THE BEHAVIOR OF SHOOT APICES OF LOLIUM-TEMULENTUM IN-VITRO AS THE BASIS OF AN ASSAY SYSTEM FOR FLORIGENIC EXTRACTS

Previous experiments have shown that shoot apices excised from plants of L. temulentum that had been exposed to one long day (LD) could form inflorescence primordia in vitro if gibberellic acid (GA3) was presen t in the medium whereas apices from plants in short days (SD) could no t. We show here that apices from older plants grown under high irradia nce can undergo inflorescence differentiation in vitro after one LD ev en in the absence of GA3, as can apices from plants in SD if GA3 is pr esent in the medium. For apices excised from both SD and one LD plants , the order of effectiveness of gibberellins for inflorescence inducti on was 2,2-dimethyl GA4>GA5>GA3>GA1, in agreement with their ranking f or effectiveness on intact plants. Application of GA3 to leaves before apex excision can substitute for GA3 in the growth medium. The presen ce of GA3 in the medium is not required until 4-6 days after excision from plants given one LD, and appears to be necessary for differentiat ion beyond the spikelet primordia stage. Three hypotheses concerning t he relation between GAs and the LD stimulus to flowering, as affected by plant age, are considered.