Inoculation with the endophytic bacterium Herbaspirillum seropedicae promotes growth, nutrient uptake and photosynthetic efficiency in rice

Main conclusion: Higher vacuolar proton pump activity may increase plant energy and nutrient use efficiency and provide the nexus between plant inoculation with Herbaspirillum seropedicae and growth promotion. Abstract: Global change and growing human population are exhausting arable land and resources, including water and fertilizers. We present inoculation with the endophytic plant-growth promoting bacterium (PGPB) Herbaspirillum seropedicae as a strategy for promoting growth, nutrient uptake and photosynthetic efficiency in rice (Oryza sativa L.). Because plant nutrient acquisition is coordinated with photosynthesis and the plant carbon status, we hypothesize that inoculation with H. seropedicae will stimulate proton (H+) pumps, increasing plant growth nutrient uptake and photosynthetic efficiency at low nutrient levels. Plants were inoculated and grown in pots with sterile soil for 90 days. Herbaspirillum seropedicae endophytic colonization was successful and, as hypothesized, inoculation (1) stimulated root vacuolar H+ pumps (vacuolar H+-ATPase and vacuolar H+-PPase), and (2) increased plant growth, nutrient contents and photosynthetic efficiency. The results showed that inoculation with the endophytic bacterium H. seropedicae can promote plant growth, nutrient uptake and photosynthetic efficiency, which will likely result in a more efficient use of resources (nutrients and water) and higher production of nutrient-rich food at reduced economic and environmental costs.info:eu-repo/semantics/publishedVersio

Genome of Herbaspirillum seropedicae Strain SmR1, a Specialized Diazotrophic Endophyte of Tropical Grasses

The molecular mechanisms of plant recognition, colonization, and nutrient exchange between diazotrophic endophytes and plants are scarcely known. Herbaspirillum seropedicae is an endophytic bacterium capable of colonizing intercellular spaces of grasses such as rice and sugar cane. The genome of H. seropedicae strain SmR1 was sequenced and annotated by The Paraná State Genome Programme—GENOPAR. The genome is composed of a circular chromosome of 5,513,887 bp and contains a total of 4,804 genes. The genome sequence revealed that H. seropedicae is a highly versatile microorganism with capacity to metabolize a wide range of carbon and nitrogen sources and with possession of four distinct terminal oxidases. The genome contains a multitude of protein secretion systems, including type I, type II, type III, type V, and type VI secretion systems, and type IV pili, suggesting a high potential to interact with host plants. H. seropedicae is able to synthesize indole acetic acid as reflected by the four IAA biosynthetic pathways present. A gene coding for ACC deaminase, which may be involved in modulating the associated plant ethylene-signaling pathway, is also present. Genes for hemagglutinins/hemolysins/adhesins were found and may play a role in plant cell surface adhesion. These features may endow H. seropedicae with the ability to establish an endophytic life-style in a large number of plant species

Humic and fulvic acids as biostimulants in horticulture

Maintaining food production for a growing world population without compromising natural resources for future generations represents one of the greatest challenges for agricultural science, even compared with the green revolution in the 20th century. The intensification of agriculture has now reached a critical point whereby the negative impacts derived from this activity are now resulting in irreversible global climate change and loss in many ecosystem services. New approaches to help promote sustainable intensification are therefore required. One potential solution to help in this transition is the use of plant biostimulants based on humic substances. In this review we define humic substances in a horticultural context. Their effects on nutrient uptake and plant metabolism are then discussed and a general schematic model of plant-humic responses is presented. The review also highlights the relationship between the chemical properties of humified matter and its bioactivity with specific reference to the promotion of lateral root growth. Finally, we summarize and critically evaluate experimental data related to the overall effect of humic substances applied to horticultural crops. Current evidence suggests that the biostimulant effects of humic substances are characterized by both structural and physiological changes in roots and shoots related to nutrient uptake, assimilation and distribution (nutrient use efficiency traits). In addition, they can induce shifts in plant primary and secondary metabolism related to abiotic stress tolerance which collectively modulate plant growth as well as promoting fitness. In conclusion, the exogenous application of humic substances within agronomic systems can be used to aid the development of sustainable intensification. As most humic substances used in agriculture are currently derived from non-renewable resources like coal and peat, the promotion of this technology also requires the development of new sustainable sources of humic products (e.g. organic wastes)

Humic substances from vermicompost enhance urban lettuce production

International audienceUrban agriculture is growing worldwide with the growth of cities. Urban agriculture represents about 20 % of Cuban agriculture. In Cuba, urban agriculture is institutionalized and organized with ecological principles. For instance, local agriculture enhances food security and decreases the use of nonrenewable fertilizers. However, organic crop production in urban environments is challenging because of intensive plant nutrient requirements and disease incidence. Here, we tested an innovative technology based on plant growth promoters isolated from vermicompost and applied directly to lettuce leaves. We monitored plant metabolism by measuring the activities of nitrate reductase, an enzyme linked to N assimilation, and of phenylalanine ammonia lyase, an enzyme linked to plant defense. The experiment was conducted in the organic urban system in Guines, Cuba. We applied liquid humates at 10, 15, or 20 mg C L−1 once at the seedling stage and again 15 days after transplantation. Our results show that humates at 15 mg C L−1 shortened by 21 days the lettuce production cycle, allowing early harvesting without changing quality while increasing yields expressed as the number of leaves per plant. Humate application also decreased total carbohydrate, increased protein, increased nitrate uptake, and stimulated nitrate reductase and phenylalanine ammonia lyase in lettuce leaves

Biostimulants Using Humic Substances and Plant-Growth-Promoting Bacteria: Effects on Cassava (<i>Manihot esculentus</i>) and Okra (<i>Abelmoschus esculentus</i>) Yield

Traditional agriculture represents the most-extensive food-producing segment in the world. However, these agroecosystems are widely and closely associated with rural poverty, reflecting the dualism between the subsistence and the commodity-producing sector in the peripheric countries. Therefore, socially adapted technologies may be a reliable and helpful methodology to enhance subsistence crop production. Humic substances are natural organic biostimulants extractable as water suspensions from renewable sources such as agricultural biomass and farming residues. These easy-to-handle extracts may be mixed with plant-growth-promoting bacteria (PGPB) and used as biostimulants within a low-cost technological application in the circular economy strategy. Few investigations have been focused on the use of biostimulant practices on marginal or subsistence crops. Cassava (Manihot esculenta Crantz) and okra (Abelmoschus esculentus) are two essential foods for poor communities of rural territories in tropical and subtropical countries. The aim of this study was to evaluate the effect of the foliar application of a humic/PGPB mixed biostimulant on cassava and okra crops grown in an agricultural soil with very low natural fertility. In pot trials, the applied biostimulant improved the plant development with a 200% increase of the root weight in cassava, while the preservation of active diazotrophic bacteria was improved by 10- and 100-times in cassava and okra in the mixed formulation with humic acid. In real field systems, the plant treatment increased the yield of cassava and okra by 70% and 50%, respectively thereby allowing a simultaneous nitrogen savings with the best yield performance obtained at the lower N fertilization rate. The use of biostimulants can play a role in the transition process, helping the food security and the autonomy of impoverished farmers. Combining the elements of traditional knowledge and modern science is essential to create innovative technologies enabling the sustainable management of agroecosystems

Arbuscular mycorrhizal fungi induce differential activation of the plasma membrane and vacuolar H+ pumps in maize roots.

Roots undergo multiple changes as a consequence of arbuscular mycorrhizal (AM) interactions. One of the major alterations expected is the induction of membrane transport systems, including proton pumps. In this work, we investigated the changes in the activities of vacuolar and plasma membrane (PM) H(+) pumps from maize roots (Zea mays L.) in response to colonization by two species of AM fungi, Gigaspora margarita and Glomus clarum. Both the vacuolar and PM H(+)-ATPase activities were inhibited, while a concomitant strong stimulation of the vacuolar H(+)-PPase was found in the early stages of root colonization by G. clarum (30 days after inoculation), localized in the younger root regions. In contrast, roots colonized by G. margarita exhibited only stimulation of these enzymatic activities, suggesting a species-specific phenomenon. However, when the root surface H(+) effluxes were recorded using a noninvasive vibrating probe technique, a striking activation of the PM H(+)-ATPases was revealed specifically in the elongation zone of roots colonized with G. clarum. The data provide evidences for a coordinated regulation of the H(+) pumps, which depicts a mechanism underlying an activation of the root H(+)-PPase activity as an adaptative response to the energetic changes faced by the host root during the early stages of the AM interaction