Shoot-root interaction effects on nitrate reductase and glutamine synthetase activities in rose (Rosa x hybrida cvs Ilseta and Mercedes) graftlingss

Flower formation in greenhouse roses (Rosa x hybrida) is generally promoted by grafting on various rootstocks rather than propagating ungrafted plants from cuttings. The number of flowers per plant in roses is also positively correlated with the nitrogen content in the nutrient solutions as well as by ammonium ion proportion of the total nitrogen. It could be, therefore, that the differences among the effects of various root systems on flower formation in rose plants are associated with differences in assimilation of nitrogen, in either nitrate or ammonium-forms or both. This assumption was examined by measurements of the nitrate content as well as of the nitrate reductase (NR) (E.C. 1.6.6.1) and glutamine synthetase (GS) (E.C. 6.3.1.2) activities in roots and leaves of 6-week-old plants propagated from cuttings (own-root plants) or graftlings, i.e., concomitantly grafted and rooted roses cvs. Mercedes, Ilseta or Rosa indica major, used as understocks. The data obtained showed that the nitrate contents in the roots of cuttings were higher than those in the leaves, whereas that in the roots of R. indica was higher than those in roots of the two cultivars. The content of NO3- in roots and leaves of the graftlings was affected by the grafting procedure and was in good agreement with the nitrate reductase activity in plant organs. The activity of nitrate reductase in the leaves of cuttings was higher than in their roots, whereas in graftlings, its activity was promoted in the roots and inhibited in the leaves, in all scion-root combinations. Glutamine synthetase activity in roots and leaves of either cuttings or graftlings was 4-5 orders of magnitude higher than NR activity. Similar to NR activity GS activity in the leaves of own-root plants was higher than that in their roots. However, unlike the NR activity, GS activity in roots and leaves of the graftlings was not markedly altered following the grafting procedure.