LIGHT-INDUCED REVERSIBLE LOCAL FUSIONS OF THYLAKOID MEMBRANES IN THE PRESENCE OF DIBUCAINE OR TETRACAINE

The dynamics of structural changes in pea chloroplasts in the presence of 25-50 mu M dibucaine or tetracaine has been examined using electro n microscopy. The light-induced uptake of anesthetic cations by thylak oids is attended by the appearance of local fusions of stroma-exposed thylakoid membranes. The first membrane protrusions and interthylakoid contacts are observed after 4 s illumination and they become numerous by 10 s. As a result, a network of anastomoses is formed which is mai ntained during at least 10 min. These effects are reversible in the da rk and can be reproduced several times. The formation of membrane fusi ons is inhibited by the addition of protonophore. It is supposed that the energy-dependent uptake of protonated anesthetics by thylakoids le ads to an increase in positive surface charge and thus a lateral press ure on the inner side of the thylakoid membrane. The appearance of mem brane protrusions (crinkles) having the positive curvature of their in ner surface may be considered as a way of compensating for lateral pre ssure. Presumably, anastomoses result from the fusion of crinkles to a djacent thylakoids.