Relationship between leaf development, carboxylase enzyme activities and photorespiration in the C4-plantPortulaca oleraceaL.
✍ Scribed by Robert A. Kennedy
- Publisher
- Springer-Verlag
- Year
- 1976
- Tongue
- English
- Weight
- 532 KB
- Volume
- 128
- Category
- Article
- ISSN
- 0032-0935
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✦ Synopsis
Ribulose diphosphate (RuDP) and (PEP) phosphoenolpyruvate carboxylase enzyme activities were studied in young, mature, and senescent Portu- laca oleracea leaves. While the absolute amount of both the C3 (RuDP) and C4 (pEP) carboxylase is less in senescent leaves than in mature leaves, RuDP carboxylase activity is reduced to a lesser degree. In senescent leaves, PEP carboxylase activity equals 10% of that in mature tissue, but RuDP carboxylase is 27% of that in mature leaves. The same ontogenetic series was also used to determine photorespiration rates and responses to several gas treatments. Young and mature leaves were unaffected by changes in the light regime or oxygen concentrations, and exhibited typical C4plant light/dark 14CO2 evolution ratios. Senescent leaves, on the other hand, have photorespiration ratios similar to C3-plants. In addition, senescent leaves were affected by minus CO/, 100% 02 and N 2 in a manner expected of Ca-plants, but not C4-plants. These results are discussed in terms of a relative increase in activity of the C3 cycle in later developmental stages in this plant.