Date posted: 01 October 2013
In our last blog, Plant Puberty, we looked at the early phase of stem elongation (stage 30-39). We can now report that this phase progressed well, with the stems extending nicely. It is easy to take plant growth for granted, as it just seems to happen. What is surprising though, is how the elongation of the plant occurs in such a precise, regimented manner, for example:
- each tiller (stem) is made up of around 14 nodes
- as the tiller begins to grow the space inbetween each node (the internode) stretches and grows (the nodes start only 1mm apart then stretch out)
- each internode only begins to elongate when the leaf associated with it has reached its full size
- once that internode is half its final length the one above is triggered to grow. This pattern continues until all internodes have extended.
During stem elongation the plant has a huge demand for nutrients and moisture. These are required to not only fuel the growth of the plant, but to support the continued development of the barley head and its reproductive structures. If nutrient and fertiliser needs are not met, the plant will abort (kill off!) some of its tillers to try and support successful growth in its strongest tillers. The nutrients from the dead (aborted) tillers are recycled and used to keep the remaining tillers alive.
While all this is occurring, the head is also rising up along the stem in “the boot” (stage 40-49). The boot is actually the tightly coiled flag leaf (the top leaf). This nifty design helps protect the reproductive organs until they have reached maturity.
As the head moves up the stem the flag leaf begins to swell, indicating that the plant is almost ready to expose its head. Over the coming weeks, the boot will open up, revealing the head and we will be ready for flowering.
The ol’ barley plant is a pretty clever sort. Did you know that the plant actually tries to prepare itself for stem elongation by maximising its ability to make its own food. The plant sets all of its newly formed leaves up on an angle which ensures it will capture the maximum amount of sunlight, to drive maximum photosynthesis. Photosynthesis at this stage is of huge importance as the energy made is directed to the grains and is used to help the grains grow and fill. Clever huh!
Visit the Barley crop at the Adelaide Botanic Gardens and get up close and personal with some of the plants to see what stage each of them are at. Is there a bulging boot on the main stem? Can you see the hairy awns sticking out of the flag leaf? Maybe you can see the grain itself?
References: Barley Growth and Development (2010) NSW government Industry and Investment