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.

1994, Carbohydrate starvation is a major determinant of the loss of greening capacity in cotyledons of dark-grown sugar beet seedlings, -Physiol, Plant, 91: 56-64.The transition of cotyledons from heterotrophy to autotrophy is a critical step of seedling establishment. We have studied the greening capacity of sugar beet (Beta vulgaris L. cv, Vega) cotyledons in relation to carbohydrate and energy metabohsm during dark growth. During early growth, sugar beet cotyledons behaved mainly as a lipid-mobilizing and gluconeogenic tissue providing substrates to the seedling. Reserve mobilization was followed by a maximum of the adenine nucleotide pool on day 6 in strict correlation with the maximum of greening capacity. This was immediately followed by the onset of a typical situation of carbohydrate starvation characterized by substrate limitation of respiration, a decrease in the adenine nucleotide pool and, as shown by the respiratory quotient and the loss of proteins, a probable utilization of cellular proteins and lipids to sustain respiration. The conversion from etioplast to chloroplast, as determined by the rate of chlorophyll synthesis, was less and less efficient as carbohydrate starvation continued, finally leading to incomplete and heterogeneous greening on day 12, The relationship of the loss of greening capacity with carbohydrate starvation is discussed.

The transition of cotyledons from heterottophy to autotrophy is a critical step of seedling establishment. We have studied the greening capacity of sugar beet (Beta vulgaris L. cv. Véga) cotyledons in relation to carbohydrate and energy metabolism during dark growth. During early growth, sugar beet cotyledons behaved mainly as a lipid‐mobilizing and gluconeogenic tissue providing substrates to the seedling. Reserve mobilization was followed by a maximum of the adenine nucleotide pool on day 6 in strict correlation with the maximum of greening capacity. This was immediately followed by the onset of a typical situation of carbohydrate starvation characterized by substrate limitation of respiration, a decrease in the adenine nucleotide pool and, as shown by the respiratory quotient and the loss of proteins, a probable utilization of cellular proteins and lipids to sustain respiration. The conversion from etioplast to chloroplast, as determined by the rate of chlorophyll synthesis, was less and less efficient as carbohydrate starvation continued, finally leading to incomplete and heterogeneous greening on day 12. The relationship of the loss of greening capacity with carbohydrate starvation is discussed.