摘要:

Using quartz optical fibres, penetration of both monochromatic (310 nm) and polychromatic UV‐B (280–320 nm) radiation in leaves ofBrassica napusL. (cv. Ceres) was measured. Plants were grown under either visible light (750 μmol m−2s−1photosynthetically active radiation) or with the addition of 8. 9 KJ m−2day−1biologically effective UV‐B (UV‐BBE) radiation. Results showed that of the 310 nm radiation that penetreated the leaf, 90% was within the intial one third of the leaf with high attenuation in the leaf epidermis, especially in UV‐treated plants. Polychromatic UV‐B radiation, relative to incident radiation, showed a relatively uniform spectral distribution within the leaf, except for collimated radiation. Over 30% of the UV‐screening pigments in the leaf, including flavonoids, were found in the adaxial epidermal layer, making this layer less transparent to UV‐B radiation than the abaxial epidermis, which contained less than 12% of the UV‐screening pigments. UV‐screening pigments increased by 20% in UV‐treated leaves relative to control leaves. Densely arranged epicuticular wax on the adaxial leaf surface of UV‐treated plants may have further decreased penetration of UV‐B radiation by reflectance. An increased leaf thickness, and decreases in leaf area and leaf dry weight wer

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01727.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The photosynthetic light saturation curve in duckweed was lowered by 20–25% after ozone exposure (300 nmol mol−1, 1 h). The light flux and oxygen concentration during ozone‐exposure had no effect on reduction of net photosynthesis. Net photosynthesis and photorespiration were both depressed by about 40% after exposure for 1 h to 360 nmol mol−1ozone. We could not find any change in dark respiration after ozone exposure below 300 nmol mol−1. When the concentration of ozone was doubled from 150 nmol mol−1to 300 nmol mol−1, the uptake of ozone in duckweed changed from 100 nmol m−2s−1to 170 nmol m−2s−1. We found no differences in fluorescence (pattern) between ozone treated plants and the control plants during a period of 150 min after ozone treatment, but there was an increase in synthesis of the Dl‐protein and a significant reduction in degradation after ozone treatment (300 nmol mol−1, 1 h). These results, together with fluorescence measurements, indicate that photochemical electron transport was not responsible for the ozone‐induced redu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01728.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The reasons for the inability of recalcitrant mesophyll protoplasts to divide and re‐enter the cell cycle are unknown. Changes in protein profile, indole‐3‐acetic acid (IAA)‐oxidase and peroxidase activities, and isoenzymes were compared in protoplasts of recalcitrant grapcvine (Vitis vinifera) L. cv. Sultanina) and regenerating tobacco (Nicotiana tabacum) L. cv. Xanthi). Using [35S]‐methionine. SDS‐PAGE and two‐dimensional separation of proteins, differences in protein profile during protoplast culture were assessed. The changes in the de novo synthesized proteins were both qualitative and quantitative between the two species. The number of proteins which changed was double in tobacco compared to grapevine protoplasts. Peroxidase and IAA‐oxidase activities increased significantly in tobacco protoplasts during culture whereas in grapevine they remained low. In tobacco protoplasts. 3 and 7 basic and acidic peroxidases, respectively, were induced during protoplast culture. which were not detected in the intact leaf, whereas in grapevine no new peroxidases were induced during pro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01729.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Differential thermal analysis (DTA) was used to determine the exothermic responses in dormant stems and excised lengths of stem ofSalix dasycladosWimmer subjected to artificial freezing treatments.The presence of ice on the surfaces of intact stems restricted the mechanism of freezing avoidance to temperatures above –4°C. In contrast, excised lengths of stem started to freeze as soon as the ambient temperature fell below –2°C, demonstrating that extracellular ice formation takes place earlier if cut surfaces are present. Exposure of dormant excised lengths of stem to subfreezing temperatures for more than 8 weeks did not alter their nucleation temperature not their exothermic differential responses. Early extracellular crystallisation of freezable cellular water provides conditions that allow dormantSalix dasycladosstems or excised lengths of stem to survive extreme freezing stress.Crystallisation of extracellular and cellular water took place in the cortex, and did not result in visual damage or reduced survival. This nucleation of extracellular water took place over the same temperature range whether the excised dormant lengths of stem were partly (bark only) or completely thawed. Exposure of dormant tissue to 20°C for up to 24 h did not alter the level of freezing tolerance, nor did it increase the susceptibility of excised lengths of stem to damage by extreme temperature fluctu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01730.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Three β‐galactosidase (EC 3. 2. 1. 23) isozymes were purified from the mesocarp of ripe fruit ofPersea americanaMill. cv. Lula. and their effects on pectin derived from mature‐green tomato fruit were investigated. The β‐galactosidases had pl values of 5. 0,5. 1 and 5. 2. and molecular weights of 41. 49 and 54 KDa. respectively. There was a partial degradation of pectin resulting in the release of monomeric galactose upon treatment with avocado β‐galactosidase. This degradation resulted in increased pectin solubility and decreased apparent average molecular size as determined by microfiltration and gel permeation by high‐performance liquid chromatography. The increase in solubility was due. in part. to an apparent decrease in the ability of pectin molecules to aggreg

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01731.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The application of 4 h light followed by 2 h darkness (4/2 h), compared to 16 h light‐8 h darkness (16/8 h). induced very different patterns of CO2evolution from proliferating shoots ofPrunus cerasiferain vitro. Under the former light/dark regime, fresh and dry weights of shoot clutures and the number of newly formed shoots were increased. Cultures under 4/2 h showed a higher photosynthetic capacity at an earlier stage of growth but this did not appear to be a factor in the enhanced growth. It is suggested that phytochrome may be involved in determining a different pattern of growt

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01732.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Polysiphonia lanosa(L.) Tandy is a marine red alga that usually grows epiphytically on the fucaleAscophyllum nodosum(L.) Le Jolis. The present work was conducted in order to obtain more information on the relationships between these two algae, especially as regards the metabolism and long‐distance transport of phosphorus. Three types of experiments were carried out using labelled phosphorus. (1) Comparative study of the metabolism of32P1absorbed by the tissues of each species. By means of two‐dimensional chromatography and autoradiography, it was shown that32P1was rapidly incorporated into organic soluble compounds (adenosine triphosphate, hexose monophosphate, uridine diphosphoglucose, phosphoenolpyruvate + phosphoglyceric acid). Although the two algae belong to different phylae the phosphorylated compounds were not very different. The energy charges (0. 72 for both species) were in the usual range for aerobic plant tissues. On the other hand the incorporation of32P1into the insoluble P0fraction was doubled inP. lanosacompared to inA. nodosum(ca 80 and 40%, respectively). At the source level, the air bladder ofA. nodosum.the same soluble compounds (inorganic phosphate, P1adenosine triphosphate, hexose monophosphate. etc.) represented the likely forms transported. A part of the soluble P0fraction may return to the P1fraction. (2) In translocation experiments conducted in situ,32P1locally injected into an air bladder moved over long distances not only through the thallus ofA. nodosumbut also intoP. lanosa.The reciprocal transfer remained unsuccessful. (3) The32P1represented the predominant compound identified in the two species: this argues in favour of P1as the translocated form of phosphorus. Our results support the hypothesis of a parasitic rather than a simple epiphytic relationship between the two al

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01733.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Suspension cultured cells ofCatharanthus roseuswere used to study the effects of excess sugar, and phosphate or nitrogen starvation on growth and respiration. Excess sugar resulted in a higher dry weight but the cell number was not significantly higher than in the controls. After inoculation in phosphate‐free medium almost no growth was observed, whereas in medium without nitrogen some growth still occurred, indicating that the medium contains more than enough nitrogen and only a limited amount of phosphate. The maintenance respiration in the nitrogen‐free medium was lower than in the control, probably as a result of a lower protein production. In phosphate‐free medium, however, the maintenance respiration was higher, because the cyanide‐resistant pathway was engaged and the P/O ratio was decreased. InCatharanthus roseuscells the cyanide‐resistant pathway is engaged upon phosphate or nitrogen starvation in combination with excess sugar, while excess sugar, as such, does not engage the cyanide‐resistant pathway. In the presence of excess sugar the rate of glycolysis is adenylate‐controlled. It is only in combination with mineral starvation that the rate of glycolysis does not match the capacity of the cytochrome pathway, resulting in an overflow via the alternative pathway. After combination of mineral starvation with a low sugar supply the rate of glycolysis is controlled by both the substrate supply and the adenylates, and the cyanide‐resistant pathway

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01734.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The quiescent centre of primary roots ofZea maysL. (cvs LG 11 and Golden Bantam) consists of a population of slowly cycling diploid cells. These metabolically inactive cells may be triggered to synthesise DNA under specific conditions and constitute a good model for studying the regulation of the cell cycle. An excision and squash technique is described for the quiescent centre which, when coupled with Feulgen and fluorochrome staining, allows nuclear DNA contents to be determined by microdensitometry in less than a day. This technique was coupled with experiments in which excised quiescent centres were placed on solid culture medium into which hormones and radioactive DNA precursors were incorporated. In complementary and control experiments [methyl‐3H]thymidine was supplied to intact roots (with or without root caps) by means of fibre‐glass cubes as donors.Progression of the cell cycle was followed by microdensitometry and autoradiography. Distribution of DNA content was similar in excised and squashed quiescent centres and in histological sections. Labelling experiments showed that the quiescent centre is made up of cells that differ in their cycle time. While some labelled cells had reached mitosis after 8 h, others were still in G2after 16 h of continuous labelling. Excision and culture of the quiescent centre resulted in a dramatic activation of the cell cycle as shown by the labelling index that increased from 15% in intact roots fed during 16 h with [methyl‐3H]thymidine to 31% in excised quiescent centres to which radioactive precursor was supplied during the same time. Supplying hormones (50 μMabscisic acid [ABA], 0. 1 μMzeatin, 1 μMzeatin riboside) to quiescent centres via the culture medium restored their inactivity (labelling indices dropped to 1% after ABA. and to 11% after zeatin and zeatin riboside treatments. respe

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01735.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The effects of assimilate supply on the growth of individual fruits during different stages of fruit development were analysed in cucumber (Cucumis sativusL. cv. Corona). The assimilate supply was varied by maintaining different numbers of fruits per plant or maintaining different irradiances. The growth rate of a cucumber fruit strongly increased with increasing assimilate supply, but its growing period was not noticeably affected. At a low assimilate supply both cell number and cell size were reduced. Increasing the assimilate supply at different stages of fruit development showed that the early development of a cucumber fruit was not crucial for setting its growth potential. A small number of cells, due to a low assimilate supply, during early fruit development, was to a great extent compensated by an increased expansion rate of individual cells. It is concluded that cell number is not an important determinant of fruit size in cucumber, although fruit size is often positively correlated with cell number. In the early stages of fruit development the effect of irradiance on the fruit growth rate depends on the presence of an earlier developed fruit because of dom‐inance between fruits. In later stages of fruit development, a decrease in irradiance reduced the growth rate of all fruits relatively to the same extent independent of age or presence of other fruit

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1993.tb01736.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY