Expression of cell wall invertase from maize cell suspension culture aftera long term chelation of extracellular calcium

The cell wail-bound form of invertase (EC 3.2.1.26) from a maize cell suspe nsion culture was affected by removal of extracellular calcium, over time, at RNA, protein and enzyme activity level. The increase in enzyme activity was detected in cells treated with 5 mM EGTA, which preferentially chelates extracellular Ca2+. Although the enzyme activity of EGTA-treated cells was low and similar to the control after 24 hours of incubation, it started to increase soon thereafter. It reached the maximum after 96 hours, when a de cline of invertase activity had already been detected in the control sample s. The amount of the invertase protein corresponds to its determined specif ic activity. Calcium depletion also induced Incw1 mRNA accumulation, and th e concentration of Incw1 mRNA in EGTA-treated cells was 1.7 times higher th an in the control after the first 24 hours. It remained high in the next 24 hours and slowly decreased throughout a 96 hour-incubation. At the end of the experiment the transcript level decreased and reached that of the contr ol. The possible association of the cell wall invertase with the cell wall- bound calcium is discussed.