Thermal dependence of malate synthase activity and its relationship to the thermal dependence of seedling emergence

Cotton yields are often reduced by low temperatures at early planting dates. Improved seedling metabolism at low temperatures may enhance seedling performance. The glyoxylate cycle plays a role in the metabolism of stored lipids, and thus thermal limitations on the function of malate synthase (EC 4.1.3.2) may be involved in low-temperature limitations on seedlings. The thermal dependencies of the apparent K(M) and maximal velocity for the malate synthases from cotton (Gossypium hirsutum L.) and sunflower (Helianthus annuus L.) were determined across a 15-45 degrees C thermal range and used to estimate the thermal dependence of reaction velocity. The thermal dependence of seedling emergence was monitored for both species. The thermal dependencies of predicted reaction velocity and the measured rates of seedling emergence are correlated (cotton r(2) = 0.9, sunflower r(2) = 0.76) and suggest that the thermal dependencies of enzymes predicted from basic kinetic parameters may be useful indicators of the thermal dependence of more complex whole-plant processes.