ISSN:
1432-2048
Keywords:
Prunus
;
Cornus
;
Cold hardiness
;
Supercooling
;
Xylem parenchyma
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Treatment of stem sections of peach (Prunus persica (L.) Batsch) and flowering dogwood (Cornus florida L.) with macerase, an enzyme mixture rich in pectinase, for 24–48 h resulted in a complete flattening of the low-temperature exotherm (LTE) as determined by differential thermal analysis (DTA). Ultrastructural analysis of macerase-treated tissue demonstrated a nearly complete digestion of the pit membrane (black cap and primary cell-wall) of nearly 100% of the xylem-parenchyma cells examined after 48 h of exposure to the enzyme. Additionally, the underlying amorphous layer was partially degraded in up to 57% of the cells examined. The macerase treatment had no visible effect on secondary cell-walls of xylem tissue. In contrast, treatment of stem tissue with cellulysin (mostly cellulase) resulted in a shift of the LTE to warmer temperatures as determined by DTA, and a digestion of only the outermost layer of the pit membrane in nearly 100% of the cells examined, with little or no effect on the underlying layers. Treatment of tissue with 25 mM sodiumphosphate buffer also resulted in a shift of the LTE to warmer temperatures but the shift was not as great as in cellulysin-treated tissue. The shift was associated with a partial degradation of the outermost layer of the pit membrane in dogwood (33–45% of the cells examined) but not in peach (3–7% of the cells). Collectively, the data indicate that pectins may be an integral structural element of the pit membrane and that this portion of the cell-wall, along with the underlying amorphous layer, play a major role in forming a barrier to water movement and growth of ice crystals. This barrier allows xylem parenchyma of some species of woody plants to undergo deep supercooling.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01102426
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