Adaptation of Male Reproductive Sphere of Common Juniper to Climate
Weather conditions have a significant effect on spring development phenorhytmic of juniper male reproductive structures. The most sensitive and vulnerable to adverse external conditions stage of development is meiosis of microsporocytes. Long-term steady temperature fall in 2017 led to slowdown in life processes and delay of meiosis and its suspension in prophase I. The delay of the spring development of juniper male reproductive structures in 2017 amounted to 20-30 days. Active phase of meiosis (MI-AII) had began only after accumulated amount of physiologically active heat approximated to long-term annual average at which this phase of development is the most common in the research area. The total duration of the active phase of juniper meiosis did not exceed 2-3 days. There were the same distinctive disorders (agglutination in MI-AI and MII-AII and uneven disjunction in AI and AII) that are inherent to juniper in meiosis at temperatures close to the long-term annual average. Disorders in microsporocytes meiosis should be considered as one of the significant reasons leading to decrease of pollen viability. However, it is not obvious which disorders in meiosis are lethal and lead to degeneration or sterility of developing pollen grains. There was a significant increase in the number of pollen grains and tubes teratologies in2017. The relative number of undeveloped pollen grains with degenerative features has increased. The number of small undeveloped and deformed pollen grains is more than 3 times higher than the same long-term annual average (2.3 %) for the research area. Attenuated response of pollen grains on hydration consisting of slowing of hydrophilic capsule formation and exine rupture had been observing. The percentage of pollen grains germinated into pollen tubes was close to the values distinctive for junipers of the research area. There was a weakened growth of pollen tubes in vitro. The most part of male pollen grains either germinated into short (not more than 100 µm) pollen tubesor a significant part of pollen grains didn’t germinate at all or stopped in their development at the stage of slipper-shape. The male reproductive sphere of Common Juniper is adapted to the local climate. In the process of evolution juniper has developed mechanisms allowing surviving under temporary cooling conditions during the active spring development of male reproductive structures. One of these mechanisms is very short duration of the most vulnerable stages of development (differentiation of sporogenic tissues, isolation of microsporocytes and active phases of microsporocytes meiosis) of male reproductive structures.