Changes in carbohydrates and freezing tolerance during cold acclimation ofred raspberry cultivars grown in vitro and in vivo

Changes in LT50 and carbohydrate levels in response to cold acclimation wer e monitored in vitro and in vivo in red raspberry (Rubus idaeus L,) cultiva rs with different levels of cold hardiness, Entire micropropagated plantlet s or shoot tips from 3 cultivars were harvested before, during and after co ld acclimation, Cane samples from container-grown plants of 4 cultivars wer e harvested before and during cold acclimation and deacclimation, Samples w ere evaluated for cold hardiness (LT50) by controlled freezing, then analyz ed for carbohydrates, including starch, sucrose, glucose, fructose and raff inose, Hardiness of cold-acclimated 'Muskoka' and 'Festival' was superior t o that of 'Titan' or 'Willamette). In vitro plantlets had higher levels of soluble carbohydrates on a dry weight basis and higher ratios of sucrose:(g lucose + fructose) than the container-grown plants. Total soluble carbohydr ates, primarily sucrose, accumulated during cold acclimation in both plantl ets (33-56% relative increase) and plants (143-191% relative increase). Suc rose increased 124-165% in plantlets and 253-582% in container-grown plants during acclimation and declined rapidly to the level of control plants dur ing deacclimation, Glucose and fructose also accumulated, but to a lesser e xtent than sucrose, Raffinose concentrations were very low, but increased s ignificantly during cold acclimation. In vitro, genotype hardiness was rela ted to the high concentrations of total soluble carbohydrates, sucrose and raffinose, In vivo, hardier genotypes had lower concentrations of starch th an the less hardy genotypes, These results demonstrated the importance of s oluble carbohydrates, especially sucrose, in cold hardening of red raspberr y and that the in vitro conditions or controlled acclimation conditions do not necessarily reflect the phenomena observed in vivo.