Movement of ¹⁴C-labeled Sugars into Kernels of Wheat (Triticum aestivum L.)

Abstract

An anatomical study of wheat (Triticum aestivunt L.) kernels 14 days after anthesis revealed that the tracheary elements of the pericarp vascular bundle are not in direct continuity with those of the rachilla. The phloem was continuous from the rachilla into the crease of the pericarp.Shortly after exposure of the flag leaf to '4CO2, relatively high proportion of the "C extracted from the pericarp and endosperm was found in glucose and fructose. With additional time, the percentage of 14C in the monosaccharides declined and that in sucrose increased to a maximum 3 hours after "CO2 exposure. The monosaccharides comprised about onehalf of the soluble sugars extracted from the pericarp. Based on these observations, it appeared that sucrose hydrolysis might be prerequisite to sugar movement from the terminal phloem elements in the pericarp and into the endosperm. However, when "4C-fructosyl-sucrose was injected into the peduncle, there was little additional randomization of the 14C between the glucose and fructose moieties of sucrose extracted from the pericarp and endosperm compared to the rachis sucrose. If we assume that injected sucose was transported to the kernels via the phloem, then either sucrose moves out of the terminal phloem elements in the pericarp and into the endosperm unaltered, or if hydrolysis and resynthesis are a prerequisite to transport into the endosperm, the products of hydrolysis are not freely available for isomerization.Phloem elements responsible for the transport of sugars from leaves to developing maize (Zea mays L.) kernels terminate in the pedicel (upper rachilla) (14). Sugars in transit to a developing kernel move out of the phloem elements in the pedicel through the placento-chalazal tissue and into the endosperm ' (7) concluded that nutrients entering a wheat kernel through the vascular bundle at the base of the crease move across the chalaza and out into the endosperm through the nucellar projection.We showed previously that sucrose is cleaved to glucose and fructose prior to or during movement into the starchy endosperm of maize (27) both edges of the assimilate chamber to form a gas-tight seal around the flag leaves. Four 300-w General Electric4 cool lamps positioned above the photosynthetic chamber (Fig. 1B) supplied approximately 3100 ft-c of light intensity at the level of the flag leaves. The flag leaves of 10 plants, growing in separate pots, were enclosed in the assimilation chamber. A vacuum pump was attached to the air inlet and greenhouse air was pulled through the chamber for 30 min. Following the 30-min equilibration period, the vacuum pump was removed and the '4CO2 generator was inserted between the air inlet and outlet forming a closed system. To generate "4CO2, 0.5 ml of 80% lactic acid was added to a vial containing 1 mg of Ba'4CO3 (129 uCi). The released '4CO2 was swept into the chamber by 'Mention of a trademark name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the United States Department of Agriculture ...

Characterization of a Granule-Bound Starch Synthase Isoform Found in the Pericarp of Wheat

“…The pericarp is the wall of the mature ovary and surrounds the entire seed (Sakri and Shannon, 1975). Investigations of wheat pericarp morphology showed that blueblack-staining starch granules appear in this tissue at about the time of anthesis (Eckerson, 1917;Sandstedt, 1946;Jenkins et al, 1975).…”

A Kinetic and Microautoradiographic Analysis of [14C]Sucrose Import by Developing Wheat Grains

“…In wheat grains, where assimilates must pass through the crease tissues to reach the endosperm (Ugalde and Jenner, 1990), we have shown that the sucrose in these tissues consists basically of a single well-mixed compartment. As shown by others (Sakri and Shannon, 1975;Ho and Gifford, 1984), sucrose moves without inversion from the phloem to the endosperm. This knowledge is fundamental for confident interpretation of observations concerning sucrose movement into the grain, especially where experimental conditions alter the transport rate.…”

“…Some observations are available on this topic (Jenner, 1974;Sakri and Shannon, 1975;Donovan et al, 1983;Ho and Gifford, 1984;Lingle and Chevalier, 1984;Ugalde and Jenner, 1990), but they are not sufficiently detailed for quantitative compartmental analysis. Our aim was to develop a compartmental model of sucrose pools within the maternal grain tissues by following 14 C kinetics at several points along the transport pathway from the peduncle phloem to the endosperm cavity and to localize the sites of these pools within the tissues.…”

[14C]Sucrose Uptake and Labeling of Starch in Developing Grains of Normal and segl Barley

“…The palea and lemma were removed from each grain, and the grains from several spikes of each genotype were pooled for each experiment. Five grains were incubated in 10-ml beakers containing 1 4,8,12,16,20. Paleas and lemmas were removed and the pericarps were carefully peeled off.…”

“…We investigated segl, a mutant of the cultivar Betzes, which produces seed with 35 to 55% of normal dry weight (2). Mutant 11), but not of wheat (Triticum aestivum L.) (6)(7)(8). Sucrose hydrolysis during transport into barley endosperm has not been studied using '4C-labeled sugars, but in a recent study of wheat and barley involving enzyme assays and sugar analysis it was suggested that sucrose is not cleaved as it enters the endosperm of either species (1).…”