Tolerance of Douglas Fir Somatic Plantlets to Aluminum Stress: Biological, Cytological, and Mineral Studies.

Aluminum (Al) is well known as a potent inhibitor of plant growth and development. It is notably present in soils in the soluble and bioavailable form Al3+ when the soil pH drops below 5. This situation is frequent, especially in softwood forests when litter decomposition is slow. In the present work, we studied the effects of Al3+ on the growth and development of Douglas fir plantlets. Somatic plantlets, regenerated via somatic embryogenesis, were grown in vitro on media supplemented with different concentrations of aluminum chloride (AlCl3): 0 µM, 200 µM, 500 µM. and 1 mM. We show that a concentration of 500 µM AlCl3 in medium significantly reduced root elongation (-21.8%), as well as stem growth (-14.6%). Also, a 25% reduction in dry mass of the plantlets was observed in presence of a concentration of 200 µM of AlCl3. Histological analysis of root tissues revealed significant damage, especially in conducting vessels. In addition, mineral cation content of plantlets was disturbed under Al exposure. More particularly, the Mg and K contents of needles and the Ca content of stems and needles were significantly reduced in presence of a concentration of 500 µM AlCl3 in the culture medium (-35.6%, -33.5%, -24%, and -34% respectively). However, all these damages appeared at relatively high Al concentrations when compared with other herbaceous species. This study shed light on the ability of Douglas fir in vitro plantlets to cope with the acid-driven toxicity of Al.

Use of a Pleurotus ostreatus Complex Cell Wall Extract as Elicitor of Plant Defenses: From Greenhouse to Field Trial.

Fungi constitute an abundant source of natural polysaccharides, some of them harboring original structures which can induce responses in mammalian or plant cells. An alkaline extract from the edible mushroom Pleurotus ostreatus has been obtained and called Pleuran complex cell wall extract (CCWE). It consists of a glucan-peptide complex whose components fall in a quite broad range of molecular weights, from 30 to 80 kDa. Pleuran extract has been tested on cultivated plants in laboratory conditions and also during field trial for its capacity to stimulate plant defenses in response to pathogen attack. Following Pleuran CCWE treatment, enhanced levels of various biochemical markers associated with plant responses have been observed, including enzymatic activities (e.g., peroxidase) or expression of some pathogenesis-related genes. In addition, during field experiments, we have noticed significant reductions in disease symptom levels in relation to different plant/pathogen systems (wheat/septoria, vine/mildew). These results confirmed that Pleuran CCWE could be used as an elicitor of plant defenses and could help in reducing pesticide applications against plant pathogens.

Fractal structures and silica films formed by the Treignac water on inert and biological surfaces.

The Treignac water is a natural mineral water containing mainly orthosilicic acid. On inert substrates, it forms a silica film with fractal structures which cannot be reproduced in laboratory-reconstituted water. These structures form by condensation of orthosilicic acid monomers, following the Witten-Sander model of diffusion-limited aggregation. On biological surfaces, such as tomato leaves, the Treignac water forms a silica film with a different morphology and devoid of fractal structures. The filmogenic properties of this natural mineral water are here discussed in the context of crop protection, as the silica film can provide a barrier and a platform for the immobilization of elicitors of plant defense responses.

Agar Extraction By-Products from Gelidium sesquipedale as a Source of Glycerol-Galactosides.

Alkaline treatment is a common step largely used in the industrial extraction of agar, a phycocolloid obtained from red algae such as Gelidium sesquipedale. The subsequent residue constitutes a poorly valorized by-product. The present study aimed to identify low-molecular-weight compounds in this alkaline waste. A fractionation process was designed in order to obtain the oligosaccharidic fraction from which several glycerol-galactosides were isolated. A combination of electrospray ion (ESI)-mass spectrometry, ¹H-NMR spectroscopy, and glycosidic linkage analyses by GC-MS allowed the identification of floridoside, corresponding to Gal-glycerol, along with oligogalactosides, i.e., (Gal)2⁻4-glycerol, among which α-d-galactopyranosyl-(1→3)-ß-d-galactopyranosylα1-2⁻glycerol and α-d-galactopyranosyl-(1→4)-ß-d-galactopyranosylα1-2⁻glycerol were described for the first time in red algae.