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The effects of metabolites, protein phosphorylation and malate inhibition on phosphoenolpyruvate carboxylase (PEPC) activity were investigated at pH 7.0 in partially purified enzyme from maize leaves. Glycine, glucose 6-phosphate or alanine stimulated the activity two- to three-fold. Glycine and glucose 6-phosphate increased the affinity for PEP by factors of eight and four respectively. These metabolites changed the response of the enzyme activity to pH. Activity increased between pH 6.8 and 8.0 by 10-fold in the absence and 26% in the presence of these metabolites. In vitro phosphorylation of PEPC increased the activity two-fold in the absence but not in the presence of these metabolites. Malate was a strong inhibitor of PEPC, the KI value being 0.25-0.5 mM. Protein phosphorylation and the above metabolites increased the Ki value by factors of three and 12 respectively, but they synergistically increased the Ki 50-fold, thus providing maximal protection against malate inhibition. In the crude extracts from light- and dark-adapted leaves in the presence of a physiological concentration of malate (20 mM), PEPC activity comparable to the photosynthetic rate was obtained only from the light-adapted leaves in the presence of metabolites indicating that both light-induced protein phosphorylation and metabolic activators were essential for PEPC activation during photosynthesis. We propose that both these factors act synergistically to modulate PEPC during photosynthesis in maize.

Accelerated aging is known to reduce seed viability and vigor in many crop species. This study was undertaken to evaluate the effect of accelerated aging on germination potential, germination percentage, electric conductivity, acid value and peroxide value. Compared with common peanut, high oleic acid peanut were more beneficial to health and can significantly improve the storability of seed. Eight high oleic acid (range of oleic acid content: 74.95%-80.6%) and two common varieties were used in this experiment. Six treatments were contained, natural aging of kernels, natural ageing of pods, accelerated aging was achieved by incubating seed at 40°C and 100% relative humidity in a closed chamber for 4, 6, and 8 days. The results showed that: the changes of germination potential and germination percentage of natural aging were not significant for high oleic acid peanuts, smaller than that of the common varieties. No matter artificial aging or natural aging treatment, compared with non-aging treatment, electric conductivity gradually increased, but high oleic acid varieties remained at low levels. The acid value of each variety increased gradually with the aging time, comparison between aging treatments, the difference between high oleic acid varieties was not significant, not the same with the common varieties. The peroxide value of 8 high oleic acid varieties was zero under each aging treatment, but the peroxide value of two common varieties increased with the aging time. The variation rules of all indicators of artificial aging for 4 days and 6 days were the same with the two natural aging treatments. So artificial aging for 4 days and 6 days can be used for high oleic acid aging test, replace natural aging, which not only shortens the test time but also ensuring the best effect.

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