ABA may affect the dormancy in triticale caryopses by inhibition of embryo class I RNases,enzymes involved in Pi release

The main objective of this study was to analyze the differences in profiles of RNase activities from triticale embryos (Triticosecale, cv. Ugo) between dormant and non-dormant caryopses and to determine the influence of exogenous abscisic acid (ABA) on the activities of these enzymes. The major RNase from the examined tissue was detected following SDS-PAGE, with substrate-based gel assay, described by Yen and Green (Plant Physiol 97:1487–1493, 1991). The activities of enzymes were characterized according to their pH optima, ion dependence, EDTA sensitivity and DNase activity. In embryos with arrested growth (in a natural way by dormancy or artificially by ABA treatment), the activity of two enzymes—24 and 27 kDa—belonging to class I RNases was completely inhibited, whereas that of two other RNases of this family—23 and 25 kDa—was detectable. However, the activity of the class I ribonucleases (enzymes responsible for cellular P_i release) was very low. Moreover, in contrast with non-dormant caryopses, imbibing embryos of dormant or ABA-treated seeds contained 13- and 14-kDa enzymes. These enzymes have not been classified so far, and their specific properties are different from the generally accepted properties of ribonucleolytic enzymes. In addition to the above results, the P_i content in the analyzed samples was determined by the Ames (Methods Enzymol 8:115–118, 1966) method. The results suggest a very low and constant level of inorganic phosphate in dormant samples as well as an evidently decreasing P_i content in embryos under the influence of ABA treatment. The inhibition of the class I RNases activity induced by abscisic acid implies that one of the roles of ABA in seed dormancy may consist in arresting the catabolic release of P_i, which results in retarding the embryo’s growth.