CHLOROPLAST MOVEMENT AS RESPONSE TO WOUNDING IN ELODEA-CANADENSIS

Chloroplast movement was studied in intact, detached or cut leaves of Elodea canadensis Michx. The influence of external factors (light, tem perature, water supply) acid of leaf age on activity and pattern of ch loroplast movement was observed. Chloroplast movement does not occur i n unsevered leaves; in leaves severed either by detachment or by a lat eral incision, chloroplast movement occurs at room temperature in simi lar patterns. In midrib cells axial chloroplast movement starts within 10 min after setting the wound, almost independently from external co nditions. In epidermis cells, lateral chloroplast movement is time-lim ited depending on the pretreatment of the plant (light, dark, cold). L ateral chloroplast movement is minimal in young leaves and maximal in mature leaves. In the morning hours chloroplast movement is restricted to midrib cells, but in the afternoon additional lateral movement occ urs. Predarkening of plants reduced lateral chloroplast movement, but continuous illumination activated the movement. Cooling of plants to t he temperature of melting ice (+5 degrees C) inhibited chloroplast mov ement in detached and incised leaves. However, after transfer to room temperature, axial chloroplast movement started within 20 min, and lat eral chloroplast movement started within 40 min. The velocity of movem ent was highest after several warm-cold-warm changes following detachm ent or incision (maximum 36.8 mu m s(-1)). The time course of chloropl ast movement coincides with rapid changes of the membrane potential wi th low amplitudes (humming, 4 to 7 mV), which was recorded with microe lectrodes impaled into the midrib of the attached leaf. Cutting a leaf of the third, last-formed generation initiated a sudden depolarizatio n (from -200mV to -140mV) and a subsequent hyperpolarization to -240mV , which slowly increased, but after 10 min suddenly changed to the hum ming period in the range of -200 mV +/- 1.5 mV. It is concluded that c hloroplast movement is initiated and enhanced by wound reactions trans mitted from cell to cell via plasmodesmata.