Effects of temperature and desiccation on ex situ conservation of nongreen fern spores

Abstract

Spore longevity is comparable to orthodox seed longevity under ambient storage conditions, with wide variation among species and shelflife extended by drying or cooling. However, faster aging during freezer storage may indicate a similar syndrome of damage experienced by seeds categorized as "intermediate". The damage is avoided by storage at -80°C or liquid nitrogen temperatures, making cryoconservation an effective and broadly applicable tool to extend fern spore longevity. The study demonstrates that spore banks are a feasible approach for ex situ conservation of this important plant group.

The effect of moisture content and temperature on spore aging in Osmunda regalis

“…The desiccation level of spores (from 19.4 to 4.8 % MC) was also modified by equilibrating at different RH levels (from 96 to 10 %) using saturated salt solutions for a week (Li and Shi 2015). Their studies and ours demonstrated that an internal relative humidity of green spores, similar to that of non-green (Ballesteros and Walters 2007b;Ballesteros et al 2012), can be easily manipulated by equilibration at different relative humidity 2) after 10 days post-sowing in blue-violet light, d spore after the first atypical division (arrow), e abnormally growing 2-3-celled prothalli possessing few chloroplasts, f decayed, 5-celled prothallus at 10 days post-sowing, g mass production of 2-3-celled prothalli from spores thawed after 6 years storage under liquid nitrogen; viewed after 28 h post-sowing, h a normally developed 3-celled prothallus rich in chloroplasts; viewed after 28 h; mixture of white and blue-violet light, i a 2-month-old cordate gametophyte derived from a cryo-stored spore. Ac apical cytoplasmic cap, Pc Protonemal cell, R rhizoid, Rc rhizoidal cell, arrow cell wall values.…”

Photo-oxidation modulates green fern spore longevity during dry storage

“…1-3 mg divided across the four dishes) and were placed at a constant temperature of 20 ± 2 °C under constant dark conditions or under a 16-h photoperiod at 200 µmol m −2 s −1 at 20 ± 2 °C. Germination percentage after 15 and 30 days of culture was used to quantify viability of green and non-green spores, respectively (after Ballesteros et al , 2012Ballesteros et al , 2017. Germination was calculated for each plate by counting the number of germinated spores that were observed out of 100 spores selected at random, at ×40 magnification under a light microscope.…”

“…Spores of both species were germinated on the mineral culture medium for fern spores described by Dyer (1979), enriched with 100 U mL −1 of the fungicide Nystatin (Sigma-Aldrich, MO, USA), and solidified with 1.1% agar (e.g. Ballesteros et al 2012Ballesteros et al , 2017. Four Petri dishes were sowed with the subsample of spores (i.e.…”

“…Dehisced green and non-green spores were collected after the fronds were left in place for 5-7 (T. barbara)/7-10 (C. dentata) days. The spores were then sieved to remove residual particles, transferred into vials, and stored at − 80 °C to preserve their original viability (Ballesteros et al , 2012 until the experiments were initiated (about 4 months after spore collection). Spores were thawed from − 80 °C by placing the vials in a 40 °C water bath for 5 min.…”

“…When dried to ambient conditions (usually at 20-25 °C and relative humidity between 30 and 60%) green and non-green spores form glasses but under such conditions the former generally age faster (Lloyd and Klekowski 1970;Hoekstra 2005;Shi 2014, 2015;Ballesteros et al 2017). The unicellular nature of fern spores makes them a very convenient model to study desiccation tolerance and longevity in dry plant germplasm, as the complications of data interpretation related to tissue complexity are avoided (Ballesteros et al 2012(Ballesteros et al , 2017. However, little is known about the mechanisms that modulate longevity in fern spores and whether viability loss in green and non-green spores are governed by the same mechanisms (Ballesteros 2010).…”