英语语法分析

Tapetal cells always contain rich DNA, RNA and protein.

绒毡层细胞始终含丰富的DNA、RNA、蛋白质。

In tetrad stage, the structures of tapetal cells begin to dissociate.

四分体时期，绒毡层细胞内部结构开始解体。

Tapetal cells degenerate completely when pollen grains reach maturity.

当花粉成熟时，绒毡层细胞完全解体。