POLLEN GRAIN STRUCTURE AND POLLINATION IN THE <i>RIBES</i> (GROSSULARIACEAE) REPRESENTATIVES

Abstract

Currant is an important small-fruit crop that has long been used for medicinal purposes. The systematic position of the genus Ribes in the kingdom Plantae is perceived by researchers unambiguously. However, the internal taxonomy of the genus Ribes and the systematic position of some species in the genus remains a matter of debate.The study of the morphology, fertility and viability of pollen grains is also an important indicator in determining phylogenetic relationships in the genus Ribes. Comparative poral-colpus analysis of pollen makes it possible to determine the similarities and differences in different species and the degree of genetic relatedness of the compared forms. The processes of pollination and germination of pollen in the pistil style in the Grossulariaceae are poorly covered in the cited literature.These problems became the ground for the study, the purpose of which was to determine the characteristics of pollen grains, pollination and germination of pollen on both the pistil stigma and artificial nutrient medium in Ribes species in order to identify species characterized by pollen of maximum viability, suitable for breeding work in the conditions of St. Petersburg.The objects of the study were plants of the Ribes species from the open ground collection of the Komarov Botanical Institute RAS (R. sachalinense, R. sanguineum, R. rubrum, R. mandschuricum, R. spicatum, R. saxatile, R. aureum, R. alpinum, R. nigrum), as well as the species growing in nursery of the N.I. Vavilov All-Russian Institute of Plant Genetic Resources: R. dikuscha, R. hudsonianum, R. nigrum subsp. europeum, R. nigrum subsp. sibiricum, R. pauciflorum, R. ussuriense. Pollen was examined using a Zeiss EVO-40 scanning electron microscope at the Center for Collective Use of Atomic Force and Electron Microscopy, Herzen University.It was revealed that the studied Ribes plants have normally developed pollen grains of a spherical or elliptical shape, with concave lateral planes, the pollen is porate-colpate. Currant pollen is characterized by wide polymorphism both between different species and within the same species. In all studied species, there are deviations in morphological structure of pollen grains; such pollen does not germinate on an artificial nutrient medium. The most deformed pollen was observed in Ribes mandshuricum, R. ussuriense, R. alpinum, R. dikusha, and R. pauciflorum (12.7–6.7%). The pollen of medium size (21–49 μm) is the most suitable for fertilization. The largest share of the medium-sized pollen is found in Ribes sanguineum, R. ussuriense, R. saxatile and R. aureum (91.8–94.6%). The studied plants have a high percentage of morphologically formed (fertile) pollen (the share of stained pollen is 80.3–96.4%). At the same time, the pollen has a rather low viability when germinated on an artificial nutrient medium, with the pollen of Ribes sanguineum, R. spicatum, R. nigrum, R. ussuriense, R. aureum germinates germinating better than the others (45–29%). Often, the pollen grains germinate with disturbances, which is reflected in the direction of their growth. In some species of Ribes, pollen is able to germinate while still inside the anther. The percentage of pollen germination inside the anther is unequal in the flowers taken from different parts of the inflorescence; the best germination is found in the pollen from the flowers of the central zone of the inflorescence.The pollinators of the Ribes flowers in St. Petersburg are representatives of genera Apis, Bombus and a lacewing Chrysopa oculata. There are 2 peaks of pollinators’ activity: in the morning (10–11 a.m.) and in the evening (5–6 p.m.).The germination of pollen grains on the pistil stigma in the studied plants is active. At a relatively high air temperature, the passage of the pollen tube to the ovule takes 3–5 days. In the ovules on the first day of flowering, mature embryo sacs ready for fertilization are observed. On the walls of the ovary, 4 hemi-orthotropic ovules develop, arranged in 6–10 “levels”. The pollen enters the stigma in a two-celled state. The division of the generative cell into two spermia occurs in the pollen tube during the growth of the latter. The germination of the pollen tube in the canal of the pistil style often occurs with disturbances.The conducted studies allow to recommend the species Ribes sanguineum, R. spicatum, R. nigrum, R. aureum for use in Ribes breeding in the conditions of St. Petersburg.