The Role of Roots in Control of Bean Shoot Growth*

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Abstract
Restriction of root growth by growing bean plants (Phaseolus vulgaris L.) in very small pots led to the development of dwarf plants. The leaves of those plants were smaller and their internodes shorter than those of control plants which were grown in larger pots and had developed a more extensive root system. A large quantity of starch—much more than in control plants — accumulated in the leaves and shoots of the dwarf plants. Increasing the amount of minerals which was supplied to the roots, enhanced leaf growth of the control plants but failed to affect the dwarf ones, in spite of the fact that in both cases the treatment increased the content of N, P and K in all the plant organs. The leaf water content was similar in both treatments, but the leaf water potential was higher in the dwarf plants. Exogenous application of gibberellic acid (GA3) to the dwarf plants overcame the reduction of stem growth completely, and that of the leaves partially. Application of the cytokinin, benzyladenine (BA) did not affect stem growth, but increased that of the primary leaves. A combined supply of GA2 + BA restored completely the growth of the stem and the primary leaves, and partially that of the trifoliate leaves. It is concluded that a limited root system restricts shoot growth through an hormonal system in which at least gibberellins and cytokinins are involved, and that the dwarfing is not a consequence of mineral or assimilate deficiency, or due to water stress.