Compensation Gravitropism

the compensation reaction of bending coprinus stem. c - compensating part of stem.

bending mushroom stems follow regularities not common in plants. after turning horizontal normal vertical orientation apical part (region c in figure below) starts straighten. part gets straight again, , curvature concentrates near base of mushroom. effect called compensation (or sometimes, autotropism). exact reason of such behavior unclear, , @ least 2 hypotheses exist.

the hypothesis of plagiogravitropic reaction supposes mechanism sets optimal orientation angle other 90 degrees (vertical). actual optimal angle multi-parameter function, depending on time, current reorientation angle , distance base of fungi. mathematical model, written following suggestion, can simulate bending horizontal vertical position fails imitate realistic behavior when bending arbitrary reorientation angle (with unchanged model parameters).
the alternative model supposes “straightening signal”, proportional local curvature. when tip angle approaches 30° signal overcomes bending signal, caused reorientation, straightening resulting.

both models fit initial data well, latter able predict bending various reorientation angles. compensation less obvious in plants, in cases can observed combining exact measurements mathematical models. more sensitive roots stimulated lower levels of auxin; higher levels of auxin in lower halves stimulate less growth, resulting in downward curvature (positive gravitropism).