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A Functional Calvin Cycle Is Not Indispensable for
the Light Activation of C4
Phosphoenolpyruvate Carboxylase Kinase and Its Target
Enzyme in the Maize Mutant
bundle sheath
defective2-mutable1
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We used a pale-green maize (Zea mays L.) mutant that fails to accumulate ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to test the working hypothesis that the regulatory phosphorylation of C4 phosphoenolpyruvate carboxylase (PEPC) by its Ca2+-insensitive protein-serine/threonine kinase (PEPC kinase) in the C4 mesophyll cytosol depends on cross-talk with a functional Calvin cycle in the bundle sheath. Wild-type (W22) and bundle sheath defective2-mutable1 (bsd2-m1) seeds were grown in a controlled environment chamber at 100 to 130 μmol m−2 s−1 photosynthetic photon flux density, and leaf tissue was harvested 11 d after sowing, following exposure to various light intensities. Immunoblot analysis showed no major difference in the amount of polypeptide present for several mesophyll- and bundle-sheath-specific photosynthetic enzymes apart from Rubisco, which was either completely absent or very much reduced in the mutant. Similarly, leaf net CO2-exchange analysis and in vitro radiometric Rubisco assays showed that no appreciable carbon fixation was occurring in the mutant. In contrast, the sensitivity of PEPC to malate inhibition in bsd2-m1 leaves decreased significantly with an increase in light intensity, and there was a concomitant increase in PEPC kinase activity, similar to that seen in wild-type leaf tissue. Thus, although bsd2-m1 mutant plants lack an operative Calvin cycle, light activation of PEPC kinase and its target enzyme are not grossly perturbed. 相似文献
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Monoxenic cultures of Heterodera zeae, the corn cyst nematode (CCN), were established on root explants of corn Zea mays L., cv. Kenworthy. The life cycle of H. zeae was determined from light anti scanning electron microscopic observations of the root explants grown in the dark at 29.5 ± .5 C under gnotobiotic conditions. The life cycle, from the time the explants were inoculated with second-stage larvae (L2) to the first appearance of newly hatched second-generation L2, required 22 days. The occurrence of males was rare suggesting that reproduction in H. zeae is parthenogenetic. 相似文献