Journal of Plant Growth Regulation

Putrescine (Put) and arbuscular mycorrhizal fungus (AMF) play an effective role in plant growth and development. However, although studies on the use of putrescine in field conditions are limited, there are no studies on its use with AMF. In this research, the effects of putrescine and AMF applications on yield, plant and fruit development, fruit biochemicals, flowering, and harvest were investigated in strawberry Festival cultivar. Two doses of putrescine (100 and 150 ppm), two types of AMF, (Funneliformis mosseae/FM and Gigaspora margarita/GM), and their interactions were used. The results show that putrescine affected AMF colonization and mycorrhizal dependence. Especially in F. mosseae species, it was observed that colonization increased with putrescine interactions. Also, highest yield was determined as 346.12 g in G. margarita and 150-ppm Put interaction application. The interaction application of F. mosseae and 150-ppm putrescine had the highest amount of vitamin C with an increase of 78% compared to the control. Again, it was observed that this application had the highest amount of catechin and rutin (5.385 and 1.055 mg 100 g−1, respectively). However, only putrescine applications came to the fore in terms of the development of the crown length of the plant and the sugar content. It was determined that G. margarita applications extended the harvest period in this study. These results showed that the yield, vegetative growth, and fruit biochemical content of strawberry could be increased with the interaction application of F. mosseae and 150-ppm putrescine. All in all, a different perspective has been brought to the use of putrescine and mycorrhiza in agricultural production and its positive effects have been revealed.

The metabolism of zeatin and that of 6-benzylaminopurine (BAP) have been compared in oat leaf segments in relation to the markedly differing ability of these cytokinins to retard senescence of such segments. Free BAP and a highly active senescence-retarding metabolite of BAP were detected in oat leaf segments supplied with BAP. The metabolite was identified by mass spectrometry and chromatography as 3-β-D-glucopyranosyl-BAP. The major metabolite of BAP was the 9-glucoside, but this lacked significant senescence-retarding activity. In contrast, in leaf segments supplied with zeatin, no free zeatin and no senescence-retarding metabolite of zeatin were detectable. The major metabolites of zeatin were adenosine, adenine nucleotides, the 9-glucoside, and unidentified polar metabolites. The differing activities of zeatin and BAP in the oat-leaf senescence bioassay appear to be, at least partially, a consequence of their differing metabolism and are not attributable to differences in uptake.

Plant growth-promoting rhizobacteria modulate root development through different mechanisms. This work was conducted to evaluate the effects of root colonization by Pseudomonas putida and Pseudomonas fluorescens in biomass production, lateral root formation, and activation of auxin signaling in Arabidopsis thaliana. Selected strains of P. putida and P. fluorescens were tested for modification of DR5::uidA, BA3::uidA and HS::AXR3NT-GUS auxin-related gene expression, and to promote root hair and lateral root formation in WT and tir1-1, tir1-1afb2-1afb3-1, arf7-1, arf19-1, arf7-1arf19-1, and rhd6 mutants. Production of cyclodipeptides with possible roles in auxin signaling was also determined in P. putida and P. fluorescens culture supernatants by gas chromatography–mass spectrometry. P. putida and P. fluorescens stimulated lateral root and root hair formation and increased plant biomass, which correlated with an induction of the auxin response. Genetic analyses suggested that growth promotion involves auxin signaling as tir1-1, tir1-1afb2-1afb3-1, arf7-1, arf19-1, and arf7-1arf19-1 mutants showed decreased lateral root response to inoculation and because P. putida and P. fluorescens restored root hair development in the rhd6 mutant. It was also found that these bacteria produce the cyclodipeptides cyclo(L-Pro-L-Val), cyclo(L-Pro-L-Phe), and cyclo(L-Pro-L-Tyr), which modulates auxin-responsive gene expression in roots. Our results suggest a role of cyclodipeptides for bacterial phytostimulation.

The involvement of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the regulation of flowering of Pharbitis nil was investigated through exogenous applications and analyses of endogenous levels. Both hormones inhibited the flowering of P. nil when they were applied before or after a single 15-h dark treatment. The inhibitory effect of ABA and IAA was significant when they were applied before the dark treatment, and the application to plumules was more effective than that to cotyledons. In all applications, the inhibitory effect of IAA was stronger than that of ABA. Endogenous levels of ABA and IAA in the plumules were compared between flower-inductive (15-h dark treatment) and noninductive (continuous light) light conditions. There was no significant difference in the ABA level between light and dark conditions, whereas the level of IAA was decreased by the dark treatment. These results suggest that biosynthesis and/or catabolism of IAA is affected by the light treatment and therefore may be involved in the regulation of early flowering processes in the apex. The inhibitory effects of ABA and IAA were reversed by an application of gibberellin A3, indicating that gibberellin A3 counteracts the flowering processes affected by ABA and IAA. Application of aminoethoxyvinylglycine restored the flowering response inhibited by IAA, which suggests the possibility that the inhibitory effect of IAA is the result of enhanced ethylene biosynthesis.

The effects of mild water stress induced by polyethylene glycol (PEG) on the activities of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR)] and their isoenzymes and the antioxidant content [ascorbate (ASC) and glutathione (GSH)] of different subcellular compartments were investigated in maize. For each subcellular compartment, the activities of almost all isoenzymes resolved on native PAGE increased after 4–12 h of exposure to water stress and declined after that, showing concomitant changes with the activities of their respective total enzymes and the antioxidant content. For each subcellular compartment, at least one isoform for the detected antioxidant enzymes was resolved, but different kinds of antioxidant isoenzymes in different subcellular compartments had different responses to water stress. The relative contribution of Fe–SOD in chloroplasts and Mn–SOD in mitochondria was higher than that in other subcellular compartments. However, in apoplasts the activities of Mn–SOD and Fe–SOD declined during the process of water stress, in contrast to those located in other subcellular compartments. The results from the activities of antioxidant (iso)enzymes demonstrated that all antioxidant enzymes in all subcellular compartments were mobilized in cooperation and responded synchronously under mild water stress, with the same trend of changes in their activity. This indicated their orchestrated effects in scavenging reactive oxygen species (ROS) in situ. Additionally, the results suggested that mitochondria and apoplasts, responding most actively, might be targets for improving plant performance under mild water stress.

Auxins (IAA, NAA, p-CPA) caused 20–30% promotion of respiration of auxin-dependent cell cultures ofNicotiana tabacum, Glycine max, Taraxacum mongolica, andAtriplex sp. and had small if any effect on respiration of auxin-independent cell cultures ofRubus sp. andScorzonera hispanica. Antiauxin (p-CPIBA) did not affect the respiration. The auxin effect on the respiration of tobacco cells was revealed 10 min after its addition to the suspension and reached a maximum value in 60 min. This stimulation preceded the induction of cell division by auxin. Mitochondria isolated from auxin-treated tobacco cells had greater oxidative and phosphorylative activity than mitochondria from untreated cells. However, isolated mitochondria did not respond to auxin. The inhibitors of respiration (cyanide, monoiodoacetate, malonate, and 2,4-dinitrophenol) eliminated auxin effect on the respiration and cell division. It is concluded that the promotion of respiration is a common event for the auxin effects both on cell extension and on cell division. This promotion is necessary for the induction of cell division and is exerted via direct activation of mitochondriain situ.

Plant MAPK cascades have been implicated in various developmental processes and in response to stresses. MAPKKs, a convergent linking point between MAPKKKs and MAPKs, play pivotal roles in MAPK cascades to regulate various stress responses in plants. Few MAPKKs have been functionally characterized in Brachypodium distachyon, a new monocot model plant. In this study, we cloned and characterized a group A MAPKK gene, designated as BdMKK6.2, from B. distachyon. Quantitative RT-PCR analysis revealed that BdMKK6.2 expression was upregulated by cold, heat, and H2O2 treatments but downregulated by PEG and ABA treatments. Transient expression of BdMKK6.2 in onion epidermal cells suggested that it was exclusively localized in the cytoplasm. Overexpression of BdMKK6.2 in transgenic tobacco plants increased their sensitivity to osmotic stress during seed germination. Moreover, BdMKK6.2 overexpression resulted in reduced tolerance to drought stress. Physiological-biochemical analyses showed that BdMKK6.2-overexpressing plants had decreased survival rates but increased water loss rates, ion leakage, malondialdehyde content, and reactive oxygen species accumulation under drought condition. In addition, the transcriptional levels of two ROS-producing genes NtRbohD and NtRbohF were upregulated, but a stress-responsive gene NtNCED1 was downregulated in BdMKK6.2-overexpressing plants compared to wild type plants. These results indicate that BdMKK6.2 is a negative regulator of drought stress response through influencing ROS homeostasis and transcription of stress-responsive gene.

Plants phenotypically adjust to environmental challenges, and the gaseous plant hormone ethylene modulates many of these growth adjustments. Ethylene can be involved in environmentally induced growth inhibition as well as growth stimulation. Still, ethylene has long been considered a growth inhibitory hormone. There is, however, accumulating evidence indicating that growth promotion is a common feature in ethylene responses. This is evident in environmental challenges, such as flooding and competition, where the resulting avoidance responses can help plants avoid adversity. To show how ethylene-mediated growth enhancement can facilitate plant performance under adverse conditions, we explored a number of these examples. To escape adversity, plants can optimize growth and thereby tolerate abiotic stresses such as drought, and this response can also involve ethylene. In this article we indicate how opposing effects of ethylene on plant growth can be brought about, by discussing a unifying, biphasic ethylene response model. To understand the mechanistic basis for this multitude of ethylene-mediated growth responses, the involvement of ethylene in processes that control cell expansion is also reviewed.

Roots of weeds that are left behind in the soil after removal of their aerial parts can reduce the growth of crops. Here we conducted an assessment to evaluate the allelopathic interference of Nicotiana plumbaginifolia roots and its rhizosphere soil on the growth of Pisum sativum L., identification of chemicals involved, the role of charcoal, the role of N and other macronutrients. Growth responses of P. sativum were analysed for (a) rhizosphere soil with and without N supplementation and (b) soil amendment with Nicotiana roots. Scanning electron microscopy-energy dispersive spectrometry (SEM–EDS) analysis of the rhizosphere soil was conducted to look for concentration of essential nutrients. Rhizosphere soil showed an inhibitory effect even with N supplementation. SEM–EDS showed a healthy concentration of essential nutrients. Root residues of Nicotiana integrated with soil do cause a reduction in seedling length (root length, shoot length) and dry biomass of recipient plant. However, a partial alleviation in growth inhibition occurred upon the addition of activated charcoal. Soils amended with root residues were rich in phenolics as compared to control. Overall, 34 compounds were reported upon GC–MS analysis which can be considered responsible for the allelopathic suppression of P. sativum. The chief component was guanosine (26.21%) followed by n-hexadecanoic acid (18.61%), oleic acid (18.29%), palmitoleic acid (4.80%), -(-)nicotine (5.09%) and solasodine (2.54%). These results show a definite role of putative allelochemicals that exerted allelopathic effects on P. sativum.

The present study was designed to examine whether exogenous sodium nitroprusside (SNP) supplementation has any ameliorating action against PEG-induced osmotic stress in Zea mays cv. FRB-73 roots. Twenty percent or 40 % polyethylene glycol (PEG6000; −0.5 MPa and −1.76 MPa, respectively) treatment alone or in combination with 150 and 300 μM SNP was applied to hydroponically grown maize roots for 72 h. Although only catalase (CAT) activity increased when maize roots were exposed to PEG-induced osmotic stress, induction of this antioxidant enzyme was inadequate to detoxify the extreme levels of reactive oxygen species, as evidenced by growth, water content, superoxide anion radical (O 2 •− ), hydroxyl radical (OH•) scavenging activity, and TBARS content. However, supplementation of PEG-exposed specimens with SNP significantly alleviated stress-induced damage through effective water management and enhancement of antioxidant defense markers including the enzymatic/non-enzymatic systems. Exogenously applied SNP under stress resulted in the up-regulation of glutathione peroxidase (GPX), glutathione S-transferase (GST), ascorbate peroxidase (APX), glutathione reductase (GR), total ascorbate, and glutathione contents involved in ascorbate–glutathione cycle. On the other hand, growth rate, osmotic potential, CAT, APX, GR, and GPX increased in maize roots exposed to both concentrations of SNP alone, but activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase decreased. Based on the above results, an exogenous supply of both 150 and 300 μM SNP to maize roots was protective for PEG-induced toxicity. The present study provides new insights into the mechanisms of SNP (NO donor) amelioration of PEG-induced osmotic stress damages in hydroponically grown maize roots.