Correlative Studies on Plant Growth and Metabolism. I. Changes in Protein and Soluble Nitrogen Accompanying Gibberellin-Induced Growth in Lettuce Seedlings

The remiiarkable inicrease in longitudinal growth of plants by applied gibberellins is well known. Information on accomlpanyvinig metabolic changes is ucl mllore limited ancd ofteln conicerned with relatively late stages of the growth response so that its hearing on the prinlarv chaniges cauised by the gibherellin is tuncertaini. The present paper deals vith clhaniges in protein anid soluible nitrogen in gibbereilinitreated letttuce seedlings. MAetabolism of the nitrogenous comipotnnids was chosen hecause increase in growth is generallv correlated with protein synthesis. This has recently been shown for growth induced by auxin (5,8) and kinins (9). No clear-cut relationship has vet been reported wvith gibberellin-induced grow th, although dislocation ill nitrogen metabolism has been inferred by the reported loss of nicotine from-ii gibberellin treated tobacco plants (1,10). The fact that gibberellin effects are imiore marked in intact plants thani in isolated sections. required that these chaniges be stud(ie(d in intact system. Lettuce seedlings were chosenl as material because the response of many epigeic seedlings to gibberellin is quite rapidl anld because it is often limited to certain organs of the seedlinlg wlhile the growth of the other parts is iuniaffecte(l. This permits one to establish correlationis between the organ most influenced by gibberellin anld the miietabolic effects of the latter on other parts wvhichl are not visibly affected. In lettulce seedlings, the gibberelliii respoinse occturs miiostly in the hvpocotlxI where as the cotyledonis and(i roots exhibit n1o imiarked changes.