Effect of petiole treatment with the auxin transport inhibitor N-1-naphthylphthalamic acid on leaf blade auxin concenration in the common bean (Phaseolus vulgaris).
This last experiment also suggests increased leaf auxin inhibits leaf growth if I assume that the NPA on the petiole, by inhibiting the movement of IAA out of the developing leaf results in an elevation of the level of the endogenous hormone in the treated leaf. That assumption is open to question, however. Others have recently reported that growing Arabidopsis seedlings on agar containing NPA resulted in plants with smaller leaves which were shown to contain lower levels of IAA. The researchers involved speculated that inhibition of auxin transport feeds back through some unknown mechanism to inhibit IAA synthesis. It is also possible in their experiment, however, that the inhibited root development resultant from NPA treatment causes poor leaf development as a consequence of poor nutrition. Poor nutrient status of the plant could then somehow down regulate IAA synthesis.
In July of 2002, I visited the lab of Jerry Cohen in the Department of Horticulture at the University of Minnesota where I measured the IAA content of NPA treated leaves and in the opposite control leaves using an established protocol. The protocol involved amino anion minicolumn and HPLC-based purification of IAA and quantification using gas chromatography-selected ion monitoring mass spectrographic analysis. As in previous experiments Phaseolus vulgaris L. var. Contender were grown under greenhouse conditions for 10-13 days. Plants with both monofoliate leaves having midribs 30-40 mm were selected for experimentation. The petiole of one monofoliate leaf on each plant was treated with 1.0 % NPA. One, 3, and 6 days following petiole treatment, treated and untreated leaves were harvested, weighed, frozen to -80[degrees], and transported to Minnesota on dry ice. Individual leaves were then analyzed for IAA content.
I found that the IAA content was consistently higher in the NPA treated leaf on all three days, for example, averaging 53.2 ng IAA / g fr. wt. in the treated leaves compared to 29.3 ng IAA / g fr. wt. in the untreated leaves on day 1. The results support the assumption that auxin transport inhibition results in elevated auxin levels and supports the hypothesis that auxin inhibits leaf development.
Christopher P. Keller
Department of Biology, Minot State University, Minot, ND 58707
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|Title Annotation:||BRIN Symposium: MSU Interactive Video Network Studio: 8:00-10:00 am|
|Author:||Keller, Christopher P.|
|Publication:||Proceedings of the North Dakota Academy of Science|
|Date:||Mar 1, 2003|
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