Plant Growth-promoting Factors Research Articles

Restoration of fumigated soil biota with plant growth-promoting rhizobacteria to counteract Meloidogyne incognita (Tylenchida: Heteroderidae) boosts eggplant growth and defenses

This study investigated the effectiveness of two plant growth-promoting rhizobacteria (PGPR) formulations, Bio Arc® 6% WP (BA, Bacillus megaterium) and BECTO Grow Roots® (BGR; Serratia marcescens, Pseudomonas putida, and P. fluorescens). Additionally, it focused on naturally infested soil that had undergone metam potassium fumigation to reduce root-knot nematode (RKN), specifically Meloidogyne incognita. It aimed to monitor eggplant response to soil biodiversity changes for 60 days of the experiment under greenhouse conditions. Our data showed that soil fumigation eliminated nematodes and reduced other microorganisms significantly. In sterilized soil, plant fresh root weight significantly decreased after the elimination of soil biota. Moreover, BGR achieved the highest plant growth vigor [fresh root (18.48%), fresh shoot (23.52%), and fresh plant weight (21.03%)], followed by BA [fresh root (11.98%), fresh shoot (20.77%), and fresh plant weight (16.38%), respectively]. Plant growth traits increased significantly following the second reinoculation of PGPR after a month. Also, the same data trend was observed in treatments inoculated with RKN + PGPR. Furthermore, BGR treatments exhibited consistent efficacy in controlling nematode infection, maintaining superior vegetative growth compared to BA treatments over time. However, BA treatments displayed a decline in plant growth when faced with repeated nematode infection. The range of gall, egg mass, and second-stage juvenile (J2s) numbers diminished after inoculation-infected plants with RKN and PGPR compared with infected plants alone. Biochemical changes in eggplant roots cultivated in sterilized soil exposed significant enhancement in total sugars, protein, and nonenzymatic antioxidants (flavonoids and phenolic content), with antioxidant activity enhanced upon inoculation of PGPR and RKN. Oppositely, the levels of enzymatic antioxidants (catalase, peroxidase, and superoxide dismutase) decreased significantly with single and double PGPR application. However, the decline was less pronounced in the BGR treatments than in BA. In contradiction of oxidative enzymes, reinoculated PGPR + RKN multiplied significantly in reinfested RKN treatments. Our findings support the use of PGPR combinations, in particular, for preventive inoculation against M. incognita. They also enhance plant growth-promoting factors and stimulate plant defenses against inevitable soil reinfestation following soil fumigation.

Study of the effect of consortia of PGPR on the growth of Trichosanthes cucumerina in a hydroponic system

Hydroponics is the method of growing plants using soil-less cultivation systems. Plant growth-promoting bacteria are the rhizosphere bacteria that help plant growth and suppress plant diseases. In this study, we have isolated PGPR from the hydroponic systems and tested the efficacy of a consortium on the growth of Trichosanthes cucumerina. Ten organisms were isolated from a pre-set hydroponic system, of which three were selected based on their plant growth-promoting abilities. The isolated strains were identified as Chryseobacterium jejuense, Pseudomonas oryzihabitans and Sphingomonas paucimobilis. These isolates produced high levels of indole-3-acetic acid as well as other plant growth-promoting factors such as cellulase, pectinase, and siderophore production. All three isolates showed biofilm formation and growth in nutrient solutions with high EC values, indicating their ability to adhere to plant root surfaces and survive in nutrient solutions to promote plant growth. A consortium of these organisms used in the deep-water hydroponic system of T. cucumerina showed a significant increase in the number of leaves and root mass compared to control plants. Since these PGPR isolates exhibited multiple traits beneficial to the host plant, it has opened new possibilities for commercial application of these isolates in the hydroponic systems.

Systematic study on the effect of seaweed fertilizer on the growth and yield of Vigna radiata (L.) R. Wilczek (Mung bean)

Seaweed (Marine algae) extracts have been reported to be beneficial to plants for early seed germination, better plant growth, improved crop yield, and also in preventing biotic and abiotic stress. They are naturally rich in plant growth-promoting factors like microelements, organic matter, vitamins, and fatty acids and can be a low-cost alternative to conventional N:P:K fertilizers and expensive organic farming techniques. Herein, the seaweed fertilizer (SF) have prepared by using three seaweeds, viz., Turbinaria ornata (TSF), Ulva intestinalis (USF), and Portieria hornemannii (PSF). The formulation was evaluated for biostimulant potential by performing a pot culture on Vigna radiata (L.) R. Wilczek, along with aqueous control, chemical fertilizer control (CFC), and organic manure control (OMC). The plants were treated with various groupings (individual and combination) of SF at six different concentrations. The study revealed that PSF (30%) stimulates maximum seed germination and an upsurge in plant growth (shoot length (28%), root length (120%), leaf count (53%), leaf area (62%), fresh weight (41%), and dry weight (54%)), pigment concentration (carotenoid (80%), chlorophyll a (29%), and chlorophyll b (41%)), and biochemical parameters of the leaves (carbohydrate (18%), protein (21%), amino acids (21%), phenolic content(49%)) when compared with aqueous control. The study revealed an 85% surge in the quantity of grains (15.568 g/plant) upon treatment with 30% PSF compared with aqueous control (8.413 g/plant). Followed by 30% (USF + PSF), 30% (TSF + PSF), and 40% PSF, have exhibited 75%, 73%, and 72% increase, respectively, compared with aqueous control. The nutrient uptake study exhibited that 30% PSF improves the efficiency of mineral uptake in V. radiata (L) plants. The results suggest that the tested SF, especially PSF, could be a low-cost and environmentally safe fertilizer. Based on this study, the formulated PSF could be used alone or partially replaced with commercial fertilizers to reduce the total cultivation cost.

Volatile Organic Compound (VOC) Profiles of Different Trichoderma Species and Their Potential Application.

Fungi emit a broad spectrum of volatile organic compounds (VOCs), sometimes producing species-specific volatile profiles. Volatilomes have received over the last decade increasing attention in ecological, environmental and agricultural studies due to their potential to be used in the biocontrol of plant pathogens and pests and as plant growth-promoting factors. In the present study, we characterised and compared the volatilomes from four different Trichoderma species: T. asperellum B6; T. atroviride P1; T. afroharzianum T22; and T. longibrachiatum MK1. VOCs were collected from each strain grown both on PDA and in soil and analysed using proton transfer reaction quadrupole interface time-of-flight mass spectrometry (PTR-Qi-TOF-MS). Analysis of the detected volatiles highlighted a clear separation of the volatilomes of all the four species grown on PDA whereas the volatilomes of the soil-grown fungi could be only partially separated. Moreover, a limited number of species-specific peaks were found and putatively identified. In particular, each of the four Trichoderma species over-emitted somevolatiles involved in resistance induction, promotion of plant seed germination and seedling development and antimicrobial activity, as 2-pentyl-furan, 6PP, acetophenone and p-cymene by T. asperellum B6, T. atroviride P1, T. afroharzianum T22 and T. longibrachiatum MK1, respectively. Their potential role in interspecific interactions from the perspective of biological control is briefly discussed.

Endophytic bacteria derived from the desert-spurge (Euphorbia antiquorum L.) suppress Fusarium verticillioides, the causative agent of maize ear and root rot

Fungal plant pathology is a huge concern to the agricultural industry across the globe. Fusarium verticillioides is recognized as the most widespread and severe pathogenic fungus associated with maize production. This study aimed to investigate the antagonistic potential of twenty-seven (27) endophytic bacteria from the Desert spurge (Euphorbia antiquorum L.) against Fusarium verticillioides causing ear and root rot in maize. The in vitro screening revealed that six (6) bacteria restricted Fusarium verticillioides mycelial growth upon direct confrontation, resulting in a 68.59% reduction and nine (9) inhibited via the production of VOMs (71.7% mycelial growth reduction). In vitro, all the tested bacteria produced several extracellular enzymes and various plant growth-promoting factors, such as indole acetic acid (IAA), ammonia, siderophores and solubilized phosphate. In the greenhouse experiment, potent endophytic bacteria significantly lowered the severity of ear and root rot disease caused by F. verticillioides in maize seedlings, with Citrobacter fruendii LPR4+ being the most effective. Moreover, the protective effect was strongly associated with PGP aptitudes, which was manifested by increases in root and shoot development by up to 79 and 28%, respectively, as well as guaiacol peroxidase and phenylalanine ammonialyase specific activities. The current data constitute the starting point toward an ecological solution to control ear and root rot disease in maize.

Utilization of Legume-Nodule Bacterial Symbiosis in Phytoremediation of Heavy Metal-Contaminated Soils.

Simple SummaryThe legume–rhizobium symbiosis is one of the most beneficial interactions with high importance in agriculture, as it delivers nitrogen to plants and soil, thereby enhancing plant growth. Currently, this symbiosis is increasingly being exploited in phytoremediation of metal contaminated soil to improve soil fertility and simultaneously metal extraction or stabilization. Rhizobia increase phytoremediation directly by nitrogen fixation, protection of plants from pathogens, and production of plant growth-promoting factors and phytohormones.With the increasing industrial activity of the growing human population, the accumulation of various contaminants in soil, including heavy metals, has increased rapidly. Heavy metals as non-biodegradable elements persist in the soil environment and may pollute crop plants, further accumulating in the human body causing serious conditions. Hence, phytoremediation of land contamination as an environmental restoration technology is desirable for both human health and broad-sense ecology. Legumes (Fabaceae), which play a special role in nitrogen cycling, are dominant plants in contaminated areas. Therefore, the use of legumes and associated nitrogen-fixing rhizobia to reduce the concentrations or toxic effects of contaminants in the soil is environmentally friendly and becomes a promising strategy for phytoremediation and phytostabilization. Rhizobia, which have such plant growth-promoting (PGP) features as phosphorus solubilization, phytohormone synthesis, siderophore release, production of beneficial compounds for plants, and most of all nitrogen fixation, may promote legume growth while diminishing metal toxicity. The aim of the present review is to provide a comprehensive description of the main effects of metal contaminants in nitrogen-fixing leguminous plants and the benefits of using the legume–rhizobium symbiosis with both wild-type and genetically modified plants and bacteria to enhance an efficient recovery of contaminated lands.

Phytoremediation-a sustainable remedial method for soil contaminated by vanadium

Vanadium amassing in the soil increased with its widespread usage in multi-field. Elevated soil vanadium confers adverse effects on living organisms involved in plants, animals, and microorganisms. Moreover, vanadium can enter the human body through the food chain and lead to potential health risks stemming from its toxicity and carcinogenicity. Therefore, the remediation of soil contaminated by vanadium is imperative. Phytoremediation, a clean phytotechnology, is gaining increasing grace in modern society that prefers spirit-enjoy persuing. However, due to the blemishes of the remediation plants per se, the remediation efficiency relying on plants alone is not attractive. Therefore, the strengthened screening of vanadium accumulator and hyperaccumulator plants should step forward. Simultaneously, it is necessary to improve phytoremediation efficiency by some complementary measures, such as inoculating plant growth-promoting bacteria, vanadium reducing bacteria, and the proper application of plant growth regulators. Overall, microbe-assisted and moderate usage of plant growth-promoting factors are promising for the phytoremediation of vanadium-contaminated soil.

Cyanobacterial biofertilizers as an alternative to chemical fertilizers in paddy fields: a review.

In India, rice is the most significant crop in terms of the total area of cultivation and fertilizers. Distributed in 44.7 million hectares, it accounts for 31.8% (5.34 million tons) of the net use of the chemical fertilizer. Continuously using chemical fertilizers in agricultural production poses a severe environmental risk. The cost of chemical fertilizers is expensive and contributing to less crop yield. There is a need to adopt alternatives for chemical fertilizers in paddy fields. Cyanobacteria are abundant in paddy fields, and it presents remarkable contribution in producing the rice crop. It fixes atmospheric nitrogen, increases the accessibility of available phosphorus, and produces innumerable plant growth-promoting factors. It requires sunlight as the source of energy for carbon and nitrogen fixation in the soil. It represents remarkable potential as a biofertilizer and thereby decreases fuel demand for chemical fertilizer production. Cyanobacterial biofertilizers are inexpensive, simple to use, and do not harm the environment. This review focuses on the potential application of cyanobacterial biofertilizers in paddy fields.

Synthetic multi-antibiotic resistant plasmids in plant-associated bacteria from agricultural soils

ObjectivesUnlike higher organisms such as domestic animals and cultivated plants, which display a robust reproductive isolation and limited dispersal ability, microbes exhibit an extremely promiscuous gene flow and can rapidly disperse across the planet by multiple ways. Thus, microbial plasmids, including synthetic replicons, containing antibiotic resistance genes are a serious risk to public health. In this short communication, we explored the presence of synthetic elements in alfalfa symbionts (Ensifer meliloti strains) from agricultural soils. MethodsA total of 148 E. meliloti isolates from alfalfa plants growing under field conditions were collected from January 2015 to June 2019. Antimicrobial susceptibility testing was performed under laboratory conditions. We identified five kanamycin-resistant E. meliloti strains (named K1-K5). Whole genome sequencing analysis and conjugations were used to identify and study the plasmids of K strains. ResultsWe found that the genomes of K strains contain ampicillin, kanamycin and tetracycline resistance genes, the reporter gene lacZ from Escherichia coli and multiple cloning sites. These sequences were found within <58-kb plasmids related to the self-transmissible IncP plasmid RP4 from human pathogen Pseudomonas aeruginosa. Conjugation experiments confirmed the ability of K strains to transfer antibiotic resistance via conjugation to the Pseudomonas background. ConclusionIn addition to the traditional analysis of plant growth-promoting factors, the commercial deregulation of putative natural inoculants should also include genomic studies to ensure a reasonable balance between innovation and caution.

Microbial community comparison of plant growth-promoting factors between invasive Erodium cicutarium and native species one year post-fire

Microbial community comparison of plant growth-promoting factors between invasive Erodium cicutarium and native species one year post-fire

Isolation and prospection of diazotrophic rhizobacteria associated with sugarcane under organic management.

Microorganisms associated with organic management are essential in nutrient transformation and release for plant use. The present study aimed to isolate, identify and characterize plant growth promoting diazotrophic rhizobacteria associated with sugarcane under organic management. Rhizospheres of organic sugarcane varieties IAC 911099 and CTC4 were sampled and inoculated onto nitrogen free NFb and Burk media. The isolated microorganisms were screened in vitro concerning their ability to produce plant growth promoting factors. Eighty-one bacteria were isolated; 45.6% were positive for the nifH gene and produced at least one of the evaluated plant growth promotion factors. The production of indole-3-acetic acid was observed in 46% of the isolates, while phosphate solubilization was observed in 86.5%. No isolates were hydrogen cyanide producers, while 81% were ammonia producers, 19% produced cellulases and 2.7%, chitinases. Microorganisms belonging to the Burkholderia genus were able to inhibit Fusarium moniliforme growth in vitro. Plant growth promoting microorganisms associated with organic sugarcane, especially belonging to Burkholderia, Sphingobium, Rhizobium and Enterobacter genera, can be environmentally friendly alternatives to improve sugarcane production.

The Tale of a Neglected Energy Source: Elevated Hydrogen Exposure Affects both Microbial Diversity and Function in Soil.

The enrichment of H2-oxidizing bacteria (HOB) by H2 generated by nitrogen-fixing nodules has been shown to have a fertilization effect on several different crops. The benefit of HOB is attributed to their production of plant growth-promoting factors, yet their interactions with other members of soil microbial communities have received little attention. Here we report that the energy potential of H2, when supplied to soil, alters ecological niche partitioning of bacteria and fungi, with multifaceted consequences for both generalist and specialist microbial functions. We used dynamic microcosms to expose soil to the typical atmospheric H2 mixing ratio (0.5 ppmv) permeating soils, as well as mixing ratios comparable to those found at the soil-nodule interface (10,000 ppmv). Elevated H2 exposure exerted direct effects on two HOB subpopulations distinguished by their affinity for H2 while enhancing community level carbon substrate utilization potential and lowering CH4 uptake activity in soil. We found that H2 triggered changes in the abundance of microorganisms that were reproducible yet inconsistent across soils at the taxonomic level and even among HOB. Overall, H2 exposure altered microbial process rates at an intensity that depends upon soil abiotic and biotic features. We argue that further examination of direct and indirect effects of H2 on soil microbial communities will lead to a better understanding of the H2 fertilization effect and soil biogeochemical processes.IMPORTANCE An innovative dynamic microcosm chamber system was used to demonstrate that H2 diffusing in soil triggers changes in the distribution of HOB and non-HOB. Although the response was uneven at the taxonomic level, an unexpected coordinated response of microbial functions was observed, including abatement of CH4 oxidation activity and stimulation of carbon turnover. Our work suggests that elevated H2 rewires soil biogeochemical structure through a combination of direct effects on the growth and persistence of HOB and indirect effects on a variety of microbial processes involving HOB and non-HOB.

Endophytic bacteria associated with endangered plant Ferula sinkiangensis K. M. Shen in an arid land: diversity and plant growth-promoting traits

Ferula spp. are traditional medicinal plants found in arid land. Large-scale excavation for extracting bioactive compounds from the plants in arid regions of Xinjiang over the last few years has, however, significantly decreased their distributions. Due to the urgent need for preservation of these plant resources, along with the need of searching for alternative source of the useful metabolites, it is important to screen the endophytic microbial resources associated with the plant Ferula sinkiangensis K. M. Shen. In the study, a total of 125 endophytic bacteria belonging to 3 phyla, 13 orders, 23 families, and 29 genera were isolated based on 16S rRNA gene sequencing data. Among the different isolates, three strains isolated from roots were potential novel species of the genera Porphyrobacter, Paracoccus and Amycolatopsis. In this study, 79.4% and 57.1% of the total isolates were capable of producing indole-3-acetic acid (IAA) and siderophore, respectively. And, 40.6% of the strains inhibit the growth of fungal pathogen Alternaria alternata, 17.2% and 20.2% strains were positive for antagonism against Verticillium dahlia 991 and V. dahlia 7, respectively. These results demonstrated that F. sinkiangensis is a rich reservoir of endophytic bacterial resources with potential for production of biologically important functions such as plant growth-promoting factors.

Herbaspirillum-plant interactions: microscopical, histological and molecular aspects

Diazotrophic species in the genus Herbaspirillum (e.g. H. frisingense, H. rubrisubalbicans and H. seropedicae) associate with several economically important crops in the family Poaceae, such as maize (Zea mays), Miscanthus, rice (Oryza sativa), sorghum (Sorghum bicolor) and sugarcane (Saccharum sp.), and can increase their growth and productivity by a number of mechanisms, including nitrogen fixation. Hence, the improvement and use of these plant growth-promoting bacteria could provide economic and environmental benefits. We review the colonization processes of host plants by Herbaspirillum spp., including histological aspects and molecular mechanisms involved in these interactions, which may be epiphytic, endophytic, and even occasionally pathogenic. Herbaspirillum can recognize plant signals that modulate the expression of colonization traits and plant growth-promoting factors. Although a large proportion of herbaspirilla remain rhizospheric and epiphytic, plant-associated species in this genus are noted for their ability to colonize the plant internal tissues. Endophytic colonization by herbaspirilla begins with the attachment of the bacteria to root surfaces, followed by colonization at the emergence points of lateral roots and penetration through discontinuities of the epidermis; this appears to involve bacterial envelope structures, such as lipopolysaccharide (LPS), exopolysaccharide (EPS), adhesins and the type three secretion system (T3SS), but not necessarily the involvement of cell wall-degrading enzymes. Intercellular spaces are then rapidly occupied, proceeding to colonization of xylem and the aerial parts of the host plants. The response of the host plant includes both the recognition of the bacteria as non-pathogenic and the induction of systemic resistance to pathogens. Phytohormone signaling cascades are also activated, regulating the plant development. This complex molecular communication between some Herbaspirillum spp. and plant hosts can result in plant growth-promotion.

Assessment of root-associated paenibacillus polymyxa groups on growth promotion and induced systemic resistance in pepper.

Twenty-nine P. polymyxa strains isolated from rhizospheres of various crops were clustered into five genotypic groups on the basis of BOX-PCR analysis. The characteristics of several plant growth-promoting factors among the isolates revealed the distinct attributes in each allocated group. Under gnotobiotic conditions, inoculation of pepper roots with P. polymyxa isolates significantly increased the biomass in 17 of total 29 treated plants with untreated plants. Experiments on induced systemic resistance (ISR) against bacterial spot pathogen Xanthomonas axonopodis pv. vesicatoria in pepper by P. polymyxa strains were conducted and only one isolate (KNUC265) was selected. Further studies into ISR mediation by the KNUC265 strain against the soft-rot pathogen Erwinia carotovora subsp. carotovora in tobacco demonstrated that the tobacco seedlings exposed to either bacterial volatiles or diffusible metabolites exhibited a reduction in disease severity. In conclusion, ISR and plant growth promotion triggered by P. polymyxa isolates were systemically investigated on pepper for the first time. The P. polymyxa KNUC265 strain, which elicited both ISR and plant growth promotion, could be potentially used in improving the yield of pepper and possibly of other crops.

Genetic diversity and characterization of heavy metal-resistant-endophytic bacteria from two copper-tolerant plant species on copper mine wasteland

The diversity of endophytic bacteria from the copper-tolerant species Elsholtzia splendens and Commelina communis was evaluated by using cultivation and cultivation-independent techniques. Phylogenetic analysis based on 16S rDNA sequences showed that the Cu-resistant isolates belonged to three major phylogenetic groups: Firmicutes, Actinobacteria and Proteobacteria. Bacillus and Acinetobacter were predominant among the Cu-resistant isolates. Sequence analysis from the 16S rDNA clone libraries of the two plant roots revealed sequences of Alpha-, Beta-, Gamma- Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. Gammaproteobacteria was predominant in the two 16S rDNA clone libraries. Thirty-two endophytic bacteria were isolated and characterized with respect to heavy metal resistance and production of plant growth-promoting factors. In experiments involving rape plants grown in vermiculite containing 4 mg kg −1 of Cu, inoculation with the isolates was found to increase the dry weights of roots (ranging from 132% to 155%) and above-ground tissues (ranging from 71% to 83%) compared to the uninoculated control. Increase in above-ground tissue Cu content varied from 63% to 125% in inoculated-rape plants cultivated in Cu-contaminated substrate compared to the uninoculated control.

Effects of drying/rewetting stress on microbial auxin production and L-tryptophan catabolism in soils

The presence of tryptophan in soil and auxin production by indigenous soil microbes are considered to be important natural plant growth-promoting factors. In order to elucidate the natural regulation of microbial auxin synthesis, we treated different soils by an air drying/rewetting cycle and measured pool sizes of auxins, auxin precursors, and degradation products of tryptophan together with a range of respiration parameters. Potential (tryptophan addition) microbial production of indole-3-acetic acid (auxin) was predominant in the equilibrated fresh soils. Auxin production depended on the soil nutrient content, and the size and metabolic status of the microbial biomass. Immediately after rewetting, potential auxin production was low, whereas potential indole-3-ethanol and anthranilic acid production as well as basal respiration were transitionally enhanced. This was concurrent with proliferation ofr-strategist microbes. After the respiration flush, the natural tryptophan contents increased, indicating cell lysis, probably caused by a rise in protozoan grazing on ther-strategists. Auxin production was high in fresh and in re-equilibrating rewetted soils, probably due to nutritional limitations under stationary conditions. Hence, this high production was attributed to theK-strategist component of the soil microflora. The differences observed in the recovery of auxin production between the different rewetted soils suggest that original activities can become re-established rapidly when the indigenous microbial community is pre-adapted to the stress. We propose that the release of tryptophan, microbial auxin, and the shift towards indole-3-ethanol production function as stimulants for root development induced by environmental fluctuations.

Plant Growth-Promoting Hormones Activate Mammalian Guanylate Cyclase Activity*

In vivo injections of plant growth-promoting hormones increase the growth of animals as well as plants. Plant growth-promoting hormones and positive plant growth regulators are known to increase RNA and protein synthesis. Since cyclic GMP also increases RNA and protein synthesis, the object of the present investigation was to determine whether physiological levels of plant growth-promoting hormones and positive plant growth regulators have part of their mechanism(s) of action through stimulation of the guanylate cyclase (EC 4.6.1.2)-cyclic GMP system. Representatives of the three classes of growth-promoting hormones were investigated. Thus, auxins (indole-3-acetic acid, indole-3-butyric acid, beta-naphthoxyacetic acid, and 2,4,5-trichlorophenoxy acetic acid), gibberellins (gibberellic acid), and cytokinins [N6-benzyl adenine, kinetin (6-furfuryl aminopurine), and beta-(2-furyl) acrylic acid] all increased rat lung, small intestine, liver, and renal cortex guanylate cyclase activity 2- to 4-fold at the 1 microM concentration. Dose response curves revealed that maximal stimulation of guanylate cyclase by these plant growth regulators was at 1 microM; there was no augmented cyclase activity at 1 nM. The guanylate cyclase cationic cofactor manganese was not essential for augmentation of guanylate cyclase by these plant growth-promoting regulators. The antioxidant butylated hydroxytoluene did not block the enhancement of guanylate cyclase by these plant growth-promoting factors. These data suggest that guanylate cyclase may play a role in the mechanism of action of plant growth-promoting hormones and even of positive plant regulators at the cellular level.

Pectinase and plant growth-promoting factors in the salivary glands of the larva of the bug, Lygus disponsi

Pectinase was detected in the salivary gland of the larvae of Lygus disponsi. The pectinase activity per bug may increase gradually from the first instar larva to the adult. The salivary gland of the third instar larva contained substances indirectly promoting plant growth, i.e. the factor promoting the activity of 3-indoleacetic acid (IAA) or the factor inhibiting the activity of IAA-oxidase, whereas those of the fourth and 5th instar larvae seemed to contain, in addition, auxins which directly promote plant growth. Larvae of all instars had a significant promoting factor only in fraction III of the salivary gland solution. The larvae are as toxic as the adults to sugar beet plants. The presence of pectinase and plant growth-promoting factors in the salivary gland is compared among mirid bugs, and their significance is discussed.