In ornamental geophytes, conventional vegetative propagation is not economically feasible due to very slow development and ineffective methods. It can take several years until a new plant is formed ...and commercial profitability is achieved. Therefore, micropropagation techniques have been developed to increase the multiplication rate and thus shorten the multiplication and regeneration period. The majority of these techniques rely on the formation of new bulbs and their sprouting. Dormancy is one of the main limiting factors to speed up multiplication in vitro. Bulbous species have a period of bulb dormancy which enables them to survive unfavorable natural conditions. Bulbs grown in vitro also exhibit dormancy, which has to be overcome in order to allow sprouting of bulbs in the next vegetation period. During the period of dormancy, numerous physiological processes occur, many of which have not been elucidated yet. Understanding the process of dormancy will allow us to speed up and improve breeding of geophytes and thereby achieve economic profitability, which is very important for horticulture. This review focuses on recent findings in the area of bulb dormancy initiation and release in fritillaries, with particular emphasis on the effect of plant growth regulators and low-temperature pretreatment on dormancy release in relation to induction of antioxidative enzymes' activity in vitro.
(centaury) is a traditionally used medicinal plant, with a spectrum of secondary metabolites with confirmed healing properties. Centaury is an emerging model in plant developmental biology due to its ...vigorous regenerative potential and great developmental plasticity when cultured in vitro. Hereby, we review nearly two decades of research on somatic embryogenesis (SE) in centaury. During SE, somatic cells are induced by suitable culture conditions to express their totipotency, acquire embryogenic characteristics, and eventually give rise to somatic embryos. When SE is initiated from centaury root explants, the process occurs spontaneously (on hormone-free medium), directly (without the callusing phase), and the somatic embryos are of unicellular origin. SE from leaf explants has to be induced by plant growth regulators and is indirect (preceded by callusing). Histological observations and culture conditions are compared in these two systems. The changes in antioxidative enzymes were followed during SE from the leaf explants. Special focus is given to the role of arabinogalactan proteins during SE, which were analyzed using a variety of approaches. The newest and preliminary results, including centaury transcriptome, novel potential SE markers, and novel types of arabinogalactan proteins, are discussed as perspectives of centaury research.
The bulb is the main propagation organ of snake’s head fritillary (Fritillaria meleagris L.), a horticulturally attractive and rare geophyte plant species. In this study, we investigated the effect ...of soaking bulbs in GA3 solution (1, 2, and 3 mg L−1) combined with low-temperature treatment (7 °C) on breaking the dormancy of in vitro bulbs. Sugar status (total soluble sugars, glucose, and fructose content) was analyzed in different parts of the sprouted bulbs. The results showed that the soluble sugar concentration was highest in bulbs soaked in GA3. The main sugar in fritillary bulbs was glucose, while fructose content was much lower. Glucose concentration dramatically increased after bulb chilling (7 °C), and its accumulation was predominantly detected in the lower sprout portion during the first weeks of sprouting. Sugar concentration was significantly lower in nonchilled bulbs, which indicates the importance of low temperature in bulb development and sprouting.
Centaurium erythraea
Rafn. is a medicinal plant rich in secoiridoids and xanthones and used for gastrointestinal disorders, fever, anemia and many other conditions.
C. erythraea
is characterized with ...extraordinary developmental plasticity and manageability in vitro; thus we propose it as an excellent experimental model system for studies in developmental biology. Hereby we describe regeneration of centaury from leaf explants that can proceed via somatic embryogenesis or organogenesis on inductive media containing 2,4-D and CPPU. In the absence of growth regulators, shoots and roots appeared without callusing, on light or in darkness, respectively. Indirect somatic embryogenesis was induced in the presence of growth regulators occurring both on light and in darkness. Light was obligatory for indirect shoot development, where adventitious buds formed simultaneously with somatic embryos. Dynamic changes of antioxidative activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) in response to morphogenetic changes were followed during developmental pathways in vitro. Wounding of centaury leaves immediately induced all SOD and CAT isoforms but caused a decrease in POX activity. In control leaves and leaf explants, three Cu/Zn-SOD activities were detected, which gradually decreased on inductive treatments on light, but remained unchanged during growth in darkness. Morphogenetic paths on all hormonal and light treatments where characterized with dynamic changes of CAT activity (comprised of three major CAT isoforms), but generally CAT was reduced during morphogenesis induction. POX activity was strongly induced during morphogenesis in all treatments.
Bulbs are the main vegetative reproductive organs of Fritillaria meleagris L. In nature, as well as in vitro, they become dormant and require low temperatures for further growth during the next ...vegetative period. In the present study, using 10 μM of gibberellic acid (GA3), or gibberellin biosynthesis (GA) inhibitors—ancymidol (A) and paclobutrazol (P)—the dynamic changes in soluble sugars, fructose and glucose content, fresh weight and sprouting capacity were investigated. F. meleagris bulbs were cultured on medium with GA3 and GA inhibitors for 1, 2 and 5 weeks at two different temperatures (24 and 7 °C). GA3 improved bulb fresh weight, as well as sprouting percentage at both tested temperatures, compared to the control. The highest fresh weight increase (57.7%) and sprouting rate (29.02%) were achieved when bulbs were grown at 24 °C for 5 weeks. In addition, soluble sugar content was the highest in bulbs grown for 5 weeks on medium supplemented with GA3. The main sugar in fritillary bulbs was glucose, while fructose content was lower. The sensitivity of bulbs to GA inhibitors differed and significantly affected sugar content in bulbs. To our knowledge, this is the first study of the sugar composition in F. meleagris bulbs during breaking of the bulb’s dormancy and its sprouting.
Arabinogalactan proteins (AGPs) are cell wall hydroxyproline-rich glycoproteins with diverse functions in plant growth and development. In this work the role of AGPs was comparatively studied in four ...developmental pathways that can be induced from centaury leaf explants—indirect somatic embryogenesis (ISE), indirect and direct shoot development (ISD and DSD) and direct root development (DRD). The addition of β-
d
-glucosyl Yariv (βGlcY) reagent, a synthetic phenylglycoside that specifically crosslinks AGPs, to the growth medium reduced the number of somatic embryos and adventitious buds formed per explant. The morphogenetic paths can be arranged in order of increasing sensitivity to βGlcY as: DRD (insensitive) < ISD < DSD ≪ ISE. The content of AGPs increased during all processes, but the accumulation of AGPs was the most rapid during ISE and when ISE and ISD occurred simultaneously. We have identified four centaury AGP transcripts,
CeAGP1–CeAGP4
, of which
CeAGP1, 2
and
4
code for fasciclin-like AGPs. CeAGP3 is an AG peptide with conserved DUF1070 domain. Expression pattern of these genes indicated specific involvement of CeAGP1 in ISE and unspecific involvement of CeAGP3 in morphogenesis.
Common centaury (Centaurium erythraea Rafn.) is a plant species that can inhabit saline soils. It is known as a plant with high spontaneous regeneration potential in vitro. In the present work we ...evaluated shoots and roots salinity tolerance of non‐transformed and three AtCKX transgenic centaury lines to graded NaCl concentrations (0, 50, 100, 150, 200 mM) in vitro. Overexpression of AtCKX genes in transgenic centaury plants resulted in an altered cytokinins (CKs) profile leading to a decline of bioactive CK levels and, at the same time, increased contents of storage CK forms, inactive CK forms and/or CK nucleotides. Significant increment of fresh shoot weight was obtained in shoots of non‐transformed and AtCKX1 transgenic line only on medium supplemented with 50 mM NaCl. However two analysed AtCKX2 transgenic lines reduced shoot growth at all NaCl concentrations. In general, centaury roots showed higher tolerance to salinity than shoots. Non‐transformed and AtCKX1 transgenic lines tolerated up to 100 mM NaCl without change in frequency of regeneration and number of regenerated plants. Roots of two analysed AtCKX2 transgenic lines showed different regeneration potential under salt stress. Regeneration of transgenic AtCKX2‐26 shoots even at 200 mM NaCl was recorded. Salinity stress response of centaury shoots and roots was also evaluated at biochemical level. Free proline, malondialdehyde and hydrogen peroxide content as well as antioxidative enzymes activities were investigated in shoots and roots after 1, 2, 4 and 8 weeks. In general, adition of NaCl in culture medium elevated all biochemical parameters in centaury shoots and in roots. Considering that all analysed AtCKX transgenic centaury lines showed altered salt tolerance to graded NaCl concentrations in vitro it can be assumed that CKs might be involved in plant defence to salt stress conditions.
Shoots and roots of non‐transformed and three AtCKX transgenic centaury lines were evaluated to salinity tolerance on graded NaCl concentrations (0, 50, 100, 150, 200 mM) in vitro. Centaury roots showed higher tolerance to salinity than shoots. Morphogenic potential of AtCKX1 transgenic line was similar to non transformed line. Significant difference in morphogenic response of two investigated AtCKX2 transgenic lines were also determined. The addition of NaCl in culture medium elevated free proline, malondialdehyde, hydrogen peroxide content as well as antioxidative enzymes activities in all analysed centaury shoots and in roots.
Plant hormones regulate numerous developmental and physiological processes. Abiotic stresses considerably affect production and distribution of phytohormones as the stress signal triggers. The ...homeostasis of plant hormones is controlled by their de novo synthesis and catabolism. The aim of this work was to analyse the contents of total and individual groups of endogenous cytokinins (CKs) as well as indole-3-acetic acid (IAA) in AtCKX overexpressing centaury plants grown in vitro on graded NaCl concentrations (0, 50, 100, 150, 200 mM). The levels of endogenous stress hormones including abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) were also detected. The elevated contents of total CKs were found in all analysed centaury shoots. Furthermore, increased amounts of all five CK groups, as well as enhanced total CKs were revealed on graded NaCl concentrations in non-transformed and AtCKX roots. All analysed AtCKX centaury lines exhibited decreased amounts of endogenous IAA in shoots and roots. Consequently, the IAA/bioactive CK forms ratios showed a significant variation in the shoots and roots of all AtCKX lines. In shoots and roots of both non-transformed and AtCKX transgenic centaury plants, salinity was associated with an increase of ABA and JA and a decrease of SA content.
In this study, the effects of foliar applied methyl jasmonate (MeJA) on drought-stressed Impatiens walleriana growth and leaf physiology parameters: stomatal conductance, chlorophyll, flavonoid, ...anthocyanin, and nitrogen balance index (NBI), were evaluated. These parameters could serve as indicators of drought tolerance of I. walleriana, a popular horticultural plant worldwide that is very sensitive to drought. The experiment included four treatments: control, drought-stressed plants sprayed with distilled water, drought-stressed plants sprayed with 5 µM MeJA, and drought-stressed plants sprayed with 50 µM MeJA. Foliar spraying with MeJA was performed twice: seven days before and on the day of drought induction. The stressed plant groups were non-irrigated to achieve soil water contents (SWC) of 15 and 5%, while control plants were well-watered throughout the experiment (35-37% SWC). The results of this study showed that drought significantly reduced I. walleriana fresh and dry shoot weight, as well as total leaf area, but did not impact on dry matter content. The foliar application of MeJA improved growth parameters of I. walleriana, depending on the elicitor concentration and drought intensity. Stomatal conductance was slightly reduced at 5% SWC, and foliar applied MeJA at both concentrations. The flavonoid index was slightly reduced at 15 and 5% SWC when 50 µM MeJA was foliar applied, while there were no observed changes in the anthocyanin index in any treatments. The foliar application of 50 µM MeJA increased the chlorophyll index and NBI of I. walleriana at 5% SWC, indicating a contribution of the elicitor to plant drought tolerance at the physiological level.
Induction of in vitro morphogenesis of mature zygotic embryos of Fritillaria meleagris L. was investigated. Somatic embryogenesis and whole plant regeneration were achieved. Isolated zygotic embryos ...were cultured on MS medium that contained 3% sucrose, 0.7% agar, 250.0 mg/l casein hydrolysate, 250.0 mg/l L-proline, 80 mg/l adenine sulfate and 1.0 mg/l 2, 4-dichlorophenoxyacetic acid (2, 4-D) or thidiazuron (TDZ). Embryogenic callus was derived from mature zygotic embryos after 4 weeks on TDZ containing medium. Somatic embryos at the early stages of development arose from the surface of the embryogenic callus. Multiplication of somatic embryos, formation of bulblets and shoot development were observed on the same medium. Scale sections prepared from the formed bulblets were cultured on MS media supplemented with 2, 4-D (0.1 to 10.0 mg/l) and TDZ (0.05 to 2.0 mg/l). Somatic embryos and bulblets were frequently produced from the scale sections. This is a successful report of plant regeneration through somatic embryogenesis for this very important medicinal and horticultural plant. Histological observation revealed that plants of F. meleagris L. were regenerated via somatic embryogenesis.
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