Confirmation of the role of auxin and calcium in the late phases of adventitious root formation

Poplar shoots raised in vitro were induced to root by incubation on an auxi n (NAA) containing medium for 7 h. After 13 days on an auxin-free medium, 9 7% of the treated shoots had rooted. The introduction of known antiauxins ( PCIB, PBA, POAA) into the rooting expression auxin-free medium, after the 7 -h induction by NAA, completely (PCIB and PEA) or severely (POAA) inhibited rooting. The exclusion of calcium from the expression auxin free medium re duced the percentage of rooting by about 42%. The inhibition was still high er in the presence of EGTA, a calcium chelator. Lanthanum chloride, a calci um channel blocker, also completely inhibited rooting, when incorporated in to the auxin free medium, with or without calcium. These results support pr evious hypotheses about the implication of both endogenous auxin and calciu m in the late phases of the adventitious rooting process.