The Response of Picea abies Somatic Embryos to UV-B Radiation Depends on the Phase of Maturation

Abstract

Ultraviolet-B (UV-B) radiation is a key environmental signal which initiates diverse responses that affect the metabolism, development, and viability of plants. In keeping with our previous studies, we concentrated primarily on how UV-B radiation affects Norway spruce [Picea abies (L.) Karst.] somatic embryo maturation and how phenolics and polyamines (PAs) are linked to the defense response invoked by UV-B irradiation. We treated clusters of Norway spruce embryogenic culture (EC) with UV-B during the five stages of embryo maturation (early, cylindrical, precotyledonary, cotyledonary, and mature embryos). For the first time, we take an advantage of the unique environmental scanning electron microscope AQUASEM II to characterize somatic embryos in their native state. The severity of the irradiation effect on embryonal cell viability was shown to be dependent on the intensity of radiation as well as the stage of embryo development, and might be related to the formation of protoderm. The response of early embryos was characterized by an increase in malondialdehyde (MDA), a marked decrease in PA contents and a decline in phenolics. The reduced ability to activate the defense system seems to be responsible not only for the severe cell damage and decrease in viability but also for the inhibition of embryo development. The significant reduction in spermidine (Spd), which has been reported to be crucial for the somatic embryo development of several coniferous species, may be causally linked to the limited development of embryos. The pronounced decrease in cell wall-bound ferulic acid might correspond to failure of somatic embryos to reach more advanced stages of development. Embryos at later stages of development showed stress defense responses that were more efficient against UV-B exposure.

Desiccation as a Post-maturation Treatment Helps Complete Maturation of Norway Spruce Somatic Embryos: Carbohydrates, Phytohormones and Proteomic Status

“…Prolonged maturation resulted in callus formation on the surface of most embryos. The onset of callogenesis was detected after only six weeks of maturation ( Eliášová et al, 2018 ). Callus never formed on desiccated embryos.…”

Correction of the Supersonic Flow Impact on the Results of the Inserted Temperature Probe in the Differentially Pumped Chamber

“…The air is compressed and experiences an adiabatic increase in temperature. Therefore, total air temperature is higher than the static (or ambient) air temperature (9,10).…”

The humidity level matters during the desiccation of Norway spruce somatic embryos

“…In the first series of experiments, morphologically fully mature somatic embryos were collected after 5 weeks of maturation, embryos were characterized by apical meristem surrounded with elongated cotyledons, hypocotyl and radicle with root apical meristem and the root cap, and with protoderm on the embryo surface, as described in Eliášová et al (2018). Embryos were either immediately germinated or treated with high relative humidity desiccation.…”

“…), and polyamines (PAs). Fischerová et al 10.3389/fpls.2022.968982 Among the osmotically active substances generated during dehydration, PAs play an important role (Vondrakova et al, 2010;Vondráková et al, 2015;Cvikrova et al, 2016;Salo et al, 2016;Eliášová et al, 2018;Chen et al, 2019). PAs are ubiquitous biogenic amines that are involved in various cellular functions in all organisms (Handa et al, 2018;Igarashi and Kashiwagi, 2019).…”