Relationships between leaf expansion and MeOH-soluble (cytosol) and cell-wall fractions, and their sugar composition prior to silking in flint corn lines were studied. A greater husk leaf area of one genotype, X-15 is mainly due to prolonged and higher rate of expansion. Prior to rapid expansion of husk leaf area, neutral sugars in the cytosol fraction accounted for most of the non-starch carbohydrates (56-62 %), while hemicellulose and cellulose fractions accounted for less than 20 %. In mature leaf parts, however, sugars in the cytosol fraction decreased but those in hemicellulose and cellulose fractions increased by 30 % and 42 %, respectively. The predominant sugar in the cytosol fraction was glucose (Glc), while in the hemicellulose fraction xylose (Xyl) and arabinose (Ara) dominated. During rapid expansion of husk leaves, "$C was incorporated at a higher rate into hemicellulose than cellulose, and this process was more active in X-15 than in other genotypes. During an identical period, "$C atom % excess in Xyl increased markedly in the hemicellulose fraction, however it remained low in the cytosol one. The current results suggest that synthesis of Xyl and xylan plays an important role in renewal of hemicellulose, which may be required for expansion.

No abstract

Some corn (Zea mays L.) genotypes produce husk leaves (laminae extending from the husk) that on a per unit area basis, contribute more photosynthate to grain production than culm leaves. Furthermore, a high correlation between husk leaf area and dry weight has been observed, but little is known about the changes in cell components during development of husk leaves. A field experiment was conducted to quantify methanol (MeOH)‐soluble fraction (cytosol) and incorporation of 13C‐labeled photosynthate in cell walls from 9 d before silking (DBS) to silking. The ear leaf of flint corn (F1 of N‐19 by X‐15) was subjected to 13CO2 eight DBS. Leaf area, dry weight, and photosynthetic activity of the husk leaves, and sugar content of various cell components were measured continuously during the 9‐d period. The husk leaf attained one‐half of its maximum apparent photosynthetic rate (Po) when it had 8% of its maximum leaf area at 4 DBS. At 9 DBS, neutral sugars in the MeOH‐soluble fraction accounted for most of nonstarch carbohydrates within the husk leaf (68%), while hemicellulose and cellulose fractions accounted for <10%. At silking, however, sugars in the hemicellulose and cellulose fractions increased by 23 and 56%, respectively. Results of 13CO2 labeling suggest that during rapid husk leaf development, MeOH‐soluble fraction decreases, while the hemicellulose fraction fluctuates, and cellulose fraction increases.

No abstract