THE EFFECTS OF VARIOUS SUBSTANCES ON THE COMPARATIVE GROWTH OF EXCISED TOMATO ROOTS OF CLONES CARRYING DWARF AND NORMAL ALLELES

Lee , Addison E. (U. Texas, Austin.) The effects of various substances on the comparative growth of excised tomato roots of clones carrying dwarf and normal alleles. Amer. Jour. Bot. 46(1) : 16-21. Illus. 1959.—Excised tomato roots carrying the wd gene for dwarfness and its comparable normal allele, wd+, were cultured under various conditions in an effort to provide information as to the physiological differences between the 2 root clones. Two percent is the optimal sucrose concentration for both roots, although wd roots appear to be relatively more tolerant to high sucrose concentration than wd+ roots. The addition of yeast extract, casein hydrolysate, 1, 3-diphenylurea, and a combination of the last 2 in standard medium fail to improve growth of either wd or wd+ roots. The growth of wd roots is favored by the dark while that of wd+ roots is favored by the light. The addition of IAA to the medium fails to stimulate either type. The effects of eosin added to the medium in various concentrations were studied. High concentrations were inhibitory, but the effect of a concentration of 10^-9 g./ml. provided some evidence of an auxin differential between the two clones of roots. The effects of antiauxins were also investigated, but all of those used reduced the growth of both wd and wd+ roots. It was concluded that although there may be some differences in the auxin metabolism between wd and wd+ roots, it is not likely that this is the cause of dwarfism in the wd roots. Kinetin was found to stimulate both wd and wd+ roots in a concentration of 1.0γ/l. but the stimulation was not differential. Gibberellic acid was found to inhibit both wd and wd+ roots in relatively high concentrations. It had little effect on wd roots in relatively low concentrations, but was inhibitory to wd+ roots even in very low concentrations. Thus these substances appear not to be the cause of the dwarf condition of the wd roots.     

AUXIN,CYTOKININ AND GROWTH OF EXCISED ROOTS OF BRYOPHYLLUM CALYCINUM

Excised roots 1 cm long of Bryophyllum calycinum required exogenous auxin (α-naphthaleneacetic acid) for growth in still culture in a medium of sucrose, mineral salts and vitamins. Little or no growth occurred with the addition of cytokinin (6-benzylaminopurine) alone to the basal medium. Best growth was obtained with combinations of 1 μg of auxin and 1 or 2 μg of cytokinin in 50 ml of medium. Larger amounts of the two phytohormones resulted in reduced growth.     

ON THE EFFECTS OF DMSO IN CATION TRANSPORT BY EXCISED BARLEY ROOTS

Dimethyl sulfoxide (DMSO) in concentrations of up to 10% by volume stimulates the uptake of zinc by excised barley roots. In the same concentration it severely depresses uptake of sodium and of rubidium. It does not seem to affect the permeability of the membrane since roots treated with desorption solutions which were 10% in DMSO did not lose more of the preferred ion than did roots desorbed in solutions not containing DMSO. Oxygen utilization (measured in the Warburg respirometer) was reduced when DMSO was present. It is suggested that DMSO is a poisoning agent which interferes with cation transport by attacking some aspect of metabolism and not by influencing the permeability of the membrane.