Lijun Gan

Hydrogen Peroxide Is a Second Messenger in the Salicylic Acid-Triggered Adventitious Rooting Process in Mung Bean Seedlings

In plants, salicylic acid (SA) is a signaling molecule that regulates disease resistance responses, such as systemic acquired resistance (SAR) and hypertensive response (HR). SA has been implicated as participating in various biotic and abiotic stresses. This study was conducted to investigate the role of SA in adventitious root formation (ARF) in mung bean (Phaseolus radiatus L) hypocotyl cuttings. We observed that hypocotyl treatment with SA could significantly promote the adventitious root formation, and its effects were dose and time dependent. Explants treated with SA displayed a 130% increase in adventitious root number compared with control seedlings. The role of SA in mung bean hypocotyl ARF as well as its interaction with hydrogen peroxide (H2O2) were also elucidated. Pretreatment of mung bean explants with N, N’-dimethylthiourea (DMTU), a scavenger for H2O2, resulted in a significant reduction of SA-induced ARF. Diphenyleneiodonium (DPI), a specific inhibitor of membrane-linked NADPH oxidase, also inhibited the effect of adventitious rooting triggered by SA treatment. The determination of the endogenous H2O2 level indicated that the seedlings treated with SA could induce H2O2 accumulation compared with the control treatment. Our results revealed a distinctive role of SA in the promotion of adventitious rooting via the process of H2O2 accumulation. This conclusion was further supported by antioxidant enzyme activity assays. Based on these results, we conclude that the accumulation of free H2O2 might be a downstream event in response to SA-triggered adventitious root formation in mung bean seedlings.

In Site Bioimaging of Hydrogen Sulfide Uncovers Its Pivotal Role in Regulating Nitric Oxide-Induced Lateral Root Formation

Hydrogen sulfide (H2S) is an important gasotransmitter in mammals. Despite physiological changes induced by exogenous H2S donor NaHS to plants, whether and how H2S works as a true cellular signal in plants need to be examined. A self-developed specific fluorescent probe (WSP-1) was applied to track endogenous H2S in tomato (Solanum lycopersicum) roots in site. Bioimaging combined with pharmacological and biochemical approaches were used to investigate the cross-talk among H2S, nitric oxide (NO), and Ca2+ in regulating lateral root formation. Endogenous H2S accumulation was clearly associated with primordium initiation and lateral root emergence. NO donor SNP stimulated the generation of endogenous H2S and the expression of the gene coding for the enzyme responsible for endogenous H2S synthesis. Scavenging H2S or inhibiting H2S synthesis partially blocked SNP-induced lateral root formation and the expression of lateral root-related genes. The stimulatory effect of SNP on Ca2+ accumulation and CaM1 (calmodulin 1) expression could be abolished by inhibiting H2S synthesis. Ca2+ chelator or Ca2+ channel blocker attenuated NaHS-induced lateral root formation. Our study confirmed the role of H2S as a cellular signal in plants being a mediator between NO and Ca2+ in regulating lateral root formation.

GA(3) enhances root responsiveness to exogenous IAA by modulating auxin transport and signalling in Arabidopsis.

Key messageWe used auxin-signalling mutants, auxin transport mutants, and auxin-related marker lines to show that exogenously applied GA enhances auxin-induced root inhibition by affecting auxin signalling and transport.AbstractVariation in root elongation is valuable when studying the interactions of phytohormones. Auxins influence the biosynthesis and signalling of gibberellins (GAs), but the influence of GAs on auxins in root elongation is poorly understood. This study was conducted to investigate the effect of GA3 on Arabidopsis root elongation in the presence of auxin. Root elongation was inhibited in roots treated with both IAA and GA3, compared to IAA alone, and the effect was dose dependent. Further experiments showed that GA3 could modulate auxin signalling based on root elongation in auxin-signalling mutants and the expression of auxin-responsive reporters. The GA3-enhanced inhibition of root elongation observed in the wild type was not found in the auxin-signalling mutants tir1-1 and axr1-3. GA3 increased DR5::GUS expression in the root meristem and elongation zones, and IAA2::GUS in the columella. The DR5rev::GFP signal was enhanced in columella cells of the root caps and in the elongation zone in GA3-treated seedling roots. A reduction was observed in the stele of PAC-treated roots. We also examined the effect of GA3 on auxin transport. The enhanced responsiveness caused by GA3 was not observed in the auxin influx mutant aux1-7 or the efflux mutant eir1-1. Additional molecular data demonstrated that GA3 could promote auxin transport via AUX1 and PIN proteins. However, GA3-induced PIN gene expression did not fully explain GA-enhanced PIN protein accumulation. These results suggest that GA3 is involved in auxin-mediated primary root elongation by modulating auxin signalling and transport, and thus enhances root responsiveness to exogenous IAA.

Effects of exogenous gibberellic acid3 on iron and manganese plaque amounts and iron and manganese uptake in rice.

Gibberellins (GA) regulate various components of plant development. Iron and Mn plaque result from oxiding and hydroxiding Fe and Mn, respectively, on the roots of aquatic plant species such as rice (Oryza sativa L.). In this study, we found that exogenous gibberellic acid3 (GA3) spray decreased Fe plaque, but increased Mn plaque, with applications of Kimura B nutrient solution. Similar effects from GA3, leading to reduced Fe plaque and increased Mn plaque, were also found by scanning electron microscopy and energy dispersive X-ray spectrometric microanalysis. Reduced Fe plaque was observed after applying GA3 to the groups containing added Fe2+ (17 and 42 mg•L-1) and an increasing trend was detected in Mn plaques of the Mn2+ (34 and 84 mg•L-1) added treatments. In contrast, an inhibitor of GA3, uniconazole, reversed the effects of GA3. The uptake of Fe or Mn in rice plants was enhanced after GA3 application and Fe or Mn plaque production. Strong synergetic effects of GA3 application on Fe plaque production were detected. However, no synergetic effects on Mn plaque production were detected.

An ethylene and ROS-dependent pathway is involved in low ammonium-induced root hair elongation in Arabidopsis seedlings.

Root hairs are plastic in response to nutrient supply, but relatively little is known about their development under low ammonium (NH4(+)) conditions. This study showed that reducing NH4(+) for 3 days in wild-type Arabidopsis seedlings resulted in drastic elongation of root hairs. To investigate the possible mediation of ethylene and auxin in this process, seedlings were treated with 2,3,5-triiodobenzoic acid (TIBA, auxin transport inhibitor), 1-naphthylphthalamic acid (NPA, auxin transport inhibitor), p-chlorophenoxy isobutyric acid (PCIB, auxin action inhibitor), aminoethoxyvinylglycine (AVG, chemical inhibitor of ethylene biosynthesis), or silver ions (Ag(+), ethylene perception antagonist) under low NH4(+) conditions. Our results showed that TIBA, NPA and PCIB did not inhibit root hair elongation under low NH4(+) conditions, while AVG and Ag(+) completely inhibited low NH4(+)-induced root hair elongation. This suggested that low NH4(+)-induced root hair elongation was dependent on the ethylene pathway, but not the auxin pathway. Further genetic studies revealed that root hair elongation in auxin-insensitive mutants was sensitive to low NH4(+) treatment, but elongation was less sensitive in ethylene-insensitive mutants than wild-type plants. In addition, low NH4(+)-induced root hair elongation was accompanied by reactive oxygen species (ROS) accumulation. Diphenylene iodonium (DPI, NADPH oxidase inhibitor) and dimethylthiourea (DMTU, ROS scavenger) inhibited low NH4(+)-induced root hair elongation, suggesting that ROS were involved in this process. Moreover, ethylene acted together with ROS to modulate root hair elongation under low NH4(+) conditions. These results demonstrate that a signaling pathway involving ethylene and ROS participates in regulation of root hair elongation when Arabidopsis seedlings are subjected to low NH4(+) conditions.

γ-Aminobutyric acid addition alleviates ammonium toxicity by limiting ammonium accumulation in rice (Oryza sativa) seedlings.

Excessive use of nitrogen (N) fertilizer has increased ammonium (NH4+ ) accumulation in many paddy soils to levels that reduce rice vegetative biomass and yield. Based on studies of NH4+ toxicity in rice (Oryza sativa, Nanjing 44) seedlings cultured in agar medium, we found that NH4+ concentrations above 0.75 mM inhibited the growth of rice and caused NH4+ accumulation in both shoots and roots. Use of excessive NH4+ also induced rhizosphere acidification and inhibited the absorption of K, Ca, Mg, Fe and Zn in rice seedlings. Under excessive NH4+ conditions, exogenous γ-aminobutyric acid (GABA) treatment limited NH4+ accumulation in rice seedlings, reduced NH4+ toxicity symptoms and promoted plant growth. GABA addition also reduced rhizosphere acidification and alleviated the inhibition of Ca, Mg, Fe and Zn absorption caused by excessive NH4+ . Furthermore, we found that the activity of glutamine synthetase/NADH-glutamate synthase (GS; EC 6.3.1.2/NADH-GOGAT; EC1.4.1.14) in root increased gradually as the NH4+ concentration increased. However, when the concentration of NH4+ is more than 3 mM, GABA treatment inhibited NH4+ -induced increases in GS/NADH-GOGAT activity. The inhibition of ammonium assimilation may restore the elongation of seminal rice roots repressed by high NH4+ . These results suggest that mitigation of ammonium accumulation and assimilation is essential for GABA-dependent alleviation of ammonium toxicity in rice seedlings.

Characterization and expression analysis of cytokinin biosynthesis genes in Fragaria vesca

Strawberry is one of the most economically important fruit crops in the world. Cytokinins (CKs) play a critical role in plant growth and development, as well as the stress response, and the level of CKs in plants is regulated by synthesis and degradation pathways. The key synthetic enzymes of CKs are isopentenyl transferases (IPTs) and LONELY GUYS (LOGs). We surveyed the strawberry genome and identified seven FvIPT genes and nine FvLOG genes. We analyzed gene structures, conserved domains, and their phylogenetic relationships with rice and Arabidopsis. The isoelectric points and glycosylation sites of the proteins were predicted. We also analyzed tissue- or organ-specific expression patterns of the FvIPT and FvLOG genes. The FvIPT and FvLOG genes showed different expression profiles in different organs. Most FvIPT and FvLOG genes were down-regulated in response to osmotic stress, high-temperature treatment, and exogenous abscisic acid (ABA) application, suggesting possible roles of these genes in the plants’ resistance to abiotic stresses. In addition, we found that the results of bioinformatics analyses to identify cis-regulatory elements may not be consistent with experimental expression data; thus, computer-predicted putative cis-elements need to be confirmed by experiments. Our systematic analyses of the FvIPT and FvLOG families provide a foundation for characterizing the function of these genes in the regulation of growth, development, and stress tolerance in Fragaria vesca, as well as a reference for improving stress tolerance by manipulating CK content.

Plasma membrane H + -ATPase is involved in methyl jasmonate-induced root hair formation in lettuce ( Lactuca sativa L.) seedlings

Key messageOurresultsshowthatmethyljasmonateinducesplasmamembraneH+-ATPaseactivityandsubsequentlyinfluencestheapoplasticpHoftrichoblaststomaintainacellwallpHenvironmentappropriateforroothairdevelopment.AbstractRoot hairs, which arise from root epidermal cells, are tubular structures that increase the efficiency of water absorption and nutrient uptake. Plant hormones are critical regulators of root hair development. In this study, we investigated the regulatory role of the plasma membrane (PM) H+-ATPase in methyl jasmonate (MeJA)-induced root hair formation. We found that MeJA had a pronounced effect on the promotion of root hair formation in lettuce seedlings, but that this effect was blocked by the PM H+-ATPase inhibitor vanadate. Furthermore, MeJA treatment increased PM H+-ATPase activity in parallel with H+ efflux from the root tips of lettuce seedlings and rhizosphere acidification. Our results also showed that MeJA-induced root hair formation was accompanied by hydrogen peroxide accumulation. The apoplastic acidification acted in concert with reactive oxygen species to modulate root hair formation. Our results suggest that the effect of MeJA on root hair formation is mediated by modulation of PM H+-ATPase activity.

Hydrogen sulfide is a novel gasotransmitter with pivotal role in regulating lateral root formation in plants.

Hydrogen sulfide (H2S), the third gasotransmitter after nitric oxide (NO) and carbon monoxide (CO), is a critical neuromodulator in the pathogenesis of various diseases from neurodegenerative diseases to diabetes or heart failure. The crosstalk between NO and H2S has been well established in mammalian physiology. In planta, NO is demonstrated to regulate lateral root formation by acting downstream of auxin. The recent reports revealed that H2S is a novel inducer of lateral root (LR) formation by stimulating the expression of cell cycle regulatory genes (CCRGs), acting similarly with NO, CO, and IAA. Interestingly, during the initiation of lateral root primordia, IAA is a potent inducer of endogenous H2S and CO, which is produced by L-cysteine desulfhydrase (LCD) and heme oxygenase-1 (HO-1), respectively. The increasing evidences suggest that H2S-promoted LR growth is dependent on the endogenous production of CO. In addition, our results indicate that the H2S signaling in the regulation of LR formation can be associated to NO and Ca2+. In this addendum, we advanced a proposed schematic model for H2S-mediated signaling pathway of plant LR development.

Antagonistic effect of indole-3-acetic acid on kinetin-stimulated amaranthin accumulation in the cotyledons ofAmaranthus mangostanusseedlings

ABSTRACT Light triggered the initiation of amaranthin biosynthesis in cotyledons of Amaranthus mangostanus L. seedlings. Cytokinin induced amaranthin synthesis in the dark and increased the accumulation of amaranthin under light irradiation. No studies have explored whether indole-3-acetic acid (IAA) can affect kinetin-induced amaranthin accumulation in seedlings of A. mangostanus L. In this study, we found that IAA inhibited both the kinetin- and light-induced synthesis of amaranthin. In the dark, 10.0 mg l−1 IAA caused a 68% reduction in amaranthin production after induction by 5.0 mg l−1 kinetin. In the presence of light, 10.0 mg l−1 IAA resulted in a 50% decrease in amaranthin synthesis following induction by 5.0 mg l−1 kinetin. In addition, IAA could reverse kinetin-induced amaranthin accumulation under red, blue, or far-red light conditions. Our results suggest that IAA had an antagonistic effect on the light-induced or cytokinin-stimulated accumulation of amaranthin in the cotyledons of A. mangostanus L. seedlings.