, this gene is up-regulated by light or it is expressed under darkness. Fd-Gogat specific activity, protein and mRNA increased after light treatment in rice shoots. In roots, the activity and the protein content remained constant, whereas the mRNA is repressed by light treatment. The results obtained using a specific probe, situated in the 3′ untranslated region of the OsGog2 cDNA, indicated that OsGog2 gene is up-regulated by light and that its expression is tissue specific and suggested that a dark expressed Fd-Gogat gene could be present in rice similarly as in Arabidopsis.