Effects of Ethylene on the Ultrastructure of Nucleus in Tomato Pericarp Cell During Ripening
LIU Yu, WU Dun-Su, WU You-Mei and GUO Yi-Song(Shanghai Institute of Plant Physiology, Academia Sinica, Shanghai 200032)
During the ripening of tomato fruit (Lycopersicon esculentum Mill Dahong) the ultrasturture of nucleus in pericarp cell was observed by freeze-fracture and transmission electron microscopy. It was found that before the onset of ripening (green mature, G), the volume of heterochromatin was 45% of nuclear volume (Plate Ⅰ1). From the onset of ripening (B stage), heterochromatin was dispersed and decreased in volume (Plate Ⅰ 2). At the turning stage the volume of heterochromatin decreased and was dispersed evenly (Plate Ⅰ 3). At the fully ripening and overripening stages, the nucleus became abnormal, and the structure of chromatin collapsed (Plate Ⅰ 4, 5). When the ripening of fruit was accelerated by treatment with ethylene at B stage, heterochromatin was converted into euchromatin and disappeared, and, in the meantime, the number of nuclear pore increased to that at advanced ripening stage (Plate Ⅰ 1—4). The effect of ethylene was eliminated by adding NBD, a competitive inhibitor of ethylene action, simultaneously with ethylene treatment, and chromatin and nuclear pores remained the same as before treatment (Plate Ⅰ 5, 6).