V-A菌根真菌对柑桔吸收钙素效应的研究初报

应用放射性同位素~(45)Ca示踪来探明泡囊—丛枝菌根真菌对柑桔吸收钙素的作用。两次盆栽试验,施用含~(45)Ca(NO_3)_2的Hoagland营养液,分别在红壤及无土基质人工接种菌根真菌Glomus citricolum于枳(Poncirus trifoliata)和构头橙(Citrus aurantium)实生苗根系,以不接种为对照。结果表明在红壤中接种2个月后,枳已形成菌根,5个月的菌根感染率为24.5％。在无土基质中,菌根的形成更好;接种3个月后,构头橙的菌根感染率为49.5％,并且发生丰富的泡囊。在红壤中,有菌根枳实生苗的地上部从肥料中吸收的钙素和全钙含量都比无菌根的增加75％左右。在无土基质中,有菌根的枳和构头橙实生苗地上部含钙量及放射性强度都比无菌根的显著增高。放射性自显影直接地显示了菌根真菌将吸收的~(45)Ga运转至地上茎叶中,对构头橙的效应更明显。     

Citrus replant problem in Iraq I. Possible role of soil fungi and nematodes

The role of soil fungi and nematodes in citrus replant problems was investigated. Several pathogenic and non-pathogenic fungi and the nematodeTylenchulus semipenetrans were isolated in about equal abundance from soils which displayed or did not display replant problems. However, in almost all trees showing evidence of decline, infection by the fungusPhytophthora citrophthora had advanced through the roots until it had reached the tree crown. Fumigation of old citrus soil with methyl bromide greatly increased the growth of sour organe. The application of Nemacure, Benomyl and Ridomil 5G confirmed the important role of pathogenic and non-pathogenic fungi and nematodes in the citrus replant problem. Inoculation of methyl bromide-treated soil with the pathogenic and non-pathogenic fungi separately or in combination further confirmed the previous experiments and also revealed an important role ofP. citrophthora andFusarium solani when replanting citrus in old citrus orchards.     

The use of intercalating dye molecules in the study of chromatin structure

This paper reviews the field of chromatin structure studied by means of dye molecules believed to intercalate within DNA. The emphasis is on dyes whose binding properties are the best characterized (ethidium bromide (EB). actinomycin D(AMD), proflavine (PF)) but studies in which less common dye molecules are used are also considered. A comparison is made between the binding of these dyes to purified DNA and to whole or partially deproteinized chromatin in order to investigate both the availability of DNA in chromatin and the localization of chromosomal proteins or the DNA backbone.     

Changes in carbohydrates and mineral elements in Citrus leaves during flowering and fruit set

Mineral elements and metabolizable carbohydrates in Citrus leaves [ Citrus sinensis (L.) Osbeck cv. Washington navel] have been determined from bud sprouting until the end of the June drop and related to fruitlet growth and abscission. Mineral elements in old leaves decreased during the spring flush of growth and reached minimum values at flower opening, coinciding with a peak in abscission. This was followed by a rapid recovery in potassium and nitrogen to the initial values, with little change afterwards. Old leaves accumulate carbohydrates until flowering, and lose them during post-anthesis at a constant rate for more than 4 months; this rate of export is unaltered by the presence of a nearby growing fruit. Inflorescence leaves accumulate carbohydrates and mineral elements during post-anthesis; during the June drop there is an interruption in the accumulation of nitrogen and a net loss of phosphorus, potassium and carbohydrates from these leaves, coinciding with the attainment of the maximum growth rate of the fruit.
The two main periods of abscission coincide with minima in the amount of reserves in leaves, suggesting that a limitation in metabolite supply may be the primary cause of drop. There is a closer relationship of the fruit with inflorescence leaves than with old mature ones; however, the regulation of carbohydrate levels in the inflorescence leaves cannot be simply explained in terms of source-sink relationships with the nearby growing fruit, and the smaller size of inflorescence leaves vs. vegetative ones is not due to the presence of the flower during leaf development.     

The longevity and activity of the primary root of maize

The longevity of the main root cylinder and the laterals of the primary root of maize plants was determined under controlled greenhouse conditions by means of nuclear staining with acridine orange. The cortex of the main root was found to be alive for the whole life-span of the plant, whereas the life-span of the root hairs was only 2 to 3 days as evidenced by electronmicroscopical examination of cell integrity. The onset of senescence of laterals was observed at the older part of the main root at the 6-leaf stage of the plant. Senescence of 1st and 2nd order laterals commenced near the root tip a few days after their protrusion and advanced towards the basal region of the root. In any root segment death of the cortex cells preceeded that of the stele. At the late grain filling stage all laterals along the main root exhibited advanced senescence, but stainable nuclei were seen in the root tissues of the basal part of 1^st order laterals (both cortex and stele) as well as of the 2^nd order laterals which emerged from that root segment. The pattern of the dying of the root tissue is discussed with regard to the P-nutrition of the shoot system by the primary root.     

O-methylation of flavonoids by cell-free extracts of calamondin orange

Cell-free extracts of calamondin orange (Citrus mitis) catalysed the O-methylation of almost all hydroxyls of a number of flavonoids, indicating the existence in citrus tissues of ortho, meta, para and 3-O-methyltransferases. The latter, hitherto unreported enzyme, catalysed the formation of 3-O-methyl ethers of galangin and quercetin. The stepwise O-methylation of a number of compounds, especially quercetin and quercetagetin, tends to suggest a coordinated sequence of O-methylations on the surface of a multienzyme complex. The methyl acceptor abilities of the flavonoid substrates used are discussed in relation to their hydroxyl substitution patterns and their negative electron density distribution.     

Mammalian cell genetics. 3. Characterization of x-ray-induced forward mutations in Chinese hamster cell cultures

X-irradiation induces forward mutations from 8-azaguanine sensitvity to resistance in Chinese hamster cells in culture. At this locus the number of induced mutations increases non-linearly with X-ray exposure. The mutation rate increase from 4.2·10⁻⁷ per locus per R with 200 R to 1.8·10⁻⁶ per locus per R with 1200 R. Several factors including cell density markedly influence the mutational yield. Reversion tests using specific chemical mutagens on 72 randomly isolated, azaguanine-resistant mutants suggest that both point mutations and chromosome deletions might have occurred in the hamster cells after exposure to ionizing radiation.     

温州蜜柑果实生长动态特征及影响因子的分析

金衢盆地柑桔生产历史悠久。近10年来发展很快,已形成浙江第二个柑桔产区。由于受东亚季风气候影响,该区柑桔不但冬季易遭冻害,而且夏秋易受高温干旱危害,冬季的低温冻害和夏季的高温干旱是造成桔柑减产的两个主要