Calcium silicate mitigates the physiological stress induced by 6-benzylaminopurine during the in vitro multiplication of Quercus robur

Abstract

For Quercus species, efficient large-scale proliferation may be dependent on or enhanced by exposure to synthetic cytokinins, such as 6-benzylaminopurine (BAP). However, it can also induce physiological disturbances. In contrast to BAP, the addition of silicon to the medium has been carried out to improve the characteristics related to growth and physiology during in vitro culture. We aimed to assess the morphophysiological modulations in Quercus robur shoots exposed to BAP and calcium silicate (CaSiO3), used alone or synergistically, during in vitro multiplication. Shoots were cultured with BAP at 0 or 3.50 μM combined with CaSiO3 concentrations at 0, 6, 12, or 18 μM. The morphophysiological traits and photosynthetic apparatus functioning were quantified at 46 days of growth. De novo shoot regeneration was verified only in explants cultured under BAP exposure. Shoots cultured with CaSiO3 supplementation and BAP-free media had the largest leaf area, which was a response to larger epidermal cells. Additionally, thicker tissues (adaxial epidermis, palisade, and spongy parenchyma) were observed in leaves that grew under CaSiO3. BAP supplementation induced shoots with a ∼18% reduction of the contents of chlorophyll and phenolic compounds. BAP also induced harmful effects on the photosynthetic apparatus, reducing 8% of the fraction of oxygen-evolving complex (OEC centers) and 33% of active reaction centers (RC/CSm). Such results were attenuated when the shoots were co-exposed to CaSiO3. The positive effects of CaSiO3 were confirmed by the ≥ 42% increase in the total performance index (PI(TOTAL)). The addition in the concentration range between 12 and 18 μM CaSiO3 can mitigate the harmful effects of BAP during the in vitro multiplication phase of Q. robur.