Abstract:
Alternating temperature (22°C / -1°C) pretreatments were effective for
increasing cold hardiness and recovery of cryopreserved meristems. Combining low
temperature pretreatment with abscisic acid (ABA) or sucrose treatments reduced the
time required for optimal cold hardiness of meristems. Desiccation tolerance was
directly correlated with increased cold hardiness and recovery of cryopreserved
meristems.
In v/fro-grown pear (Pyrus L.) plantlets were cold acclimated for up to 16 weeks,
then shoot tips were either cryopreserved by slow freezing or tested for cold hardiness.
Cold acclimation (CA) consisted of alternating temperatures or constant low temperature.
Both alternating and constant low temperature CA significantly improved the cold
hardiness and cryopreservation regrowth of pear meristems compared with non-acclimated
controls. Alternating temperature treatment was significantly better than
constant low temperature treatment. Photoperiod and the length of thermoperiod had
little or no effect on cold hardiness and cryopreservation regrowth. Some genotypes required only one week alternating temperature treatment for high regrowth but others
needed more than 10 weeks. Pretreatment of shoots with ABA slightly increased
cryopreserved meristem regrowth and shoot cold hardiness. However, ABA
significantly shortened the CA requirement for high cryopreservation regrowth. The
optimal pretreatment for recovery of cryopreserved meristems was 3-wk on medium
with 50 μM ABA followed by 2-wk CA.
Alternating temperature pretreatments were necessary for successful
cryopreservation of Rubus meristems. Shoot tip survival of cryopreserved R parvifolius
L. increased greatly after 3-wk CA while R caesius L. required 6 or more weeks.
Histological studies showed that all cryopreserved R parvifolius shoot tips continued to
grow and regenerated directly from the meristematic domes.
Alternating-temperature pretreatments significantly increased cryopreserved
meristem regrowth of five genotypes each of Lolium and Zoysia grasses, and also
significantly increased the dehydration tolerance of both grasses. Lolium genotypes
responded to slow freezing and encapsulation-dehydration with 60-100% regrowth,
but produced less than 15% regrowth following vitrification. Zoysia responded with
greater than 60% regrowth following encapsulation-dehydration when dehydrated to
less than 22% water, but did not respond well to other methods.
