Kinetin-treated Flax Seedlings as Models for the Integration of the Plant Body
AMONG the many morphological experiments performed on various seedlings1 a recent experiment indicated in Fig. 1 seems to be particularly suitable to further the understanding of the growth correlations which are responsible for the integration of the plant body. Seedlings of Linum usitatissimum when decapitated above the first leaf pair always replace the lost top, when the cotyledonary buds grow out vigorously and prevent the development of the buds which are above them in the axils of the first two leaves, because the cotyledonary buds exhibit a much more advanced embryonic development because the cotyledons have a larger area than the first leaves. Kinetin immediately applied in 1 per cent lanolin to the bud of the first leaf caused it to expand, as in other cases2–4, but the cotyledonary shoots, even in this case, grew out more strongly and finally inhibited the shoot pretreated with kinetin (Fig. 1a).
Tetra-co-ordination of Nickel(II)—Some Complexes with Cyclohexylphosphine
THE problem of the tetra-co-ordination of nickel(II) has recently been the object of much interest1–3 owing to the peculiar situation of this ion in the field of co-ordination chemistry, and because of the many opportunities for testing theoretical predictions on the structural, magnetic and optical properties of transition metal complexes. Of particular interest are the complexes of the type NiX22PR3. These seem to be clear examples of pure tetra-co-ordination around nickel(II). We had previously examined by X-rays the crystal structure of the red diamagnetic compound4 NiBr22PEt3, and found it to be transplanar as expected. We did not detect any co-ordination along the other axis (unpublished work), as occurs in other cases, for example, in nickel bisdimethylglyoxime5.
Engineering bio-inks for 3D bioprinting cell mechanical microenvironment
Three-dimensional (3D) bioprinting has become a promising approach to construct­ing functional biomimetic tissues for tissue engineering and regenerative medicine. In 3D bioprinting, bio-inks are essential for the construction of cell microenviron­ment, thus affecting the biomimetic design and regenerative efficiency. Mechanical properties are one of the essential aspects of microenvironment, which can be char­acterized by matrix stiffness, viscoelasticity, topography, and dynamic mechanical stimulation. With the recent advances in functional biomaterials, various engineered bio-inks have realized the possibility of engineering cell mechanical microenviron­ment in vivo. In this review, we summarize the critical mechanical cues of cell micro­environments, review the engineered bio-inks while focusing on the selection princi­ples for constructing cell mechanical microenvironments, and discuss the challenges facing this field and the possible solutions for them.