Abstract
Several changes were shown in rice callus cultures with abscisic acid (ABA) treatment. First, callus growth was inhibited, especially at a high concentration (2×10-4 M) of ABA. Secondly, white, dry and compact regions were formed in the callus at higher frequency. Thirdly, two kinds of callus structures were observed at ABA-treated culture stage with a scanning electron microscope (SEM). White regions and yellow regions at macroscopical level corresponded to relatively smooth, undulated structures and rough-surfaced structures, respectively at SEM level. Moreover, the dark condition in which ABA was treated enhanced the frequency of appearance of white regions in the callus and advanced the developmental stage leading to plant regeneration. When the calli having white regions were predominantly transferred on the regeneration medium, they showed the highest potential to regenerate plantlets. Nevertheless, the ability of such regions to regenerate plantlets was not affected by illumination in the ABA-treated culture at all. Several morphological types in plant regeneration processes could be observed after 7 days of the regeneration culture. Some of them showed ordinary organogenesis and others malformed processes.
