Studies onC-glycosides in higher plants

The intracellular distribution of bergenin and related compounds was examined in mesophyll cell protoplasts ofSaxifraga stolonifera. Vacuoles ofS. stolonifera leaves contained 46% to 55% of the bergenin and related compounds. It was also noted that 50% of the gallic acid was located in chloroplasts. From the results obtained it was concluded that bergenin and norbergenin were primarily localized in the vacuoles, but gallic acid was distributed equally in vacuoles and chloroplasts.     

Studies onC-glycosides in higher plants

The biosynthesis of bergenin and arbutin in the organs ofSaxifraga stolonifera has been studied by tracer techniques. Among the organs tested, the leaves showed the highest incorporation of label fromd-glucose-U-¹⁴C into bergenin and arbutin under continuous light, although every organ is more or less able to synthesize both glucosides. The incorporation rate into bergenin was higher in the young leaves, whereas the synthesis of arbutin became active in the mature leaves. The fact that the addition of unlabeled gallic acid enhanced the incorporation of label into bergenin suggests that gallic acid may be a likely glucosyl acceptor in bergenin biosynthesis.     

Studies of vegetative compatibility-incompatibility in higher plants

Summary In order to elucidate the events that lead to cellular autolysis, and thus better understand the mechanism of cellular incompatibility betweenSedum telephoides andSolanum pennellii stems, we have followed the appearance and fate of the hydrolytic enzyme acid phosphatase in both the compatibleSedum autograft and the incompatibleSedum/Solanum heterograft. Acid phosphatase was localized by a modified Gomori-type reaction. Following an initial association with the endoplasmic reticulum and dictyosomes by 6–10 hours after grafting, acid phosphatase activity in the compatibleSedum autograft was associated primarily with the plasmalemma, tonoplast, and vacuole. This strict compartmentation in membranes or organelles and absence of enzyme from the cytosol was maintained throughout the development of the compatible autograft inSedum. Although acid phosphatase activity in the incompatible heterograft betweenSedum andSolanum was initially similar to the compatible autograft inSedum, a marked difference in enzyme localization occurred in the two graft partners over time.Solanum cells accumulated increased amounts of acid phosphatase, but the enzyme remained sequestered in the plasmalemma, tonoplast, and vacuole. In comparableSedum cells, however, there was a dramatic increase in acid phosphatase activity in the cytosol, often without any prior compartmentation within the vacuole. This high activity of acid phosphatase in theSedum cytosol was correlated with cellular autolysis, death, and eventual cell collapse to form the characteristic necrotic layer that insulates the stock from the scion. These results suggest that the lethal cellular senescence associated withSedum cells of the incompatible heterograft is correlated with a cytoplasmic release of acid phosphatase. A similar release of the enzyme does not occur in theSolanum stock or in the compatibleSedum autograft. Thus, while acid phosphatase synthesis and/or activation is induced in both the compatible and incompatible grafts, incompatibility betweenSedum andSolanum involves a failure ofSedum cells to isolate hydrolytic enzymes from the cytosol, which subsequently leads to cellular necrosis.Supported in part by grants from the Academic Senate of UCLA, Sigma Xi, the American Philosophical Society, and the URC of Baylor University.     

高等植物GA 20-氧化酶研究进展

GA20-氧化酶（GA 20-oxidase）是高等植物体内GA生物合成途径中最重要的限速酶,它能够催化从GA12到GA9及GA53到GA20-系列的氧化反应。作者对近年来有关GA20一氧化酶的特征,GA20一氧化酶基因及编码蛋白、GA20一氧化酶基因表达调控进行了综合评述,并对GA20一氧化酶基因转化在农业、林业、;园艺业方面的应用前景进行了展望。     

Endoreduplication in higher plants

Cell polyploidisation can be achieved by endoreduplication, which consists of one or several rounds of DNA synthesis in the absence of mitosis. As a consequence, chromosomes with 2ⁿ chromatids are produced without change in the chromosome number. Endoreduplication is the most common mode of polyploidisation in plants and can be found in many cell types, especially in those undergoing differentiation and expansion. Although accumulating data reveal that this process is developmentally regulated, it is still poorly understood in plants. At the molecular level, the increasing knowledge on plant cell cycle regulators allows the acquisition of new tools and clues to understand the basis of endoreduplication control and, in particular, the switch between cell proliferation and cell differentiation.     

Rhodanese in higher plants

Rhodanese activity was detected in crude leaf extracts of 12 randomly selected plant species consisting of 9 non-cyanophoric and 3 cyanophoric species. In each case, the enzyme exhibited high activity at pH 10·4 and 55°. There appeared to be no correlation between rhodanese activity and the cyanophoric nature of the plant.     

高等植物体内的肌动蛋白

植物肌动蛋白是植物细胞生物学领域发展起来的热点,它涉及植物细胞的分裂机制。细胞运动,细胞器运动,细胞的极性,细胞空间形状的维持,物质运输等,对高等植物肌动蛋白的性质,功能,研究方法及分子生物学领域的研究作了综述。并对该领域存在的问题及应用前景作了展望。     

Studies on chloroplast division in young leaf tissues of some higher plants

Summary The process of chloroplast division in young leaves of four species (bean, spinach, wheat, and maize) was investigated by light and electron microscopy. Two types of division, i.e., by fission, and by partition were observed.Chloroplast division by fission prevailed in the plant species examined, as shown by the relative abundance of dumbbell-shaped plastids, the characteristic stage in this type of division. Electron dense material, most commonly in the shape of a ring structure in the isthmus of the dividing plastid, was nearly always present in wheat and maize. Similar, but less distinct structures were usually observed in the neck region of constricted bean and spinach chloroplasts.Chloroplast division by partition was found in young leaf tissues of bean and spinach, but was not observed in wheat and maize. The main indication of this type of division is a centripetal invagination of the inner limiting membrane of the plastid envelope which progressively divides the chloroplast stroma into two, nearly equal, parts. Specific membraneous structures resembling myelin figures were usually found close to a dividing chloroplast and may participate in chloroplastokinesis.     

DNA repair in higher plants

Numerous studies have demonstrated a requirement in plants for repair of DNA damage arising from either intrinsic or extrinsic sources. Investigations also have revealed a capacity for repair types of DNA damage, and conversely, identified mutants apparently defective in such repair. This article provides a concise overview of nuclear DNA repair mechanisms in higher plants, particularly those processes concerned with the repair of UV-induced lesions, and includes surveys of UV-sensitive mutants and genes implicated in DNA repair.     

Retroelements in higher plants.

Representatives of several classes of retroelements have been characterized in a broad range of plant species, where they appear at variable and sometimes very high copy numbers. So far, only a very small number of plant elements have been shown to be active, and this activity seems to be restricted to specific situations of 'genomic shock'. Although it is not yet known whether the presence of retroelements is linked to the high level of variability found in plant genomes, it is now clear that retrotransposons are ancient and ubiquitous components of plant genomes, and could play an important role in plant evolution.     

Microtubule-associated proteins in higher plants

A variety of microtubule-associated proteins (MAPs) have been reported in higher plants. Microtubule (MT) polymerization starts from the γ-tubulin complex (γTuC), a component of the MT nucleation site. MAP200/MOR1 and katanin regulate the length of the MT by promoting the dynamic instability of MTs and cutting MTs, respectively. In construction of different MT structures, MTs are bundled or are associated with other components—actin filaments, the plasma membrane, and organelles. The MAP65 family and some of kinesin family are important in bundling MTs. MT plus-end-tracking proteins (+TIPs) including end-binding protein 1 (EB1), Arabidopsis thaliana kinesin 5 (ATK5), and SPIRAL 1 (SPR1) localize to the plus end of MTs. It has been suggested that +TIPs are involved in binding of MT to other structures. Phospholipase D (PLD) is a possible candidate responsible for binding of MTs to the plasma membrane. Many candidates have been reported as actin-binding MAPs, for example calponin-homology domain (KCH) family kinesin, kinesin-like calmodulin-binding protein (KCBP), and MAP190. RNA distribution and translation depends on MT structures, and several RNA-related MAPs have been reported. This article gives an overview of predicted roles of these MAPs in higher plants.     

Sulphate activation in higher plants

Summary ATP-sulphurylase was detected in extracts of roots and leaves of several species of higher plant. The enzyme occurs in the supernatant fraction, has a pH optimum of 8.0 and an absolute requirement for Mg²⁺ ions. Sulphurylase activity is inhibited by selenate and molybdate but not by cysteine, methionine, glutathione, or thiol reagents. The synthesis of sulphurylase by turnip, lettuce, tomato, and Lemna plants grown under aseptic conditions is neither induced by sulphate nor repressed by cystine, and in the latter respect sulphate activation in plants differs from than in micro-organisms. APS-kinase could not be detected in extracts of any tissue although its product was stable under the conditions used. Sulphate reduction in higher plants may thus proceed via adenylysulphate and not via phosphoadenylylsulphate as in many micro-organisms.     

Messenger DNA in higher plants

Evidence is presented that, as in animal and human cells, plant cells can release a newly-synthesized DNA which can freely circulate in the plants. This DNA enters cells and their nuclei where it may be integrated and be expressed so acting, apparently, as a messenger-DNA.     

D-amino acids in higher plants

Although there appear to be no exceptions to the rule that proteins are composed solely of the L-isomers of amino acids, D-amino acids and derivatives of them do occur rather widely in living organisms. In some cases they have well-understood functions, but in other cases their occurrence raises interesting questions. Several peptide antibiotics contain D-amino acids (1). The peptido-glycans of Gram-positive bacterial cell walls contain D-glutamic acid, D-alanine, and D-asparagine (2). D-amino acids are also found in animals, chiefly annelids and insects (3). In this paper some aspects of D-amino acids in higher plants will be reviewed.