When pollen maturating , many small calcium precipitates distributed in its cytoplasm, especially in nucleus.接近开花时的成熟花粉粒细胞质中, 细小的钙颗粒主要分布在营养细胞和生殖细胞中....

maturating的音标：...

v.成熟( maturate的现在分词 )...