ABSCISIC-ACID AND HIGH OSMOTICUM REGULATION OF DEVELOPMENT AND STORAGE RESERVE ACCUMULATION IN SUGARCANE SOMATIC EMBRYOS

Both abscisic acid and high osmoticum influence (somatic) embryogenesis in plants. However, the specific effects of these bioregulators on general aspects of embryogenesis and storage reserve accumulation, in particular, remain quite unclear. Our results showed that abscisic acid and sorbitol could, depending upon their concentrations, act in ways that are either beneficial or detrimental to the frequency of somatic embryogenesis in sugarcane (Saccharum officinarum L.) callus cultures. Complementary studies of sectioned scutellar tissues, using transmission electron microscopy were conducted to examine the in situ localization of storage reserves in cells of somatic embryos treated with: (i) 10(-5) M ABA; (ii) 9% sorbitol; (iii) 10(-5) M ABA and 9% sorbitol; and (iv) untreated embryos (control) for 14 days. They indicated that these substances elicited storage reserve accumulation differently. Whilst ABA-treated embryos allocated significantly more of their cell volumes to protein bodies with no visible amyloplasts, sorbitol-treated embryos allocated more cell volumes to prominent starch grains and numerous lipid bodies. It is concluded that the specific control mechanism (s) of influence due to these compounds is probably different, as reflected in the varying patterns of amyloplasts (or starch grains), protein- and lipid bodies visualized in the scutellar cells.