Gibberellic acid and flower development

There’s a great article in Plant Growth Regulation that looks at sepals and their role in rose flower development. It appears that they provide significant photosynthate (sugars and such) for flower development and also produce gibberellic acid. In addition, when they are removed and there is less GA, the flower has greater sensitivity to ethylene.

So, with what we already know about the potential to prevent pollinated flowers from aborting as easily with GA applications about 10 days after pollination, it would be very wise for us to keep our sepals in good shape. I do not remove them at emasculation, but a friend of mine does. My thoughts were just that why should I wound more of the flower than I need to and they may help shade the hypanthium tissue some so the young seeds do not bake in the sun as much. THere appears to be more going on than that considering what was learned about their role with GA. Following is the article which can be accessed part way down this site:

Contribution of sepals and gibberellin treatments to growth and development of rose (Rosa hybrida) flowers

pp. 255-261



An earlier thread that seems to fit in with this one:


Very interesting. After reading this, the first question that popped into my head was, how might the sepal gibberellic acid affect the pollination and development of seeds? I searched lightly with that in mind and came upon the following two articles:

Increased barley haploid production following gibberellic acid treatment[/url]

Effects of gibberellic acid treatment for pollen sterility induction on the physiological activity and endogenous hormone levels of the seed in safflower[/url]

(you’ll need the Acrobat reader for the second one, a .PDF document)

What was suggested to me from these is that while applying extra gibberellic acid to developing ovaries is probably not a good idea as it might effectively reduce the quality and germinability of the embryo by disrupting the rose’s internal hormones, leaving the sepals intact to produce natural gibberellic acid in the right quantity might prove very helpful. On the other hand, the Plant Growth Regulation study was only concentrating on petals and flower development by removing sepals very early (in young bud stage?) and didn’t get into the effects on developing seeds or hips, so it’s at least possible that the plant makes up for any gibberellic acid missing in those parts after sepals are removed. Also, sepals degrade over time on most rose hips, some dehiscing altogether - so if they play any role in the seeds’ early development, it’s probably still safe to remove them after some period of time, although the benefits of sepal removal are also probably reduced over time. I would be especially careful to leave sepals now if I suspected ethylene might be causing problems, so this might be particularly useful to those who breed in enclosed spaces like a greenhouse or when the flower is being pollinated right after an emasculation.

I’m a bit torn now, because removing sepals around the time of emasculation was an important defense for me against hip rot during the warm, humid time of year that most roses have their main flush here. Sepal giberellic acid, if it’s beneficial to breeders, is only useful if the hip actually doesn’t rot anyway of course, so I wonder if there might not be some happy medium - roses have five sepals, I wonder if it needs them all, or would two be good enough? Is there any way I could easily shelter the young hip with sepals to prevent excessive moisture buildup? Much more to ponder… thanks for sharing this with us, David.