Vol 54, No 5 (2023)

The review is devoted to the analysis and generalization of modern knowledge about the mechanisms underlying the ontogeny of the male gametophyte envelope. New and earlier data on exine development аre discussed, and recurrent phases in the development of exine of phylogenetically distant plant species are emphasized. Though exine formation has been shown to be dependent on plenty of genes, the reiteration of exine patterns in different plant species (e. g. columellate, granular, “white-lined” lamellae) suggests that these patterns are based on some non-biological principles of space-filling operations. However, mechanisms involved remained obscure until it became clear that the sequence of structures observed during exine development coincided with the sequence of self-assembling micellar mesophases. It was discovered later that another physical-chemical process – phase separation – participated in exine formation. To confirm that exine-like patterns are capable of generating in vitro by simple physical processes, and their formation does not require regulation at the genome level, some our and other authors’ in vitro experiments were undertaken; the data obtained are discussed. Several series of our new experiments on modeling exine development with mixtures of urface-active substances resulted in some patterns simulating the main types of natural exine. Transmission electron microscopy analysis of the samples has shown that patterns simulating the full range of exine types were obtained by joint action of phase separation and micellar self-assembly. The reconsideration and analysis of our and other authors’ morphogenetic and modeling data revealed that molecular-genetic mechanisms and physical forces work in tandem, with considerable input of physical processes.

Wood formation (xylogenesis) in trees depends on photosynthesis and respiration. Temperature and precipitation affect photosynthesis and respiration and accordingly growth processes in a tree. We studied xylem and phloem cell formation, cell wall biomass accumulation, photosynthesis productivity, and trunk respiration in Scots pine trees growing in eastern Siberia (Russia) in the years with contrasting summer-weather conditions. The number of cells in the differentiation zones and the morphological parameters of the cells produced by the cambium were determined on samples taken mainly after 10 days of the growing season from the trunks of 10 trees. The activity of cambium and the accumulation of cell wall biomass at individual stages of tree ring wood formation and their relationship to the photosynthetic productivity of the crown and the cost of stem respiration were assessed. The division of cambial cells into xylem or phloem sides depended on the combination of temperature/precipitation in separate periods of the season and on reactions of photosynthesis and respiration to these factors. Biomass accumulation was bimodal with maxima in June (development of early wood) and predominantly in August (development of thick-walled late tracheids). This was due to the optimal combination of air temperature and moisture, which provided a sufficient influx of assimilates and their low consumption by respiration. It is shown that cambial activity and accumulation of biomass in the cell walls of Scots pine annual wood rings depend on the cumulative effect of temperature and precipitation on photosynthesis and stem respiration throughout the growing season. Fluctuations in external factors changed the balance between the inflow of photoassimilates and their utilization. As a result, photoassimilates were used not only for the synthesis of cell wall biomass, but were also partly converted to reserve substances, in particular, into starch. Our study expands understanding of the internal processes that lead to the formation of wood under the influence of external factors.

Adaptive maternal effects that increase the adaptability of offspring are often caused by stressful conditions that persist in the environment for an extended period of time. The question arises, what is the threshold at which maternal effects cease to be adaptive for offspring and lead to developmental disorders? One of the stressors is considered to be unpredictable changes in environmental conditions. We aimed to test whether a mother’s inhabitation of unstable environment could lead to a decrease of developmental robustness in the embryos of the gastropod mollusk Lymnaea stagnalis. The laboratory population of snails was split into two groups. For the first group, conditions were maintained as stable as possible, with constant water exchange and excessive feeding. The second group was kept under unstable (stressful) conditions, with episodic feeding and water exchange. It turned out that unstable conditions alone did not affect the frequency of developmental anomalies in the offspring. Since serotonin is presumably plays the role of the signaling molecule mediating the maternal effect in L. stagnalis, we subjected embryos of both groups to the biochemical precursor of serotonin (5-HTP). After incubation in 5-HTP, the proportion of embryos with developmental anomalies was significantly higher among the offspring of mothers living in unstable conditions. We confirmed the important role of serotonin as a factor mediating communication between the organisms of mother and offspring by revealing serotoninergic innervation of the hermaphroditic gland (ovotestis) and accumulation of serotonin in the cytoplasm of forming oocytes. Our experiments suggest that under the stressful environmental conditions, serotonin accumulation by the oocyte/zygote may increase to a maladaptive level and lead to a decrease in the robustness of embryonic development.