M. Ángeles Revilla

In vitro plant regeneration from cotyledon and hypocotyl segments in two bell pepper cultivars

In vitro plant regeneration has been obtained from Capsicum annuum cvs. Pico and Piquillo. Shootbuds were induced from hypocotyl and cotyledon segments after 15–20 days of culture on MS basal medium supplemented with IAA and BAP or Zeatin. Shoot-buds grew into rosettes that rooted in MS plus NAA (0.1 mg/l) and IBA (0.05 mg/l) after 15 days. The small plantlets were successfully transferred to pots with a mixture of peat and perlite and maintained under greenhouse conditions. Elongation took place when the plantlets were growing in the greenhouse.

Genetic and epigenetic stability of cryopreserved and cold-stored hops (Humulus lupulus L.)

Conventional cold storage and cryopreservation methods for hops (Humulus lupulus L.) are available but, to our knowledge, the genetic and epigenetic stability of the recovered plants have not been tested. This study analyzed 51 accessions of hop using the molecular techniques, Random Amplified DNA Polymorphism (RAPD) and Amplified Fragment Length Polymorphism (AFLP), revealing no genetic variation among greenhouse-grown controls and cold stored or cryopreserved plants. Epigenetic stability was evaluated using Methylation Sensitive Amplified Polymorphism (MSAP). Over 36% of the loci were polymorphic when the cold and cryo-treated plants were compared to greenhouse plants. The main changes were demethylation events and they were common to the cryopreserved and cold stored plants indicating the possible effect of the in vitro establishment process, an essential step in both protocols. Protocol-specific methylation patterns were also detected indicating that both methods produced epigenetic changes in plants following cold storage and cryopreservation.

Epigenetic changes detected in micropropagated hop plants

Micropropagation is a widely used technique in hops (Humulus lupulus L.). However, to the best of our knowledge, the genetic and epigenetic stability of the microplants has never been tested before. In the present study, two hop accessions were established in vitro and micropropagated for 2 years. The genetic and epigenetic stability of the in vitro plants was analyzed with several molecular techniques: random amplified DNA polymorphism (RAPD), retrotransposon microsatellite amplified polymorphism (REMAP), and methylation-sensitive amplification polymorphism (MSAP). No genetic variation among control and treated plants was found, even after 12 cycles of micropropagation. Epigenetic variation was detected, first, when field and in vitro samples were compared. Nearly a 30% of the detected fragments presented the same pattern of alterations in all the vitroplants. Second, lower levels of epigenetic variation were detected among plants from the different subcultures. Part of this detected variation seemed to be accumulated along the 12 sequential subcultures tested.

Cryopreservation of in vitro-grown shoot-tips of hop (Humulus lupulus L.) using encapsulation/dehydration

Abstract A cryopreservation procedure using encapsulation/dehydration was established for shoot-tips obtained from in vitro-grown shoots of hop. After dissection, shoot-tips were encapsulated in medium with alginate and 0.5 M sucrose. Optimal conditions consisted of preculture for 2 days in solid medium with 0.75 M sucrose, or in increasing sucrose concentrations, desiccation for 4 h with silicagel in a flow cabinet (16% water content) followed by rapid freezing and slow thawing. Shoot recovery after freezing 60 min in liquid nitrogen was around 80%. No phenotypical changes were observed in the recovered plants from cryopreserved shoot-tips growing in the field.

Endogenous Hormonal Profiles in Hop Development

Changes in gibberellins (GAs), indole-3-acetic acid (IAA), and cytokinins associated with the transition from vegetative growth to reproductive growth in Humulus lupulus L. buds and leaves harvested at fortnight intervals were studied. During vegetative growth, GA1 increased gradually and the lowest content was observed during flower development. Both GA3 and GA4 showed a dramatic increase in the samples taken from the apical part of axillary branches from plants 4–5 m high, which corresponds to the maximum vegetative development prior to macroscopically visible inflorescences. Notable increases in the cytokinins trans-zeatin (t-Z), isopentenyladenine (iP), and the riboside and ribotide forms of iP were also obtained. The auxin, indole-3-acetic acid, was the most abundant plant hormone, and its content was highest during vegetative growth. These results show for the first time a relationship between endogenous hormone profiles and both vegetative and reproductive development in hop plants, which may be relevant for future research on the control of the flowering by exogenous hormone applications.

Survival cryopreservation of hop shoot tips monitored by differential scanning calorimetry

Differential scanning calorimetry is used for monitoring the survival conditions of hop (Humulus lupulus L.) shoot tips under cryopreservation. The survival is related to the absence of formation and growing of ice crystals during the cooling process as shown by the absence of heat effect from ice formation. Samples with different degrees of humidity were obtained through a controlled process of dehydration.

The influence of European and American wild germplasm in hop (Humulus lupulus L.) cultivars

Microsatellite variation at the nuclear and chloroplast genomes was evaluated for wild European and wild American hops, in order to assess the genetic diversity and origin of cultivated hops. Seven nuclear loci and 32 chloroplast loci were used in the analysis of 182 hop accessions including wild European (68), wild American (48), and cultivars (66). A total of 116 alleles were identified using 7 nuclear microsatellites showing different averages of polymorphism and distribution in the wild American and European accessions and cultivars. Two main groups were established as revealed by several statistical analyses; one including European wild accessions and cultivars and a second group consisting of American wild accessions. Three polymorphic chloroplast microsatellite loci were detected, six alleles were scored which defined a total of five haplotypes that were exclusive or presented different distribution between American and European wild accessions. A major influence of the wild European haplotypes was detected among hop cultivars. To the best of our knowledge, this is the first work reporting the use of chloroplast microsatellites in hops.

Differential scanning calorimetry applied to the storage at ultra low temperatures of olive and hop in vitro grown shoot-tips

Abstract Differential scanning calorimetry was used for monitoring the survival conditions of olive in vitro grown shoot-tips under cryopreservation (−196°C), as well as for establishing the storage conditions at temperatures higher than liquid nitrogen. Olive survival is related to the absence of formation and growing of ice crystals during the cooling process. These results are compared with those obtained in hop. The final storage temperature is given as a function of the shoot tip survival to the dehydration step and the absence of ice crystal growth during cooling and warming.

Evaluation of Microsatellite Detection Using Autoradiography and Capillary Electrophoresis in Hops

Two sequence tagged sites (STS) detection techniques were used in the identification of 25 hop cultivars. In cultivar identification, capillary electrophoresis is more efficient than autoradiography. First, it was more sensitive in detection of fragments that allowed observation of the instability in the locus 7a82 due to the small size differences of its alleles. Additionally, the fluorescent detection of fragments was a nonsubjective technique suitable of automation that increased the flexibility of work because no radioactive labeling or long vertical polyacrylamide electrophoresis was needed. Only two cultivars, Hersbrucker and Hallertauer, were indistinguishable, but further molecular analysis revealed that both were included in a separate cluster within the European hop cultivars. The statistical analysis of fluorescence and radioactive detection data including allelic frequencies, heterozygosity, and probability of identity are displayed in this study, which corroborates the following advantages of the capillary electrophoresis technique: high sensitivity, amenable to automation, and its nonsubjectivity. Therefore, fluorescent-labeled primer microsatellite detection by capillary electrophoresis is a powerful tool in cultivar identification for hop breeders, merchants, and brewers.