Factors affecting cactus recruitment in semiarid Chile: A role for nurse effects?

The nurse-protégé hypothesis states that adult plants of one species provide micro-environmental conditions that favor the establishment of seedlings of a second species with no effect for the first species. Several studies suggest this effect should be prevalent in arid and semiarid zones as adult plants often provide shelter from low moisture and high temperature. Echinopsis chiloensis and Eulychnia acida are endemic columnar cacti that inhabit the arid and semiarid zones of Chile. In this study, we examined the pattern of recruitment of both cactus species at Reserva Nacional Las Chinchillas, located ～60 km east from the Pacific coast. We determined number, growth and survivorship of young cacti (<30 cm height) through biannual monitoring between 2009 and 2012 in microhabitats that strongly differ in their abiotic variables (minimum and maximum temperature and mean relative humidity, moisture content, and physical and chemical soil characteristics), under five different shrub species and in open spaces, and examined the association of these cacti with potential nurse plants. Most young cacti occurred under shrubs, the microhabitat having the lowest mean and maximum temperatures and the highest relative humidity. In particular, E. chiloensis and E. acida were found under the shrubs Flourensia thurifera and Bahia ambrosioides, respectively, in a higher frequency than expected by chance, suggesting that these shrub species behave as nurse plants through species-specific effects than are not accounted for by differences in soil nutrients.     

Intra and interspecific sequence variation in closely related species of Cereus (CACTACEAE)

In comparative phylogenetic and population genetic studies, one of the most crucial steps is to select appropriate DNA markers, a decision based primarily on the estimated variation in markers in cross-taxonomic surveys. To assess whether genetic variation at the intraspecific level in one species predicts the variation in another closely related species we used two congeneric species of Cereus (Cactaceae: Cereeae). We screened and characterized eight noncoding plastid regions (trnS-trnG, atpI-atpH, trnT-trnL, psbD-trnT, petL-psbE, 3'rps16-5'trnk, trnG intron, and trnL intron), and one nuclear gene (PhyC) in Cereus fernambucensis and C. hildmannianus. A total of 40 individuals from 15 populations were characterized according to nucleotide diversity, number of haplotypes, and number of potentially informative characters. The results revealed that nucleotide substitutions and indels are the main source of variation, with the largest divergence between species found in trnS-trnG. The trnL intron and petL-psbE showed intraspecific variability in both species. The psbD-trnT, atpI-atpH, trnS-trnG, and trnT-trnL, which are the most variable regions in one species, showed no variation in the other. Finally, the nuclear gene PhyC showed more resolution between Cereus species than within species. We thus found considerable heterogeneity among widely used plastid markers, even between closely related species, and suggest the use of PhyC as a marker for phylogenetic inference in these species. These results reinforce the need of screening as a preliminary step to conduct phylogeographic or phylogenetic studies in face of unpredictable sequence variation of molecular markers in plants.     

Two simple tetrahydroisoquinoline alkaloid N-oxides from cacti

Tehuanine N-oxide was isolated from Pachycereus pringlei, and deglucopterocereine N-oxide was isolated from Pterocereus gaumeri. These     

Variations in aspartic acid racemization in uniformly preserved plants about 11000 years old

Amino acid racemization forms a basis for determining the chronology and paleotemperature of old plant constituents. Disparity in the extent of aspartic acid racemization was found in different taxa of plants subjected to the same environmental history and found in close proximity within an ancient packrat midden. One taxon showed different rates of aspartic acid racemization in two different anatomical sites. Temperature, pH and time being virtually identical in this one micro-environment within the midden, the differences in racemization rates may have been ultimately derived from physiological variants among the plants. Thus, at least, aspartic acid racemization data should be used selectively.     

In vitro cold storage of cork oak shoot cultures

Friable callus cultures were initiated from cotyledons and hypocotyls of Opuntia ficus-indica. Explants from cotyledons produced significantly more callus than those from hypocotyls. Optimum callus growth was observed on Murashige & Skoog medium supplemented with 0.9 μM 6-furfurylaminopurine, 2.3 μM 2,4-dichlorophenoxyacetic acid, 1.0 μM 4-amino 3,5,6-trichloropicolinic acid, 400 mg l^-1 casein hydrolysate and 3% sucrose. The same medium without agar was used for establishing cell suspensions. This revised version was published online in June 2006 with corrections to the Cover Date.