During maize (Zea mays L.) growth, the stalk elongates in a sigmoidal pattern. This overall pattern arises from the variable growth rates of individual internodes comprising the maize stalk. To discern differences in growth rate among internodes of the stalk, individual elongation rates and patterns were determined in a single‐cross hybrid. When each of 12 aboveground internodes (7 through 18) of growth‐chamber‐grown plants reached approximately 10 mm in length, they were dotted along their lengths with black acrylic paint at 1‐mm intervals and photographed daily over 35 d. Full‐scale photographs documented that all internodes elongated sigmoidally, in a basipetal direction. Elongation began slowly and uniformly throughout the length of the undeveloped internode during the first 2 to 3 d, increased in rate and shifted basipetally from the upper internode region toward the middle, and later, toward the basal region of the enlarging internode. Elongation decelerated in the intercalary meristem region during the final days of internode lengthening. Internodes 8 through 12 elongated similarly with the greatest dally growth rates. Internodes 13 and 14, which supported developing ears, had the longest elongation periods but slower growth rates and shorter final lengths than other internodes. Internode 15 had a rapid rate of growth like I8 through 12, but an elongation pattern similar to I13 and 14. Evidence from this study indicates that the relative position of internodes in the emerging stalk hierarchy and the functional role of internodes in stalk development influences individual internode growth rate, elongation period, and developmental pattern.
To ascertain the temporal relationships of phenylpropanoid and lignin pathway enzymes, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol-NADPH dehydrogenase (CAD), with lignin concentration, PAL and CAD activities and lignin concentrations were assessed during progressive development of the 10th internode in maize (Zea mays L). Enzyme activities were quantified and lignin concentrations were determined by the detergent system of fiber fractionation from lower, middle, and upper sections of the elongating internode harvested 3, 5, 7, 9, 11, 13, and 15 days after the internode had reached 10 mm in length. Over 15 days, a coordinated, sequential, and basipetal pattern of enzyme activities and lignin accumulation evolved through the internode, spanning the stages of rapid elongation, cellular differentiation, and secondary cell wall formation. PAL activity was initiated first, rising to peak activity in elongating tissue, and falling basipetally in tissues as they matured. CAD activity rose in fully elongated, maturing internode tissue where PAL activity was waning following its peak activity. Lignin accumulated in tissues with high CAD activity. CAD activity and lignin deposition patterns were similar : simultaneously increasing in activity and deposition over time while activity and deposition also shifting basipetally through the internode, keeping pace with secondary cell wall formation. Lignin concentration correlated significantly with CAD, but not with PAL.
Mini-watermelon [Citrullus lanatus (Thunb.)] cultivars Valdoria and Vanessa were evaluated at 20, 30, 40, or 50 days after anthesis to determine maturity at harvest. Fruit circumference, weight, ground spot color, and number of senescent tendrils were measured as external indicators for each watermelon. Soluble solids content (SS), pH, and SS:total acid ratio (SS:TA) of each watermelon were determined to provide an indication of internal maturity. Regression and Akaike Information Criterion fit statistics analyses were performed to determine significant relationships and best predictors for external indicators of internal maturity factors. In this study, external predictors were most closely linked to fruit pH rather than to SS or SS/TA. Of the external indicators tested, fruit weight, circumference, number of senescent tendrils, and International Commission on Illumination (CIE) b* color coordinate values of the ground spot were best related to fruit pH. According to the regression models, two completely senesced tendrils, a circumference of 53 cm, weight of 3 kg, and CIE b* coordinate ground spot value of 40 are each sufficient to predict maturity when pH is used as the internal indicator of maturity under the conditions of this experiment.
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