LOW-TEMPERATURE TOLERANCE AND ACCLIMATION OF OPUNTIA SPP AFTER INJECTING GLUCOSE OR METHYLGLUCOSE

Cellular tolerances to subzero temperatures, as judged by the accumula tion of a vital stain, were compared between Opuntia ficus-indica, a w idely cultivated but low-temperature-sensitive cactus, and the widely ranging, winter-hardy Opuntia humifusa. Lowering the day/night tempera tures from 30 degrees 20 degrees C to 10 degrees/0 degrees C increased tolerance of lower temperatures (acclimation) and generally increased the cladode (stem segment) concentrations of the putative cryoprotect ants fructose, glucose, sucrose, mannitol, sorbitol, total amino acids , and proline. Compared to reducing the day/night air temperatures by 20 degrees C, injecting 400 mM glucose into the cladodes induced about 70% greater low-temperature tolerance (5 degrees C for O. ficus-indic a and 19 degrees C for 0. humifusa). The glucose injections caused an even greater percentage increase in most of the putative cryoprotectan ts but reduced the concentration of total amino acids and proline. Aft er the reduction of temperatures or glucose injections, increases in t otal solutes were greater in the cladodes for the species exhibiting g reater low-temperature tolerance and acclimation, O. humifusa. However , the relative changes in the concentrations of specific sugars and po lyhydroxy alcohols were inconsistent with the relative changes in low- temperature tolerance caused by glucose injections compared with lower ing the air temperatures for both species. Moreover, the injection of 400 mM of the nonmetabolizable 3-O-methylglucose into plants at 30 deg rees/20 degrees C caused an increase in low-temperature tolerance simi lar to that caused by reducing the air temperatures by 20 degrees C bu t 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.