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.
An investigation was made of the loss of stability of polymer rods exposed to disturbances in the form of camber of the rod and eccentricity of load application. At present, polymeric materials are being used not only as fencing constructions and as constructions of 'secondary' value but also as bearing elements. Polymer rods for the strengthening of suspended constructions are an example. These rods undergo both elongation and compression.
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.
ROS are known to be accumulated in stigmas of different species and can possibly perform different functions important for plant reproduction. Here we tested the assumption that one of their functions is to control membrane potential and provoke synthesis of unique proteins in germinating pollen. We used spectrofluorometry and spectrophotometry to detect H2O2 in stigma exudate, quantitative fluorescent microscopy of pollen tubes and flow cytometry of pollen protoplasts to reveal effects on membrane potential, and a label‐free quantification approach to study pollen proteome changes after H2O2 treatment. We found that in both growing pollen tubes and pollen protoplasts exudate causes plasmalemma hyperpolarization similar to that provoked by H2O2. This effect is abolished by catalase treatment and the ROS quencher, MnTMPP. Inhibitory analysis indicates probable participation of Ca2+‐ and K+‐conducting channels in the observed hyperpolarization. For a deeper understanding of pollen response, we analysed proteome alterations in H2O2‐treated pollen grains. We found 50 unique proteins and 20 differently accumulated proteins that are mainly involved in cell metabolism, energetics, protein synthesis and folding. Observed hyperpolarization and proteome alterations agree well with previously reported stimulation of pollen germination by H2O2 and sensitivity of Ca2+‐ and K+‐conducting channels to this ROS. Thus, H2O2 is one of the active substances in tobacco stigma exudate that stimulates various physiological processes in germinating pollen.
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