But why is the growth of axillary buds stimulated by cutting off the terminal (or apical) bud?
The most common explanation of this is the long-known, and somewhat confounding, phenomenon called “apical dominance”.
In the previous post regarding the biology of pruning, “new” scientific evidence (well, it was new in 2010) was presented about how apical dominance works on the cellular level.
Fast forward to 2015….
Currently there are new reports of scientific experiments that may significantly alter the way we explain the cellular mechanisms of apical dominance.
In 2014, a paper published in PNAS (see Ref. 1 below) claimed that sugars may indeed be more important than plant hormones in stimulating the growth of axillary buds in plants after removal of the apical buds.
Basically, here’s the story: “It is commonly accepted that the plant hormone auxin mediates apical dominance. However, we have discovered that apical dominance strongly correlates with sugar availability and not apically supplied auxin. We have revealed that apical dominance is predominantly controlled by the shoot tip’s intense demand for sugars, which limits sugar availability to the axillary buds. These findings overturn a long-standing hypothesis on apical dominance and encourage us to reevaluate the relationship between hormones and sugars in this and other aspects of plant development.” (from Ref. 1 below)
Increasingly, over the past few years, sugars – sucrose, and in particular trehalose 6-phosphate (T6P) – have been implicated in the regulation of plant growth and development (e.g., see Ref. 2 below), especially in the case of apical dominance.
But apical dominance is a complex process, and it’s likely that both sugars and plant hormones are involved in the story (see Ref. 3 below).
1. Mason, M. M., et al. (2014) “Sugar demand, not auxin, is the initial regulator of apical dominance.” Proc. Natl. Acad. Sci. (USA), Vol. 111, pp. 6092–6097. (Full Text)
2. Van den Ende, W. (2014) “Sugars take a central position in plant growth, development and, stress responses. A focus on apical dominance.” Frontiers in Plant Science, Vol. 5, p. 313.(Full Text)
3. Rameau, C., et al. (2015) “Multiple pathways regulate shoot branching.” Frontiers in Plant Science, p. 741 (Full Text)
For More Information: Here is a 40-minute YouTube video of a seminar about Ref. 1:
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