Involvement Of K+ In Leaf Movements During Suntracking

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the leaves; the leaves orient themselves parallel to the sun’s rays. Plants
that exhibit paraheliotropic behavior usually do so at midday, when the sun’s
rays are perpendicular to the ground. This reorientation takes place only in
leaves of plants that are capable of nastic light-driven movements, such as the
trifoliate leaf of Erythrina spp. (Herbert 1984). However, this phenomenon has
been observed in other legume species that exhibit diaheliotropic leaf movement
as well. Their movement is temporarily transformed from diaheliotropic to
paraheliotropic. In doing so, the interception of solar radiation is maximized
during the morning and late afternoon, and minimized during midday. The leaves
of Crotalaria pallida also exhibit nyctinastic, or sleep, movements, in which
the leaves fold down at night. The solar tracking may also provide a
competitive advantage during early growth, since there is little shading, and
also by intercepting more radiant heat in the early ...

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That the pulvinus is the site for light perception was the accepted
theory for many years. However, experiments with L. palaestinus showed that the
proximal 3-4 mm of the lamina needed to be exposed for a diaheliotropic response
to occur. If the light is detected by photoreceptors in the laminae, somehow
this light signal must be transmitted to the cells of the pulvinus. There are
three possible ways this may be done. One is that the light is channeled to the
pulvinus from the lamina. However, this is unlikely since an experiment with
oblique light on the lamina and vertical light on the pulvinus resulted in the
lamina responding to the oblique light. Otherwise, the light coming ...

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