ULTRASTRUCTURAL CHANGES OF PLASTIDS IN FLAX EMBRYOS CULTIVATED IN VITRO

Abstract

The ultrastructure of plastids in the cells of flax cotyledons was investigated at three stages during embryogenesis and germination: (1) immature 14‐day old green embryos excised from seeds, (2) 24‐day old embryos which yellowed following a 10‐day cultivation in vitro and (3) 34‐day old embryos which grew for 20 days on the medium and after a temporary loss of pigment regreened and germinated. For comparison, the ultrastructure of chloroplasts from the mature leaves was also investigated. The chloroplasts of 14‐day old embryos are characterized by a well‐developed system of both the grana and the intergranal lamellae and stroma which contains starch grains and phytoferritin. During cultivation in vitro the dimensions of plastids decrease and the internal structure of the chloroplasts undergoes disintegration. In the stroma of plastids of the 24‐day old embryos, lamellae of different length, vesicles and electron‐dense, membrane‐bound bodies and numerous plastoglobulin can be identified and amoeboid plastids occur in the cells. During continued cultivation the dimensions of plastids again increase and in them again differentiation of the system of grana and intergranal lamellae can be observed. The structure of plastids in the 34‐day old embryos is in good agreement with the structure of those in the mature, assimilating leaves of flax. The results indicate that the basic developmental pathway takes place in the same plastids of the flax embryos once during the embryogenesis and once during germination. Copyright © 1981, Wiley Blackwell. All rights reserved