Benzylaminopurine-induced coupling between calmodulin and Ca-ATPase in wheat root microsomal membranes

Calcium-binding proteins in fungi and higher plants

Calcium has long been known to be required for many vital processes in fungi and plants. High levels of calcium are found in cell walls, vacuoles, and most organelles. In contrast, very low levels of calcium are present in the cytosol of fungal and plant cells. The most recent evidence indicates that calcium is a true second messenger in fungi and plants. Because cyclic AMP does not appear to be a second messenger in plants, calcium is the only known second messenger. Calcium-binding proteins are involved in the events that accompany the action of calcium as a second messenger; three types have been identified in fungi and plants. The first group includes several proteins that bind 45 Ca2+ and are not known to have any enzymatic activity. A second type includes the many enzymes from fungi and plants stimulated by millimolar levels of calcium. The third type of calcium-binding protein, calmodulin, responds to micromolar levels of Ca2+ by binding to certain enzymes and stimulating them. Calmodulin has been detected in every eukaryote thus far examined. The amino acid composition of several fungal and plant calmodulins have been elucidated and found to be very similar to calmodulin from animals. Eight enzymes from fungi and plants have been reported to be regulated either directly or indirectly by calmodulin. Calmodulin antagonists have been used to study the possible involvement of calmodulin in many cellular processes in fungi and plants.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation of ATPase activity by auxin is dependent on ATP concentration

The effect of auxin on membrane-bound ATPase activity was studied in a plasma membrane-enriched fraction from zucchini hypocotyls. The apparent KM of ATPase activity for ATP was decreased in the presence of 10(-6) M auxin so that at very low ATP concentrations the stimulation of ATPase activity was most obvious. The weak auxin analogue, 2,3-dichlorophenoxyacetic acid, stimulated much less than the active auxin 2,4-dichlorophenoxyacetic acid.

The effect of calmodulin and far-red light on the kinetic properties of the mitochondrial and microsomal calcium-ion transport system from corn

The kinetic properties of active Ca(2+) transport into mitochondria and microsomal membrane vesicles prepared from coleoptiles of dark-and light-grown corn seedlings have been studied. The apparent values for K m and V max for Ca(2+) of the mitochondrial transport system from dark-grown plants are about one order of magnitude higher than those from the microsomal transport system. Calmodulin has no effect on the Ca(2+) accumulation into mitochondria whereas the apparent maximum transport velocity and affinity for Ca(2+) of the microsomal Ca(2+)-transport system are both increased by calmodulin. When intact corn seedlings are irradiated with far-red light, the calmodulin-induced increase of the apparent maximum transport velocity and affinity for Ca(2+) can no longer be observed. From these data it can be concluded that the low cytoplasmic Ca(2+) concentration in the cytoplasm of coleoptile cells from dark-grown corn is maintained by a calmodulin-regulated Ca(2+) pump. Irradiation with photomorphogenically active far-red light lowers the Ca(2+)-transport activity and thus causes an increase of the cytoplasmic, free-Ca(2+) concentration. The physiological implications will be discussed.