Adventitious Rooting of Lavandula x intermedia Cuttings

Due to challenges associated with lavender propagation, Texas hybrid lavender (lavandin) growers require revised propagation information. Therefore, experiments investigated effects of media and plant growth regulators (PGR) on rooting of three different lavandin (Lavandula x intermedia) cultivars. PGRs applied to cuttings were naphthaleneacetic acid (NAA), or indole-3-butyric acid (IBA) at three concentrations. In addition, four rooting media were examined. Cuttings exposed to a peat moss/sand medium had the greatest mean overall rooting percentage, number of roots, and regardless of cultivar, cuttings exposed to the peat moss/sand medium had the longest roots. In general, mean rooting data were also greatest for cuttings dipped in NAA at 0.5 and 1.0 g·L−1 (500 and 1000 ppm, respectively). Overall, across all media and PGR treatments ‘Grosso' cuttings tended to have the greatest rooting percentage and longest roots. In addition, compared to the no PGR treatment, ‘Provence' and ‘Hidcote Giant' cuttings exposed to the peat moss/sand medium and greater PGR concentrations produced cuttings with an increased mean rooting percentage and longer roots. When rooting lavandin cultivars, results indicate correct media selection, PGR formulation, and PGR concentration determine propagation success. Index words: lavandin, Lavandula x intermedia Emeric ex Loisel, peat moss, perlite, rooting percentage, root quality, sand. Chemicals used in this study: indole-3-butyric acid (IBA; 0.5, 1.0, and 1.5 g.L−1); naphthaleneacetic acid (NAA; 0.5, 1.0, and 1.5 g.L−1). Species used in this study: ‘Grosso', ‘Provence', and ‘Hidcote Giant' lavandin (Lavandula x intermedia Emeric ex Loisel.).

Brassinosteroids in Plants: Crosstalk with Small-Molecule Compounds

Brassinosteroids (BRs) are known as the sixth type of plant hormone participating in various physiological and biochemical activities and play an irreplaceable role in plants. Small-molecule compounds (SMCs) such as nitric oxide (NO), ethylene, hydrogen peroxide (H2O2), and hydrogen sulfide (H2S) are involved in plant growth and development as signaling messengers. Recently, the involvement of SMCs in BR-mediated growth and stress responses is gradually being discovered in plants, including seed germination, adventitious rooting, stem elongation, fruit ripening, and stress responses. The crosstalk between BRs and SMCs promotes plant development and alleviates stress damage by modulating the antioxidant system, photosynthetic capacity, and carbohydrate metabolism, as well as osmotic adjustment. In the present review, we try to explain the function of BRs and SMCs and their crosstalk in the growth, development, and stress resistance of plants.

The Involvement of Glucose in Hydrogen Gas-Medicated Adventitious Rooting in Cucumber

Hydrogen gas (H2) and glucose (Glc) have been reported as novel antioxidants and signal molecules involved in multiple biological processes in plants. However, the physiological roles and relationships of H2 and Glc in adventitious rooting are less clear. Here, we showed that the effects of different concentrations Glc (0, 0.01, 0.05, 0.10, 0.50 and 1.00 mM) on adventitious rooting in cucumber were dose-dependent, with a maximal biological response at 0.10 mM. While, the positive roles of hydrogen rich water (HRW, a H2 donor)-regulated adventitious rooting were blocked by a specific Glc inhibitor glucosamine (GlcN), suggesting that Glc might be responsible for H2-regulated adventitious root development. HRW increased glucose, sucrose, starch and total sugar contents. Glucose-6-phosphate (G6P), fructose-6-phosphate (F6P) and glucose-1-phosphate (G1P) contents were also increased by HRW. Meanwhile, the activities of sucrose-related enzymes incorporating sucrose synthase (SS) and sucrose phosphate synthase (SPS) and glucose-related enzymes including hexokinase (HK), pyruvate kinase (PK) and adenosine 5′-diphosphate pyrophosphorylase (AGPase) were increased by HRW. Moreover, HRW upregulated the expression levels of sucrose or glucose metabolism-related genes including CsSuSy1, CsSuSy6, CsHK1, CsHK3, CsUDP1, CsUDP1-like, CsG6P1 and CsG6P1-like. However, these positive roles were all inhibited by GlcN. Together, H2 might regulate adventitious rooting by promoting glucose metabolism.

Molecular basis of differential adventitious rooting competence in poplar genotypes

Recalcitrance to adventitious root (AR) development is a major hurdle for propagation of commercially important woody plants. Although significant progress has been made to identify genes involved in subsequent steps of AR development, the molecular basis of recalcitrance to form AR between easy-to-root compaired to difficult-to-root genotypes remain unknown. To address this, we generated cambium tissue specific transcriptomic data from stem cutting of hybrid aspen, T89 (difficult-to-root) and hybrid poplar OP42 (easy-to-root) and used transgenic approaches to verify the role of several transcription factors (TF) in the control of adventitious rooting. Increased peroxidase activity is often positively correlated with better rooting and in agreement, an enrichment of differentially expressed genes encoding Reactive Oxygen Species (ROS) scavenging proteins was observed in OP42 compared to T89. OP42 cambium cells displayed a more intense transcriptional reprograming as highlighted by the higher number of differentially expressed TF compared to T89. PtMYC2, a potential negative regulator, was less expressed in OP42 compared to T89. Using transgenic approaches, we demonstrated that PttARF17.1 and PttMYC2.1 negatively regulate adventitious rooting. These results thus provide insight into molecular basis of genotypic differences in AR and implicate differential expression of master regulator MYC2 as a critical player in this process.

Somatic Embryogenesis; A Highly Promising Technique for Conservation of Tecomella Undulata – A Multi-Purpose Tree on the Verge of Extinction

Over-exploitation of trees by increasing human population has put an enormous pressure especially on those species having slow growth and low reproduction rate. Desert teak (Tecomella undulata (Sm.) Seem) a multipurpose agroforestry tree of arid zone has fallen on the verge of extinction in Iran due to lack of efficient seed reproduction. Inherent low adventitious rooting has caused vegetative mass macro- and micropropagation (organogenesis pathway) of this tree to be unsuccessful. Somatic embryogenesis (SE) pathway by production of bipolar embryo capable of development into a complete plantlet can solve the problem. Hence, a research was carried out to evaluate the feasibility of in vitro regeneration of the tree by SE. Ovary extracted from un-pollinated flower was cultured in the media supplemented with different auxins and cytokinins (CKs). The results showed α-naphthalene acetic acid (NAA) was superior in induction of embryogenic callus (EC). NAA ranging 5.4–21.5 µM could induce the highest ECs which exhibited developing pro-embryogenic masses (PEMs) and globular somatic embryos. Both CKs, thidiazuron (TDZ) and N6-benzyladenine (BA), though induced good callogenesis at low concentrations but the formed calli were non-embryogenic. Proliferation of NAA–induced ECs revealed that hormone-free medium is the best choice. However, the media containing 40.5 and 54 µM NAA alone could also induce somatic embryos along with callus proliferation. Effort for maturation of the obtained globular, hear-shaped and torpedo embryos did not yield satisfactory results. Low BA-contained medium led to secondary SE. More research is expected to be undertaken to optimize SE in desert teak.