Colleters in leaves of Mespilus germanica L. (Rosaceae): Micromorphology, histochemistry and fluorescence.

New data on the micromorphology, histochemistry, and fluorescence of colleters on leaf structures at different stages of development (leaf blade, stipules, and petiole) of Mespilus germanica L. are presented. Colleters are found on the tips of the teeth of both young and mature leaf blades and stipules, less often on the petioles. The leaf veins approach the leaf tooth, but no vascularization was found in the colleter. On leaf structures inside the bud, young colleters were observed in the form of finger-shaped or rounded outgrowths consisting of isodiametric cells. Mature colleters are multicellular secretory structures that have a head on a short stalk. The central part of the head consists of densely packed parenchymal cells, which are surrounded by radially elongated palisade-like secretory cells covered with a cuticle. The main secretion process of the colleter falls on the period of active growth of leaf structures. The secreted substances accumulated in the intercellular spaces of the palisade-like cells of the head and then were released outside in the form of translucent vesicles. The secretion products were released when the cuticle was ruptured and spread over the surface of the head and tooth of the leaf blade and stipules. After the end of secretion, the sizes of the head of the colleter decreased, and an abscission zone appeared in the cells of the colleter stalk, along the border of which a fracture occurred when the head fell off. Histochemical analysis of the contents of the colleter showed the presence of polysaccharides, especially at a young age, substances of a phenolic nature and lipids at a more mature age. In the fluorescence spectrum of young leaf colleter secretion, a peak at 671-672 nm was observed upon excitation at 405 and 473 nm. The obtained data on Mespilus germanica L. colleter can be used in the taxonomy of Pyrinae and Rosaceae.

Lipid Fatty Acids from the Pericarp of Cydonia oblonga Mill. and Mespilus germanica L. are Involved in Plant Adaptation to Altitudinal Zonality.

The composition of fatty acids of total lipids of the outer and parenchymal parts of the pericarp in Cydonia oblonga Mill. and Mespilus germanica L. (Maloideae, Rosaceae), growing in the Northern Caucasian mountains at altitudes of 300, 500, 700, and 1200 m above sea level in various natural zones from experimental sites, was studied for the first time. It is established that the altitude of plant growth is largely correlated with the changes in the FA composition of the outer, but not the parenchymal, part of the pericarp. The nature of this variability suggests that the adaptation of plants to the conditions of significant temperature differences in the mountains is associated with the regulation of cell membrane fluidity, based on the interaction of opposite processes of synthesis of polyunsaturated and very-long-chain fatty acids.

Tannosomes in the Pericarp Cells of Maloideae (Rosaceae).

Data on the presence of structural units termed tannosomes in the pericarp cells of Maloideae has been obtained for the first time. Tannosomes merge in the vacuoles to form "tannoglobules."

The Gene Encoding the Universal Stress Protein AtUSP is Regulated by Phytohormones and Involved in Seed Germination of Arabidopsis thaliana.

For the first time, the organ-specific expression pattern of the AtUSP (At3g58450) gene, which also undergoes hormonal regulation, was shown. The USP protein encoded by this gene is involved in seed germination of Arabidopsis thaliana and, unlike abscisic acid, stimulates this process.

ABA and IAA control microsporogenesis in Petunia hybrida L.

The formation of fertile male gametophyte is known to require timely degeneration of polyfunctional tapetum tissue. The last process caused by the programmed cell death (PCD) is a part of the anther program maturation which leads to sequential anther tissue destruction coordinated with pollen differentiation. In the present work, distribution of abscisic acid (ABA) and indole-3-acetic acid (IAA) in developing anthers of male-fertile and male-sterile lines of petunia (Petunia hybrida L.) was analyzed by using the immunohistochemical method. It was established that the development of fertile male gametophyte was accompanied by monotonous elevation of ABA and IAA levels in reproductive cells and, in contrast, their monotonous lowering in tapetum cells and the middle layers. Abortion of microsporocytes in the meiosis prophase in the sterile line caused by premature tapetum degeneration along with complete maintenance of the middle layers was accompanied by dramatic, twofold elevation in the levels of both the phytohormones in reproductive cells. The data obtained allowed us to conclude that at the meiosis stage ABA and IAA are involved in the PCD of microsporocytes.

[Auxin Abolishes Inhibitory Effects of Methylcyclopropen and Amino Oxyacetic Acid on Pollen Grain Germination, Pollen Tube Growth, and the Synthesis of ACC in Petunia].

As established by us earlier, ethylene behaves as a regulator of germination, development, and growth of male gametophyte during the progamic phase of fertilization. However, the mechanisms of the regulation of these processes remain so far unstudied. It is believed that the main factor providing variety of the ethylene responses is its interaction with other phytohormones. According to our working hypothesis, ethylene controls germination of pollen grains (PGs) and growth of pollen tubes (PTs) by interacting with auxin, which, as the available data indicate, is likely a key regulator of plant cell polarization and morphogenesis and one of the factors modulating the biosynthesis of ethylene at the level of ACC-synthase gene expression. In the present work, on germinating in vitro male gametophyte and the pollen-stigma system for petunia (Petunia hybrida L.) effects of phytohormones (ethylene and IAA) and known blockers repressing ethylene reception (1-methylcyclopropene, 1-MCP), the synthesis of ACC (amino oxyacetic acid, AOA) and transport IAA (triyodbenzoynaya acid, TYBA) on PGs germination, PTs growth and the synthesis of ACC were investigated. According to the data obtained, exogenous ethylene and IAA stimulated both PGs germination and PTs growth. 1-MCP and TYBA completely inhibited the first process, whereas IAA abolished the inhibitory action of 1-MCP and AOA on both the above processes. Etrel only partially weakened the inhibitory effect of TYBA. Examination of ACC synthesis modulation with AOA showed that IAA does not affect the level of ACC in germinating in vitro male gametophyte and nonpollinated stigmas, while this phytohormone insignificantly raised the level of ACC and abolished the inhibitory effect of AOA on its synthesis in the pollenstigma system. Pollination of stigmas with the pollen preliminarily treated with 1-MCP led to 2.5-fold decline in both the rate of PT growth and the level of ACC. At the same time, IAA abolished the inhibitory action of 1-MCP recovering the synthesis of ACC and growth of PTs to the control values. All these results, taken together, provide evidence for the interaction of the signal transduction pathways of ethylene and auxin at the level of ACC biosynthesis in the course of germination and growth of petunia male gametophyte during the progamic phase of fertilization.

[Exogenous IAA and ABA Stimulate Germination of Petunia Male Gametophyte by Activating Ca(2+)-Dependent K(+)-Channels and by Modulating the Activity of Plasmalemma H(+)-ATPase and Actin Cytoskeleton].

To date, the molecular mechanisms underlying the osmoregulation of pollen grains (PGs) related to the maintenance of their water status and allowing pollen tubes (PTs) to regulate concentrations in them of osmolytes and transmembrane water transport remain to be not so far characterized. In the present work, the data on the participation of IAA and ABA in the osmoregulation of germinating in vitro petunia male gametophyte were obtained. It has been established that the growth-stimulating effect of these phytohormones is due to their action on intracellular pH (pHc), the membrane potential of plasmalemma (PM), the activity of PM H(+)-ATPase, K(+)-channels in the same membrane and organization of actin cytoskeleton (AC). Two possible targets of the action of these compounds are revealed. These are represented by (1) PM H(+)-ATPase, electrogenic proton pump responsible for polarization of this membrane, and (2) Ca(2+)-dependent K+-channels. The findings of the present work suggest that the hormone-induced pHc shift is involved in cascade of the events including the functioning of pH-dependent K+-channels. It was shown that the hormoneinduced hyperpolarization of the PM is a result of stimulation of electrogenic activity of PM H(+)-ATPase and the hormonal effects are mediated by transient elevation in the level of free Ca(2+) in the cytosol and generation of reactive oxygen species (ROS). The results on the role of K(+) ions in the control of water-driving forces for transmembrane water transport allowed us to formulate the hypothesis that IAA and ABA stimulate germination of PGs and growth of PTs by activating K(+)-channels. In addition, the studies performed showed that the AC of male gametophyte is sensitive to the action of exogenous phytohormones, with to more extent to the action of IAA. As judged by the action of latrunculin B (LB) the AC may serve as the determinant of the level of endogenous phytohormones that most likely participate in the regulation of the polar growth of PTs impacting on the pool of F-actin in their apical and subapical zones.