positive curvatures of 30 to 40 degrees (Bünning 1959). The negative and positive trau-
matropic response of both roots and shoots indicates the participation of message trans-
mission from the wound site to the cells showing differential growth. Such a wound mes-
sage may be transmitted chemically (through the action of hormones or proteins),
electrically (through the generation and propagation of action potential), and/or mechan-
ically (through activated mechanosensory Ca2+channels). It remains to be determined
whether only one or the combined action of these three wounding messages regulates
traumatropism. The significance of traumatropism to the plant may be to offer initial pro-
tection to injury, reinforced later on by the systemic long-distance signaling induced in
the wound response (Schilmiller and Howe 2005).
6.7 Overview
Sensory systems in plants may consist more of a network of interconnected response
chains rather than a series of separate stimulus reception-transduction pathways.
Dissection of this complex network will require the development of innovative method-
ologies in conjunction with present technologies to resolve the mechanism of perception
and assessment that controls organ-bending responses to these diverse stimuli.
6.8 Acknowledgments
This work is dedicated to Professor Barbara G. Pickard, whose comprehensive know-
ledge of the field has been the source of many invaluable suggestions from which my
studies on hydrotropism have profited greatly. We warmly thank Yoloxóchitl Sánchez for
drawing the figures and Manuel Saucedo for his enormous contribution in the isolation
of the super-hydrotropic mutants. We are grateful to all past and present members of the
laboratory for their contributions and discussions on hydrotropism. We also gratefully ac-
knowledge financial support by the Mexican Council for Science and Technology
(CONACYT grant No. 462022Q), the Universidad Nacional Autónoma de México
(Dirección General de Asuntos del Personal Académico Grant No. IN224103), and the
University of California Institute for Mexico and the United States (UC Mexus).
6.9 Literature cited
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Barthèlèmy A. 1884. De l’action de la chaleur sur les phénomènes de végétation. Compte Rendus
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Behrens H.M., Gradmann D., Sievers A. 1985. Membrane potential responses following gravis-
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Behrens H.M., Weisenseel M.H., Sievers A. 1982. Rapid change in the pattern of electric current
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