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

用<Ca^(2+)>研究了豌豆染色质结构与其模板活性的关系。天然染色质的吸收光谱随<Ca^(2+)>浓度的增加而变化。当<Ca^(2+)>存在时，两个Tm消失，出现一个新的更高的Tm。可引起染色质半完全沉降的<Ca^(2+)>浓度对于溶解的天然染色质（更浓缩，尺寸更大）比超声染色质（更浓缩，尺寸更小）要低得多。EGTA存在下重组的染色质比<Ca^(2+)>存在下重组的染色质Tm低。这些结果表明染色质以<Ca^(2+)>聚集。添加少量EGTA可以促进溶解的天然染色质的模板活性，但对超声或变性DNA的模板活性没有促进作用。用DNase <II>裂解，再用Bio-Gel A 5m柱层析，将染色质分离为模板活性片段和非活性片段。当染色质片段在<Ca^(2+)>或EGTA存在下进行色谱分析时，洗脱模式表明<Ca^(2+)>组装了适度消化的染色质组分。此外，在螯合和非螯合条件下，染色质组分的总模板活性降低了<Ca^(2+)>，活性组分在不同的部分被洗脱。为了了解<Ca^(2+)>对体内豌豆根染色质的影响，比较了在全营养培养基和缺乏<Ca^(2+)>培养基培养的豌豆根染色质的一些特性。染色质的熔化曲线和消化率表明，<Ca^(2+)>饥饿条件下染色质结构变得不稳定。

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.