Phosphoenolpyruvate carboxylase inHydrillaplants with varying CO2compensation points
✍ Scribed by Jocelyne Ascencio; George Bowes
- Publisher
- Springer
- Year
- 1983
- Tongue
- English
- Weight
- 938 KB
- Volume
- 4
- Category
- Article
- ISSN
- 0166-8595
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✦ Synopsis
Incubation of the submersed aquatic macrophyte, Hydrilla verticillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 ttl CQ/1) and low (6 to 8 ~1 C02/1 ) CO 2 compensation points (I'), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high P plants to 0.2 in low I" plants. These ratios resemble the values in terrestrial C 3 and C 4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low F plants indicated the Vmax was up to 3-fold greater in the low F plants. The Km (HCO~) values were 0.33 and 0.22 mM for the high and.low r plants, respectively. The Km (PEP) values for the high and low I" plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg 2÷) values were 0.10 and 0.22mM for the high and low r plants, respectively.
Malate inhibited both PEP carboxylase types similarly. The enzyme from low F plants was protected by malate from heat inactivation to a greater extent than the enzyme from high r plants. The results indicated that C 4 acid inhibition and protection were not reliable methods to distinguish C3 and C 4 PEP carboxylases. The PEP carboxylase from low F plants was inhibited more by NaC1 than that from high F plants.
These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C 3 and C 4 species with the low F enzyme being different from the high F enzyme, and closer to a C a type.
Resnmen. A1 incubar la macrofita acufitica sumergida (MAS) Hydrilla verticillata Royle, pot un periodo de hasta 4 semanas en c~tmaras de crecimiento con condiciones semejantes a las de invierno (bajas temperaturas y dl'as cortos) o de verano (altas temperaturas y dtas largos), se originaron cambios en el punto de compensacidn de CO2 (F) de las plantas a valores de 130 a 150~1 COJ1 y 6-8~1 CO2/1, respectivamente. Las actividades tanto de la RiBP carboxilasa como de la PEP carboxilasa aumentaron durante la incubacidn, pero el aumento mgts significativo fu~ de la actividad de la PEP carboxilasa en las plantas en la condici6n de verano. Este aumento reduj6 la relaci6n RiBP/PEP carboxilasa de 2.6 en las plantas con alto F a 0.2 en las plantas con bajo r. Estos valores se asemejan a los de especies C 3 y C 4 terrestres, respectivamente.