Two forms of NADP-dependent malic enzyme in expanding maize leaves
1Istituto Botanico, Università di Bologna, Via Irnerio 42, I-40126, Bologna, Italy.
Planta
|January 11, 2014
Summary
Two NADP-dependent malic enzyme isozymes in maize leaves differ significantly. Etiolated leaves have a cytosolic type 1, while green leaves develop a more stable chloroplast type 2 during photosynthesis.
Area of Science:
- Biochemistry
- Plant Physiology
- Enzymology
Background:
- Maize leaves contain NADP-dependent malic enzyme (NADP-ME), crucial for carbon metabolism.
- Isozymes of NADP-ME exhibit distinct biochemical properties and cellular localization.
- Understanding these isozymes is key to elucidating photosynthetic pathways in C4 plants.
Purpose of the Study:
- To characterize and compare the properties of two major NADP-ME isozymes in maize (Zea mays L.).
- To investigate the developmental regulation and cellular localization of these isozymes.
- To understand the role of NADP-ME isozymes in photosynthetic differentiation.
Main Methods:
- Purification and characterization of NADP-dependent malic enzyme isozymes from etiolated and green maize leaves.
- Determination of kinetic parameters (Km, pH optimum), molecular weight, and isoelectric points (pI).
- Assessment of NAD-dependent activity and stability of purified isozymes.
Main Results:
- Etiolated leaves possess a cytosolic type 1 NADP-ME (pI 5.28, Km 0.3-0.6 mM) with low NAD-dependent activity.
- Green leaves exhibit a dominant chloroplast type 2 NADP-ME (pI 4.90, Km 0.10-0.15 mM), which is more stable and has higher NAD-dependent activity.
- Type 2 isozyme levels increase significantly during photosynthetic differentiation, replacing type 1.
Conclusions:
- Maize NADP-ME isozymes (type 1 and type 2) display distinct biochemical and regulatory properties.
- Type 1 is likely cytosolic, while type 2 is associated with bundle-sheath cell chloroplasts.
- The developmental switch from type 1 to type 2 isozymes is integral to photosynthetic differentiation in maize.
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