The Arabidopsis thaliana AtOPT3 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of peptide/modified peptide transporters found in archebacteria, bacteria, fungi, and plants. A null mutation in AtOPT3 resulted in embryo lethality, indicating an essential role for AtOPT3 in embryo development. In this article, we report on the isolation and phenotypic characterization of a second AtOPT3 mutant line, opt3-2, harboring a T-DNA insertion in the 5# untranslated region of AtOPT3. The T-DNA insertion in the AtOPT3 promoter resulted in reduced but sufficient AtOPT3 expression to allow embryo formation in opt3-2 homozygous seeds. Phenotypic analyses of opt3-2 plants revealed three interesting loss-of-function phenotypes associated with iron metabolism. First, reduced AtOPT3 expression in opt3-2 plants resulted in the constitutive expression of root iron deficiency responses regardless of exogenous iron supply. Second, deregulation of root iron uptake processes in opt3-2 roots resulted in the accumulation of very high levels of iron in opt3-2 tissues. Hyperaccumulation of iron in opt3-2 resulted in the formation of brown necrotic areas in opt3-2 leaves and was more pronounced during the seed-filling stage. Third, reduced AtOPT3 expression resulted in decreased accumulation of iron in opt3-2 seeds. The reduced accumulation of iron in opt3-2 seeds is especially noteworthy considering the excessively high levels of accumulated iron in other opt3-2 tissues. AtOPT3, therefore, plays a critical role in two important aspects of iron metabolism, namely, maintenance of whole-plant iron homeostasis and iron nutrition of developing seeds.

Stand establishment and early vigor are critical to the successful production of cotton (Gossypium hirsutum L.). Rapid early growth could provide significant advantages to young plants relative to diseases, insects, and weeds. The objectives of this research were to identify traits that contribute to differences in early growth, characterize genotypic variation in early vigor among modern cultivars and advanced breeding lines, and determine the effect of the seed production environment on early vigor. Early growth of 10 genotypes from private companies and 18 unreleased breeding lines was compared through measurements of leaf area and biomass under field conditions in 2 yr. A positive correlation of seed weight and rapid early growth was observed up to 32 d after planting (DAP). Cotyledon area was positively associated with shoot dry weight over the course of the first 52 DAP. Significant genotypic differences were observed for cotyledon and total leaf areas, and for cotyledon, first true leaf, total leaf, stem, and total shoot dry weights in both years within approximately the first 4 wk after planting. No correlation between lint yield and rapid early growth was found. For the first 17 (2009) and 32 (2008) DAP—but not after that—plants grown from seeds produced in distinct environments differed in early vigor. Overall, seeds from breeding lines produced more vigorous seedlings than did seeds of commercial genotypes. Although heritability of the examined traits has not been established, the broad range in values and significant genotypic variation suggest that breeding for enhanced early vigor should be possible without compromising yield.

In comparison with other annual crops, cotton (Gossypium hirsutum L.) seedlings develop slowly after emergence. More rapid seedling development can provide advantages in limiting disease, insect, and weed impacts on cotton seedlings. Information on the mechanisms determining early vigor in cotton is limited. Therefore, three genotypes previously identified to differ in seedling vigor and one commercial cultivar were selected for detailed characterization of early growth in greenhouse and field conditions. Growing environment and genotype effects were significant for many of the measured traits. Environmental conditions prevailing in field and greenhouse conditions differentially affected seedling growth, including cotyledon biomass, root weight ratio (RWR), net assimilation rate (NAR), and specific leaf area (SLA). Genotypic differences were found in one or both environments for cotyledon area, area of the first leaf, total leaf area, and leaf, stem, root, and total biomass. Leaf weight ratio (LWR), stem weight ratio (SWR), RWR, LAR, and SLA differed among genotypes at most stages, but this was not the case for relative growth rate and NAR. The high‐vigor genotype generally had longer roots, larger cotyledons, greater cotyledon, stem, and total biomass, and greater SWR and RWR than the low‐vigor genotype. The low‐vigor genotype had the greatest LAR, SLA, and LWR among the four genotypes. Results obtained in this study suggest that factors such as the efficiency of photoassimilate conversion into biomass, energy density of the biomass, root carbon exudation, and/or photosynthetic rates differ between the low‐vigor and high‐vigor genotypes.

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