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Trichome densities of leaflets differed on plants of Lycopersicon esculentum, L. hirsutum, L. hirsutum f. globratum and two interspecific hybrids grown under an 8-h photophase with (long days (LD)) or without (short days (SD)) a 4-h night interruption. Response to the 2 photoperiods depended on the genotype of plant and the particular type of trichome. Generally, the densities of Type IV trichomes — short, glandular trichomes having a single tip cell — were greater under SD and densities of Type VI trichomes — short, glandular trichomes with a multicellular tip — were greater under LD. Densities of Type V trichomes — short, non-glandular trichomes — did not differ between LD and SD. Quantities of 2-tridecanone and two 15-carbon compounds were not significantly altered by the night interruption.

Conidia and conidiophores from synchronously sporulating cultures of Stemphylium botryosum were fixed and embedded at successive intervals for examination under the electron microscope. The spore initial arises as a small bud at the tip of the conidiophore, and no discontinuity between the conidiophore wall and the spore can be detected. The single-celled bud and the tip cell of the conidiophore have very similar cytoplasmic features. Besides the usual cellular organelles, irregularly shaped electron-transparent areas in which membrane systems seem to perform some internal secretory activity between the leaflets themselves are present. Globules of the slightly electron-dense material originating in these specialized areas can also be found next to the plasma membrane where they are released and presumably participate in wall formation. Such a secretory system has not been described before and may be of particular importance in higher fungi which are known to lack a true Golgi apparatus.

Highlights • Single tip cells or groups of leading cells develop at the forefront of growing tissues. • Tip cells regulate tubule growth and morphogenesis. • Tip cells develop distinctive patterns of gene expression and specialised characteristics. • Tip cells are required for health and may be involved in the progression of cancer., The normal development of an organ depends on the coordinated regulation of multiple cell activities. Focusing on tubulogenesis, we review the role of specialised cells or groups of cells that are selected from within tissue primordia and differentiate at the outgrowing tips or leading edge of developing tubules. Tip or leading cells develop distinctive patterns of gene expression that enable them to act both as sensors and transmitters of intercellular signalling. This enables them to explore the environment, respond to both tissue intrinsic signals and extrinsic cues from surrounding tissues and to regulate the behaviour of their neighbours, including the setting of cell fate, patterning cell division, inducing polarity and promoting cell movement and cell rearrangements by neighbour exchange. Tip cells are also able to transmit mechanical tension to promote tissue remodelling and, by interacting with the extracellular matrix, they can dictate migratory pathways and organ shape. Where separate tubular structures fuse to form networks, as in the airways of insects or the vascular system of vertebrates, specialised fusion tip cells act to interconnect disparate elements of the developing network. Finally, we consider their importance in the maturation of mature physiological function and in the development of disease.

Wellcome Trust; 095718/Z/11/Z - Wellcome Trust; BB/N013174/1 - Biotechnology and Biological Sciences Research Council; PG/16/2/31863 - British Heart Foundation

The material used in this investigation is the root nodules of pea (Pisum sativam), which was fixed in Bouin's fluid, imbedded in paraffin, sectioned at thicknesses of 10-13μ and stained in Heidenhain's iron-alum-haematoxylin. According to this investigation, mitosis have been odserved during the meristematic region and amitosis during the early development of the bacteroid tissue. At the beginning of the am itosis, the nucleolus is gradually developed and becomes somewhat oval in shape (Fig. 2), and later, a constriction appears in the centre of nucleolus. At about the same time a constriction appears in the nucleoli (Fig. 3, 4) to separate them in two daughter nucleoli (Fig. 5, 6). In the bacteroid tissue, the nucleolus of almost every cell shows a small spherical bud which can be stained as deeply as the nucleolus itself. The amitosis and the buddings of nucleoli, which occur in the cells of the bacteroid tissue indicate some particular conditions in the cell. The chromosome numbers in meristematic region of the root-nodule of pea is 28, although 14 in foot tip cell.