Changes in Chloroplast Fine Structure During the Autumnal Senescence of Betula Leaves

Abstract

During the ageing and senescence of leaves of the birch tree, Betula verrucosa Ehrb., from the fully expanded green state to the yellow terminal condition, the shape of the chloroplasts alters and their volume decreases to less than one-fifth. Associated with these changes is an initial increase in the number of chloroplast lamellae and size of the grana but this is followed by the breakdown of the membrane systems. The chloroplast lipid globules increase considerably in size but show little increase in number. The structure of the chloroplast membranes is described in detail. Small particles approximately 8 × 5 nm, become visible on the inner surfaces of the thylakoid membranes during chloroplast breakdown. The chloroplasts are the first organelles to show signs of senescence and are the last to remain after the other organelles have all broken down. The observations are discussed in relation to the senescence of chloroplasts of herbaceous plants and the development of chromoplasts of fruits.