58 research outputs found
Changing concepts in plant hormone action
Summary: A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be synthesized everywhere and can influence different growth and development processes at different places. The concept of physiological activity under hormonal control cannot be dissociated from changes in concentrations at the site of action, from spatial differences and changes in the tissue's sensitivity to the compound, from its transport and its metabolism, from balances and interactions with the other phytohormones, or in their metabolic relationships, and in their signaling pathways as well. Secondary messengers are also involved. Hormonal involvement in physiological processes can appear through several distinct manifestations (as environmental sensors, homeostatic regulators and spatio-temporal synchronizers, resource allocators, biotime adjusters, etc.), dependent on or integrated with the primary biochemical pathways. The time has also passed for the hypothesized ‘specific' developmental hormones, rhizocaline, canlocaline, and florigen: root, stem, and flower formation result from a sequential control of specific events at the right places through a coordinated control by electrical signals, the known phytohormones and nonspecific molecules of primary and secondary metabolism, and involve both cytoplasmic and apoplastic compartments. These contemporary views are examined in this revie
Quantification of endogenous levels of IAA, IAAsp and IBA in micro-propagated shoots of hybrid chestnut pre-treated with IBA
Endogenous levels of indole-3-acetic acid (IAA),
indole-3-acetylaspartic acid (IAAsp) and indole-3-butyric
acid (IBA) were measured during the first 8 d of in vitro
rooting of rootstock from the chestnut ‘M3’ hybrid by high
performance liquid chromatography (HPLC). Rooting was
induced either by dipping the basal ends of the shoots into a
4.92-mM IBA solution for 1 min or by sub-culturing the
shoots on solid rooting medium supplemented with 14.8-
μM IBA for 5 d. For root development, the induced shoots
were transferred to auxin-free solid medium. Auxins were
measured in the apical and basal parts of the shoots by
means of HPLC. Endogenous levels of IAA and IAAsp
were found to be greater in IBA-treated shoots than in
control shoots. In extracts of the basal parts of the shoots,
the concentration of free IAA showed a significant peak 2 d
after either root inductive method and a subsequent gradual
decrease for the remainder of the time course. The
concentration of IAAsp peaked at day 6 in extracts of the
basal parts of shoots induced with 14.8-μM IBA for 5 d,
whereas shoots induced by dipping showed an initial
increase until day 2 and then remained stable. In extracts
from basal shoot portions induced by dipping, IBA
concentration showed a transient peak at day 1 and a plateau between day 2 and 4, in contrast to the profile of
shoots induced on auxin-containing medium, which
showed a significant reduction between 4 and 6 d after
transferred to auxin-free medium. All quantified auxins
remained at a relatively low level, virtually constant, in
extracts from apical shoot portions, as well as in extracts
from control non-rooting shoots. In conclusion, the natural
auxin IAA is the signal responsible for root induction,
although it is driven by exogenous IBA independently of
the adding conditions
Analysis of BAC end sequences in oak, a keystone forest tree species, providing insight into the composition of its genome
<p>Abstract</p> <p>Background</p> <p>One of the key goals of oak genomics research is to identify genes of adaptive significance. This information may help to improve the conservation of adaptive genetic variation and the management of forests to increase their health and productivity. Deep-coverage large-insert genomic libraries are a crucial tool for attaining this objective. We report herein the construction of a BAC library for <it>Quercus robur</it>, its characterization and an analysis of BAC end sequences.</p> <p>Results</p> <p>The <it>Eco</it>RI library generated consisted of 92,160 clones, 7% of which had no insert. Levels of chloroplast and mitochondrial contamination were below 3% and 1%, respectively. Mean clone insert size was estimated at 135 kb. The library represents 12 haploid genome equivalents and, the likelihood of finding a particular oak sequence of interest is greater than 99%. Genome coverage was confirmed by PCR screening of the library with 60 unique genetic loci sampled from the genetic linkage map. In total, about 20,000 high-quality BAC end sequences (BESs) were generated by sequencing 15,000 clones. Roughly 5.88% of the combined BAC end sequence length corresponded to known retroelements while <it>ab initio </it>repeat detection methods identified 41 additional repeats. Collectively, characterized and novel repeats account for roughly 8.94% of the genome. Further analysis of the BESs revealed 1,823 putative genes suggesting at least 29,340 genes in the oak genome. BESs were aligned with the genome sequences of <it>Arabidopsis thaliana</it>, <it>Vitis vinifera </it>and <it>Populus trichocarpa</it>. One putative collinear microsyntenic region encoding an alcohol acyl transferase protein was observed between oak and chromosome 2 of <it>V. vinifera.</it></p> <p>Conclusions</p> <p>This BAC library provides a new resource for genomic studies, including SSR marker development, physical mapping, comparative genomics and genome sequencing. BES analysis provided insight into the structure of the oak genome. These sequences will be used in the assembly of a future genome sequence for oak.</p
Endogenous auxin and cytokinin levels in shoots of a nonrooting tobacco mutant
peer reviewed[No abstract available
Hormonal control of adventitious rooting: Progress and questions
peer reviewedAccording to the traditional concept, adventitious rooting is a single developmental process, controlled by one single chief actor, auxin. This concept is out-of-date. This review develops the arguments for rooting as a process consisting of successive physiological phases, with different exogenous requirements. The levels of auxins, peroxidases, phenolic compounds, cytokinins, polyamines, and ethylene undergo typical changes during these phases. Their complex interactions are far from being elucidated. The changes characterizing the rooting inductive phase may be similar to those occurring during flowering evocation. Thus these changes seem to be more indicative of a shift in a developmental programme than of a specific organogenic process
Polymorphism analysis of genomic regions associated with broad-spectrum effective blast resistance genes for marker development in rice
Cultivated European rice germplasm is
generally characterized by moderate to high sensitivity
to blast, and blast resistance is therefore one of the
most important traits to improve in rice breeding. We
collected a panel of 25 rice genotypes containing 13
broad range rice resistance genes that are commonly
used in breeding programs around the world: Pi1, Pi2,
Pi5, Pi7, Pi9, Pi33, Pib, Pik, Pik-p, Pita, Pita2, Piz and
Piz-t. The efficiency of the selected Pi genes towards
Italian blast pathotypes was tested via artificial inoculation
and under natural field infection conditions. To
characterize haplotypes present in the chromosomal
regions of the blast resistance genes, a polymorphism
search was conducted in the sequence regions adjacent
to the blast resistance by examining DNA from the
Pi gene donors with a panel of 5\u20137 potential receivers
(cultivated European rice genotypes). Seven InDel and
8 presence/absence polymorphisms were directly
detected by gel analysis after DNA amplification,
while sequencing of 12.870 bp through 32 loci in
different genotypes revealed 85 SNP (one SNP every
151 bp). Seven SSRs were additionally tested revealing
5 polymorphic markers between donors and
receivers. Polymorphisms were used to develop 35
PCR-based molecular markers suitable for introgressing
of Pi genes into a set of the European rice
germplasm. For this last purpose, allelic molecular
marker variation was evaluated within a representative
collection of about 95 rice genotypes. Polymorphic
combinations allowing introgression of the broad
spectrum resistance genes into a susceptible genetic
background have been identified, thus confirming the
potential of the identified markers for molecularassisted
breeding
Assessment of genetic diversity in Italian rice germplasm related to agronomic traits and blast resistance (Magnaporthe oryzae)
Italy is the only country in Europe with a significant land area used for rice production. In this paper, the genetic diversity of 172 national varieties and 47 foreign accessions (ITALORYZA collection) was investigated using a set of neutral markers evenly distributed throughout the 12 chromosomes. Out of the 218 alleles detected in our analysis, 17 and 29% were specific to the Italian and foreign accessions, respectively. From the neighbour-joining tree generated, six sub-groups of temperate japonica germplasm were identified. Plant height and grain type measured in the source collection were fitted to the phylogenetic tree, along with the period of variety registration. This integrated genotype–phenotype analysis revealed that specific sub-groups are characterized by uniform classes of grain type, or by similar plant size, or by period of release in the market. The whole collection was also evaluated for leaf blast resistance by inoculating the plants with three strains of Magnaporthe oryzae, representing the pathogen genetic diversity existing in Italy. Only 15 out of 172 Italian accessions (8.7%) were resistant to all three fungal strains. The correlation between genotype and leaf blast phenotype revealed that the most highly resistant Italian varieties are included in a single germplasm sub-group derived from US varieties. This study represents the starting point for carrying out detailed phenotype–genotype wholegenome association studies and identification of the genetic basis of important agronomic traits for rice cultivation in temperate climates
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