More whorled-thoughts:
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Phyllotaxy describes the geometric pattern of leaves and flowers, and has intrigued botanists and mathematicians for centuries1,2. How these patterns are initiated is poorly understood, and this is partly due to the paucity of mutants3. Signalling by the plant hormone auxin appears to determine the site of leaf initiation [figured that out already :)]; however, this observation does not explain how distinct patterns of phyllotaxy are initiated4.
abphyl1(abph1) mutants of maize initiate leaves in a decussate pattern (that is, paired at 180°), in contrast to the alternating or distichous phyllotaxy observed in wild-type maize and other grasses5. Here we show that ABPH1 is homologous to two-component response regulators and is induced by the plant hormone cytokinin. ABPH1 is expressed in the embryonic shoot apical meristem, and its spatial expression pattern changes rapidly with cytokinin treatment. We propose that ABPH1 controls phyllotactic patterning by negatively regulating the cytokinin-induced expansion of the shoot meristem, thereby limiting the space available for primordium initiation at the apex.
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http://www.nature.com/nature/journal/v430/n7003/full/nature02778.html
Another keyword in there is "regulators", phyllotaxy / leaf arrangement as well as fasciation mutation in flowers etc is controlled by homeotic /regulator genes.
"Regulated initiation of leaves or flowers from the shoot meristem gives rise to the familiar geometric patterns observed throughout the plant kingdom. The mechanism by which these patterns, termed phyllotaxies, are generated, remains unclear."
"Studies of aberrant phyllotaxy1 Mutants of Maize Indicate Complex Interactions between Auxin and Cytokinin Signaling in the Shoot Apical Meristem1[W][OA
One of the most fascinating aspects of plant morphology is the regular geometric arrangement of leaves and flowers, called phyllotaxy. The shoot apical meristem (SAM) determines these patterns, which vary depending on species and developmental stage. Auxin acts as an instructive signal in leaf initiation, and its transport has been implicated in phyllotaxy regulation in Arabidopsis (Arabidopsis thaliana). Altered phyllotactic patterns are observed in a maize (Zea mays) mutant, aberrant phyllotaxy1 (abph1, also known as abphyl1), and ABPH1 encodes a cytokinin-inducible type A response regulator, suggesting that cytokinin signals are also involved in the mechanism by which phyllotactic patterns are established.
Therefore, we investigated the interaction between auxin and cytokinin signaling in phyllotaxy. [....] These studies highlight a complex interaction between auxin and cytokinin signaling in the specification of phyllotactic patterns and suggest an alternative model for the generation of altered phyllotactic patterns in abph1 mutants. We propose that reduced auxin levels and PIN1 expression in abph1 mutant SAMs delay leaf initiation, contributing to the enlarged SAM and altered phyllotaxy of these mutants."
abph1 is a mutant that has opposite phyllotaxy like mj instead of the alternate it should have. They suggest it is reduced auxin levels that result in a delay of the leaf initiation which in turn 'contributes' to the change in phyllotaxy. At the same time they highlight a "complex" interaction between auxins and cytokinin signaling as a factor.
If a reduced auxin level can delay leaf initiation it makes sense a higher auxin concentration speed it up.... Either way, removing apical bud affects the auxin concentrations and affects the "interaction between auxins and cytokinin signaling" as well.
As interesting as it is, I don't necessarily need to know why it generates a certain patterns opposed to another, it's the inheritance I care about most.
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IAA (auxin) regulates an amazingly diverse array of processes in plant growth and development ranging from embryo patterning to growth responses to tropic stimuli (Woodward and Bartel 2005). Auxin response involves a large-scale reprogramming of gene expression affecting hundreds of auxin-regulated genes."
There are "auxin-regulated genes", let's assume (just) one of those or a linked combination of those are for phyllotaxy. There are also regulator genes, that is genes that regulate the production of hormones such as auxin ad cytokinin. So auxin-regulated genes, and auxin regulator genes... perhaps I need a specific 'version' of both for it to whorl. The auxin regulator genes that cause the irregularity of the auxin production and the auxin-regulated genes that cause whorled phyllotaxy as a results.
That complicates matters obviously, but, cytokinin could play a large role here, or more specifically the ratio / concentrations of cytokinin vs auxins. So there are also cytokinin regulated genes... and genes that regulate cytokinin production.
I bet a real botanist and/or a geneticist would fall out of his chair laughing reading some of this thread but I think I'm on to something :joyful:
