Endogenous gibberellins (GAs) were extracted from safflower (Carthamus tinctorius L .) stems and detected by capillary gas chromatography-mass spectrometry from which GA,, GA 3 , GA ' ,, GA,,, GA,,, and probably, GA" were detected . The detection of these GAs suggests that the early 13-OH biosynthetic pathway is prevalent in safflower shoots . Deuterated GAs were used as internal standards and GA concentrations were determined in stems harvested at weekly intervals . GA I and GA 19 levels per stem increased but concentrations per gram dry weight decreased over time . GA 20 was only detected in young stem tissue .
Gibberellic acid (GA 3 ) was also applied in field trials and both GA 3 and the GA biosynthetic inhibitor, paclobutrazol, were applied in growth chamber tests . GA 3 increased epidermal cell size, internode length, and increased internode cell number causing stem elongation . Conversely, paclobutrazol reduced stem height, internode and cell size, cell number and overall shoot weight . In field tests, GA 3 increased total stem weight, but decreased leaf weight, flower bud number and seed yield . Thus, GA 3 promoted vegetative growth at the expense of reproductive commitment . These studies collectively indicate a promotory role of GAs in the control of shoot growth in safflower, and are generally consistent with gibberellin studies of related crop plants.