Maize starchy endosperm mutants have kernel phenotypes that include a brittle texture, susceptibility to insect pests, and inferior functional characteristics of products made from their flour. At least 18 such mutants have been identified, but only in the cases of opaque2 ( o2 ) and floury2 ( fl2 ), which affect different aspects of storage protein synthesis, is the molecular basis of the mutation known. To better understand the relationship between the phenotypes of these mutants and their biochemical bases, we characterized the protein and amino acid composition, as well as the mRNA transcript profiles, of nearly isogenic inbred lines of W64A o1 , o2 , o5 , o9 , o11 , Mucuronate (

maximum grain size. A growth chamber study by Badu-Apraku et al. (1983) shows a more dramatic yield loss The average temperature in the U.S. Corn Belt during the grainassociated with high temperatures during the period of filling period of maize (Zea mays L.) is above optimum for maximum grain yield. The objectives of this study were to determine the effects grain filling . They observed a 42% loss in grain weight of an extended period of high temperature during grain filling on per plant when day/night temperature from 18 d postkernel growth, composition, and starch metabolism of seven maize silking to maturity was increased from 25/15 to 35/15ЊC, inbreds. Plants were exposed to heat stress (33.5/25؇C) or control (25/ a6 ЊC rise in average daily temperature. 20؇C) day/night temperature treatments in a greenhouse from 15 dThe interaction of heat stress with other environmenafter pollination (DAP) until maturity, and the experiment was contal factors in the field, such as drought stress, makes it ducted in triplicate over time. Root zone temperature was maintained difficult to study the effect of high temperature on maize at 25/20؇C in both treatments. No significant interaction occurred yield in isolation. Furthermore, it may be difficult to between genotype and temperature treatments for nine grain traits. separate the effects of heat stress occurring during grain Heat stress lengthened the duration of grain filling on a heat unit filling from a previously occurring heat stress. The use (HU) basis, but an overcompensatory reduction in kernel growth rate per HU resulted in an average mature kernel dry weight loss of 7% of controlled environments makes it possible to study (P ϭ 0.06). Proportionally similar reductions occurred for starch, more precisely how high temperature treatment affects protein, and oil contents of the kernel. Heat stress also reduced kernel maize grain filling. However, controlled-environment density. A survey of 11 enzymes of sugar and starch metabolism studies should strive to mirror conditions in the field as extracted from developing endosperm revealed that ADPglucose pyclosely as possible. As described below, conditions of rophosphorylase, glucokinase, sucrose synthase, and soluble starch root temperature and photyosynthetically active radiasynthase were most sensitive to the high temperature treatment. Howtion (PAR) intensity can differ between the field and ever, upon adjusting enzyme activities with measured temperature controlled environment and have been shown to be coefficients (i.e., Q 10 ), only ADPglucose pyrophosphorylase exhibited important factors that help determine how plants rereduced activity. Results indicate that chronic heat stress during grain spond to high temperature.filling moderately restrains seed storage processes and select enzymes of starch metabolism to similar degrees across multiple maize inbreds.

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Antibodies were used to probe the degree of association of starch biosynthetic enzymes with starch granules isolated from maize (Zea mays) endosperm. Craded washings of the starch granule, followed by release of polypeptides by gelatinization i n 2 % sodium dodecyl sulfate, enables distinction between strongly and loosely adherent proteins. Mild aqueous washing of granules resulted in near-complete solubilization of ADP-glucose pyrophosphorylase, indicating that little, if any, ADP-glucose pyrophosphorylase is granule associated. In contrast, all of the waxy protein plus significant levels of starch synthase I and starch branching enzyme II (BEll) remained granule associated. Stringent washings using protease and detergent demonstrated that the waxy protein, more than 85% total endosperm starch synthase I protein, and more than 45% of BEll protein were strongly associated with starch granules. Rates of polypeptide accumulation within starch granules remained constant during endosperm development. Soluble and granule-derived forms of BEll yielded identical peptide maps and overlapping tryptic fragments closely aligned with deduced amino acid sequences from BEll cDNA clones. These observations provide direct evidence that BEll exits as both soluble and granule-associated entities. We conclude that each of the known starch biosynthetic enzymes i n maize endosperm exhibits a differential propensity to associate with, or t o become irreversibly entrapped within, the starch granule.Starch has been the subject of much recent interest, with intensive efforts devoted toward improved understanding of its structure, function, biosynthesis, and degradation. Parameters such as the ratio of amylose to amylopectin,

The relative role of the maternal source and the filial sink in controlling the composition of maize (Zea mays L.) kernels is unclear and may be influenced by the genotype and the N supply. The objective of this study was to determine the influence of assimilate supply from the vegetative source and utilization of assimilates by the grain sink on the final composition of maize kernels. Intermated B73×Mo17 recombinant inbred lines (IBM RILs) which displayed contrasting concentrations of endosperm starch were grown in the field with deficient or sufficient N, and the source supply altered by ear truncation (45% reduction) at 15 d after pollination (DAP). The assimilate supply into the kernels was determined at 19 DAP using the agar trap technique, and the final kernel composition was measured. The influence of N supply and kernel ear position on final kernel composition was also determined for a commercial hybrid. Concentrations of kernel protein and starch could be altered by genotype or the N supply, but remained fairly constant along the length of the ear. Ear truncation also produced a range of variation in endosperm starch and protein concentrations. The C/N ratio of the assimilate supply at 19 DAP was directly related to the final kernel composition, with an inverse relationship between the concentrations of starch and protein in the mature endosperm. The accumulation of kernel starch and protein in maize is uniform along the ear, yet adaptable within genotypic limits, suggesting that kernel composition is source limited in maize.