Circumnutation in <i>Phaseolus vulgaris</i>. I. Growth, osmotic potential and cell ultrastructure in the free‐moving part of the shoot

Abstract

Circumnutation of Phaseolus vulgaris L. cv. Blanc de Juillet twining shoots was examined at the cellular level. Cell growth was monitored inside the free‐moving part of the shoot as a function of time and position with respect to the terminal bud. Complete elongation of epidermal cells required &gt;7 days. A 60% increase in length of the cells in the bending zone was observed. Scanning and transmission electron microscopy studies showed the elasticity of cell walls, the extent of plasmodesmata and endoplasmic reticulum of epidermal cells. The osmotic potential in epidermal cells of the bending zone displayed significant differences only between the concave and convex sides. The pattern of cell growth in twining shoots is discussed. Circumnutation could be seen as a consequence of periodic turgor changes inducing periodic growth.