The (~)-abscisic acid content of pea shoots has been determined using gas-liquid chromatography. In both tall and dwarf cultivars no significant difference was observed between plants grown in the dark or under red light. Nor was the difference between the tall and dwarf cultivars themselves significant.
The plant growth inhibiting substance (~-)-abscisic acid (ABA) is known to have a widespread distribution throughout the plant kingdom (Addicott and Lyon, 1969). As a result of earlier work with ~his substance it seemed to the author that dwarfism in plants may be an expression of the content of ABA in the plant tissue. Preliminary experiments (Barnes and Light, 1969) appeared to indicate a higher ABA content in dwarf than in tall peas, and thus to suggest a direct role in dwarfism. Recently, however, more extensive experiments have failed to confirm this result and prompt this brief report on the continued work.
The ABA content of peas (Pisum sativum L.) was determined by a modification of the extraction and gas-liquid chromatographic (GLC) procedure used previously (Barnes and Light, 1969), The peas, a tall (Gradus) and a dwarf cultivar (Progress No. 9), were grown in a controlled-environment chamber at 25 ~ C, either without light or with continuous red light. The light source was two 100-W bulbs fitted with red filters, approximately 25 cm above the plants. After 10 days the shoo~s (800 g) were excised, homogenised in 95% methanol, and the resulting slurry was stirred at 3~ for 16 h in the dark. After filtration the extraction was repeated with the residue. The combined filtrates were evaporated at 40~ and the residue was dissolved in 5% aqueous sodium bicarbonate (10 ml), acidified to pH 2.5, and the ABA extracted into diethyl ether (2 x 50 ml). The crude ABA in this ether extract was purified by thin-layer chromatography (TLC) on Silica gel G (Merck), first in the solvent mixture: n-butanol, 2; n-propanol, 6; 0.88 ammonia, 1; water, 2; and second in benzene, 100; ethyl acetate, 50; acetic acid, 2. The ultraviolet-absorbing band, chromatographing with an authentic sample of ABA, was eluted in each case with ethyl acetate.
Quantitation by GLC was carried out in a Perkin-Elmer F-11 twin-column instrument with a flame ionisation detector. The glass column (ca. 90 cmx 6.5 ram)