Jonathan M. Frantz

Detection, Distribution, and Quantification of Silicon in Floricultural Crops utilizing Three Distinct Analytical Methods

Silicon (Si) detection, distribution, and quantification in plants was compared using electron beam analysis (EBA; scanning electron microscopy coupled with energy dispersive X‐ray analysis), colorimetric analysis, and inductively coupled plasma–optical emission spectroscopy (ICP‐OES) in 14 economically important floriculture species. Using EBA, Si was identified most commonly around the base of trichomes and along the leaf margins. The ICP‐OES processing and analysis for Si using sodium hydroxide (NaOH) resulted in damaged torches and microwavable Teflon® vessels that required expensive replacement at the end of each run, but this was not the case in the colorimetric method or with a potassium hydroxide (KOH)–based matrix in the ICP‐OES. The results of these analyses suggest there is agreement between quantification methods, and EBA has a lower detection limit of about 300 mg kg−1 dry weight of Si. Several new floriculture species (zinnia, impatiens, verbena, and calibrachoa) were identified that take up and accumulate Si in significant concentrations.

A Model of Canopy Photosynthesis Incorporating Protein Distribution Through the Canopy and Its Acclimation to Light, Temperature and CO2

BACKGROUND AND AIMS The distribution of photosynthetic enzymes, or nitrogen, through the canopy affects canopy photosynthesis, as well as plant quality and nitrogen demand. Most canopy photosynthesis models assume an exponential distribution of nitrogen, or protein, through the canopy, although this is rarely consistent with experimental observation. Previous optimization schemes to derive the nitrogen distribution through the canopy generally focus on the distribution of a fixed amount of total nitrogen, which fails to account for the variation in both the actual quantity of nitrogen in response to environmental conditions and the interaction of photosynthesis and respiration at similar levels of complexity. MODEL A model of canopy photosynthesis is presented for C(3) and C(4) canopies that considers a balanced approach between photosynthesis and respiration as well as plant carbon partitioning. Protein distribution is related to irradiance in the canopy by a flexible equation for which the exponential distribution is a special case. The model is designed to be simple to parameterize for crop, pasture and ecosystem studies. The amount and distribution of protein that maximizes canopy net photosynthesis is calculated. KEY RESULTS The optimum protein distribution is not exponential, but is quite linear near the top of the canopy, which is consistent with experimental observations. The overall concentration within the canopy is dependent on environmental conditions, including the distribution of direct and diffuse components of irradiance. CONCLUSIONS The widely used exponential distribution of nitrogen or protein through the canopy is generally inappropriate. The model derives the optimum distribution with characteristics that are consistent with observation, so overcoming limitations of using the exponential distribution. Although canopies may not always operate at an optimum, optimization analysis provides valuable insight into plant acclimation to environmental conditions. Protein distribution has implications for the prediction of carbon assimilation, plant quality and nitrogen demand.

Influence of Silicon on Resistance of Zinnia elegans to Myzus persicae (Hemiptera: Aphididae)

ABSTRACT Studies were conducted to examine the effect of treating Zinnia elegans Jacq. with soluble silicon on the performance of the green peach aphid, Myzus persicae (Sulzer). Z. elegans plants were irrigated every 2 d throughout the duration of the experiment with a nutrient solution amended with potassium silicate (K2SiO2), or a nutrient solution without K2SiO2. Length of the prereproductive period and survivorship of M. persicae were not affected by K2SiO2 treatment, but total cumulative fecundity and the intrinsic rate of increase (rm ) were slightly reduced on Z. elegans plants receiving soluble silicon. Quantification of silicon contentin leaf tissues using inductively coupled plasmaoptical emission spectroscopy (ICP-OES) confirmed significantly higher silicon concentrations in plants treated with K2SiO2 compared with control plants. High performance liquid chromatography-mass spectrometry (HPLC-MS) analysis was used to identify and quantify phenolic acids and flavonols in leaf tissue of z. elegans. Compared with untreated control plants, significant elevations in 5-caf-feoylquinic acid, p-coumaroylquinic acid, and rutin were detected in leaves of Z. elegans plants treated with K2SiO2, but none of seven other phenolics were significantly affected. Similarly, a slight elevation in guaiacol peroxidase activity was detected in plants treated with K2SiO2 Overall, these results indicate treatment of Z. elegans with soluble silicon provides a modest increase in resistance levels to M. persicae, which may be caused in part by defense-related compounds.

Proteomic analysis of Arabidopsis thaliana leaves in response to acute boron deficiency and toxicity reveals effects on photosynthesis, carbohydrate metabolism, and protein synthesis.

Boron (B) stress (deficiency and toxicity) is common in plants, but as the functions of this essential micronutrient are incompletely understood, so too are the effects of B stress. To investigate mechanisms underlying B stress, we examined protein profiles in leaves of Arabidopsis thaliana plants grown under normal B (30 μM), compared to plants transferred for 60 and 84 h (i.e., before and after initial visible symptoms) in deficient (0 μM) or toxic (3 mM) levels of B. B-responsive polypeptides were sequenced by mass spectrometry, following 2D gel electrophoresis, and 1D gels and immunoblotting were used to confirm the B-responsiveness of some of these proteins. Fourteen B-responsive proteins were identified, including: 9 chloroplast proteins, 6 proteins of photosynthetic/carbohydrate metabolism (rubisco activase, OEC23, photosystem I reaction center subunit II-1, ATPase δ-subunit, glycolate oxidase, fructose bisphosphate aldolase), 6 stress proteins, and 3 proteins involved in protein synthesis (note that the 14 proteins may fall into multiple categories). Most (8) of the B-responsive proteins decreased under both B deficiency and toxicity; only 3 increased with B stress. Boron stress decreased, or had no effect on, 3 of 4 oxidative stress proteins examined, and did not affect total protein. Hence, our results indicate relatively early specific effects of B stress on chloroplasts and protein synthesis.

Polyacrylamide Hydrogel Properties for Horticultural Applications

Polyacrylamide (PAAm) hydrogels are commonly employed to ensure soil hydration in horticulture, but studies have shown that they have a minimal effect on crop life and quality. The reasons for this poor performance are not understood since the commercial hydrogels have not been adequately characterized. PAAm hydrogels were synthesized and their properties were measured along with those of commercial hydrogels. Hydrogel swelling, density, and SEM analyses showed that the commercial hydrogels were most likely a derivative of PAAm with ionic groups and they were able to retain moisture for only a few hours.

Interactive effects of elevated CO2 and ozone on leaf thermotolerance in field-grown Glycine max.

Humans are increasing atmospheric CO2, ground-level ozone (O3), and mean and acute high temperatures. Laboratory studies show that elevated CO2 can increase thermotolerance of photosynthesis in C3 plants. O3-related oxidative stress may offset benefits of elevated CO2 during heat-waves. We determined effects of elevated CO2 and O3 on leaf thermotolerance of field-grown Glycine max (soybean, C3). Photosynthetic electron transport (et) was measured in attached leaves heated in situ and detached leaves heated under ambient CO2 and O3. Heating decreased et, which O3 exacerbated. Elevated CO2 prevented O3-related decreases during heating, but only increased et under ambient O3 in the field. Heating decreased chlorophyll and carotenoids, especially under elevated CO2. Neither CO2 nor O3 affected heat-shock proteins. Heating increased catalase (except in high O3) and Cu/Zn-superoxide dismutase (SOD), but not Mn-SOD; CO2 and O3 decreased catalase but neither SOD. Soluble carbohydrates were unaffected by heating, but increased in elevated CO2. Thus, protection of photosynthesis during heat stress by elevated CO2 occurs in field-grown soybean under ambient O3, as in the lab, and high CO2 limits heat damage under elevated O3, but this protection is likely from decreased photorespiration and stomatal conductance rather than production of heat-stress adaptations.

Silicon delays Tobacco ringspot virus systemic symptoms in Nicotiana tabacum.

Soluble silicon (Si) provides protection to plants against a variety of abiotic and biotic stress. However, the effects of Si on viral infections are largely unknown. To investigate the role of Si in viral infections, hydroponic studies were conducted in Nicotiana tabacum with two pathogens: Tobacco ringspot virus (TRSV) and Tobacco mosaic virus (TMV). Plants grown in elevated Si showed a delay in TRSV systemic symptom formation and a reduction in symptomatic leaf area, compared to the non-supplemented controls. TRSV-infected plants showed significantly higher levels of foliar Si compared to mock-inoculated plants. However, the Si effect appeared to be virus-specific, since the element did not alter TMV symptoms nor did infection by this virus alter foliar Si levels. Hence, increased foliar Si levels appear to correlate with Si-modulated protection against viral infection. This is all the more intriguing since N. tabacum is classified as a low Si accumulator.

Analysis of Arsenic Uptake by Plant Species Selected for Growth in Northwest Ohio by Inductively Coupled Plasma–Optical Emission Spectroscopy

Abstract Arsenic (As) contamination is widespread in the industrial areas of northwest Ohio. Plant species that both take up As and are appropriate for the climate and growth conditions of the region are needed for phytoremediation to be successfully employed. Actively growing plants from 22 species of native genera were exposed to As in hydroponics systems (either 0, 10, or 50 mg As L−1; 1 week) and commercially available potting mix (either 0, 10, 25, 100, or 250 mg As L−1; 2 weeks), depending on their growth conditions. Aboveground plant tissues were harvested and digested, and concentrations of As were determined by inductively coupled plasma–optical emission spectrometry. The highest tissue concentrations of As (mg As kg−1 dw) were recorded in seven plant species: Rudbeckia hirta (661), Helenium autumnale (363 in tissues formed after exposure to As), Lupinus perennis (333), Echinacea purpurea (298), Coreopsis lanceolata (258), Lepidium virginicum (214), and Linum lewisii (214). These seven species are ecologically diverse, which suggests that phytoremediation of As using diverse assemblages of plants may be an option for a variety of environments.

Rare excitatory amino acid from flowers of zonal geranium responsible for paralyzing the Japanese beetle

The Japanese beetle (JB), Popillia japonica, exhibits rapid paralysis after consuming flower petals of zonal geranium, Pelargonium x hortorum. Activity-guided fractionations were conducted with polar flower petal extracts from P. x hortorum cv. Nittany Lion Red, which led to the isolation of a paralysis-inducing compound. High-resolution–MS and NMR (1H, 13C, COSY, heteronuclear sequential quantum correlation, heteronuclear multiple bond correlation) analysis identified the paralytic compound as quisqualic acid (C5H7N3O5), a known but rare agonist of excitatory amino acid receptors. Optical rotation measurements and chiral HPLC analysis determined an l-configuration. Geranium-derived and synthetic l-quisqualic acid demonstrated the same positive paralytic dose–response. Isolation of a neurotoxic, excitatory amino acid from zonal geranium establishes the phytochemical basis for induced paralysis of the JB, which had remained uncharacterized since the phenomenon was first described in 1920.

Impact of a short-term heat event on C and N relations in shoots vs. roots of the stress-tolerant C4 grass, Andropogon gerardii

Global warming will increase heat waves, but effects of abrupt heat stress on shoot-root interactions have rarely been studied in heat-tolerant species, and abrupt heat-stress effects on root N uptake and shoot C flux to roots and soil remains uncertain. We investigated effects of a high-temperature event on shoot vs. root growth and function, including transfer of shoot C to roots and soil and uptake and translocation of soil N by roots in the warm-season drought-tolerant C4 prairie grass, Andropogon gerardii. We heated plants in the lab and field (lab=5.5days at daytime of 30+5 or 10°C; field=5days at ambient (up to 32°C daytime) vs. ambient +10°C). Heating had small or no effects on photosynthesis, stomatal conductance, leaf water potential, and shoot mass, but increased root mass and decreased root respiration and exudation per g. (13)C-labeling indicated that heating increased transfer of recently-fixed C from shoot to roots and soil (the latter likely via increased fine-root turnover). Heating decreased efficiency of N uptake by roots (uptake/g root), but did not affect total N uptake or the transfer of labeled soil (15)N to shoots. Though heating increased soil temperature in the lab, it did not do so in the field (10cm depth); yet results were similar for lab and field. Hence, acute heating affected roots more than shoots in this stress-tolerant species, increasing root mass and C loss to soil, but decreasing function per g root, and some of these effects were likely independent of direct effects from soil heating.