Mary E. Lucero

Do symbiotic microbes have a role in plant evolution, performance and response to stress?

Vascular plants have been considered as autonomous organisms especially when their performance has been interpreted at the genome and cellular level. In reality, vascular plants provide a unique ecological niche for diverse communities of cryptic symbiotic microbes which often contribute multiple benefits, such as enhanced photosynthetic efficiency, nutrient and water use and tolerance to abiotic and biotic stress. These benefits are similar to improvements sought by plant scientists working to develop ecologically sustainable crops for food, fiber and biofuels. Native desert plants include a community of indigenous endosymbiotic fungi that are structural components with cells, tissues, cell cultures, and regenerated plants. These fungi regulate plant growth and development and contribute genes and natural products that enable plants to adapt to changing environments. A method developed for transferring these endophytes from cell cultures to non-host plants promises to be a revolutionary approach for the development of novel plant germplasm and has application in the field of plant biotechnology.

A Retention Index Calculator Simplifies Identification of Plant Volatile Organic Compounds

INTRODUCTION Plant volatiles (PVOCs) are important targets for studies in natural products, chemotaxonomy and biochemical ecology. The complexity of PVOC profiles often limits research to studies targeting only easily identified compounds. With the availability of mass spectral libraries and recent growth of retention index (RI) libraries, PVOC identification can be achieved using only gas chromatography coupled to mass spectrometry (GCMS). However, RI library searching is not typically automated, and until recently, RI libraries were both limited in scope and costly to obtain. OBJECTIVE To automate RI calculation and lookup functions commonly utilised in PVOC analysis. METHODOLOGY Formulae required for calculating retention indices from retention time data were placed in a spreadsheet along with lookup functions and a retention index library. Retention times obtained from GCMS analysis of alkane standards and Koeberlinia spinosa essential oil were entered into the spreadsheet to determine retention indices. Indices were used in combination with mass spectral analysis to identify compounds contained in Koeberlinia spinosa essential oil. RESULTS Eighteen compounds were positively identified. Total oil yield was low, with only 5 ppm in purple berries. The most abundant compounds were octen-3-ol and methyl salicylate. The spreadsheet accurately calculated RIs of the detected compounds. CONCLUSION The downloadable spreadsheet tool developed for this study provides a calculator and RI library that works in conjuction with GCMS or other analytical techniques to identify PVOCs in plant extracts.

Volatile Composition of Gutierrezia sarothrae (Broom Snakeweed) as Determined by Steam Distillation and Solid Phase Microextraction

Abstract Volatiles of Gutierezia sarothrae (broom snakeweed, snakeweed) were isolated from ground, composite tissues by steam distillation and by solid phase microextraction (SPME), then separated and analyzed by gas chromatography with mass spectral and flame ionization detection. Compounds detected varied in quantity between isolation protocols. In the oil, cryptone (6.4%) and β-eudesmol (5.9%) were the only compounds comprising more than 5% of the chromatographic peak area. In samples prepared by solid-phase microextraction, limonene (10.4%), β-pinene (9.6%), β-eudesmol (8.0%), sabinene (7.8%), cryptone (6.5%), α-pinene (5.5%) and o-cymene (5.2%) accounted for 53% of the extracted volatiles. The results revealed a complex volatile composition from which unique compounds may still be identified.

Transport of Phenolic Compounds from Leaf Surface of Creosotebush and Tarbush to Soil Surface by Precipitation

During the last 100 years, many desert grasslands have been replaced by shrublands. One possible mechanism by which shrubs outcompete grasses is through the release of compounds that interfere with neighboring plants. Our objective was to examine the movement of secondary compounds from the leaf surface of creosotebush and tarbush to surrounding soil surfaces via precipitation. Units consisting of a funnel and bottle were used to collect stemflow, throughfall, and interspace precipitation samples from 20 creosotebush (two morphotypes) and 10 tarbush plants during three summer rainfall events in 1998. Precipitation samples were analyzed for total phenolics (both species) and nordihydroguaiaretic acid (creosotebush only). Phenolics were detected in throughfall and stemflow of both species with stemflow containing greater concentrations than throughfall (0.088 and 0.086 mg/ml for stemflow and 0.022 and 0.014 mg/ml for throughfall in creosotebush morphotypes U and V, respectively; 0.044 and 0.006 mg/ml for tarbush stemflow and throughfall, respectively). Nordihydroguaiaretic acid was not found in any precipitation collections. The results show that phenolic compounds produced by creosotebush and tarbush can be transported to the soil surface by precipitation, but whether concentrations are ecologically significant is uncertain. Nordihydroguaiaretic acid was not present in the runoff from creosotebush.

The Essential Oil Composition of Psorothamnus scoparius (A. Gray) Rydb.

Abstract Psorothamnus scoparius (broom dalea) was collected from the Jornada Experimental Range in south central New Mexico. Current years growth was collected from 10 plants, all found within an approximate 50 in radius of the GPS coordinates N32°41.286′ and W106°46.922′ during June, 2000. Composite samples were steam distilled, and the essential oil was analyzed using GC with FID and GC/MS. Mass spectra and retention indices were used to identify 64 compounds. Retention indices and EI mass spectra are also provided for 15 unknowns. γ-Terpinene (22.3%), p-cymene (14.0%) and α-pinene (9.0%) were the major constituents of the oil.

The Composition of Dalea formosa Oil Determined by Steam Distillation and Solid-Phase Microextraction

Abstract Dalea formosa Torr. (feather dalea, featherplume) was collected from the Jornada Experimental Range in south central New Mexico. Current years growth was collected from 10 plants, all found within an approximate 50 m radius of the GPS coordinates N32°40.645′ and W106°33.601′ during July 2001. Composite samples of the plants were steam distilled in triplicate, and the composite oil was analyzed using both GC-FID and GC/MS. The volatile composition of plants collected from the same site was also examined using solid-phase microextraction (SPME) with a 100 μm polydimethylsiloxane fiber. Mass spectra and retention indices were used to identify 58 previously described compounds. The retention index and EI mass spectra are provided for one unknown. The most abundant constituents of the oil were α-pinene (31.7%), camphene (8.4%) and limonene (8.1%). In contrast, α-pinene (33.6%), β-pinene (13.2%) and camphene (11.1%) were the most abundant constituents of the SPME samples. This difference in composition may be due to either sampling technique or harvesting time.

Composition of Ceanothus gregii oil as determined by steam distillation and solid-phase microextraction.

Abstract Ceanothus gregii Gray was collected from the Jornada Experimental Range in south central New Mexico. Current years growth was collected from ten plants found within an approximate 50 m radius of N32°40.605′ and W106°33.486′at an altitude of 1,741 m during July 2001. Composite samples of the plants were steam distilled in triplicate, and the composite oil was analyzed using both GC-FID and GC/MS. The volatile composition of the same plants was also examined using solid-phase microextraction (SPME) with a 100 mm polydimethylsiloxane fiber. Mass spectra and retention indices were used to identify 41 previously described compounds. Methyl salicylate (16.8%), hexanal (11.8%) and decanal (7.0%) were the major identified compounds.