Bipolar pollen germination in blue spruce (Picea pungens).

Direct growth of a pollen tube is an effective mechanism of sperm delivery characteristic for the majority of seed plants. In most cases, only one tube grows from one grain to perform the delivery function; meanwhile in Picea the appearance of two tubes from a single pollen grain is quite common during in vitro germination. Here, we describe the phenomenon of bipolar germination and test two hypotheses on its nature and possible role in gametophyte functioning. The hypothesis on "trophic" function of multiple tubes provoked by poor nutrition discussed in literature was not confirmed by in vitro growth tests; bipolar germination strongly decreased with lowering sucrose availability. The highest proportion of bipolar germination occurred in optimal conditions. We then assumed that bipolar germination occurs because turgor pressure is a non-directional force and effective systems of cell wall mechanical regulation are lacking. In hypertonic medium, bipolar germination was sufficiently lower than in isotonic medium, which was consistent with prediction of the «mechanical¼ hypothesis. Scanning electron microscopy and fluorescence microscopy analysis of pollen morphology and cell wall dynamics during both types of germination showed that the appearance of a single tube or bipolar germination depends on the extension of exine rupture. Cell wall softening by short-term ·OH treatment sufficiently decreased the percent of bipolar germination without affecting total germination efficiency. We concluded that mechanical properties of the cell wall and turgor pressure could shift the balance towards one of the germination patterns.

The Role of BAR Domain Proteins in the Regulation of Membrane Dynamics.

Many cellular processes are associated with membrane remodeling. The BAR domain protein family plays a key role in the formation and detection of local membrane curvatures and in attracting other proteins, including the regulators of actin dynamics. Based on their structural and phylogenetic properties, BAR domains are divided into several groups which affect membrane in various ways and perform different functions in cells. However, recent studies have uncovered evidence of functional differences even within the same group. This review discusses the principles underlying the interactions of different groups of BAR domains, and their individual representatives ,with membranes.

[Sporopollenin accumulation in Nicotiana tabacum L. microspore wall during its development].

Accumulation of sporopollenin components in microspore wall, its polymerization dynamics and possible participation of reactive oxygen species (ROS) in this process has been studied. For this purpose fluorescent and electron microscopy (TEM) was used. It has been determined that phenylpropanoid components of sporopollenin that form the exine accumulate in the microspore cell wall at the middle and late tetrad stages. At the late tetrad stage, they fully cover the microspore surface and accumulate abundantly in aperture areas. In accordance with this, numerous thick sporopollenin lamellae, electron-dense and acetolysis-resistant, emerge in aperture areas. Exine in the areas between apertures includes both acetolysis-resistant sporopollenin and washout components. These particular parts of the wall are intensively stained with fluorescent dye MitoSOX, which detects the presence of ROS. The staining disappeared after the treatment of microspore with superoxide dismutase, demonstrating the presence of superoxide in the exine. Superoxide easily converts to hydrogen peroxide, which can cause oxidative polymerization of sporopollenin components, leading to the formation of chemically stable biopolymer. The data obtained favor the hypothesis of ROS involvement in the formation of sporopollenin.

[Quaternary structure formation by recombinant analogues of spider silk].

A study has been conducted on the morphology of artificial spider silk fibers, prepared from recombinant analogues of spiridons 1 and 2. It has been shown that by stretching out the "as spun" fiber, a reorganization of its spongy matrix occurs, which leads to the formation of microfibrills, followed by a reduction of the diameter of the fiber. The durability of an artificial fiber depends on the degree of stretching and on the substructure of the microfibrills. The model process of artificial fibers preparation reproduces to the great detail the natural process of spider web spinning. Future applications of this model include production of biomaterials with unique properties.