EFFECT OF TEMPERATURE ON THE STARCH CONTENT OF POTATO CALLUS-TISSUE

Starch content was determined in Lemhi Russet callus grown on MS medium for 2 and 4 weeks at 25, 15, and 5-degrees-C with 50-mu-M 2,4-D or 10-mu-M picloram as the only plant growth regulator. A treatment of 5-degrees-C for 4 weeks followed by 25-degrees-C for 2 and 4 weeks was included to simulate reconditioning. Callus starch content ranged from 0.01 to 0.08% on a wet weight basis and 0.5 to 4.0% on a dry weight basis. Starch content was highest after 2 weeks at 25 and 15-degrees-C and decreased with time in a similar manner at both 25 and 15-degrees-C. Starch content decreased at 5-degrees-C, then increased significantly during simulated reconditioning at 25-degrees-C. Starch content was higher in callus grown with 50-mu-M 2,4-D than in callus grown with 10-mu-M picloram. After staining the callus with I2-KI solution, starch granule formation was observed in the callus grown with 50-mu-M 2,4-D, while little granule formation was observed in the callus grown with 10-mu-M picloram.