Slađana Jevremović

Morpho-histological study of direct somatic embryogenesis in endangered species Frittilaria meleagris

Direct somatic embryogenesis of Frittilaria meleagris L. was induced using leaf base explants excised from in vitro grown shoots. Somatic embryos occurred at the basal part of leaf explants 4 weeks after culture on a Murashige and Skoog (MS) medium supplemented with various concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) or kinetin (KIN). The highest number of somatic embryos (SEs) were formed (9.74) from leaf explant on MS medium supplemented with 0.1 mg dm−3 2,4-D after 4 weeks of culture initiation. An initial exposure to a low concentration of KIN in the medium also enhanced SEs induction. Our observations by light and scanning electron microscopy revealed that SEs originate directly from the epidermal and subepidermal layers of leaf explant. The developmental stages of somatic embryogenesis from the first unequal cell division through the meristematic clusters, multi-cellular globular somatic embryos to the fully formed cotyledonary embryos were determined. After 4 weeks on MS medium without plant growth regulators, SEs developed into bulblets.

Endogenous Phytohormones in Spontaneously Regenerated Centaurium erythraea Rafn. Plants Grown In Vitro

Phytohormones are important regulators of numerous developmental and physiological processes in plants. Spontaneous morphogenesis of the common centaury (Centaurium erythraea Rafn.) is possible on nutrition medium without addition of any plant growth regulator depending solely on endogenous phytohormone levels. Thus, this plant species represents a very good model system for the investigation of numerous physiological processes under phytohormonal control in vitro. We analysed the total amount of endogenous cytokinins (CKs) including the contents of their individual groups in shoots and roots of C. erythraea plants grown in vitro. The total amount of endogenous CKs was 1.4 times higher in shoots than in roots. Inactive or weakly active N-glucosides found to predominate in both organs of centaury plants, whereas free bases and O-glucosides represented only a small portion of the total CK pool. Consequently, centaury roots showed higher IAA content as well as IAA/free CK base ratios compared to shoots. Centaury tissues also showed increased levels of “stress hormones”. In contrast to SA, considerably higher levels of ABA were found in centaury shoots than in roots. Our results could serve as a basis for understanding and elucidating spontaneous de novo shoot organogenesis and further plant regeneration of C. erythraea in vitro.

Changes in cytokinin content and altered cytokinin homeostasis in AtCKX1 and AtCKX2-overexpressing centaury (Centaurium erythraea Rafn.) plants grown in vitro

The plant hormones cytokinins (CKs) regulate a number of physiological processes. Their homeostasis is controlled by the rate of de novo synthesis and the rate of catabolism. The aim of this work was to analyze the content of total as well as individual groups of endogenous CKs in AtCKX1 and AtCKX2-overexpressing centaury (Centaurium erythraea Rafn.) plants grown in vitro. Transgenic CKX plants represent a suitable model system for studying physiological and morphological processes controlled by CKs. In this work we clearly demonstrate a significant effect of AtCKX transgenes on CK metabolism in transgenic centaury plants. However, shoots and roots of only one AtCKX1 line and three AtCKX2 lines with a significant reduction of bioactive CKs were obtained. We also show that changes in the CKs metabolism considerably affected endogenous indole-3-acetic acid (IAA) levels in plant tissues. All analyzed transgenic AtCKX centaury lines exhibited decreased amount of endogenous IAA in shoots as well as in roots. Consequently, the IAA/bioactive CK forms ratios showed a significant variation in the shoots and roots of all analyzed AtCKX centaury transformants.

Esterase and peroxidase isoforms in different stages of morphogenesis in Fritillaria meleagris L. in bulb-scale culture

Morphogenesis in vitro is a complex and still poorly defined process. We investigated esterase and peroxidase isoforms detected in bulb scale, during Fritillaria meleagris morphogenesis. Bulbs were grown either at 4 °C or on a medium with an increased concentration of sucrose (4.5%) for 30 days. After these pre-treatments, the bulb scales were further grown on nutrient media that contained different concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin (KIN) or thidiazuron (TDZ). Regeneration of somatic embryos and bulblets occurred at the same explant. The highest numbers of somatic embryos and bulblets were regenerated on the medium containing 2,4-D and KIN (1mg/L each), while morphogenesis was most successful at a TDZ concentration between 0.5 and 1mg/L. Monitoring of esterases and peroxidases was performed by growing bulb scales on a medium enriched with 2,4-D and KIN or TDZ (1mg/L), and the number and activity of isoforms were followed every 7 days for 4 weeks. In control explants, six isoforms of esterase were observed. Three isoforms of peroxidase were not detected in the control bulb scale, which has not begun its morphogenesis process.

Alteration of flower color in Iris germanica L. ‘Fire Bride’ through ectopic expression of phytoene synthase gene ( crtB ) from Pantoea agglomerans

Key messageGenetic modulation of the carotenogenesis inI. germanica‘Fire Bride’ by ectopic expression of acrtBgene causes several flower parts to develop novel orange and pink colors.AbstractFlower color in tall bearded irises (Iris germanica L.) is determined by two distinct biochemical pathways; the carotenoid pathway, which imparts yellow, orange and pink hues and the anthocyanin pathway, which produces blue, violet and maroon flowers. Red-flowered I. germanica do not exist in nature and conventional breeding methods have thus far failed to produce them. With a goal of developing iris cultivars with red flowers, we transformed a pink iris I. germanica, ‘Fire Bride’, with a bacterial phytoene synthase gene (crtB) from Pantoea agglomerans under the control of the promoter region of a gene for capsanthin–capsorubin synthase from Lilium lancifolium (Llccs). This approach aimed to increase the flux of metabolites into the carotenoid biosynthetic pathway and lead to elevated levels of lycopene and darker pink or red flowers. Iris callus tissue ectopically expressing the crtB gene exhibited a color change from yellow to pink-orange and red, due to accumulation of lycopene. Transgenic iris plants, regenerated from the crtB-transgenic calli, showed prominent color changes in the ovaries (green to orange), flower stalk (green to orange), and anthers (white to pink), while the standards and falls showed no significant differences in color when compared to control plants. HPLC and UHPLC analysis confirmed that the color changes were primarily due to the accumulation of lycopene. In this study, we showed that ectopic expression of a crtB can be used to successfully alter the color of certain flower parts in I. germanica ‘Fire Bride’ and produce new flower traits.

Micropropagation of Iris sp.

Irises are perennial plants widely used as ornamental garden plants or cut flowers. Some species accumulate secondary metabolites, making them highly valuable to the pharmaceutical and perfume industries. Micropropagation of irises has successfully been accomplished by culturing zygotic embryos, different flower parts, and leaf base tissues as starting explants. Plantlets are regenerated via somatic embryogenesis, organogenesis, or both processes at the same time depending on media composition and plant species. A large number of uniform plants are produced by somatic embryogenesis, however, some species have decreased morphogenetic potential overtime. Shoot cultures obtained by organogenesis can be multiplied for many years. Somatic embryogenic tissue can be reestablished from leaf bases of in vitro-grown shoots. The highest number of plants can be obtained by cell suspension cultures. This chapter describes effective in vitro plant regeneration protocols for Iris species from different types of explants by somatic embryogenesis and/or organogenesis suitable for the mass propagation of ornamental and pharmaceutical irises.