Structure characteristics and function of maize endosperm transfer cells

Abstract

Endosperm transfer cells develop wall ingrowths to enlarge plasma membrane area and facilitate nutrient transport. In order to clarify structure characteristics and changes of maize endosperm transfer cells, the different developmental stages of the maize fruits (caryopses) were investigated using different types of microscopy. The results indicated that (1) Maize endosperm transfer cells exhibited spatial and temporal organizational characteristics. The transfer cells of endosperm at polar end developed wall ingrowths close to maternal transport tissues. The initial wall ingrowths developed in the outermost layer were very dense, but the initial wall ingrowths formed later in the inner layers were few. Endosperm transfer cells degenerated first in the inner layers and subsequently the outermost layer. (2) Except wall ingrowths, the cell inner structures underwent degeneration to reduce resistant of nutrient transport. (3) The occurrence of many mitochondria in the developing endosperm transfer cells probably supplied energy for wall material synthesis of wall ingrowths and solute exchange of plasma membrane outlining beneath the wall ingrowths. (4) The endosperm transfer cell development could be influenced by the caryopsis vascular system and the placentochalaza via the sugar level control. (5) The endosperm transfer cell development was coordinated with the growth of caryopsis, embryo, and starchy endosperm. Thus, we concluded that endosperm transfer cells played a very important part in maize caryopsis growth and their development was affected by maternal transport tissues and filial sink tissues.