Реферат: Untitled Essay Research Paper Involvement of K

this perception is transduced to the pulvinus, and finally, how this signal can effect a

physiological response (Donahue and Vogelmann).

In the species Crotalaria pallida, blue light seems to be the

wavelength that stimulates these leaf movements (Scmalstig). It has been implicated in the

photonastic unfolding of leaves and in the diaheliotropic response in Mactroptilium

atropurpureum and Lupinus succulentus (Schwartz, Gilboa, and Koller 1987). However, the

light receptor involved can not be determined from the data. The site of light perception

for Crotalaria pallida is the proximal portion of the lamina. No leaflet movement occurs

when the lamina is shaded and only the pulvinule is exposed to light. However, in many

other plant species, including Phaseolus vulgaris and Glycine max, the site of light

perception is the pulvinule, although these plants are not true suntracking plants. The

compound lamina of Lupinus succulentus does not respond to a directional light signal if

its pulvini are shaded, but it does respond if only the pulvini was exposed. 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 from the lamina would be

drowned out by the light shining on the pulvinus. Another possibility is that some

electrical signal is transmitted from the lamina to the pulvinus as in Mimosa. It is also

possible that some chemical is transported from the lamina to the pulvinus via the phloem.

These chemicals can be defined as naturally occuring molecules that affect some

physiological process of the plant. They may be active in concentrations as low as 10-5 to

10-7 M solution. Whatchemical, if any, is used by C. pallida to transmit the light signal

from the lamina of the leaflet to its pulvinule is unknown. Periodic leaf movement factor

1 (PLMF 1) has been isolated from Acacia karroo, a plant with pinnate leaves that exhibits