THE EFFECT OF ONION JUICE ON THE GROWTH RESPONSE TO AUXIN

Abstract

The reported effect of onion juice in enhancing the physiol. activity of auxins on plants was studied using the curvature of slit pea stems and the straight growth of pea stem sections. Onion juice increased the growth-promoting activity both of indoleacetic acid and of 2,4-D in these tests. The increase of curvature was approx. proportional to the log. of the concn. of auxin used, and might be as much as 180[degree]; the increase of straight growth was 10-15% greater than that in auxin alone. The effect is not due to an auxin in the onion juice, and resides in the ether-insoluble fraction of the juice. Analysis of the juice demonstrated that the 2.5% dilution used contained 0.14% reducing sugar and about 2x10-4[image] soluble phosphate. Sugar and phosphate in these concns. were found to have nearly the same effect on the pea test as onion juice. Sucrose was as effective as glucose and the optimum potassium phosphate concn. was 4x10-3[image]. Instead of potassium phosphate, KC1 could be substituted with equal effect. KC1 alone could duplicate more than half the effect of onion juice, and when combined with 0.3% sugar was fully as effective as the juice. Mannitol was ineffective as a substitute for sugars. It is concluded that the action of onion juice in these tests was due to its content of sugar, phosphate and K ions. Appln. to herbicide expts. is suggested.