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Development and Growth Regulation

Role of Salicylic Acid and Benzoic Acid in Flowering of a Photoperiod-Insensitive Strain, Lemna paucicostata LP6 ¹

Smithsonian Environmental Research Center, Rockville, Maryland 20852

Lemna paucicostata LP6 does not normally flower when grown on basal Bonner-Devirian medium, but substantial flowering is obtained when 10 µM salicylic acid (SA) or benzoic acid is added to the medium. Benzoic acid is somewhat more effective than SA, and the threshold level of both SA and benzoic acid required for flower initiation is reduced as the pH of the medium is lowered to 4.0. SA- or benzoic acid-induced flowering is enhanced in the simultaneous presence of 6-benzylaminopurine (BAP), although BAP per se does not influence flowering in strain LP6. Continuous presence of SA or benzoic acid in the culture medium is essential to obtain maximal flowering. A short-term treatment of the plants (for first 24 h) with 10 µM SA or benzoic acid, followed by culture in the basal medium containing 1 µM BAP can, however, stimulate profuse flowering. Benzoic acid is more effective than SA, and the effect is more pronounced at pH 4 than at 5.5. Thus, under these conditions, flowering is of an inductive nature. Experiments with [¹⁴C]SA and [¹⁴C]benzoic acid have provided evidence that at pH 4 there is relatively more uptake of benzoic acid than SA, thus leading to an increased flowering response. The data obtained from the experiments designed to study the mobility of [¹⁴C]SA and [¹⁴C]-benzoic acid from mother to daughter fronds indicate that there is virtually no mobility of SA or benzoic acid between fronds.

³ Present address: USDA/SBIR, Room 323 Aerospace Building, 901 D Street, S.W., Washington, DC 20250-2200.

¹ Supported by a postdoctoral fellowship to J.P.K. from the Smithsonian Institution, Washington, DC.