Leaf Turgor Potential, Plant Growth and Photosynthesis in Organically Fertilized Sweet Corn

A greenhouse pot experiment was conducted using a complete random design with six replications. A pressure-volume curve analysis was employed to study the effects of organic fertilizers on plant water relations in sweet corn (Zea mays L. cv.Honey-bantam) in terms of leaf osmotic concentration (CS), osmotic potentials at full turgid status (πFT) and at incipient plasmolysis (πIp), and of symplastic (ζsym) and apoplastic (ζapo) fractions in the tissue water compartment in relation to photosynthetic capacity (PC) and dry mass accumulation. At the seedling stage (day 15), plants with chemical fertilizer treatments showed lower πFT, πIp and ζapo and higher CS, ζsym and PC than those with organic fertilizer treatments.Compared to PC and relative growth, where values from day 15 to day 75 were first lower for organic treatments and then higher, ζsym and CS values were similar, while πFT and πip were opposite being higher then lower. Dry mass production with organic fertilizcr was higher than or close to the chemical fertilizer treatments in the later growth stage (day 75),though dry mass production with chemical fertilizers was much higher in the early and middle growing stages (days 15 and 45). Increased photosynthesis and dry mass production in later growth stages due to organic fertilizers were associated with increased osmotic concentration in the tissue and the symplastic fraction of the tissue water compartment. These might favor stomatal opening and biochemical activities.

Obtaining the transgenic poplars with low lignin content through down-regulation of 4CL

The antisense 4CL (4-coumarate: CoA ligase) gene was transformed into triploid Chinese white poplar (Populus tomentosa) mediated by Agrobacterium tumefaciens. PCR and Southern blot analysis indicated that antisense 4CL gene had been integrated into the genome of the transgenic Chinese white poplars. The antisense gene had also been expressed, which was indicated by RT-PCR and Western analysis. Klason lignin content assay showed that repression of 4CL expression could result in remarkable reduction of lignin content in transgenic poplars, with most reduction of 41.73% compared with that of wild type in this paper. But there is no significant difference in holocellulose content be-tween trans- genic and wild poplars. We considered that 4CL might not be the metabolism control point between lignin and carbohy- drate biosynthesis. The stems of transgenic poplars displayed red-brown color with different levels after the bark was peeled, while those of untransformed plants were white. No visible differences in growth and development were observed between transgenic and wild plants. Wiesner reaction analysis of the transgenic plant stems with reduced lignin content exhibited red color, while that of untrans-formed plant was typically purple-red.

Synthesis of medium-chain-length-polyhydroxyalkanoates in tobacco via chloroplast genetic engineering

Medium-chain-length-polyhydroxyalkanoates (mcl-PHAs) belong to the group of microbial polyesters con- taining monomers ranging from 6 to 14 carbons in length. The key enzymes of their biosynthesis are PHA-polymerase (product of phaC gene) and 3-hydroxyacyl-acyl carrier pro- tein-CoA transferase (product of phaG gene). With aadA (aminoglycoside 3′-adenylyltransferase) gene as screening marker, two chloroplast transformation vectors of pTC2 harboring phaC2 gene only and pTGC harboring both phaC and phaG genes were constructed and introduced into to- bacco chloroplast genome through particle bombardment. PCR and Southern blot analysis confirmed the insertion of the introduced genes into chloroplast genome. The content of mcl-PHAs accumulated in transgenic plants was analyzed by gas chromatography, mcl-PHAs accumulated up to 4.8 mg/g dry weight (dw) in transgenic line S4-3; their monomers were 3-hydroxyoctanoate and 3-hydroxydecanoate. Accumulation of mcl-PHAs polymers in the tobacco chloroplast was also observed by transmission electron microscopy. To our knowledge, this is the first report on the synthesis of mcl- PHAs in tobacco via chloroplast genetic engineering.