Ectomycorrhizal fungus supports endogenous rhythmic growth and corresponding resource allocation in oak during various below- and aboveground biotic interactions

A Fine-Tuning of the Plant Hormones, Polyamines and Osmolytes by Ectomycorrhizal Fungi Enhances Drought Tolerance in Pedunculate Oak

The drought sensitivity of the pedunculate oak (Quercus robur L.) poses a threat to its survival in light of climate change. Mycorrhizal fungi, which orchestrate biogeochemical cycles and particularly have an impact on the plant's defense mechanisms and metabolism of carbon, nitrogen, and phosphorus, are among the microbes that play a significant role in the mitigation of the effects of climate change on trees. The study's main objectives were to determine whether ectomycorrhizal (ECM) fungi alleviate the effects of drought stress in pedunculate oak and to investigate their priming properties. The effects of two levels of drought (mild and severe, corresponding to 60% and 30% of field capacity, respectively) on the biochemical response of pedunculate oak were examined in the presence and absence of ectomycorrhizal fungi. To examine whether the ectomycorrhizal fungi modulate the drought tolerance of pedunculate oak, levels of plant hormones and polyamines were quantified using UPLC-TQS and HPLC-FD techniques in addition to gas exchange measurements and the main osmolyte amounts (glycine betaine-GB and proline-PRO) which were determined spectrophotometrically. Droughts increased the accumulation of osmolytes, such as proline and glycine betaine, as well as higher polyamines (spermidine and spermine) levels and decreased putrescine levels in both, mycorrhized and non-mycorrhized oak seedlings. In addition to amplifying the response of oak to severe drought in terms of inducible proline and abscisic acid (ABA) levels, inoculation with ECM fungi significantly increased the constitutive levels of glycine betaine, spermine, and spermidine regardless of drought stress. This study found that compared to non-mycorrhized oak seedlings, unstressed ECM-inoculated oak seedlings had higher levels of salicylic (SA) and abscisic acid (ABA) but not jasmonic acid (JA), indicating a priming mechanism of ECM is conveyed via these plant hormones. According to a PCA analysis, the effect of drought was linked to the variability of parameters along the PC1 axe, such as osmolytes PRO, GB, polyamines, and plant hormones such as JA, JA-Ile, SAG, and SGE, whereas mycorrhization was more closely associated with the parameters gathered around the PC2 axe (SA, ODPA, ABA, and E). These findings highlight the beneficial function of the ectomycorrhizal fungi, in particular Scleroderma citrinum, in reducing the effects of drought stress in pedunculate oak.

Plant Age and Soil Texture Rather Than the Presence of Root Hairs Cause Differences in Maize Resource Allocation and Root Gene Expression in the Field

Understanding the biological roles of root hairs is key to projecting their contributions to plant growth and to assess their relevance for plant breeding. The objective of this study was to assess the importance of root hairs for maize nutrition, carbon allocation and root gene expression in a field experiment. Applying wild type and root hairless rth3 maize grown on loam and sand, we examined the period of growth including 4-leaf, 9-leaf and tassel emergence stages, accompanied with a low precipitation rate. rth3 maize had lower shoot growth and lower total amounts of mineral nutrients than wild type, but the concentrations of mineral elements, root gene expression, or carbon allocation were largely unchanged. For these parameters, growth stage accounted for the main differences, followed by substrate. Substrate-related changes were pronounced during tassel emergence, where the concentrations of several elements in leaves as well as cell wall formation-related root gene expression and C allocation decreased. In conclusion, the presence of root hairs stimulated maize shoot growth and total nutrient uptake, but other parameters were more impacted by growth stage and soil texture. Further research should relate root hair functioning to the observed losses in maize productivity and growth efficiency.

Streptomycetaceae and Promicromonosporaceae: Two Actinomycetes Families from Moroccan Oat Soils Enhancing Solubilization of Natural Phosphate

Soil actinomycetes explorations appear to be an efficient alternative as biofertilizers to optimize the use of phosphorus (P) resources and enhance plant growth. This research aimed to explore the distribution of actinomycetes isolated from four different rhizospheric Moroccan oat soils and to investigate their potential for P solubilization. The distribution of actinomycetes was significantly more abundant in Settat (9.68%), Tangier (7.38%), and Beni Mellal (6.87%) than in the Merchouch-Rabat (4.90%) region. A total of 235 actinomycete strains were isolated from all sites and tested for their ability to grow on a synthetic minimum medium (SMM) containing insoluble natural rock phosphate (RP) or synthetic tricalcium phosphate (TCP) as the unique P source. One hundred forty-three isolates (60.8%) had the ability to grow in the SMM with RP whereas only twenty-five isolates (17%) had the most active growth using the SMM with TCP. Eight isolates with the most active growth in solid SMM were selected for their P solubilization abilities in liquid SMM cultures. The highest amount of P solubilized was 163.8 µg/mL for RP and 110.27 µg/mL for TCP after 5 days of culture. The biosolubilization process of AM2, the most efficient RP and TCP solubilizing strain, probably implied the highest excretion of siderophore substances. Eight of these strains were shown to belong to the Streptomyces genus and one to the Promicromonospora genus. These findings bolster the phosphate biosolubilization abilities of actinomycetes and may participate in increasing agricultural yields in an eco-efficient and environmentally friendly manner.