TRICHOBLASTS IN HYDROCHARIS. II. NUCLEIC ACIDS, PROTEINS AND A CONSIDERATION OF CELL GROWTH IN RELATION TO ENDOPOLYPLOIDY

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Abstract
As shown previously, the trichoblasts of Hydrocharis morsus‐ranae L. are the smaller, more proximal (i.e., basal) products of unequal divisions of protodermal cells in the root tip. During development their nuclei and nucleoli attain greater volume than those of individual adjacent ordinary epidermal cells, the products of the sister cell of the original unequal division. Histochemical tests, microspectrophotometric measurements and historadioautographs show that the trichoblasts also contain more nucleohistone, total protein, nucleolar and cytoplasmic RNA, and more nuclear DNA than neighboring cells at the same distance from the root apex. The trichoblasts fail to divide, and their nuclei become increasingly polyploid with distance from the root tip until they have approximately 8 times as much DNA as the nuclei of adjacent epidermal cells, or about 18 times as much as the cells from which both types of cells originated. It is suggested that all plant cells pass through two phases of enlargement, an initial phase characterized by synthesis of DNA and cytoplasmic constituents and a later phase characterized by extensive vacuolation and intake of water. Because of the delayed maturation, the inhibition of cytokinesis, and the polyploid nature of the trichoblasts of Hydrocharis, these phases are more readily separable than in many other cells. Polyploidy is probably not a necessary prerequisite for formation of a root hair, though it affects the degree of cell growth, but a delay in maturation is probably one essential factor in the differentiation of such cells.
Funding Information
  • National Science Foundation (GB‐6591)