Pollen germination and pollen tube growth are common to all seed plants, but these processes first developed in gymnosperms and still serve for their successful sexual reproduction. The main body of data on the reproductive physiology, however, was obtained on flowering plants, and one should be careful to extrapolate the discovered patterns to gymnosperms. In recent years, physiological studies of coniferous pollen have been increasing, and both the features of this group and the similarities with flowering plants have already been identified. The main part of the review is devoted to physiological studies carried out on conifer pollen. The main properties and diversity of pollen grains and pollination strategies in gymnosperms are described.

Pollen grain is a unique haploid organism characterized by two key physiological processes: activation of metabolism upon exiting dormancy and polar tube growth. In gymnosperms and flowering plants, these processes occur in different time frames and exhibit important features; identification of similarities and differences is still in the active phase. In angiosperms, the growth of male gametophyte is directed and controlled by its microenvironment, while in gymnosperms it is relatively autonomous. Recent reviews have detailed aspects of interaction between angiosperm female tissues and pollen such as interactions between peptides and their receptors; however, accumulated evidence suggests low-molecular communication, in particular, through ion exchange and ROS production, equally important for polar growth as well as for pollen germination. Recently, it became clear that ROS and ionic currents form a single regulatory module, since ROS production and the activity of ion transport systems are closely interrelated and form a feedback loop.

The concept of ROS as an important factor controlling pollen germination and tube growth has become generally accepted in the last decade. However, the relationship between various ROS and their significance for the success of in vivo germination and fertilization remained unexplored. For the present study, we collected Nicotiana tabacum stigma exudate on different stages of stigma maturity before and after pollination. Electron paramagnetic resonance (EPR) and colorimetric analysis were used to assess levels of O^•₂⁻ and H₂O₂ on stigma. Superoxide dismutase activity in the stigma tissues at each stage was evaluated zymographically. As the pistil matured, the level of both ROS decreased markedly, while the activity of SOD increased, and, starting from the second stage, the enzyme was represented by two isozymes: Fe SOD and Cu/Zn SOD, which was demonstrated by the in-gel inhibitory analysis. Selective suppression of Cu/Zn SOD activity shifted the ROS balance, which was confirmed by EPR. This shift markedly reduced the rate of pollen germination in vivo and the fertilization efficiency, which was estimated by the seed set. This result showed that hydrogen peroxide is a necessary component of stigma exudate, accelerates germination and ensures successful reproduction. A decrease in O^•₂⁻ production due to NADPH oxidase inhibition, although it slowed down germination, did not lead to a noticeable decrease in the seed set. Thus, the role of the superoxide radical can be characterized as less important.

A pollen grain is a unique haploid organism characterized by a special composition and structure. The pollen of angiosperms and gymnosperms germinate in fundamentally similar ways, but the latter also have important features, including slow growth rates and lower dependence on female tissues. These features are, to some extent, due to the properties of pollen lipids, which perform a number of functions during germination. Here, we compared the absolute content and the fatty acid (FA) composition of pollen lipids of two species of flowering plants and spruce using GC-MS. The FA composition of spruce pollen differed significantly, including the predominance of saturated and monoene FAs, and a high proportion of very-long-chain FAs (VLCFAs). Significant differences between FAs from integumentary lipids (pollen coat (PC)) and lipids of gametophyte cells were found for lily and tobacco, including a very low unsaturation index of the PC. The proportion of VLCFAs in the integument was several times higher than in gametophyte cells. We found that the absolute content of lipids in lily pollen is almost three times higher than in tobacco and spruce pollen. For the first time, changes in the FA composition were analyzed during pollen germination in gymnosperms and angiosperms. The stimulating effect of H₂O₂ on spruce germination also led to noticeable changes in the FA content and composition of growing pollen. For tobacco in control and test samples, the FA composition was stable.