The use of plant stress biomarkers in assessing the effects of desiccation in zygotic embryos from recalcitrant seeds: challenges and considerations

Abstract

Zygotic embryos from recalcitrant seeds are sensitive to desiccation. In spite of their sensitivity, rapid partial dehydration is necessary for their successful cryopreservation. However, dehydration to water contents (WCs) that preclude lethal ice crystal formation during cooling and rewarming generally leads to desiccation damage. This study investigated the effects of rapid dehydration on selected stress biomarkers (electrolyte leakage, respiratory competence, rate of protein synthesis, superoxide production, lipid peroxidation, antioxidant activity and degree of cellular vacuolation) in zygotic embryos of four recalcitrant-seeded species. Most biomarkers indicated differences in the levels of stress/damage incurred by embryos dried to WCs < and >0.4 g·g(-1) , within species; however, these changes were often unrelated to viability and percentage water loss when data for the four species were pooled for regression analyses. Dehydration-induced electrolyte leakage was, however, positively related with percentage water loss, while biomarkers of cellular vacuolation were positively related with both percentage water loss and viability. This suggests that electrolyte leakage and degree of cellular vacuolation can be used to quantify dehydration-induced stress/damage. Biomarkers such as superoxide production, whilst useful in establishing the nature of the dehydration stress incurred may not be able to distinguish the effects of different WCs/drying times. Irrespective of which biomarker is used, the data suggest that understanding differences in desiccation sensitivity across recalcitrant-seeded species will remain a challenge unless these biomarkers are related to a generic desiccation stress index that integrates the effects of percentage water loss and drying time.

Viability of embryonic axes of Araucaria angustifolia after freezing using two cryopreservation methods

“…One of the most commonly used techniques for species with recalcitrant seeds has been the encapsulation of embryos after pre-culture in a solution with high concentration of sucrose, which dehydrates the plant material and removes most or all of the freezable water. Sucrose, when it infiltrates into plant tissues, helps to maintain viability during dehydration and freezing by stabilizing the cellular membranes (Sershen et al, 2016;Matsumoto, 2017). Moreover, by replacing the water content, sucrose maintains phospholipid membranes in the liquid crystalline phase and promotes the vitrification of the cytoplasm (Bandupriya et al, 2007).…”

“…Cryopreservation, which consists of freezing plant tissue to a temperature of -196 °C, is the most suitable method for the conservation of recalcitrant seeds (Pammenter & Berjak, 2014) and it is the ideal method for preserving germplasm as it requires minimal space and little maintenance (Pammenter & Berjak, 2014;Kwaśniewska et al, 2017). At low temperatures, the metabolism of the cells is reduced, deterioration of the plant material does not occur, and after thawing, metabolic activities return to normal (Bandupriya et al, 2007;Tahtamouni et al, 2015;Sershen et al, 2016), maintaining their characteristics during cryopreservation (Shibli et al, 2016;Shahab et al, 2017).…”

Dehydration Sensitivity at the Early Seedling Establishment Stages of the European Beech (Fagus sylvatica L.)

“…Moreover, ROS induced lipid peroxidation impacts membrane integrity and results in cellular leakage [37]. Thus, electrolyte leakage, as one of the plant stress biomarkers used to quantify dehydration-induced damage [38] and decline in viability [39,40], was applied in this study. We focused on the characterization of the sensitivity of developing beech seedlings to dehydration to improve the understanding of natural regeneration with implications for forestry.…”

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“…Berjak et al, 2011;Normah et al, 2011;Wesley-Smith et al, 2014). Sershen et al (2016), consider that dehydration does not necessarily affect the viability of the explants and that they are the processes of cooling and subsequent thawing, which leads to losses of viability (Sershen et al, 2012). This may explain why the recovery of seedlings after cryopreservation of embryos and embryonic axes that survive without anomalies to partial dehydration is very low, between 0-30% (Ballesteros et al, 2014) and / or with a high incidence of abnormal seedlings, i.e.…”