Nature and utilization of seed reserves during germination and heterotrophic growth of young sugar beet seedlings

Abstract

The seed reserves of sugar beet (Beta vulgaris L.) are starch, located exclusively in the perisperm, and lipids, proteins and a small quantity of soluble sugars, located mainly in the cotyledons. It is shown that lipids are the main respiratory substrate used during germination whereas starch and remaining lipids are only hydrolysed after root extrusion, to sustain root and hypocotyl growth. By removing the perisperm during imbibition, it was demonstrated that lipids and proteins alone are sufficient for viable seedling development, though such seedlings grew less than those developing in the presence of perisperm. The utilization of seed reserves was followed during seedling development in the dark in various organs. At 20°C, the reserves were sufficient for 8 d of growth in the dark, the hypocotyl attaining a length of 5 cm. Specific problems relating to field establishment of sugar beet are discussed in relation to these results.

Modifications of Etioplasts in Cotyledons during Prolonged Dark Growth of Sugar Beet Seedlings (Identification of Etiolation-Related Plastidial Aminopeptidase Activities)

“…However, the presence of starch in proplastids and etioplasts ( Fig. 1, a and b) was consistent with the increase of starch content in the embryo from d 2 to d 6, in parallel with the mobilization of starch from the perisperm (E1 Amrani et al, 1992). The amount of carotenoid per cotyledon ( Fig.…”

“…The situation changed between d 6 and d 8, when the amount of protein per plastid remained constant, whereas aminopeptidase activity continued to increase, in parallel with the beginning of Glc limitation, which is most significantly highlighted by the decrease of Glc content and of the adenine nucleotide pool from d 6 and by the effect of exogenous Glc on the greening capacity (El Amrani et al, 1992, 1994. Furthermore, the negative effect of light on the plastidial Ala aminopeptidase activity shows that this activity was related to prolonged etiolation and neither to proplastidetioplast development nor to etioplast-chloroplast development.…”

“…Other types of plastids such as barley chloroplasts have also been shown to contain several aminopeptidase activities (Thayer et al, 1988). These aminopeptidase activities may be normally expressed during plastid development or related to prolonged etiolation per se or to one of its consequences such as Glc limitation (El Amrani et al, 1992, 1994. A number of proteolytic processes with distinct functions have been associated with plastid biogenesis.…”

“…Germination and growth were carried out in the dark at 2OOC. Complete germination as determined by the emergence of the radicle was obtained in 4 d (El Amrani et al, 1992). In some experiments, plantlets were then exposed to light at 400 pmol photon m-'s-' from a metal halide lamp (HQI-TS 400W/D; Osram, Paris, France).…”

“…1, a and b) showed the transformation of proplastids at d 4 into etioplasts at d 6 with the development of the prolamellar body. The dry embryo of sugar beet does not contain amyloplasts (E1 Amrani et al, 1992). However, the presence of starch in proplastids and etioplasts ( Fig.…”