Plant cells contain various types of plastid, the best known among which is the chloroplast. Apart from their predominant interest for the work on photo synthesis, however, chloroplasts have attracted considerable attention for other reasons. This pertains to extranuclear inheritance of cell organelles and, particularly important for this series, to the participation of chloroplasts as discrete and partly autonomous cell constituents in the developmental biochemistry of plants. This volume is composed of articles by investigators who are actively involved in work on various aspects of research on chloroplasts. Each author has independently covered and analyzed as comprehensively as possible the particular aspects assigned to him. This has the advantage of bringing out many different facets of the situation, though some overlapping has-to be taken into account. We are sure that this volume will enable the reader to gain a broad theoretical and experimental basis for the understanding of the development of chloroplasts and the relationship between plant cells and these organelles."

Three years have elapsed since the publication of the first edition of this book (in German). The continued interest of our readers and the rapid progress of our knowl edge in many fields necessitates a thoroughly revised and somewhat enlarged new edition. Cell differentiation is a prerequisite of life. It is defined as the prooess leading to the qualitatively and quantitatively selective realization of distinct parts of a given genetic material. Cell differentiation comprises five main aspects: (1) signal reception and transformation, (2) selective rearrangements of the genetic material, (3) differen tial gene expression, (4) organization of gene expression programs and (5) intercellular coordination of cell differentiation within the developmental programs of multicellular organisms. Despite the bewildering multiplicity of its results, i.e., the differentiated phenotypes of cells, there are apparently fundamental similarities with respect to the molecular mechanisms of the process itself. These mechanisms constitute the central subject of this book."