Influence of Mechanical Stress on Auxin-Stimulated Growth of Excised Pea Stem Sections

The auxin to cytokinin ratios are described for promoting growth in the in vitro cultures of soybean (Glycine max (L.) Merr. cv. Bragg) and perennial clover (Trifolium repens L. cv. Regal Ladinc). Callus growth was induced on somatic tissue with 50:1 auxin to cytokinin (w/w) ratio. A 5:1 ratio served for initiation of cell suspensions from callus and for subsequent growth of callus from cells in suspension. A 1:2 ratio served for regeneration of buds and plantlets from the callus grown from cells. Although (2,4-dichlorophenoxy) acetic acid was the auxin for suspension and regenerative cultures, (2,4,5-trichlorophenoxy)acetic acid was the more effective auxin for initiation of callus on somatic tissue. All cultures were grown with 6-furfurylaminopurine as the cytokinin. The phytohormones strongly influenced the rates of culture growth, but determination of culture type was augmented by dl-alpha tocopherol acetate and iron. Tocopherol and a relatively high complement of iron promoted growth of juvenile cultures, whereas low level of iron and absence of tocopherol favored growth to comparatively more differentiated cultures. Without tocopherol, no callus formed on somatic tissue during the allotted period of incubation. Tocopherol plus a complement of low iron enabled growth of callus on rapidly growing somatic tissue. A high level of iron enabled comparatively more callus growth but suppressed growth of somatic tissue. In suspension cultures tocopherol and a high iron level enhanced dispersion of cells. A low iron complement in the absence of tocopherol induced growth of callus from cells and subsequent regeneration of buds and plantlets from the callus.