ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00571.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00572.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Apoptosis is a feature of animal cells that explains some aspects of programmed cell death in plants. Differences between plant and animal cell development require that concepts be reexamined to signify how plant cells have evolved the need for cell elimination in the meristematic growth habit, life cycle, and alternation of generations. Central to this theme is the regulation of divisional cycles for mitosis, meiosis, apomeiosis, and their related sexual and asexual reproductive processes. Apoptosis depends on the coordinated expression of genes regulating divisional cycles and apoptotic pathways so that irreversible nuclear and cytoplasmic elimination occurs. Cellular degradation products are salvaged to sustain adaptation, viability, structural function, and ontogeny. The cell wall is usually retained and further differentiated or eliminated. A model of factors predisposing apoptosis and comprising checkpoints in cell divisional cycles is presented for comparisons among plant and animal cells.

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:It is well accepted that the amyloplasts of the cap are responsible for gravisensing in primary roots. However, roots with starch‐depleted plastids are able to respond to gravistimulus, but their curvature is slower than that of roots containing amyloplasts. The goal of our experiment was to analyse the effects of natural variations of statolith starch in the gravitropic response of lentil roots to a stimulation in the horizontal position. In lentil seedlings grown in the vertical position for 26 h, the volume of the amyloplasts in the statocytes differed between individual roots. The amount of starch in the cap was determined parallel to the rate of gravitropic curvature. There was no statistical correlation between the intensity of the gravitropic response and the starch content in the statocytes. Lentil roots were treated with gibberellic acid (GA3) at 32°C in order to reduce the volume of starch in the statoliths. There was 53% less starch in the cap of GA3treated roots as compared to the cap of control roots. But there was no relationship between starch content in the cap and the responsiveness of the root to a gravistimulus, except when the amount of starch was sma

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Photoinhibition of photosynthesis was measured in two Mediterranean Corallinaceae,Jania rubensandCorallina mediterranea, using pulse‐amplitude modulation (PAM) fluorescence and oxygen production on site. Both algae were found to be adapted to low irradiances of solar radiation and easily inhibited by exposure to excessive radiation. Both algae were impaired even in their natural habitat under overhanging rocks which protected them from direct solar radiation, except for a few hours in the early morning. Recovery from photoinhibition of both the photosynthetic quantum yield, defined as Fv′/Fm′, and oxygen production took several hours and was not complete. Judging from both parameters indicated above,Janiaseems to be even more sensitive thanCorallina, even though the former alga was found in more exposed hab

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The photosynthetic performance ofLasallia pustulataandUmbilicaria spodochroawas measured both in the field on granitic rock in southern Norway and in the laboratory under controlled conditions of light and temperature. In the field thallus temperatures varied between − 2 and + 5 °C during the daylight period in January 1994.In situwater contents were between 50 and 400% d.wt. inL. pustulataand between 100 and 500% d.wt. inU. spodochroa. The lichens were active during the whole period of investigation. Photosynthetic rates reached 13.03 μmol CO2g Chl−1s−1inL. pustulataand 5.56 μmol CO2g Chl−1s−1inU. spodochroa. Ice formation on the thallus surface did not impede CO2exchange. Light was mainly the limiting factor, as could be confirmed by the laboratory experiments. In general, habitat conditions never provided optimum photosynthetic rates but photosynthetic carbon balance was positive during 4 of the 5 days investigated. The coldest day was photosynthetically almost as efficient as the warmest day during

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Polyclonal antisera against a fusion protein of β‐galactosidase and the 20 C‐terminal amino acids of theArabidopsis thalianasucrose carrier AtSUC2 were used to determine the cellular localization of the AtSUC2 protein. Using fluorescence‐labelling on sections from different organs ofArabidopsisthe AtSUC2 protein was immunolocalized exclusively in companion cells. The presented data indicate that phloem loading inArabidopsismay be catalyzed by the AtSUC2 sucrose carrier which transports sucrose into the companion cells. No evidence for a participation of the secondArabidopsissucrose transporter AtSUC1 has been ob

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:CO2assimilation, transpiration and modulated chlorophyll fluorescence of leaves ofChenopodium bonus‐henricus(L.) were measured in the laboratory and, at a high altitude location, in the field. Direct calibration of chlorophyll fluorescence parameters against carbon assimilation in the presence of 1 or 0.5% oxygen (plus CO2) proved necessary to calculate electron transport under photorespiratory conditions in individual experiments. Even when stomata were open in the field, total electron transport was two to three times higher in sunlight than indicated by net carbon gain. It decreased when stomata were blocked by submerging leaves under water or by forcing them to close in air by cutting the petiole. Even under these conditions, electron transport behind closed stomata approached 10 nmol electrons m−2leaf area s−1at temperatures between 25 and 30 °C. No photoinactivation of photosystem II was indicated by fluorescence analysis after a day's exposure to full sunlight. Only when leaves were submerged in ice was appreciable photoinactivation noticeable after 4 h exposure to sunlight. Even then almost full recovery occurred overnight. Electron transport behind blocked stomata was much decreased when leaves were darkened for 70 min (in order to deactivate light‐regulated enzymes of the Calvin cycle) before exposure to full sunlight. Brief exposure of leaves to HCN (to inhibit photoassimilation and photorespiration) also decreased electron transport drastically compared to electron transport in unpoisoned leaves with blocked stomata. Non‐photochemical fluorescence quenching and reduction of QA, the primary electron acceptor of photosystem II was increased by HCN‐poisoning. Very similar observations were made when glyceraldehyde was used instead of HCN to inhibit photosynthesis and photorespiration. In HCN‐poisoned leaves, residual electron transport increased linearly with temperature and showed early light saturation revealing characteristics of the Mehler reaction. During short exposure of these leaves to photon flux densities equivalent to 25% of sunlight, no or only little photoinactivation of photosystem II was observed. However, prolonged exposure to sunlight caused inactivation even though non‐photochemical quenching of chlorophyll fluorescence was extensive. Simultaneously, oxidation of cellular ascorbate and glutathione increased. Inactivation of photosystem II was reversible in dim light and in the dark only after short times of exposure to sunlight. Glyceraldehyde was very similar to HCN in increasing the sensitivity of photosystem II in leaves to sunlight. We conclude from the observations that the electron transport permitted by the interplay of photoassimilatory and photorespiratory electron transport is essential to prevent the photoinactivation of photosynthetic electron transport. The Mehler and Asada reactions, which give rise to strong nonphotochemical fluorescence quenching, are insufficient to protect the chloroplast electron transport chain against p

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Flower morphology, flowering phenology, flower visitors, reproductive systems, and stigmatic receptivity of six species ofSileneandSaponaria (Silene alba, S. dioica, S. vulgaris, S. nutans, S. noctiflora. Saponaria officinalis) were studied from April to October 1993 and from April to June 1994 in natural populations around Giessen in Hessen/Central Germany and, additionally, in individuals grown from seeds in the Botanical Garden of the University of Giessen. With the exception ofSaponaria officinalisandS. noctiflora, all species were regularly visited and pollinated by crepuscular and nocturnal moths and hawkmoths, but only one species,S. alba, was exclusively pollinated by these night‐active insects. The other species showed mixed pollination syndromes in which nocturnal and diurnal insects both promoted pollen transfer. Geitonogamy or even autogamy occurred in the gynodioecious and hermaphrodite species S.vulgaris, S. nutans, S.noctiflora, andSaponaria officinalis. Silene noctiflora, the only annual species, is pseudocleistogamous; the majority of its flowers did not open, and fruit set occurred after selfing in bu

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Pollen and nectar are usually lumped together as floral rewards for pollinating bees, but they play totally different roles for flowers and bees (Table 1), as well as in the relationship between them. While flowers are specialized for certain pollinators via nectar, bees specialize on certain flowers via pollen. While flowers need pollen as a prerequisite for pollination, it is the essential larval food in bees. Thus, there is a strong competition between them for pollen. Foraging for pollen must be divided into three phases: uptake in the flower, reloading into and homeward transport within a carrying container. Bees have specializations for transport but hardly any for pollen uptake ‐ and thus for pollination. Bees actively harvesting pollen usually do not pollinate. This only happens as a consequence of contamination of the bee by pollen. From these data a scenario is provided for the evolution of bees and bee flowers. Specialized bee flowers are often characterized by their ability to hide pollen from the bees and at the same time use them as optimal pollinators. If the relationship of bees and flowers is mutualistic at all it is best described as a balanced mutual exploitatio

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00580.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY