Shoot growth and histological response of dwarf sweetgum to gibberellin

Abstract

SummaryIn addition to supplying valuable cultivars for ornamental uses, dwarf mutant tree forms may present opportunities for studying the genetic control of physiological factors affecting shoot growth. Few studies have addressed the histogenetic role of GA during shoot development, and its effect on cell pattern in mature internodes. Hence, the growth responses of two genetic dwarf sweetgum trees (Liquidambar styraiflua L. cv. Gumball and an unnamed wild dwarf tree) were examined following foliar application of gibberellic acid (GA) to young preformed leaves. Both were GA-responsive mutants and exhibited marked increases in shoot growth following treatment. GA was effective in 1) stimulating subapical meristem activity in preformed internodes which were initiated the previous season, 2) inducing cell divisions in the apical meristem proper to promote the neoformation of leaves and sylleptic lateral branches, and 3) stimulating subapical mitotic activity in neoformed internodes. Histological evaluations of cell patterns in the pith of mature internodes of GA-treated and control shoots showed that enhanced cell division accounted for 89% of the increase in final internode length; final cell length accounted for only 11% of the increase.