Behavior of calcium in plant nuclei and its regulative role on the function of chromatin

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The relationship between pea chromatin structure and its template activity was investigated in relation to <Ca^(2+)> . The absorption spectrum of native chromatin changed with increasing <Ca^(2+)> concentration. In the presence of <Ca^(2+)> the two Tms disappeared and a new higher Tm appeared. The concentration of <Ca^(2+)> to cause half complete sedimentation of chromatin was much lower for the solubilized native chromatin (more condensed and larger in size) than for the sonicated chromatin (less condensed and smaller in size). The reconstituted chromatin in the presence of EGTA showed a lower Tm than the chromatin reconstituted in the presence of <Ca^(2+)> . These results suggest that chromatin aggregate with <Ca^(2+)> . Addition of a small amount of EGTA promoted the template activity of solubilized native chromatin, but not that of sonicated or denatured DNA. Furthermore, chromatin was fractionated into template active and inactive fragments by cleavage with DNase <II> followed by fractionation with Bio-Gel A 5m column chromatography.When the chromatin fragments were chromatographed in the presence of <Ca^(2+)> or EGTA, the elution patterns suggested that <Ca^(2+)> assembled modelately digested chromatin fractions. Moreover, total template activity of chromatin fractions was reduced by <Ca^(2+)> and the active fraction was eluted at different portions under the chelated and non-chelated conditions.In order to know the effect of <Ca^(2+)> on chromatin in vivo, some properties of chromatin from pea roots cultured with full nutrients or the medium lacking <Ca^(2+)> were compared. The results concerning the melting curve and digestibility of chromatin suggest that chromatin structure became less stable in <Ca^(2+)> starved condition.