Somatic embryogenesis in Canary Island date palm

Shoot regeneration was obtained from leaves of in vitro cultures of wild pear genotypes. The highest regeneration rates, ranging from 40% to 64%, depending on the genotype, were obtained using leaves wounded by three cuts transversely to the mid-rib, a Quoirin and Lepoivre macro-salt composition, 250 mg l^-1 cefotaxime and maintaining the explants in darkness for the first 30 days (induction phase), then transferring them to an auxin-free medium in light (expression phase). A concentration of 8.8 μM BA induced the highest number of explants to produce adventitious shoots. TDZ was less effective than BA and induced hyperhydricity in regenerated shoots. The histological studies revealed that the regenerated shoots originated mainly from callus formed by epidermal and sub-epidermal cells and by cells of the vascular tissue. The regenerated shoots were micropropagated, rooted and transplanted to the soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Long-lasting <Emphasis Type="Italic">Capsicum baccatum</Emphasis> ‘Organogenic callus’ formation

Summary Capsicum regeneration is often obtained through direct (adventious) regeneration and only a few reports claim indirect regeneration (through callus) as an option to obtain complete plants. A possible reason for this may be because Capsicum cultures offer a narrow window in time for the regeneration process to occur, and after that, the ability to regenerate plants rapidly diminishes. In this study, the C. baccatum radicle-side half-seed was the explant of choice to induce the formation of callus on semisolid Murashige and Skoog (1962) medium supplemented with 5 mgl⁻¹ (22.2μM) 6-benzylaminopurine, 1 mgl⁻¹ (5.7μM) indole-3-acetic acid, and 2 mgl⁻¹ (6.1μM) gibberellic acid. Organogenic calluses developed within 4–5 mo. and were subcultured every 2 mo. thereafter. Eventual bud elongation occurred and these shoots developed into complete plants after transfer to medium without plant growth regulators. The organogenic callus type retained its organogenic ability for more than 3 yr.     

Callus Induction and Plant Regeneration in Lemna Minor L.

Callus induction was obtained on Murashige and Skogg agar medium with 45 M 2,4-dichlorophenoxyacetic acid under dark at 25°C. Among the four explant types investigated, the best callus induction was obtained from two-week old fronds to which a surgical incision was applied in the basal (meristematic) region. This treatment resulted in 89.11% of fronds producing callus which continued to proliferate for another 24 months. To obtain plant regeneration pieces of calluses were transferred onto Murashige and Skoog agar medium containing 22 M indole-3-acetic acid and 4.6 M kinetin and maintained under 16-h photoperiod (irradiance of 30 mol m^–2 s^–1) at 23°C. Green fronds formed on all callus pieces. The regenerated fronds were later transferred onto Wang medium where they formed roots. The regenerated Lemna minor L. plants obtained through indirect organogenesis did not differ morphologically from individuals forming the stock collection.     

Developmental phases and STM expression during Arabidopsis shoot organogenesis

Shoot organogenesis in Arabidopsis thaliana wasstudied with regard to the timing of key developmental phases and expression ofthe SHOOTMERISTEMLESS (STM) gene.Shoot regeneration in the highly organogenic ecotype C24 was affected byexplanttype and age. The percentage of C24 cotyledon explants producing shootsdecreased from 90% to 26% when donor seedlings were more than 6 dold, but 96% of root explants produced shoots regardless of the age of thedonorplant. Using explant transfer experiments, it was shown that C24 cotyledonexplants required about 2 days to become competent and another 8-10 days tobecome determined for shoot organogenesis. A C24 line containing the promoterofthe SHOOTMERISTEMLESS (STM) genelinked to the -glucuronidase(GUS) gene was used as a tool for determining the timingofde novo shoot apical meristem (SAM) development incotyledon and root explants. Cotyledon and root explants from anSTM:GUS transgenic C24 line were placed on shoot inductionmedium and GUS expression was examined after 6-16 days ofculture. GUS expression could be found in localizedregionsof callus cells on root and cotyledon explants after 12 days indicating thatthese groups of cells were expressing the STM gene, hadreached the key time point of determination, and were producing an organizedSAM. This was consistent with the timing of determination as indicated byexplant transfer experiments. Root explants from anSTM:GUStransgenic Landsberg erecta line and a two-step tissue culture method revealedasimilar pattern of localized GUS expression duringde novo shoot organogenesis. This is the first studydocumenting the timing and pattern of expression of theSTMgene during de novo shoot organogenesis.     

A study on the effect of genotypes,plant growth regulators and sugars in promoting plant regeneration via organogenesis from soybean cotyledonary nodal callus

We have developed an efficient protocol for callus induction and plant regeneration in three elite soybean cultivars (Williams 82, Loda and Newton). The technique is most novel in that the shoot buds developed from the nodal callus. Callus induction and subsequent shoot bud differentiation were achieved from the proximal end of cotyledonary explants on modified Murashige and Skoog (MS) media containing 2.26 M 2,4-dichlorophenoxy-acetic acid (2,4-D) and 8.8 M benzyladenine (BAP), respectively. Varying the carbon source optimized the regeneration system further. Among the various carbon sources tested, sorbitol was found to be the best for callus induction and maltose for plant regeneration.     

Rooster feathering, androgenic alopecia, and hormone-dependent tumor growth: what is in common?

Different epithelial organs form as a result of epithelial-mesenchymal interactions and share a common theme modulated by variations (Chuong ed. In Molecular Basis of Epithelial Appendage Morphogenesis, 1998). One of the major modulators is the sex hormone pathway that acts on the prototype signaling pathway to alter organ phenotypes. Here, we focus on how the sex hormone pathway may interface with epithelia morphogenesis-related signaling pathways. We first survey these sex hormone-regulated morphogenetic processes in various epithelial organs. Sexual dimorphism of hairs and feathers has implications in sexual selection. Diseases of these pathways result in androgenic alopecia, hirsutism, henny feathering, etc. The growth and development of mammary glands, prostate glands, and external genitalia essential for reproductive function are also dependent on sex hormones. Diseases affecting these organs include congenital anomalies and hormone-dependent breast and prostate cancers. To study the role of sex hormones in new growth in the context of system biology/pathology, an in vivo model in which organ formation starts from stem cells is essential. With recent developments (Yu et al. (2002) The morphogenesis of feathers. Nature 420:308-312), the growth of tail feathers in roosters and hens has become a testable model in which experimental manipulations are possible. We show exemplary data of differences in their growth rate, proliferative cell population, and signaling molecule expression. Working hypotheses are proposed on how the sex hormone pathways may interact with growth pathways. It is now possible to test these hypotheses using the chicken model to learn fundamental mechanisms on how sex hormones affect organogenesis, epithelial organ cycling, and growth-related tumorigenesis.     

Direct adventitious shoot formation on seedling radicles in seed cultures of strawberry

Mature seeds of strawberry (Fragaria x ananassa) were placed on Murashige and Skoog medium supplemented with 2.22 μM 6-benzyladenine. After four weeks of culture, and without an intervening callus phase, approximately 36% of the resulting seedling radicles had formed numerous adventitious buds near their tips. A few buds on each radicle developed into shoots, while others formed disorganized calli. Consequently, the seedlings exhibited shoot apices at both ends of the axis of polarity. Our overall results suggest that a considerable level of plasticity in organ determination occurs even in higher plants, and that exogenous growth regulators can cause a root primordium in the radicle to be converted to a shoot primordium.     

Identification and characterization of a novel extracellular matrix protein nephronectin that is associated with integrin alpha8beta1 in the embryonic kidney

The epithelial-mesenchymal interactions required for kidney organogenesis are disrupted in mice lacking the integrin alpha8beta1. None of this integrin's known ligands, however, appears to account for this phenotype. To identify a more relevant ligand, a soluble integrin alpha8beta1 heterodimer fused to alkaline phosphatase (AP) has been used to probe blots and cDNA libraries. In newborn mouse kidney extracts, alpha8beta1-AP detects a novel ligand of 70-90 kD. This protein, named nephronectin, is an extracellular matrix protein with five EGF-like repeats, a mucin region containing a RGD sequence, and a COOH-terminal MAM domain. Integrin alpha8beta1 and several additional RGD-binding integrins bind nephronectin. Nephronectin mRNA is expressed in the ureteric bud epithelium, whereas alpha8beta1 is expressed in the metanephric mesenchyme. Nephronectin is localized in the extracellular matrix in the same distribution as the ligand detected by alpha8beta1-AP and forms a complex with alpha8beta1 in vivo. Thus, these results strongly suggest that nephronectin is a relevant ligand mediating alpha8beta1 function in the kidney. Nephronectin is expressed at numerous sites outside the kidney, so it may also have wider roles in development. The approaches used here should be generally useful for characterizing the interactions of novel extracellular matrix proteins identified through genomic sequencing projects.     

In vitro shoot regeneration from leaf explants of Roman Chamomile

Murashige and Skoog (1962) medium supplemented with 1.0 to 4.5 M of BA and 1.0 M of NAA induced adventitious bud formation and shoot development in leaf explants of Roman Chamomile. A higher number of adventitious buds was observed at the proximal end of the explants. Plantlets were replicated and multiplied on MS medium supplemented with 2.25 M of BA and 0.6 M of IAA. Plantlets were rooted on MS medium supplemented with 0.5 M of IBA and successfully weaned in vivo. The plants grew to maturity with high uniformity and no morphological signs of somaclonal variation.