CRYOPHYSIOLOGY OF WOODY PLANT DORMANT BUDS
While there is ample evidence that woody plant dormant bud survival following cryopreservation depends upon inherent capacity for cold hardiness and desiccation tolerance, several additional variables may contribute to success or failure including; sampling time and interval, pre-freezing and cryopreservation protocols. Much less is known about the underlying endogenous physiological/biochemical changes required for successful cryopreservation. Research with species adapted to continental versus coastal sites, low and high altitudes, as well as cultivars bred for cold hardiness have demonstrated that the hardiest were also the most amenable to cryopreservation. The hardiest taxa were also generally the most tolerant of desiccation stress and during acclimation retained more unfreezable water. Perhaps the most underestimated, but nonetheless very critical stage, is acclimation to desiccation, and the subtle changes occurring in twigs as they enter growth cessation at the onset of endodormancy. Woody plant buds entering endodormancy in early autumn tolerated essentially no or very little water loss (Aug., Sept., Oct.), but by Nov. and Dec. as they cold acclimated major endogenous changes occurred that enabled up to 60%, fresh weight (FW) water loss, depending upon the taxa, with no injury. During this interval (window of opportunity), water content in several Malus × domestica apple cultivars could be reduced from (50 to 60% FW; 0.95 g H2O/g dry weight [DW]) to (20% FW; 0.50 g H2O/g DW). Generally, survival in LN was highest when the tissue had 20% or less liquid water at the pre-freezing temperature. The pre-freezing temperature had a greater impact on water loss than the duration at a specific pre-freezing temperature. Endogenous raffinose was highly correlated with the onset, maximum, and decline of cold hardiness in an array of diverse taxonomic species. Marginally cold hardy apple cultivars that did not survive well with conventional dormant bud cryopreservation were treated to tolerate desiccation injury and to survive LN cryopreservation by alginate/sucrose/raffinose imbibition pretreatment. Specific parameters, markers and/or indicators of low-temperature induced freeze-desiccation tolerance, in particular, would be a valuable asset in facilitating development of cryopreservation protocols that may broaden the scope of taxa that could be cryopreserved.
Stushnoff, C. (2014). CRYOPHYSIOLOGY OF WOODY PLANT DORMANT BUDS. Acta Hortic. 1039, 63-72
cryopreservation, cold hardiness, pulse proton NMR, collection window, endogenous oligosaccharides