The influence of spectral quality on the internodal response of intact bean plants to brassins

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Abstract
The response of pinto bean (Phaseolus vulgaris L.) plants to single application of brassins (10 μg) in the second‐internode assay was determined under equal levels (90 μE m−2 s−1) of photosynthetically active radiation in a controlled environment provided by cool‐white fluorescent (CWF) lamps, incandescent (INC) lamps, or a combination of the two sources. Treatment of the second internode with brassins produced a characteristic swelling of the treated internode irrespective of the spectral source used. However, the increase in radial growth of the upper portion of brassin‐treated internodes from plants grown under INC lamps was more than 50% greater than those of plants grown under CWF lamps for 7 days. Spectral quality also had a marked effect on the rate and extent of internode elongation. Brassin‐treated internodes of plants grown for 7 days under CWF lamps were more than twice as long as those of control plants, whereas those from INC or CWF + INC grown plants were significantly shorter than those of control plants. The effect of brassins was largely confined to the treated internode.