Reviewing models of auxin canalization in the context of leaf vein pattern formation in Arabidopsis

Abstract

In both plants and animals vein networks play an essential role in transporting nutrients. In plants veins may also provide mechanical support. The mechanism by which vein patterns are formed in a developing leaf remains largely unresolved. According to the canalization hypothesis, a signal inducing vein differentiation is transported in a polar manner and is channeled into narrow strands. Since inhibition of auxin transport affects venation patterns, auxin is likely to be part of the signal involved. However, it is not clear whether the canalization hypothesis, initially formulated over 25 years ago, is compatible with recent experimental data. In this paper we focus on three aspects of this question, and show that: (i) canalization models can account for an acropetal development of the midvein if vein formation is sink-driven; (ii) canalization models are in agreement with venation patterns resulting from inhibited auxin transport and (iii) loops and discontinuous venation patterns can be obtained assuming proper spacing of discrete auxin sources.

Reference

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• Movie S1: Acropetal development of a strand of high flux using the FD model, corresponding to Figure 3. The simulation was carried out for 3000 steps, and the movie records every 100th step (MP4, 960 Kb)


• Movie S2: Loop formation using the FD model, corresponding to Figure 4b. The simulation was carried out for 8000 steps, when the equilibrium was reached. (Note Figure 4b shows an earlier stage of loop formation, corresponding to step 4000, when leaf growth has stopped.) The simulation shows that, at the equilibrium, carriers along the strands operate at their maximum carrying capacity, and the additional auxin flux from the loops causes an increase in the midvein width from the points where the loops join the midvein toward the base. The movie shows every 100th simulation step (MP4, 2.5 Mb)


• Movie S3: Formation of discontinuous strands using the FD model, corresponding to Figure 6b,c. The strand linking the source on the left to the sink develops both from source to sink and from sink to source, therefore the strand is initially discontinuous. The simulation was carried out for 4000 steps, and the movie records every 100th step (MP4, 1.3 Mb)