Néstor Curvetto

Growth and productivity of different Pleurotus ostreatus strains on sunflower seed hulls supplemented with N–NH4+ and/or Mn(II)

The mycelial growth rates in lineal growth assay, yield, and production rate of five Pleurotus ostreatus strains were evaluated in response to different levels of Mn(II) and/or NH4+ in a substrate containing sunflower seed hulls as a main energy and nutritional component. Each strain showed different basal values for mycelial growth rate and biological efficiency on sunflower seed-hull substrate. Adding growth limiting mineral nutrients increased the mycelial growth rate by 13-25%. Primordia initiation for the first flush appeared between day 24 and 28 and days to the second crop ranged from 39 to 51. Biological efficiency increased over control values and reached 60-112%, depending on the strain and the concentration of Mn(II) and NH4+. This study demonstrated the advantage of selecting the most productive P. ostreatus strains in a substrate formulated with sunflower seed hulls to provide the main energy and nutritional ingredients and supplemented with Mn(II) and/or NH4+.

Accumulation patterns of phenolic compounds during fruit growth and ripening of Berberis buxifolia, a native Patagonian species

The accumulation patterns of phenolic compounds during fruit growth and ripening of Berberis buxifolia and their correlations were studied to determine the optimal time and conditions needed to obtain maximum phenolic content. Anthocyanin content increased from 1.7 to a maximum of 752.7 mg·100 g−1 FW at the end of ripening, while the flavonoid content was maximal in unripe fruits [604.0 mg (+)-catechin equivalents·100 g−1 FW]. Total phenolic compounds decreased from 968.1 to a minimum of 746.3 mg gallic acid equivalents·100 g−1 FW just as soluble solids started to accumulate; a maximum of 1522.9 mg gallic acid equivalents·100 g−1 FW was attained at the end of ripening. Both variables (1,1-diphenyl-2-picrylhydrazyl scavenging effect and reducing power) were maximum in unripe fruits, and decreased during the ripening period, although the 1,1-diphenyl-2-picrylhydrazyl scavenging effect increased again towards the end of this period. The accumulation patterns of phenols varied depending on the specific group of compounds considered, and could be correlated with fruit quality.

Polyamines and inhibitors used in successive culture media for in vitro rooting in Berberis buxifolia

Abstract Although Berberis buxifolia has been reported to propagate in vitro, rooting is difficult to achieve during subcultures, with reduced quantity and quality of roots, as is the case with many other woody species. Several cofactors of rhizogenesis have been proposed, and the role of polyamines in rooting has recently acquired relevance. Polyamines can stimulate or inhibit microshoot rooting depending on the type and concentration of polyamine and rooting phase, while polyamine inhibitors can improve rooting in some cases. A study of the in vitro rooting of B. buxifolia using polyamines and a mix of polyamine inhibitors in a two‐step culture medium is described here, in which a new successive rooting medium was successfully implemented. While polyamine inhibitors sometimes improved rooting, nutrient medium containing a low polyamine concentration (i.e., 1 μM) enhanced rooting compared with the control medium. The best micro‐shoot rooting response resulted from the addition of 1 μM spermidine during the expression phase in the absence of inhibitors in both rooting phases. Overall, incorporating polyamine in the successive media enhances the quality and quantity of roots in B. buxifolia, thus confirming their role during the induction and expression of the radicle primordia differentiation.

Electrophoretic subfractionation of low and high molecular weight humic acids fractions

SummarySoil humic acid was fractionated on a molecular weight basis either using Sephadex gel filtration or electrophoresis on a discontinuous polyacrylamide gel. Low and high molecular weight fractions obtained by these two methods were choosen for subsequent subfractionation using electrophoretic methods. The high and low molecular weight fractions yielded several subfractions after separation by isotachophoresis or isoelectric focusing. Components of the high molecular weight fractions occupied the upper portion of the mobility train; components of the low molecular weight fractions lead the mobility train. Adsorption by Sephadex was avoided by using 4M urea as an eluent. The elution of the humic substances adsorbed to the polyacrylamide gel matrix was achieved by using a 0.1M Tris −0.025M EDTA solution.

THE EFFECT OF FIRE ON SOIL HUMIC SUBSTANCES

SummaryHigh temperature effects on soil humic substances were investigated both in natural and laboratory conditions. Differential Thermal Analysis and pyrolysis show that only temperatures above 250°C produce changes in the humic acid fraction. The mean change is a loss of weight due to decarboxylation. Isotachophoretic studies also show that temperatures higher than 250°C produce alteration in the separation pattern of the different subfractions due to changes in the ‘core’ or/and in the amount of carboxyl and hydroxyl groups. Isotachophoregrams done on soil samples extracted from an area before and after fire show no differences. This result is taken as an indication that there was no direct effect of the temperature on the soil humic substances.

Pyrolysis of sunflower seed hulls for obtaining bio-oils

Bio-oils from pyrolysis of as received sunflower seed hulls (SSH), hulls previously washed with acid (SSHA) and hulls submitted to a mushroom enzymatic attack (BSSH) were analyzed. The concentration of lignin, hemicellulose and cellulose varied with the pre-treatment. The liquid corresponding to SSH presented a relatively high concentration of acetic acid and a high instability to storage. The bio-oil from SSHA showed a high concentration of furfural and an appreciable amount of levoglucosenone. Lignin was degraded upon enzymatic activity, for this reason BSSH led to the highest yield of bio-oil, with relative high concentration of acetic acid and stability to storage.

Increasing nitrate/ammonium ratio for improvement of garlic micropropagation

The effect of different culture media with different growth regulator and nitrate/ammonium ratios on split garlic shoots was studied to obtain an optimized micropropagation protocol. Three basal media: MS, BDS and BLM (i.e. BDS modified to obtain a nitrate:ammonium ratio of 35 mM:8 mM) combined with two concentrations of NAA (0.5 or 5 mM) and BAP (1 or 10 mM) were evaluated in three Colorado garlic clones: Espanol Seleccion Ascasubi (ESA), Espanol SeleccionM edanos (ESM) and I 50. In BLM medium with 5 mM NAA and 10 mM BAP the highest multiplication rates were 140, 542 and 743 shoots per split shoot after three subcultures in 140 days for clones ESA, ESM and I 50, respectively. Comparing the mean rates obtained in MS medium with those obtained in BDS medium in the same time, the latter produced 1.5-, 4- and 2.2-fold increases in the mean multiplication rates for ESA, ESM and I 50 clones, respectively; while BLM produced 5-, 3- and 10-fold increases in the mean multiplication rates. Since BDS and BLM media only differ in their NO3 ˇ :NH4 a ratio we can conclude that the differences in the multiplication rates could probably be due to an increase in the NO3 ˇ level of the BLM medium and so the multiplication ratios for these garlic clones can be greatly improved by the use of higher levels of nitrogen supplied as nitrate (35 mM NO3 ˇ :8 mM NH4 a ratio) with higher concentrations of growth regulators such as 5 mM NAA and 10 mM BAP. # 2001 Elsevier Science B.V. All rights reserved.

Peroxidase and polyamine activity variation during the in vitro rooting of Berberis buxifolia

Abstract Berberis buxifolia is a Patagonian shrub with great economic potential for tinctorial, pharmacological, and food industries. Clonal propagation is possible through in vitro culture and is also useful for metabolite production. However, this species is difficult to root, and to improve this, more knowledge of rhizogenesis processes is needed. Polyamines and peroxidases are useful biochemical markers during analysis of rooting phases for correlation with tissue morphological changes. Therefore, endogenous polyamine (putrescine, spermidine, spermine) changes, peroxidase activity evolution, and morphological development were studied to characterise the in vitro rhizogenesis of microshoots of B. buxifolia and, thus, to define the rooting phases. Polyamine and peroxidase changed significantly during the rooting period, and had opposite behaviours which were directly related to the IBA media content. The lower polyamine concentration and the higher peroxidase activity were found in a treatment with a dark period during the first four days and with IBA in the culture medium. Putrescine was the most abundant polyamine found in B. buxifolia tissues, 14‐ to 18‐fold more than spermidine and spermine, respectively. Therefore, these compounds were used to define the rooting phases: an induction phase (0 to 4–7 days) followed by an expression phase (4–7 to 28 days). The observed changes in the biochemical markers could be correlated with microscopic and macroscopic tissue observations in the microshoots, and the time course of rooting percentage. Successive culture media can be developed including polyamines, or other compounds and environmental conditions, which positively modify the studied biochemical markers behaviour.

Successive media to improve the in vitro rhizogenesis of Nothofagus nervosa (Phil.) Dim. et Mil.

In vitro rooting constitutes a difficult step during the micropropagation process of forest species. The successive media culture technique represents one way to overcome this barrier and includes modifying physical (e.g. photoperiod) and chemical (e.g. flavonoids) factors during the rooting phases. The aim of this study was to obtain a successive media protocol based on the incorporation of flavonoids during the in vitro rooting of Nothofagus nervosa. The factors evaluated were the type, concentration, and combination of flavonoids in relation to the rooting phases, the presence of IBA in the culture medium, the photoperiod, and the effect of flavonoids on total tissue peroxidase activity. The photoperiod used included a darkness period during the rooting induction stage and the presence of 0.61 µMIBA in the culture medium. The results showed that flavonoid incorporation at a concentration of 20 µM accelerated the appearance of roots and improved the quality of the already formed ones. Each type and concentration of flavonoid produced different responses, with (±)naringenin giving the best results. The latter caused a peak in the peroxidase activity that was absent in the control treatments. This work allowed identifying an optimized rooting protocol through a successive media culture technique that improved the speed of appearance, as well as the quantity and quality of roots for a single N. nervosa clone.

Esterase isozyme variation in theEragrostis curvula complex (Poaceae)

The biosystematic relationships of the apomictic complexEragrostis curvula s. lato, is investigated by disc electrophoresis of seed extracts to obtain esterase patterns of 23 accessions representing the morphological variants of this complex: curvula, conferta, robusta, chloromelas and lehmanniana. The zymograms thus obtained were classified into four groups on the basis of the presence of certain bands taken as characteristic and constant markers. Within each group variations were found in strict accordance with the morphological and cytogenetic data available on the complex. Cluster analysis showed similarity levels between the strains studied, representing different genomic groups. The esterase pattern proved useful as an additional criterion for identifying the individual taxa making up the complex and for evaluating their reciprocal relationships.