Floral initiation in Celosia cristata L.: photoperiodic requirement and isozymic changes

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Role of Abscisic Acid in the Induction of Desiccation Tolerance in Developing Seeds of Arabidopsis thaliana

In contrast to wild-type seeds of Arabidopsis thaliana and to seeds deficient in (aba) or insensitive to (abi3) abscisic acid (ABA), maturing seeds of recombinant (aba,abi3) plants fail to desiccate, remain green, and lose viability upon drying. These double-mutant seeds acquire only low levels of the major storage proteins and are deficient in several low mol wt polypeptides, both soluble and bound, and some of which are heat stable. A major heat-stable glycoprotein of more than 100 kilodaltons behaves similarly; during seed development, it shows a decrease in size associated with the abi3 mutation. In seeds of the double mutant from 14 to 20 days after pollination, the low amounts of various maturation-specific proteins disappear and many higher mol wt proteins similar to those occurring during germination are induced, but no visible germination is apparent. It appears that in the aba,abi3 double mutant seed development is not completed and the program for seed germination is initiated prematurely in the absence of substances protective against dehydration. Seeds may be made desiccation tolerant by watering the plants with the ABA analog LAB 173711 or by imbibition of isolated immature seeds, 11 to 15 days after pollination, with ABA and sucrose. Whereas sucrose stimulates germination and may protect dehydration-sensitive structures from desiccation damage, ABA inhibits precocious germination and is required to complete the program for seed maturation and the associated development of desiccation tolerance

Involvement of ethylene in the morphological and developmental response of rice to elevated atmospheric CO2 concentrations

We tested the hypothesis that increased carbohydrate flux under elevated CO2 regulates accelerated development using rice (Oryzasativa L. cv. Jarrah). Plants were grown either in flooded soil or solution culture at either 360 or 700 µ L CO2L–1. Total dry mass, shoot elongation rates (SER), tiller appearance rates (TAR) and ethylene release from intact rice seedlings were measured from 5 to 42 days after planting (DAP). At maturity, shoot and sheath length, tiller number and grain mass were also measured. Elevated CO2 had a profound effect on growth, morphology and development and the effects were more pronounced during the early growth phase. Total aboveground biomass increased at elevated CO2 and this was accounted for by enhanced tiller number. Grain yield was increased by 56% under elevated CO2 mainly due to increased tiller number and hence panicle number. TAR and SER were enhanced at elevated CO2 but SER increased only untill 25 DAP. Elevated CO2 stimulated a 2-3-fold increase in endogenous and ACC-mediated ethylene release but the ACC concentration in the leaves was little affected showing that rates of ACC synthesis matched its oxidation. Inhibition of ethylene action by 1-aminocyclopropane (1-MCP) had a more pronounced inhibitory effect on ethylene release in plants that were grown at 700 as compared to 360 µ L CO2 L–1. Feeding sucrose to intact plants enhanced ethylene synthesis and these results are consistent with the hypothesis that increased accumulation of sucrose at elevated CO2 may enhance expression of genes in the ethylene biosynthetic pathway. We conclude that increase in ethylene release may be central in promoting accelerated development under elevated CO2 and this coincides with the release of auxiliary buds and accelerated rates of tiller appearance hence increased grain yield at elevated CO2

Gene Expression Biomarkers Provide Sensitive Indicators of in Planta Nitrogen Status in Maize[W][OA]

Over the last several decades, increased agricultural production has been driven by improved agronomic practices and a dramatic increase in the use of nitrogen-containing fertilizers to maximize the yield potential of crops. To reduce input costs and to minimize the potential environmental impacts of nitrogen fertilizer that has been used to optimize yield, an increased understanding of the molecular responses to nitrogen under field conditions is critical for our ability to further improve agricultural sustainability. Using maize (Zea mays) as a model, we have characterized the transcriptional response of plants grown under limiting and sufficient nitrogen conditions and during the recovery of nitrogen-starved plants. We show that a large percentage (approximately 7%) of the maize transcriptome is nitrogen responsive, similar to previous observations in other plant species. Furthermore, we have used statistical approaches to identify a small set of genes whose expression profiles can quantitatively assess the response of plants to varying nitrogen conditions. Using a composite gene expression scoring system, this single set of biomarker genes can accurately assess nitrogen responses independently of genotype, developmental stage, tissue type, or environment, including in plants grown under controlled environments or in the field. Importantly, the biomarker composite expression response is much more rapid and quantitative than phenotypic observations. Consequently, we have successfully used these biomarkers to monitor nitrogen status in real-time assays of field-grown maize plants under typical production conditions. Our results suggest that biomarkers have the potential to be used as agronomic tools to monitor and optimize nitrogen fertilizer usage to help achieve maximal crop yields