Auxin promotes root formation; cytokinin promotes shoot formation and division. Their balance coordinates root-shoot growth and tissue culture in IB Biology HL C3.1.22.
Auxin can be used to promote the development of roots from stem and leafy cuttings in some plants. In a study into the distribution of auxin in the development of these roots, scientists measured the amount of auxin in different leaves of a shoot tip of Petunia hybrida.
The figure indicates the numbering of leaves on the shoot, from L1 as the youngest and smallest to L6 as the largest and oldest leaf. The developmental stage of L5 and L6 was very similar, so L5 was not analysed. The stem base is the lowest part of the cutting where roots may form.
The graph shows the auxin concentration in the different leaves.
Based on all the data presented and your knowledge of auxin, discuss the pattern of auxin production and distribution in the leaves and the possible relationship to root formation in leafy cuttings of Petunia hybrida.