Low-Temperature Tolerance and Acclimation of Opuntia Spp. After Injecting Glucose or Methylglucose

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Abstract
Cellular tolerances to subzero temperatures, as judged by the accumulation of a vital stain, were compared between Opuntia ficus-indica, a widely cultivated but low-temperature-sensitive cactus, and the widely ranging, winter-hardy Opuntia humifusa. Lowering the day/night temperatures from 30⚬/20⚬C to 10⚬/0⚬C increased tolerance of lower temperatures (acclimation) and generally increased the cladode (stem segment) concentrations of the putative cryoprotectants fructose, glucose, sucrose, mannitol, sorbitol, total amino acids, and proline. Compared to reducing the day/night air temperatures by 20⚬C, injecting 400 mM glucose into the cladodes induced about 70% greater low-temperature tolerance (5⚬C for O. ficus-indica and 19⚬C for O. humifusa). The glucose injections caused an even greater percentage increase in most of the putative cryoprotectants but reduced the concentration of total amino acids and proline. After the reduction of temperatures or glucose injections, increases in total solutes were greater in the cladodes for the species exhibiting greater low-temperature tolerance and acclimation, O. humifusa. However, the relative changes in the concentrations of specific sugars and polyhydroxy alcohols were inconsistent with the relative changes in low-temperature tolerance caused by glucose injections compared with lowering the air temperatures for both species. Moreover, the injection of 400 mM of the nonmetabolizable 3-O-methylglucose into plants at 30⚬/20⚬C caused an increase in low-temperature tolerance similar to that caused by reducing the air temperatures by 20⚬C but without a concomitant increase in the concentrations of six putative cryoprotectants. The relative ability of opuntias to tolerate subzero temperatures apparently depends on the tissue water, not individually on any of the six putative cryoprotectants examined.

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