Senescence of Cotyledons of Germinating Peas. Influence of Axis Tissue.

Seniescenice at the cellular, organ, and organism levels is a poorly understood but nonetheless well established fact. Regardless of the level at which senescence is studied and regardless of the possible interactions between different organs and cells of different ages and functions, senescence is an expression of events at the cellular and subcellular levels. An ideal material, therefore, for studying senescence would seeni to be a homogeneous population of nondividing cells: that is, a stationary phase cell suspensioIi culture derived from a single cell. Less ideal materials from the standpoint of homogeneity, but more readily available, are the endosperm and cotyledons of germinating seeds. The cotyledons of the pea have been selected because they are a convenient size, they are hypogeous, they do not develop into green leaf-like structures, their cells are fixed postmitotic diploid without associated endosperm cells, and their normal life span is 2 to 3 weeks. This paper describes the influence of a factor or factors from the axis tissues on the course of senescence of excised pea cotyledons. Earlier papers (4, 5) reported the formation of phosphatase and amylase activities in the cotyledons of germinating peas and the fact that the phosphatase activity did not develop in the excised cotyledons. Also the mitochondria of the excised cotyledons lost phosphorylative function after about two days and oxygen uptake capacity after 3 days. In addition, the excised cotyledons failed to incorporate glycine-C14 into TCA precipitable proteins after 3 days. These observations were sufficient to indicate an important interaction between the axis tissues and the cotyledons of the germinating pea. Although it seemed logical to suppose that some beneficial factor from the axis tissues was moving into the cotyledons, it