BackgroundDrought is one of the most important abiotic stresses causing drastic reductions in yield in rainfed rice environments. The suitability of grain yield (GY) under drought as a selection criterion has been reported in the past few years. Most of the quantitative trait loci (QTLs) for GY under drought in rice reported so far has been in the background of low-yielding susceptible varieties. Such QTLs have not shown a similar effect in multiple high- yielding drought-susceptible varieties, thus limiting their use in marker-assisted selection. Genetic control of GY under reproductive-stage drought stress (RS) in elite genetic backgrounds was studied in three F3:4 mapping populations derived from crosses of N22, a drought-tolerant aus cultivar, with Swarna, IR64, and MTU1010, three high-yielding popular mega-varieties, with the aim to identify QTLs for GY under RS that show a consistent effect in multiple elite genetic backgrounds. Three populations were phenotyped under RS in the dry seasons (DS) of 2009 and 2010 at IRRI. For genotyping, whole-genome scans for N22/MTU1010 and bulked segregant analysis for N22/Swarna and N22/IR64 were employed using SSR markers.ResultsA major QTL for GY under RS, qDTY1.1, was identified on rice chromosome 1 flanked by RM11943 and RM431 in all three populations. In combined analysis over two years, qDTY1.1 showed an additive effect of 29.3%, 24.3%, and 16.1% of mean yield in N22/Swarna, N22/IR64, and N22/MTU1010, respectively, under RS. qDTY1.1 also showed a positive effect on GY in non-stress (NS) situations in N22/Swarna, N22/IR64 over both years, and N22/MTU1010 in DS2009.ConclusionsThis is the first reported QTL in rice with a major and consistent effect in multiple elite genetic backgrounds under both RS and NS situations. Consistency of the QTL effect across different genetic backgrounds makes it a suitable candidate for use in marker-assisted breeding.

Monomeric, but polymerizable, lecithins with diacetylenic fatty acyl chains, such as l,2-bis(10,12-tricosadiynoyl)-.w-glycero-3-phosphocholine (DCg 9PC), are known to form tubular microstructures when liposomes of these lipids are cooled through their chain melting transition. These lipids are soluble in alcohols and other organic solvents, but when such solutions are diluted with water at appropriate temperatures, precipitates form. From optical and electron microscopy the precipitates are seen to consist of tubules and long, open helical structures with diameters similar to those of the tubules. These helices are all right handed when made from lipid with the naturally occurring chiral head group. For an ethanol/water system the proportion of helices and tubules depends on the ratio of the solvent to nonsolvent, as does the overall length of the tubules. The temperature, lipid concentration, and specific solvent used also affect the nature of the precipitate. For DCg 9PC the tubular and helical microstructures vary from 0.3 to 3 pm in diameter, and from 5 to over 1000 pm in length. The width and pitch of the helical ribbons are variable, resulting in a range of structures from open helices to continuous tubules depending on the solvent system used. Upon exposure to energetic radiation such as UV rays or 7-rays, the diacetylenic units polymerize without causing loss of the helical or tubular microstructure, thereby stabilizing the microstructures. Demonstration of this formation route for tubules suggests that they are thermodynamically stable, not accidental products of deforming liposomes. The existence of this polymerizable helical microstructure that may be an intermediate in the formation of tubules supports previous indications of an underlying helical structure to tubules. This precipitation method also affords a simple method of controlling the dimensions of tubules and a screening method for the discovery of other self-organizing lipid microstructures.

Molecular self-assembly is of key importance for the rational design of advanced materials. To investigate the causal relation between molecular structure and the consequent self-assembled microstructure, self-assembled tubules of diacetylenic lipids were studied. Circular-dichroism studies give experimental evidence that the formation of tubules is driven by chiral molecular packing, in agreement with recent theories of tubules. On the basis of these results, a molecular mechanism for the formation of tubules is proposed.

Several techniques for controlling the morphology of self-assembled lipid tubules are investigated by using circular dichroism spectroscopy and electron microscopy. These studies show that variations in the molecular structure of the diacetylenic phospholipid, lipid concentration, and solution conditions allow for control of the number of bilayers in the tubule walls, but not their diameter. Tubules formed in water and mixtures of alcohols adopt interesting morphologies and allow for further control of tubule structure. In addition, studies of lipids with different acyl chains show that tubule morphology is sensitive to the degree of order within the chains. Because of the chiral molecular architecture in lipid tubules, intense peaks in their circular dichroism spectra are observed. These peaks can be monitored to obtain information on the tubule morphology. This information is correlated to direct observations made using electron microscopy. Results of these studies have led to the optimization of large scale preparations of tubules for technological applications.

We describe a novel class of light-triggerable liposomes prepared from a photo-polymerizable phospholipid DC8,9PC (1,2- bis (tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine) and DPPC (1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine). Exposure to UV (254 nm) radiation for 0–45 minutes at 25°C resulted in photo-polymerization of DC8,9PC in these liposomes and the release of an encapsulated fluorescent dye (calcein). Kinetics and extents of calcein release correlated with mol% of DC8,9PC in the liposomes. Photopolymerization and calcein release occurred only from DPPC/DC8,9PC but not from Egg PC/DC8,9PC liposomes. Our data indicate that phase separation and packing of polymerizable lipids in the liposome bilayer are major determinants of photo-activation and triggered contents release.

We report on spectroscopic studies of the chiral structure in phospholipid tubules formed in mixtures of alcohol and water. Synthetic phospholipids containing diacetylenic moieties in the acyl chains self-assemble into hollow, cylindrical tubules in appropriate conditions. Circular dichroism provides a direct measure of chirality of the molecular structure. We find that the CD spectra of tubules formed in mixtures of alcohol and water depends strongly on the alcohol used and the lipid concentration. The relative spectral intensity of different circular dichroism bands correlates with the number of bilayers observed using microscopy. The results provide experimental evidence that tubule formation is based on chiral packing of the lipid molecules and that interbilayer interactions are important to the tubule structure.The self-assembly of biologically based lipids into unusual microstructures has been the subject of intense study in recent years, both for basic research and for potential applications in areas ranging from controlled release to electroactive composites (1, 2). Most long-chain phospholipids self-assemble into spherical bilayer aggregates, known as liposomes (3). However, certain synthetic phospholipids, with modified head groups or acyl chains, self-assemble into novel microstructures (4). One class of synthetic phospholipids, with photopolymerizable diacetylenic moieties in the acyl chains, was originally developed as an approach for increasing the durability of lipid bilayer aggregates (5-7). These lipids have been observed to self-assemble into hollow, cylindrical structures, known as tubules (8,9). Similar cylindrical tubules have also been observed in other synthetic surfactants (10) and in bile (11). Such tubules appear to have potential for long-term release applications such as marine antifouling (12).To explain the formation of tubules, several investigators have developed theories based on molecular chirality (11,(13)(14)(15)(16)(17)(18). Although the details of these theories differ, they are all based on the principle that chiral interactions cause the molecules to pack at a nonzero angle with respect to their nearest neighbors. This chiral packing induces a twist in the bilayer, which results in the formation of a cylindrical structure. Electron microscopy of tubules decorated with metallic particles show helical markings that suggest chiral order in the bilayers (19,20).In an earlier study, we used circular dichroism to test the theoretical concept that the formation of tubules is driven by chiral molecular packing (20). CD, the difference in the absorption of right and left circularly polarized light, arises from the chirality of a molecular architecture. This chirality can arise from either the structure of individual molecules or from the chiral packing of molecules into larger aggregates (21,22). Our experiments showed that diacetylenic lipid tubules have a very strong CD signal. By contrast, spherical liposomes of the same diacetylenic lipids have only a very weak CD signa...

We have demonstrated a new approach for imaging nanoscale patterns on three-dimensional submicrometer structures using charged particles. Nanoparticle structures were assembled onto lipid tubules through the sequential adsorption of oppositely charged polymers and silica spheres. For tubules of the zwitterionic lipid DC8,11PC, this process leads to the formation of caps on the ends of the tubules, with 50−100 silica spheres in each cap. For tubules of DC8,11PC mixed with 2% of the charged lipid DC8,9PEOH, the sequential adsorption leads to both end caps and helices of nanoparticles winding around the interior of the tubules. These results give new insight into the pattern of charge in lipid tubules.

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