Regulation of photosynthesis by brassinosteroids in plants

Brassinosteroids (BRs) regarded as plant hormone are a class of naturally occurring polyhydroxylated sterol derivatives present in all plant species. Overall growth of the plant relies on the very basic and important process of photosynthesis. BRs are found capable of preventing the loss of photosynthetic pigments either by activating or inducing the synthesis of enzymes involved in chlorophyll biosynthesis. BRs play important role in maintaining PS II efficiency by stabilizing D1 protein. It overcomes the stomatal limitations and elevates the efficiency of photosynthetic carbon fixation. BRs also act at various levels of light and dark reactions leading to enhanced carbohydrate synthesis. Therefore, it becomes important to focus and collect information related to various effects of BRs on photosynthesis and its related attributes. The present review deals with the effect of BRs on photosynthesis under normal as well as stressful conditions.     

Metabolism of brassinosteroids in plants.

Brassinosteroids represent a class of plant hormones. More than 70 compounds have been isolated from plants. Currently 42 brassinosteroid metabolites and their conjugates are known. This review describes the miscellaneous metabolic pathways of brassinosteroids in plants. There are some types of metabolic processes involving brassinosteroids in plants: dehydrogenation, demethylation, epimerization, esterification, glycosylation, hydroxylation, side-chain cleavage and sulfonation. Metabolism of brassinosteroids can be divided into two categories: i) structural changes to the steroidal skeleton; and ii) structural changes to the side-chain.     

Identification and transcription of transfer RNA genes in dinoflagellate plastid minicircles

The dinoflagellate chloroplast genome is unique in that the genes are found on small circular DNA molecules carrying from one to three genes. In addition, only 14 of the typical chloroplast-located genes have so far been discovered on minicircles, while a number have been transferred to the nucleus. We have sequenced four new minicircles from the dinoflagellate Heterocapsa triquetra, three of which carry a single protein-coding gene (psbD, psbE, petD) and one that appears to be an "empty" circle. Using the tRNA prediction programs ARAGORN and tRNAscan-SE, tRNA-Met was found in the petD circle immediately downstream of the end of petD, while tRNA-Trp and tRNA-Pro were detected in the psbE and petD circles as well as in several chimeric circles of H. triquetra and the psbA minicircles of Heterocapsa pygmaea. RT-PCR showed that the tRNAs were co-transcribed with the protein-coding genes that preceded them, and cleaved from the precursor before a poly(U) tail was added to the mRNA.     

bZIP转录因子调控植物次生代谢产物生物合成的研究进展

植物次生代谢产物是通过次生代谢产生的一类小分子有机化合物,是植物适应环境的表现,次生代谢产物也是重要药物和化工原料的来源。bZIP转录因子是普遍存在于真核生物中的一类多基因家族,可有效调控植物次生代谢产物的生物合成。本文概述了植物bZIP转录因子的结构和类型,重点阐述了bZIP转录因子调控萜类、黄酮类和生物碱等植物次生代谢产物生物合成的研究进展,并对研究前景进行了展望。深入探讨bZIP转录因子的调控机制,有助于利用基因工程技术优化植物次生代谢途径,提高次生代谢产物的含量,在新药创制、工农业生产等方面具有广泛的应用前景。     

Regulation of Phaeodactylum plastid gene transcription by redox,light, and circadian signals

Photosynthesis Research - Diatoms are a diverse group of photosynthetic unicellular algae with a plastid of red-algal origin. As prolific primary producers in the ocean, diatoms fix as much carbon...     

Metabolism of plastid terpenoids. II. Regulation of phytoene synthesis in plastid stroma isolated from higher plants

In plastid stroma the synthesis of phytoene was regulated by several factors, (i) MgCl₂ or MnCl₂ alone and the combination of both oriented selectively the incorporation of isopentenyl pyrophosphate (IPP) between phytoene and other isoprenoids including geranylgeraniol, geranyllinalool, and solanesol (ii) neutral detergents (Tween-80, Triton X-100), polyethyleneglycol and digalactosyldiglyceride liposomes stimulated the incorporation of IPP into phytoene (iii) ATP or different glycolytic intermediates enhanced the synthesis of phytoene from IPP.     

A subset of conserved tRNA genes in plastid DNA of nongreen plants.

The plastid genome of the nonphotosynthetic parasitic plant Epifagus virginiana contains only 17 of the 30 tRNA genes normally found in angiosperm plastid DNA. Although this is insufficient for translation, the genome is functional, so import of cytosolic tRNAs into plastids has been suggested. This raises the question of whether the tRNA genes that remain in E. virginiana plastid DNA are active or have just fortuitously escaped deletion. We report the sequences of 20 plastid tRNA loci from Orobanche minor, which shares a nonphotosynthetic ancestor with E. virginiana. The two species have 9 intact tRNA genes in common, the others being defunct in one or both species. The intron-containing trnLUAA gene is absent from E. virginiana, but it is intact, transcribed, and spliced in O. minor. The shared intact genes are better conserved than intergenic sequences, which indicates that these genes are being maintained by natural selection and, therefore, must be functional. For the most part, the tRNA species conserved in nonphotosynthetic plastids are also those that have never been found to be imported in plant mitochondria, which suggests that the same rules may govern tRNA import in the two organelles. A small photosynthesis gene, psbI, is still intact in O. minor, and computer simulations show that some small nonessential genes have an appreciable chance of escaping deletion.     

The chemical characteristic and distribution of brassinosteroids in plants

Brassinosteroids represent a class of plant hormones with high-growth promoting activity. They are found at low levels in pollen, anthers, seeds, leaves, stems, roots, flowers, grain, and young vegetative tissues throughout the plant kingdom. Brassinosteroids are a family of about 60 phytosteroids. The article gives a comprehensive survey on the hitherto known brassinosteroids isolated from plants. The chemical characteristic of brassinosteroids is also presented.