MODIFICATION OF THE VEGETATIVE DEVELOPMENT OF PHASEOLUS VULGARIS WITH N,N‐DIMETHYLAMINOMALEAMIC ACID

Bean plants treated with N, N-dimethylaminomaleamic acid (DMAM) were characterized by a reduction in plant height, dark-green foliage, short, thick internodes, restricted petiole extension, and, at high concentrations, a slight reduction in leaflet expansion and dry matter accumulation. DMAM specifically affects internodal and petiolar tissues. The inhibitory stimulus of DMAM is readily translocated following application to a single leaf and the subsequent suppression of stem elongation increased with increasing dose. The failure of the rachises of the trifoliate leaves to fully extend resulted in an overlapping of the bases of the lamellae of the individual leaflets. The inhibitory effects of DMAM on stem elongation can be completely reversed with gibberellin A3 (10 or 100 ppm). This might suggest that D\IAMN may be interfering with the natural synthesis of gibberellin in the plant. CHEMICAL modificatioln of vegetative plant developmeent is of ilnterest in providing an insight into growth phenomena (Kuraishi and Muir, 1963) and as a means of miodifying plant adaptation (Cathey and Mlarth, 1960; Lindstrom and Tolbert, 1960). Of special interest are certain chemicals that inhibit plant growth, naamely; 2 ,4-dichlorobenzylnicotinium chloride (Mitchell, Wirwille, and Weil, 1949), 1,2-dihydro-3, 6pyridazinedione (Schoene and Hoffnmann, 1949), (4 hydroxy 5 isopropyl 2 methylphenyl)trimethylammoniunm chloride, 1 piperidinecarboxylate (Wirwille and Mlitchell, 1950), 2 ,4dichlorobenzyltributylphosphoniuin chloride (Preston and Link, 1958) and 2-chloroethyltrimethylammoniuni chloride (Tolbert, 1960a). All of the above compounds, though differing in chemical structure, produce simiilar effects on plant growth. Treated planlts are characterized by short internodes, thick stems alnd dark-green foliage (Bukovac, 1962; MXIarth, Preston, and Mitchell, 1953; Tolbert, 1960b; Wittwer and Tolbert, 1960). These growth responses are generally opposite to those observed following treatment with the gibberellins (Brian anid Hemming, 1957; Bukovac and Wittwer, 1956; Wittwer and Tolbert, 1960). Plant-growth-inhibitinig properties have also been ascribed to miiethyl-substituted maleamic and succinamic acids (Riddell et al., 1962). In many instances, the induced growth responses from these chemicals are similar to those cited above. This report describes the modification of epicotyl extension and leaf morphology induced 1 Received for publication October 6, 1963. 2 Journal Article No. 3241 from the Michigan Agricultural Experiment Station, East Lansing. 3I wish to thank Mr. W. R. Robb for technical assistance, Dr. J. A. Riddell, Naugatuck Chemical Co., for supplying N, N-dimethylaminomaleamic acid, and Dr. J. M. Merritt, Merck and Co., for gibberellin A3. with N ,N-dimethylaminomaleamic acid, and the reversal of the inhibition of stem elongation with gibberellin A3. EXPERIMENTAL-All experiments were conducted in a greenhouse during fall and winter at the prevailing photoperiod (9-11 hr). Night temperature of 20-21 C and minimum day tenmperature of 24-25 C were maintained. Maxinmum day temperature was not controlled. An indeterminate type bean (Phaseolus vulgaris L. cv. 'Blue Lake') was selected as the test specinmen. Plants were cultured in soil or in aerated half-strength Hoagland nutrient solution. The nutrient solution was replaced at weekly intervals in those experiments longer than 1-week in duration. For soil cultures, the seeds were germinated directly in the soil medium, and 2 uniform plants per pot were selected for experimentation; for solution cultures, seeds were germinated in quartz sand and uniform seedlings transferred after 8 or 9 days. At approximately 80% expansion of the primary leaves, plants were sprayed or momentarily dipped in an aqueous solution of N,N-dimethylaminomaleamic acid (DMAM) or gibberellin A3 (GA3). Sufficient polyoxyethylene sorbitan monolaurate (Tween 20) was added to provide a final concentration of 0.1 %. Randomized block experimental designs (with 3-6 replications) were utilized, and an analysis of variance was performed on the data. Comparison among treatment means was carried out as suggested by Duncan (1955). General effects on vegetative development and flowering-Seedlings growing in soil cultures were sprayed with DMAM at expansion of the primary leaves. Each treatment consisted of 2 plants each, replicated 5 times. Plant heights and number of nodes produced per plant were recorded 45 days after treatment (Table 1). Days from seeding to anthesis and node of the first inflorescence were also recorded.