Recent literary data on inversion (turning inside out) in the embryos of flagellated algae of the genus Volvox are critically analyzed. In this process, active changes in the shape of embryonic cells and the displacement of intercellular cytoplasmic bridges play an important role. After inversion, the flagella appear on the outer side of the young colony and provide its motility. Within the genus Volvox, two main modes of embryo inversion have been recently established during the asexual developmental cycle—inversion of type A and inversion of type B—represented by the two species most thoroughly studied, respectively, Volvox carterif. nagariensis and V. globator. However, the published opinion that the inversion of V. aureus embryos is of the type B seems to be doubtful. Comparative and evolutionary aspects of embryonic inversion in Volvox are discussed with the use of data on other genera of colonial volvocine algae.

Comparative Analysis of Embryonic Inversion in Algae of the Genus Volvox (Volvocales, Chlorophyta)

The article presents a brief review of the latest experimental data on sexual reproduction in the colonial volvocine algae, which represent a promising model for research on developmental biology. The main focus is on the MID gene, which determines sex and controls the “minus”/male differentiation in iso-gamous, anisogamous, and oogamous volvocine species. The experiments on sex transformation in a model species Volvox carteri f. nagariensis are critically analyzed. Studies of the gene FUS1, which controls gamete recognition and fertilization in the isogamous and anisogamous volvocine algae, are also considered.

Advances in the Research of Sexual Reproduction in Colonial Volvocine Algae

Sweet chestnut (Castanea sativa Mill.) is a multi-purpose species cultivated for timber and nuts. However, recent years have seen a reduction in chestnut production. There are several reasons for this including abandonment of traditional cultivation practices, plant diseases, and problems during pollen differentiation. It appears that reduction in chestnut yield, recorded over recent decades, is associated with a decrease in the trees with longistaminate catkins, which are low yielding, but are fundamental for efficient pollination and the successive fertilization. Present study has been undertaken to provide new insights into the stamen and pollen morphology of four Andalusian chestnut cultivars (‘Helechal’, ‘Temprana’, ‘Vázquez’,‘Ancha de Alàjar’). It was observed that catkins in these cultivars are brachistaminate, and poor fertilization capability. The cultivar ‘Vázquez’ showed the longest stamens, and also the highest percentage of normal pollen and therefore, show highest fertilization capacity. On the other hand, shortest stamens and the lowest percentage of normal pollen grains, were recorded in cultivar ‘Ancha de Alàjar’ which cannot be considered a good pollinator.

J. Morales Gonzalez

Papers

Studies on the morphology of stamens and pollen grains in some cultivars of Spanish chestnut (Castanea sativa Mill.)