Maturation-related decline of adventitious root formation is one of the major factors affecting adventitious rooting in forest tree species. We demonstrate that inhibition of polar auxin transport promoted cambium and xylem differentiation in rooting-competent hypocotyl cuttings from Pinus radiata under conditions of adventitious root formation. Treatments with bioactive gibberellins inhibited rooting while at the same time inducing both the differentiation of a continuous ring of cambium and xylem formation. Treatments with inhibitors of gibberellin biosynthesis did not affect the rooting response. The results demonstrate that xylem parenchyma and procambial cells at the xylem poles of rooting-competent hypocotyl cuttings after excision and under conditions of adventitious root induction become adventitious root meristems or xylem, depending on the directional auxin flow. Gibberellin may interact with this pathway, inducing xylem differentiation and inhibiting rooting. We conclude that modifications of auxin flow at the rooting sites, and the priming of cambial cells to differentiate into xylem during tree ageing, may be associated with the maturation-related decline of adventitious root formation.
The present study investigated how auxin concentration and the method of application affected the formation of adventitious roots in microshoots of chestnut (Castanea sativa) and oak (Quercus robur). The activity of two urea derivatives (2, 3-MDPU and 3, 4-MDPU) was also evaluated. Microshoots were derived from basal sprouts of two mature chestnut trees (P1 and P2) and one adult oak genotype (Sainza). In chestnut, rooting percentage was positively affected by auxin in a dose-dependent manner, particularly in shoots treated with the hormone for 24 h. The effect of auxin on rooting also differed depending on the application method. In shoots treated for 24 h, the highest concentration of auxin produced the healthiest rooted plantlets, in terms of the root system and shoot quality. By contrast, in shoots treated by the basal quick-dip method, the shoot quality was best at the lowest auxin concentration. The effect of urea derivatives on the root system depended on the species as well as on the auxin concentration and application period. Use of the MDPUs improved the root system architecture of auxin-treated shoots by promoting lateral root development and triggering the synchronous initiation of root primordia at the base of the shoot. Shoot quality was also improved by MDPUs, which promoted resumption of growth and reduced shoot-tip necrosis.
Adventitious rooting of cuttings is a complex developmental process in forest species, with several exogenous and endogenous factors influencing the outcome of the process. In this study we applied an in vitro working system, comprising two lines of microshoots with the same genotype but at a different ontogenetic stages, in two different tree species (chestnut and oak). We analyzed the expression of a gene encoding an AP2/ERF transcription factor from group VII in the initial hours of the adventitious rooting induction, both in rooting competent and incompetent microshoots. The analysis revealed that expression of this gene is related to wounding, ontogenetic stage and auxin in a complex and species-specific manner. Putative induction of the gene by auxin was also analyzed in the presence of naphthyl-phthalamic acid (NPA), an auxin transport inhibitor. In situ expression analysis in chestnut relates the gene activity to cambial divisions and root primordia in rooting competent microshoots, as well as in the root apex. The putative role of the gene during adventitious roots formation is discussed.
Forest trees possess high genetic diversity and high heterozygosity which allow adaptation to changing environmental conditions. There is a tendency to propagate successful and unique genotypes, which are identified at their mature stage in the forests, for future improvement programs and conservation purposes. However, vegetative propagation of mature forest trees is still a challenge in many conifers. In this study, we focused on improving the rooting of cuttings of mature and old Pinus halepensis and its hybrids. We observed that storage of cuttings before rooting at 4°C for 4 weeks and prolong immersion of cuttings in a solution containing 400 mg/l of indole-3-butyric acid, 5 mg/l of the auxin conjugate 2-(2,4-dichlorophenoxy)propanoic acid-glycine methyl ester, and 0.01% of Amistar fungicide significantly improved rooting of mature cuttings. The active ingredient in Amistar is azoxystrobin, an uncoupler of respiration, which seems to directly promote rooting. Rooted cuttings of selected clones demonstrated unique and uniform growth performance, most likely delivering the intrinsic growth parameters of the mother trees. It was also observed that trees growing under drought stress possess improved rooting ability. By using rooted cuttings, it will be possible to study the relationship between growth rate and adaptation to semi-arid climate conditions. The ability to clonal propagate mature and old P. halepensis trees not only enables vegetative propagation of elite trees for improvement programs, but also provides an opportunity to preserve unique naturally occurring old P. halepensis genotypes.
In vitro propagation of the ornamentally interesting species Wikstroemia gemmata is limited by the recalcitrance to form adventitious roots. In this article, two strategies to improve the rooting capacity of in vitro microcuttings are presented. Firstly, the effect of exogenous auxin was evaluated in both light and dark cultivated stem segments and also the sucrose-content of the medium was varied in order to determine better rooting conditions. Secondly, different spectral lights were evaluated and the effect on shoot growth and root induction demonstrated that the exact spectral composition of light is important for successful in vitro growth and development of Wikstroemia gemmata. We show that exogenous auxin cannot compensate for the poor rooting under unfavorable light conditions. Adapting the culture conditions is therefore paramount for successful industrial propagation of Wikstroemia gemmata.
Passiflora suberosa L. (Passifloraceae) can be found throughout the Americas, and has several medicinal properties, including antioxidant, antibacterial, anti-hemolytic, hypolipidemic, and hypoglycemic activities. Germination rates of P. suberosa are low, even with dormancy breaking treatments, posing an obstacle for its multiplication. Vegetative propagation is a valuable approach to produce clones of elite individuals with important pharmacological characteristics, affording fast genetic improvement of biomass source for both phytomedicine manufacturing and bioactive compound isolation. Understanding the rooting process of this species is an important step to exploit its full potential in a sustainable way. We investigated adventitious rooting (AR) in absence or presence of exogenous auxin in P. suberosa cuttings, using a non-aerated hydroponic system. Changes in concentration of flavonoids, phenolics, hexoses, starch, and auxin, as well as peroxidase activity, were monitored along AR. Cuttings showed spontaneous rooting, although the application of exogenous indole-3-butyric acid (IBA) yielded higher number of shorter roots. Biochemical parameters, mainly concentration of carbohydrates and total phenolics, as well as peroxidase activity, varied along the course of the experiments. Based on these results, attempts were made to up- or down-modulate rooting responses by applying putative regulators to the growth solution at different time points. It was possible to block the positive effect of auxin on root development, with only minor positive impacts on the modulated control devoid of auxin. Overall analyses suggested that the rooting system proved effective and specific peroxidase activity showed partial correlation with AR, being able to suffer modulation by culture solution factors.
Summer and autumn in Israel are highly arid with not enough plants in bloom offering nectar and pollen to support the local apiary. This leads to decline in colony health and honey production. To increase food sources for honeybees, we initiated a project to clone elite Eucalyptus trees exhibiting constant and rich blooming from late summer to early winter. We induced adventitious roots from cuttings of two mature Eucalyptus trees of which nectar production and honeybees’ attraction was measured: Eucalyptus brachyphylla and Eucalyptus x trabutii. During the rooting process, a high frequency of cylindrical callus formation instead of roots was obtained. To shed light on the inner anatomy of the callus chunks, we compared their cell organization and cell-wall composition to those of roots. Whereas in the root, cells were organized in circumferential symmetry, no symmetry was found in the callus. Instead, a more chaotic accumulation of meristematic-like cells with sporadic clusters of tracheary elements laid in different directions were observed. The outer cell layer of the callus often included swollen cells with thin cell walls. Most callus cells stained more strongly for cellulose and lignin than cells in the root meristem. In addition, specific antibodies to methylesterified and de-methylesterified pectin showed differential staining of callus vs. root cells indicating cell wall differences. Strikingly, roots were seen to differentiate from the chaotic cell organization of the callus, albeit at low rates. Further investigation of the cellular and molecular mechanisms underlying callus formation, are required.
Recent studies on the seasonal dynamics of secondary tissue formation in Mediterranean trees have shown that xylogenesis depends on species and site conditions, but many questions still remain open. On the other side of the cambium, even less information is available about phloem structure and timing of its formation. We analysed intra-annual phloem variation in width and cell traits in the conducting, non-collapsed phloem (CPH) of Pinus pinea and Pinus halepensis at Mediterranean sites in southern Italy and Spain. In all investigated trees, it was possible to differentiate among the non-conducting, collapsed phloem (NCPH), and the CPH. CPH showed no evident annual growth layers; no differences in radial dimensions of early- and late phloem sieve cells, and no cyclic patterns of axial parenchyma distribution. Since it was not possible to study the seasonality of the phloem growth, we analysed the entire CPH. CPH width showed seasonal fluctuations and was generally the widest during the maximum cambial activity and narrowest during summer and winter. The radial size of newly formed sieve cells varied in relation to seasonal dynamics of cambial activity and fluctuations in local weather conditions. The number of axial parenchyma cells in CPH increased during the summer. The observed intra-annual variations in CPH width and structure seemed to be correlated with seasonal weather conditions in order to ensure a sufficient amount of conducting phloem tissue for translocation of photosynthates and signalling molecules to the actively growing tissues along the stem of a tree growing in the harsh Mediterranean conditions.
Atlas of the Hoverflies of Greece is the first of a kind within the Mediterranean region. It is the result of decades of research, many travels into the fascinating habitats of Greece (a biodiversity hotspot), visits to world museums, and many people’s passion for hoverflies.
Atlas is a concise presentation of all 418 hoverfly species for Greece known so far. The species are documented with photos and distribution GIS-maps and they are preceded by a general introduction on the hoverflies and Greek nature, and a generic key.
Atlas of the Hoverflies of Greece is a handbook for insect aficionados, students and teachers, everyone interested in nature, and managers and conservationists aiming at raising public awareness of a nature nowadays threatened more than ever.
Plant-essential oils have been considered as an important source of bioactive molecules like antimicrobials, analgesics, anti-inflammatory and anti-carcinogen agents. Biological functions of plant extracts from the genus Capsicum are unknown. In the present work, non-polar fractions of ripe and unripe fruits of Capsicum chinense Jacq. Cultivar (cv.) Jaguar and Criollo were obtained by hexane-batch extraction and tested for antimicrobial activity against Gram-negative bacterial strain Escherichia coli (ATCC 25922), Gram-positive bacterial strains Enterococcus faecalis (ATCC 29212), Staphylococcus aureus (ATCC 25923) and Staphylococcus epidermidis (ATCC 12228), and yeast Candida albicans (ATCC 90028). Non-polar fractions from ripe fruits for both cv. exhibited greater antimicrobial activity compared to unripe fruits. Implication of numbered FFA’s on observed antimicrobial activity are discussed.