M. S. Naeem

5-Aminolevulinic acid alleviates the salinity-induced changes in Brassica napus as revealed by the ultrastructural study of chloroplast

5-Aminolevulinic acid (ALA) is an important plant growth regulator which is derived from 5-carbon aliphatic amino acid. The present study investigates the interaction of increasing NaCl-salinity and ALA on plant growth, leaf pigment composition, leaf and root Na(+)/K(+) ratio and chloroplast ultrastructure in mesophyll cells of oilseed rape (Brassica napus) leaves. The plants were treated hydroponically with three different salinity levels (0, 100, 200 mM) and foliar application of ALA (30 mg l(-1)) simultaneously. Ten days after treatment, higher NaCl-salinity significantly reduced the plant biomass and height. However, ALA application restored the plant biomass and plant height under saline conditions. A concentration-dependent increase in Na(+) uptake was observed in the aerial parts of B. napus plants. On the other hand, ALA reduced Na(+) uptake, leading to a significant decrease in Na(+)/K(+) ratio. Accumulation of Na(+) augmented the oxidative stress, which was evident by electron microscopic images, highlighting several changes in cell shape and size, chloroplast swelling, increased number of plastogloubli, reduced starch granules and dilations of the thylakoids. Foliar application of ALA improved the energy supply and investment in mechanisms (higher chlorophyll and carotenoid contents, enhanced photosynthetic efficiency), reduced the oxidative stress as evident by the regular shaped chloroplasts with more intact thylakoids. On the basis of these results we can suggest that ALA is a promising plant growth regulator which can improve plant survival under salinity.

Transgenic Brassica napus L. lines carrying a two gene construct demonstrate enhanced resistance against Plutella xylostella and Sclerotinia sclerotiorum

Plant diseases and insect pests are serious threat to the growth and yield of oilseed rape. In this study, a binary vector carrying sporamin and chitinasePjChi-1 genes in tandem was introduced into Brassica napus cv. ZS 758 via Agrobacterium tumefaciens for dual resistance against disease and insect attack. Thirty-two regenerated plantlets exhibiting hygromycin resistance were selected following Agrobacterium-mediated transformation of 600 leaf petiole explants. Of these, 27 transformants were confirmed to carry the two transgenes as detected by polymerase chain reaction (PCR) with 4.5% transformation efficiency. Eight plantlets were randomly selected for further confirmation by Southern and northern blot hybridization analyses. Four plants carried single copy of the transgenes, while the remaining four plants carried either two or three copies of the transgenes. Moreover, expression of the sporamin transgene was detected by northern blot hybridization in transgenic lines, but not in wild-type plants. These eight T0 plants were grown in vitro, and inoculated with the Lepidoptera larvae of Plutella xylostella and with spores of the fungal pathogen of Sclerotinia sclerotiorum. Transgenic plants exhibited high levels of resistance to P. xylostella and S. sclerotiorum when compared to untransformed wild-type plants. Genetic analysis of T1 progeny confirmed Mendelian segregation of the introduced genes. Therefore, these transgenic lines demonstrate a promising potential for variety development of oilseed rape lines with enhanced resistance against both P. xylostella and S. sclerotiorum.

Induction of tetraploidy in Juncus effusus by colchicine

Tetraploidy was induced in vitro in mat rush (Juncus effusus L.) cultivar Nonglin-4 by exposure to colchicine (0, 50, 100 and 500 mg dm−3) for 6, 12 and 24 h. Flow cytometric analysis was used to confirm the ploidy level. Anatomical and ultrastructural analyses at cellular and subcellular levels in tetraploid and diploid control plants revealed differences between diploid and tetraploid plants. The leaf epidermis had larger stomata but lower stomatal density in tetraploid plants. In addition, mesophyll cells in tetraploid plants appeared more compact and showed less intercellular spaces along with increased size of vascular bundles. However, a significant reduction of chlorophyll content was observed in tetraploid plants that might be the result of structural modification in the lamellar membranes of chloroplasts.

In Vitro Mutagenesis and Genetic Improvement

In vitro mutagenesis is an important technique which can induce stress tolerance and improve the yield and quality of crop plants. This chapter is an effort to review and compare the useful information obtained through in vitro mutation techniques, including somaclonal variation with the current achievements and future prospects. Plant improvement based on mutations can change one or more specific traits of a cultivar, which can enhance the quality and quantity of crops. Conventional induced mutations have well-defined limitations, especially in crop-breeding applications but the use of in vitro techniques with the conjunction of conventional mutagenesis has overcome this barrier. Tissue culture techniques offer opportunity for variation induction, handling of large populations, use of ready selection methods, and rapid cloning of selected variants which can increase the efficiency of mutagenic treatments. Molecular techniques can provide a better understanding about the potential and limitations of mutation breeding. It is apparent that the relatively high number of research reports compared with the low number of cultivars released suggests that mutagenesis, in combination with tissue culture techniques, needs further coordinated and integrated investigation for the improvement of existing plants. However, in vitro mutation induction has high potential to enhance the crop yields that can be used for the improvement of life style of the mankind. Various stresses cause significant yield losses in crops and significantly affect their productivity; therefore, such techniques can contribute to resolve or reduce some of these constraints. Understanding the mechanism that regulates the expression of stress-related genes is a fundamental issue in plant biology and is utmost necessary for the genetic improvement of plants.