Pigmented Plant Tissues in Culture II. Growth, Development and Decline of Chlorophyllous Tissues

Abstract

During the phase of exponential growth in chlorophyllous callus cultures derived from Haplopappus gracilis, Hypochaeris radicata, and Acer pseudoplatamus, cells double their number on the average, and also their volume, in about 4.3, 6.6, and 9–2 days respectively. The two rates decline subsequently but cell expansion continues for a short time after division has ceased. With cultures of Oxalis dispar, however, which have an average cell generation time of about 10 days, there is first a short exponential phase dominated by division, and this is followed by a series of phases dominated alternately by either division or expansion. Chlorophyll accumulation does not occur in Haplopappus during the exponential phase (chlorophyll a decreases) but there is a slow accumulation of caro-tenoids. The bulk of the pigments accumulate during the declining phase of growth mainly after division has ceased. With Hypochaeris and Acer, on the other hand, accumulation is most intense during the exponential phase, and few pigments are added later. With Oxalis, most of the accumulation occurs after the exponential phase; carotenoids accumulate until the cessation of growth whereas chlorophylls start to decline before this. With all species, pigments decline after the cessation of growth. The loss is small in Haplopappus and the tissues are still bright green when the medium dries out: Hypochaeris and Oxalis, in contrast, eventually become colourless. The data are discussed in relation to the changes in pigment content that accompany the growth and development of a single cell in each species.