Silver nanoparticles (AgNPs) display unique biological activities and may serve as novel biostimulators. Nonetheless, their biostimulant effects on germination, early growth, and major nutrient concentrations (N, P, and K) in tomato (Solanum lycopersicum) have been little explored. Tomato seeds of the Vengador and Rio Grande cultivars were germinated on filter paper inside plastic containers in the presence of 0, 5, 10, and 20 mg/L AgNPs. Germination parameters were recorded daily, while early growth traits of seedlings were determined 20 days after applying the treatments (dat). To determine nutrient concentrations in leaves, a hydroponic experiment was established, adding AgNPs to the nutrient solution. Thirty-day-old plants were established in the hydroponic system and kept there for 7 days, and subsequently, leaves were harvested and nutrient concentrations were determined. The AgNPs applied did not affect germination parameters, whereas their application stimulated length and number of roots in a hormetic manner. In 37-day-old plants, low AgNP applications increased the concentrations of N, P, and K in leaves. As novel biostimulants, AgNPs promoted root development, especially when applied at 5 mg/L. Furthermore, they increased N, P, and K concentration in leaves, which is advantageous for seedling performance during the early developmental stages.

Background: Silicon (Si) is a beneficial element that has been proven to influence plant responses including growth, development and metabolism in a hormetic manner.Methods: In the present study, we evaluated the effect of Si on the growth and concentrations of chlorophylls, total amino acids, and total sugars of pepper plants (Capsicum annuumL.) during the early developmental stage in a hydroponic system under conventional (unstressed) conditions. We tested four Si concentrations (applied as calcium silicate): 0, 60, 125 and 250 mg L⁻¹, and growth variables were measured 7, 14, 21 and 28 days after treatment (dat), while biochemical variables were recorded at the end of the experiment, 28 dat.Results: The application of 125 mg L⁻¹Si improved leaf area, fresh and dry biomass weight in leaves and stems, total soluble sugars, and concentrations of chlorophyllsaandbin both leaves and stems. The amino acids concentration in leaves and roots, as well as the stem diameter were the highest in plants treated with 60 mg L⁻¹Si. Nevertheless, Si applications reduced root length, stem diameter and total free amino acids in leaves and stems, especially when applied at the highest concentration (i.e., 250 mg L⁻¹Si).Conclusion: The application of Si has positive effects on pepper plants during the early developmental stage, including stimulation of growth, as well as increased concentrations of chlorophylls, total free amino acids and total soluble sugars. In general, most benefits from Si applications were observed in the range of 60–125 mg L⁻¹Si, while some negative effects were observed at the highest concentration applied (i.e., 250 mg L⁻¹Si). Therefore, pepper is a good candidate crop to benefit from Si application during the early developmental stage under unstressed conditions.

Vanadium (V) can be absorbed by plants and regulate their growth and development, although contrasting effects have been reported among species and handling conditions. The objective of this work was to evaluate the beneficial effect of V on pepper plants (Capsicum annuum L.). The plants were grown in a hydroponic system with the application of four V concentrations (0, 5, 10, and 15 μM NH₄VO₃). Four weeks after the beginning of the treatments, growth, flowering, biomass, chlorophyll concentration, total amino acids, total soluble sugars, and nutrients were determined in leaves, stems, and roots. The application of 5 μM V increased plant growth, induced floral bud development, and accelerated flowering. The chlorophyll concentration varied according to the type of plant part analyzed. The concentrations of amino acids and sugars in leaves and roots were higher with 5 μM. With 10 and 15 μM V, the plants were smaller and showed toxicity symptoms. The K concentration in leaves decreased as the V dose increased (0 to 15 μM). However, 5 μM V increased the concentrations of N, P, K, Ca, Mg, Cu, Mn, and B, exclusively in stems. The application of 15 μM V decreased the concentrations of Mg and Mn in leaves, but increased those of P, Ca, Mg, Cu, and B in roots. We conclude that V has positive effects on pepper growth and development, as well as on the concentrations of amino acids and total sugars. V was antagonistic with K, Mg, and Mn in leaves, while in stems and roots, there was synergism with macro and micronutrients. Vanadium is a beneficial element with the potential to be used in biostimulation approaches of crops like pepper.

Cerium (Ce) belongs to the rare earth elements (REEs), and although it is not essential for plants, it can stimulate growth and other physiological processes. The objective of this research was to evaluate the effect of Ce on seed germination, initial seedling growth, and vegetative growth in rice (Oryza sativa L.) cv. Morelos A-98. During the germination process, the seeds were treated with Ce concentrations of 0, 4, 8, and 12 μM; after 5 d, germination percentage was recorded and after 10 d seedling growth was measured. For vegetative growth, a hydroponic system was established where 14-d-old plants without previous Ce treatment were transferred into nutrient solution. After two weeks of acclimatizing, 0, 25, 50, and 100 μM Ce were added to the nutrient solution for 28 d. Ce significantly increased germination and the initial growth variables of the seedlings. During vegetative growth, Ce increased plant height, number of tillers, root volume, and shoot fresh and dry biomass, without affecting root biomass weight. With low Ce concentrations (25 and 50 μM), the concentrations of chlorophylls and amino acids in the shoots were similar to those in the control, like amino acid concentration in the roots at a concentration of 25 μM Ce. Conversely, the concentration of total sugars increased in the shoot with the application of 25, 50, and 100 μM Ce, and in the roots with the application of 50 μM Ce. Also, Ce did not affect the concentration of macro or micronutrients in the shoots. However, in the roots, the high Ce concentration decreased the concentrations of Ca, Fe, Mn, and Zn, while the Mg concentration increased. Our results indicate that Ce, at the right concentrations, can function as a biostimulant in rice germination and growth.

The efficiency of nanoparticles covered with type A gel and loaded with KH₂PO₄, as a source of P, was evaluated on growth, phosphorus concentration and accumulation, and photosynthesis-related parameters in rice plants (Oryza sativa L. ssp. indica) cv. Morelos A-2010, under greenhouse conditions. Plants were treated for 14 days with P concentrations equivalent to 50 and 100% of those established in the Yoshida nutrient solution. Sources of P were KH₂PO₄, nano-KH₂PO₄, and nano-KH₂PO₄ with trypsin; control treatments were distilled water and nanoparticles with type A gel. The solutions were renewed every 7 d. Rice plants exhibited differential P absorption in function of the P source tested. P supplied by KH₂PO₄ had a higher uptake rate than P supplied by nano-KH₂PO₄, alone or with trypsin. Nevertheless, nano-KH₂PO₄ promoted higher physiological efficiency for P in both roots and shoots, which consequently induced higher biomass accumulation in these organs. P concentration in shoots, as well as P accumulation in shoots and roots, were positively correlated with the photosynthetic rate. Also, nano-KH₂PO₄ increased instant water use efficiency in rice plants.

Aluminum (Al) is a beneficial element for some plant species, especially when used at low concentrations. Though some transcription factors are induced by exposure to this element, no data indicate that Al regulates the expression of NAC genes in rice. In this study we tested the effect of applying 0 and 200 µM Al on growth, chlorophyll, amino acids, sugars, macronutrient concentration and regulation of NAC transcription factors gene expression in 24-day-old plants of four rice (Oryza sativa ssp. indica) cultivars: Cotaxtla, Tres Ríos, Huimanguillo and Temporalero, grown hydroponically under greenhouse conditions. Twenty days after treatment, we observed that Al enhanced growth in the four cultivars studied. On average, plants grown in the presence of Al produced 140% more root dry biomass and were 30% taller than control plants. Cotaxtla and Temporalero showed double the root length, while Huimanguillo and Cotaxtla had three times more root fresh biomass and 2.5 times more root dry biomass. Huimanguillo plants showed 1.5 times more shoot height, while Cotaxtla had almost double the root dry biomass. With the exception of Tres Ríos, the rest of the cultivars had almost double the chlorophyll concentration when treated with Al, whereas amino acid and proline concentrations were not affected by Al. Sugar concentration was also increased in plants treated with Al, almost 11-fold in comparison to the control. Furthermore, we observed a synergic response of Al application on P and K concentration in roots, and on Mg concentration in shoots. Twenty-four hours after Al treatment, NAC transcription factors gene expression was measured in roots by quantitative RT-PCR. Of the 57 NAC transcription factors genes primer-pairs tested, we could distinguish that 44% (25 genes) showed different expression patterns among rice cultivars, with most of the genes induced in Cotaxtla and Temporalero plants. Of the 25 transcription factors up-regulated, those showing differential expression mostly belonged to the NAM subfamily (56 %). We conclude that Al improves growth, increases sugar concentration, P and K concentrations in roots, and Mg concentration in shoots, and report, for the first time, that Al differentially regulates the expression of NAC transcription factors in rice.