Response of Sunflower (Helianthus annuus L.) Leaf Surface Defenses to Exogenous Methyl Jasmonate

Helianthus annuus, the common sunflower, produces a complex array of secondary compounds that are secreted into glandular trichomes, specialized structures found on leaf surfaces and anther appendages of flowers. The primary components of these trichome secretions are sesquiterpene lactones (STL), a diverse class of compounds produced abundantly by the plant family Compositae and believed to contribute to plant defense against herbivory. We treated wild and cultivated H. annuus accessions with exogenous methyl jasmonate, a plant hormone that mediates plant defense against insect herbivores and certain classes of fungal pathogens. The wild sunflower produced a higher density of glandular trichomes on its leaves than the cultivar. Comparison of the profiles of glandular trichome extracts obtained by liquid chromatography–mass spectroscopy (LC-MS) showed that wild and cultivated H. annuus were qualitatively similar in surface chemistry, although differing in the relative size and proportion of various compounds detected. Despite observing consistent transcriptional responses to methyl jasmonate treatment, we detected no significant effect on glandular trichome density or LC-MS profile in cultivated or wild sunflower, with wild sunflower exhibiting a declining trend in overall STL production and foliar glandular trichome density of jasmonate-treated plants. These results suggest that glandular trichomes and associated compounds may act as constitutive defenses or require greater levels of stimulus for induction than the observed transcriptional responses to exogenous jasmonate. Reduced defense investment in domesticated lines is consistent with predicted tradeoffs caused by selection for increased yield; future research will focus on the development of genetic resources to explicitly test the ecological roles of glandular trichomes and associated effects on plant growth and fitness

Inhibitory effect of Lycium europaeum extracts on phytopathogenic soil-borne fungi and the reduction of late wilt in maize

25 Páginas.-- 5 Tablas.-- 5 FigurasThe ability to control soil-borne pathogens in agriculture is highly conditioned by the restricted use of synthetic pesticides. Allelopathy, the antimicrobial activity of plant extracts, is a promising option against crop pathogens. Extracts from Lycium spp. such as L. barbarum, L. chinense and L. intricatum possess biological and therapeutic properties. Individual methanolic extracts from leaves and stems of the Mediterranean medicinal species L. europaeum collected in two locations of Tunisia were each evaluated in vitro against Verticillium dahliae (Vd), Sclerotinia sclerotiorum (Ss) and Harpophora maydis (Hm). The mycelial growth of the three fungi was significantly reduced by all the extracts at doses of 10 and 30 μl mL−1 (equivalent to 1 and 3 mg plant tissue mL−1). The sporulation of Hm was almost completely inhibited in all the amendments, but that of Vd was stimulated by one of the leaf extracts when 1 and 3 mg dried plant tissue mL−1 were used. Sclerotia of Ss were formed in a smaller number, their total weight increasing at extract doses equivalent to 1 mg plant tissue mL−1 and higher. In greenhouse, the pathogenicity of Hm was confirmed as early as 6 weeks after inoculation, since it caused significant decreases of weights in both roots and aboveground parts of maize. The detrimental effect of Hm on maize root weight in greenhouse was significantly counteracted by one of the leaf extracts added by watering. In total, 11 phenolic compounds were separated in the four extracts. The hydroxycinnamic acid family, including chlorogenic acid as a major compound, represented more than 50% of the total content in all the samples. Rutin was the most abundant flavonoid. The results of this work show the detrimental effect of L. europaeum extracts against the soil-borne pathogens Hm, Ss and Vd, and highlight their potential in crop protection if adequately developed into final products and used in combination with other tools.This research was partially supported by grants AGL2010–17909 (Ministerio de Economía y Competitividad, Spain) and P12-AGR1281 (Andalusian Government, Spain) and the European Regional Development Fund (ERDF). The stay of R. Tej was granted by the Ministry of Higher Education and Scientific Research in Tunisia.Peer reviewe

Seasonal variations in phytodesalination capacity of two perennial halophytes in their natural biotope

In Soliman sabkha (NE Tunisia), Tecticornia indica and Suaeda fruticosa tufts were divided into three size classes (small, medium, and big) in which the shoot sodium and potassium contents were determined in July 2007 and February 2008. Shoot dry weights per tuft and per hectare were estimated. Soil samples (20 upper centimeters) were taken from inside and outside the halophyte tufts and analyzed for electrical conductivity (EC1/10) and soluble sodium content. We found that these two parameters were significantly lower in the soil from inside the tufts than in the surrounding soil. This effect was more pronounced in winter (February 2008) when EC1/10 inside halophyte tufts was 63 to 72% lower than outside. In July 2007, the relevant reduction of EC1/10 inside the tufts was 55%. Soluble sodium content was reduced by 70.5% in winter and only 31 to 37% in summer. The ecosystem productivity was about 8.6 tonnes dry weight per hectare (t DW ha-1) with higher sodium than potassium contents (about 0.646 t Na+ ha-1 in summer and 0.752 tonnes Na+ ha-1 in winter). Regardless of the season, T. indica exhibited much higher phytodesalination capacity (77.7-94.4% of the whole shoot-removed sodium). For S. fruticosa, the decrease in soil salinity was due to roots that released sodium ions from the exchange sites and facilitated their leaching to the deeper horizons. From an ecological point of view, phytodesalination and sodium leaching enhancement are interesting processes since they provide glycophytes with a microhabitat suitable for their development, which maintains the biodiversity within the saline ecosystem

Salt effect on yield and composition of shoot essential oil and trichome morphology and density on leaves of Mentha pulegium

The aim of the present work was to study salt effect on the yield and composition of shoot essential oil (EO) and the structures responsible for its biosynthesis in Mentha pulegium L. Shoot EO was extracted by hydrodistillation and compositionwas determined by GC\u2013MSmethod. Apical and basal leaveswere taken for microscopy analyses; small fresh samples were observed directly without fixation or metallisation with environmental scanning electron microscope (ESEM) and stereomicroscope (SM). Fresh separate epidermis was used for light microscopy (LM). Salt stress enhanced EO yield by about 2.75 times and affected the percentage of menthone, which is the major compound ( 3c51%), increasing that of pulegone. Menthone, pulegone, and neomenthol constituting the monoterpene classwere found to be the principal components. The anatomical study showed three types of trichomes: (i) non-glandular, multicellular, simple hairs; (ii) small, capitate glandular trichomes; (iii) and peltate glandular trichomes. In control plants, the density and size of trichomes varied with leaf side (abaxial or adaxial) and developmental stage. Salt stress results in significant modifications affecting trichome distribution and size on both sides

Salt effect on yield and composition of shoot essential oil and trichome morphology and density on leaves of Mentha pulegium

The aim of the present work was to study salt effect on the yield and composition of shoot essential oil (EO) and the structures responsible for its biosynthesis in Mentha pulegium L. Shoot EO was extracted by hydrodistillation and compositionwas determined by GC–MSmethod. Apical and basal leaveswere taken for microscopy analyses; small fresh samples were observed directly without fixation or metallisation with environmental scanning electron microscope (ESEM) and stereomicroscope (SM). Fresh separate epidermis was used for light microscopy (LM). Salt stress enhanced EO yield by about 2.75 times and affected the percentage of menthone, which is the major compound (∼51%), increasing that of pulegone. Menthone, pulegone, and neomenthol constituting the monoterpene classwere found to be the principal components. The anatomical study showed three types of trichomes: (i) non-glandular, multicellular, simple hairs; (ii) small, capitate glandular trichomes; (iii) and peltate glandular trichomes. In control plants, the density and size of trichomes varied with leaf side (abaxial or adaxial) and developmental stage. Salt stress results in significant modifications affecting trichome distribution and size on both sides

Nutrient uptake and management under saline conditions in the xerohalophyte: Tecticornia indica (Willd.) subsp. indica

Tecticornia indica (Willd.) subsp. indica as subjected to salinity. Plants were grown under greenhouse conditions at various salinity levels (0, 100, 200 and 400 mM NaCl) over 110 days. At the harvest, they were separated into shoots and roots then analyzed for water contents, dry weights (DW), and Na+, K+, Ca2+, and Mg2+ contents. Plants showed a growth optimum at 200 mM NaCl and much better tissue hydration under saline than non-saline conditions. At this salt concentration (200 mM NaCl), shoot Na+ content reached its highest value (7.9 mmol · g–1 DW). In spite of such stressful conditions, salt-treated plants maintained adequate K+, Ca2+, and Mg2+ status even under severe saline conditions. This was mainly due to their aptitude to selectively acquire these essential cations and efficiently use them for biomass production