The Bunsen-Roscoe law, or reciprocity theorem, exp
The Bunsen-Roscoe law, or reciprocity theorem, explains this effect but cannot explain why both its positive and negative kinds can occur in the same tissue. Null nph1 mutants of Arabidopsis do not display it. Etiolation occurs when this phenomenon cannot operate, resulting in characteristically thin, yellow stems. Certain hormones activate proton pumps on one side of a cell, leading to a pH decrease that weakens the cell wall, and this phenomenon is driven by turgor in that direction. FTP, name this tendency of plants to grow toward or away from a light source.
The Bunsen-Roscoe law, or reciprocity theorem, explains this effect but cannot explain why both its positive and negative kinds can occur in the same tissue.
{phototropism} (accept {heliotropism} before “{light source}”)