Posted by: HortAlaska | January 20, 2018

Flower Bud Initiation in Herbaceous Peonies

The following paper is an exhaustive anatomical look at flower bud initiation in herbaceous peony identified as Chinese Peony. Flower buds of cultivar, ‘Dafugui’ were sampled exhaustively, fixed in an alcohol solution (FAA), then embedded in paraffin. The blocks of paraffin were then sliced into very thin sections, stained with different cellular dyes, and examined beneath the microscope. This process, by itself, deserves applause for the sheer patience it requires of the authors because the photos you see do not just happen by chance. The researchers have to sample hundreds of buds and examine thousands of thin sections before they find the exact stages of flower bud development they seek. I know a bit about this because I conducted a similar study of flower buds of lingonberry, Vaccinium vitis-idaea, for my PhD thesis years ago. It tested every iota of my patience—seeking the very early stages of flower bud initiation that are not visible with the naked eye. In regards to lingonberry, the vegetative buds showed the transition to flower buds way back in June (Fairbanks, AK) long before you could actually tell there was a flower bud present.

There are other methods of discovering this transition from vegetative buds to flower buds, but they all require harvesting a lot of buds and guessing when the flowering structures will show up. For most flowers, lingonberries and peonies included, the vegetative bud starts out as a dome shape similar to the eraser on a pencil. A trigger or triggers– could be photoperiod, age of the plant, nutrition, genetics, temperature, etc.- induces that dome to flatten out into a series of rings that give rise to a ring of sepals, another inner ring (or more) of petals,  then a ring(s) of stamens and finally the pistils. From the side (longitudinal section), they look like bumps.  In peonies, it is even more interesting because a lot of the stamens sometimes transition into petals, thus forming petaloid stamens.

The timing of these events is interesting both from the botanical standpoint of which factors might be triggering the development of flower buds but also the environmental factors that might be involved in interfering with this transition. For instance, freezing weather in autumn might stop the process of flower bud initiation and development. Maybe poor root growth and lack of nutrients prevents the transition from happening or it happens partway so the flower bud aborts.

In these Chinese flowers growing at the Heilongjiang Forest Botanical Garden, flower bud initiation begins in early September. The sequence is like this:

Early September – Flower bud initiation

Early to late September –Flower bud bract differentiation

Late September to mid October – Sepal formation

Mid October – late Nov – petal formation

Mid November – Early March – male stamen formation

April – female pistil formation

Pollen development, maturation of the anthers occurs in late winter and the female ovules develops during early spring for flowering that occurs in early to mid May.

Think about all the environmental factors that could impact this developing flower bud from September through flowering in spring. It is mind boggling to think of all the weather factors, insect pests, diseases that could interfere with flowering.

In Alaska, we have no idea when flower bud initiation begins, and the whole process would have to stop in late autumn when the ground and buds freeze. All of this development would resume some time in spring and is, no doubt, one reason why Alaska flowers bloom so much later than lower latitudes. We know that peony flower bud initiation is not mediated by photoperiod, but what are the triggers that initiate that transition from vegetative to flower buds? Anyone for a PhD?

Peng, M. FL Huang, FJ Meng, BZ Hu, XF Chen, R Luo, N Li, RF Wang, Y Zhao, QW Zou, CT Wu and JL Dai. 2017. Reproductive Biology of the Chinese herbaceous perennial peony (Paeonia lactiflora Pall.) using the paraffin method. Φyton International Journal of Experimental Botany. 86:296-305.   Peony flower bud initiation


Responses

  1. >

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  2. Pat: So very true.We know so little and there is so much to know. We need more students!

    Ron & Marji Illingworth North Pole Peonies 5730 Eielson Farm Road North Pole, Alaska 907-488-0446 (H) 1-866-535-6459 (fax) northpolepeonies.com >

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