Effects of prohexadione (BX‐112) and gibberellins on shoot growth in seedlings of Salix pentandra

Abstract

Effects of gibberellins A1, A4/7, A9, A19 and A20 and growth retardants were studied on shoot elongation in seedlings of Salix pentandra L. The growth‐retarding effects of CCC and ancymidol were antagonized by all the gibberellins tested. The novel plant growth regulator prohexadione (free acid of BX‐112), which is suggested to block 3β‐hydroxylation of gibberellins, effectively prevented shoot elongation in seedlings grown under long photoperiod. Initiation of new leaves was only slightly reduced. GA1, but not GA19 and GA20, was active in overcoming the inhibition of stem elongation of seedlings, treated with prohexadione, GA19, GA20 and GA1 are native in S. pentandra, and the results are compatible with the hypothesis that GA1 is active per se in shoot elongation, and that the effect of GA19 and GA20 is dependent on their conversion to GA1.A mixture of GA4 and GA7 was as active as GA1 in promoting shoot elongation in seedlings treated with prohexadione, while GA9 showed slight activity only when applied at high doses.