Germinating seeds of many species contain two types of β‐cyanoalanine synthase (CAS, EC 22.214.171.124) that convert HCN to β‐cyanoalanine. One is cytoplasmic CAS (cyt‐CAS), which is precipitated by 50 to 60% (NH4)2SO4 and has a pH optimum of 10.5. Cytoplasmic CAS is present at high levels in dry seed and its activity does not increase during imbibition. The activity of cyt‐CAS is not affected by exogenously applied ethylene (C2H4), except in rice (Oryza sativa cv. Sasanishiki). The second type of CAS found in seed is mitochondrial CAS (mit‐CAS), which is precipitated by 60 to 70% (NH4)2SO4 and has a pH optimum of 9.5. Mitochondrial CAS is present at low levels in dry seed, and its activity increases greatly during imbibition in the seeds of all species tested. Exposure to C2H4 stimulated mit‐CAS activity in seeds of rice, barley (Hordeum vulgare cv. Hadakamugi). cucumber (Cucumis sativus cv. Kagafushinari) and cocklebur (Xanthium pennsylvanicum). The increase in the mit‐CAS activity in cocklebur in response to C2H4 commenced alter a lag period of 2 to 3 h when the duration of soaking was short (16 h), but commenced without a lag period when the seeds were soaked for three months. Application of both chloramphenicol and cycloheximide to the axial and cotyledonary tissues of cocklebur seeds strongly inhibited growth as well as the increase in mit‐CAS activity. It is postulated that the mit‐CAS is synthesized de novo during imbibition and that its activity is regulated by C2H4, CO2 which also promotes seed germination in some species, was ineffective m stimulating mit‐CAS activity in cocklebur seeds.
|Number of pages||6|
|Publication status||Published - Apr 1995|
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology