ABSTRACT

Plasma membranes were isolated from light‐grown, 14‐day‐old maize leaves (Zea mays L. cv. Golden Cross Bantam) using aqueous two‐phase partitioning. The plasma membrane (PM) fraction contained < 0.3% of the total chlorophyll, < 0.2% of the mitochondrial marker enzyme activity, minimal contamination by endomembranes and 34% of the total PM. A calmodulin‐stimulated (Ca2++ Mg2+)‐ATPase was identified in the PM‐enriched fraction. The Ca2++ calmodulin stimulation was dependent on Mg2+, saturated at ca 25 μM total Ca2+, had a pH maximum at 7.2 and was maximally stimulated by 600 nM bovine brain calmodulin. The stimulation was not greatly affected by the anion present and showed a divalent cation specificity of Ca2+ > Sr+2 ± Mn+2 > Co2+± Cu2+ > Ba2+. The napthalenesulfonamide W7, an antagonist of calmodulin action, completely inhibited the calmodulin stimulation at 175 μM, while the less active analogue W5 was ineffective at this concentration. La3+, an inhibitor of PM Ca2+ transport, showed a 50% inhibition of calmodulin‐stimulated ATPase activity at ca 200 μM. Taken as a whole, these data demonstrate the presence of a calmodulinstimulated, (Ca2++ Mg2+)‐ATPase on the cytoplasmic surface of the plasma membrane of maize leaf cells.

No abstract

Water containing 6 mM sodium bicarbonate was used for soaking mung bean seeds for 9 hrs arid for frequent spraying of sprouts for the rest of 5 days. A concentration series of calcium as nitrate showed that 0.25 meq/1 calcium in this solution was sufficient for maximum yield in 5 days; additional calcium up to 6 meq/1 did not increase yield. The requirement for calcium was independent of the effect of calcium on partially preventing sodium uptake. Calcium in the dry seed did not replace the requirement for external calcium. The minimum calcium requirement was associated with maintaining or increasing the 9-hr. calcium content for the rest of the 5-day growing period.