Movement of ¹⁴C-Labeled Assimilates into Kernels of Zea mays L

Abstract

Invertases of the placento-chalazal and pedicel tissues are much more active than invertase from the pericarp of Zea mays L. kernels 12 to 40 days after pollination. Sucrose 9 and 10 Am at 4-day intervals from 12 to 40 days after controlled self-pollination. Husks were removed, and the cobs, with kernels attached, were frozen on Dry Ice and then lyophilized to a constant dry weight. Prior to freezing, the pericarp at the distal end of each kernel was slashed through to the endosperm to accelerate dehydration and to prevent kernel collapse. Fifty kernels were removed from each ear, and the placento-chalazal and pedicel tissues were excised, re-dried (by lyophilization), and weighed. As a measure of invertase activity in maternal tissue not involved in sugar transport, pericarp tissues from the upper half of 25 freeze-dried kernels were excised and treated as above.Samples of the placento-chalazal tissue and subsamples of a similar dry weight of pedicel and pericarp tissues (70 mg) were homogenized with a Duall' tissue grinder (Kontes Glass Co., Vineland, N. J.) in 10 mm tris-maleate buffer, pH 7.0. The suspended material was precipitated by centrifugation at 30,900g for 20 min. The precipitates were washed twice with the tris-maleate buffer and the successive extractants combined. To remove the soluble sugars, the crude extracts were dialyzed overnight against 10 mM tris-maleate buffer. pH 7.0. The dialyzed extract was adjusted to 50 ml with 10 mM trismaleate buffer and used as the source of soluble enzymes. All of the above operations were done at 4 C. This extraction procedure was a modification of that employed by Tsai et al. (13) in their study of the enzymes of carbohydrate metabolism of '

Enzyme Activities of Starch and Sucrose Pathways and Growth of Apical and Basal Maize Kernels

“…The importance of sucrose synthase was suggested by studies in which the shrunken-l maize mutant, having 10% as much sucrose synthase as normal endosperm, formed 40% less starch than normal genotypes (3) 2Abbreviations: ADPG-PPase, ADP-Glc-pyrophosphorylase; DAP, days after pollination; gdw, grams dry weight; gfw, grams fresh weight. invertase was suggested by radiotracer studies which indicated that sucrose was hydrolyzed in the cell wall free space prior to hexose uptake by endosperm cells (19,20).…”

“…It has been determined that starch synthesis in cereal grains involves the synthesis of ADP-Glc by ADPG-PPase2 and the incorporation of ADP-Glc into starch by ADP-Glc starch synthase (13). The invertase was suggested by radiotracer studies which indicated that sucrose was hydrolyzed in the cell wall free space prior to hexose uptake by endosperm cells (19,20).Earlier-forming kernels on a plant usually have higher survival probability (22), longer growth duration (24), and higher growth rates (21) than later forming kernels. In maize ears, the apical florets develop and pollinate several days after basal florets (24,25).…”

“…It has been determined that starch synthesis in cereal grains involves the synthesis of ADP-Glc by ADPG-PPase2 and the incorporation of ADP-Glc into starch by ADP-Glc starch synthase (13). The assimilation by endosperm of sucrose imported via phloem could involve sucrose synthase operating in the direction of ADP-Glc or UDPGlc and fructose formation (3) or involve invertase to form free hexose (20). The importance of sucrose synthase was suggested by studies in which the shrunken-l maize mutant, having 10% as much sucrose synthase as normal endosperm, formed 40% less starch than normal genotypes (3) 2Abbreviations: ADPG-PPase, ADP-Glc-pyrophosphorylase; DAP, days after pollination; gdw, grams dry weight; gfw, grams fresh weight.…”

“…It has been determined that starch synthesis in cereal grains involves the synthesis of ADP-Glc by ADPG-PPase2 and the incorporation of ADP-Glc into starch by ADP-Glc starch synthase (13). The invertase was suggested by radiotracer studies which indicated that sucrose was hydrolyzed in the cell wall free space prior to hexose uptake by endosperm cells (19,20).…”

Free Sugars in Relation to Starch Accumulation in Developing Rice Grain

“…Qualitative and quantitative changes in the free sugars have been studied in the developing grains of barley (11,19), corn (23), and wheat (1, 11), but not for rice. Murata et al (20) detected stachyose, aside from sucrose, glucose, and fructose in developing rice grains at the midmilky stage but did not confirm the consistent presence of raffinose.…”