摘要:

Current‐year shoots of Sitka spruce (Picea sitchensis(Bong.) Carr.) were removed from the forest canopy. After steady‐state rates of net photosynthesis were obtained in a leaf chamber, the shoots were excised in air and removed at different times to establish a relationship between net photosynthesis and xylem water potential. The experiment was repeated at five ambient carbon dioxide concentrations.Net photosynthesis remained constant over a wide range of xylem water potential and increased linearly with ambient carbon dioxide concentration between 20 and 300 cm3m−3. At low water potential net photosynthesis declined at each ambient carbon dioxide concentration and there was little difference in the potential (±0.05 MPa) at which zero photosynthesis was observed.There was a small increase in the CO2compensation concentration at low xylem water potentials, but calculated mesophyll conductance still declined at low water potential after correction for this change in compensation concentration. Mesophyll conductance reached zero within the same range of water potential as net photosynthesis. The results suggested that the non‐stomatal contribution to the decline of photosynthesis was approximately 30% until almost complete stomatal closure

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02706.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The effects of abscisic acid (ABA) on photosynthesis, dark respiration, and photorespiration were studied inLemna gibbaL. plants. The initial concentration of ABA in the nutrient solution was 10−7M and in a few experiments, 10−6M. The cultures were grown in the same solution for time periods ranging from one hour to 12 days. Net photosynthesis, measured as CO2uptake by infrared gas analyser technique, was inhibited after four hours of ABA treatment and reached a minimum after four to seven days depending on the time of the year. After 12 days a substantial recovery of photosynthesis was observed. Dark respiration was significantly stimulated after two to seven days of ABA treatment but then returned to the control level. The transient effects of ABA on photosynthesis and dark respiration corresponded to the previously measured time course of [14C]‐ABA uptake byLemna. Photorespiration measured as oxygen inhibition of photosynthesis was not affected b

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02707.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Isolated chloroplasts of barley seedlings (Hordeum vulgareL.) when kept in light, released a soluble, thermostable factor that inhibited phenylalanine ammonia‐lyase (PAL)in vitro. Highest inhibition was found when chloroplasts were suspended in PAL‐containing extract and kept in light. Efficiency of PAL activity inhibition did not depend greatly on the type of medium used for chloroplast isolation, nor on the composition of buffer in which the enzymatic activity was measured. It is proposed that in green tissues chloroplasts may participate in regulation of cytoplasmic PAL activ

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02708.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The total resistances to CO2uptake bySticta latifronsRich, andPseudocyphellaria amphistictaKremp. were separated into transport and carboxylation components by calculation after transformation of net photosynthesis rate against CO2concentration curves into a linear form. The use of this technique circumvented the problem of measuring the internal CO2concentration of the lichen thalli. Both species exhibited an increase in transport resistance at high thallus water contents and an increase in both transport and carboxylation resistances at low water contents. At low and intermediate water contents internal transport resistances were larger than carboxylation resistances when measured at limiting CO2concentrations. However, at ambient CO2concentrations carboxylation processes were the dominant factors limiting photosynthesis at all, except the high, water contents.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02709.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The gaseous exchange pathways ofSticla latifronsRich. andPseudocyphellaria amphistictaKremp. were examined using both light and scanning electron microscopes. The size and frequency of the pores in the gas exchange structures (cyphellae and pseudocyphellae) and in the medulla were measured and from these CO2diffusion resistances were calculated. Pseudocyphellae were found to be smaller and more widely spaced than cyphellae, consequently the resistance of the pseudocyphellae, was much greater than that of the cyphellae. Medulla resistances were low in both lichens and are probably unimportant, even at high water contents. No evidence of hyphal swelling was found. Gas exchange structure resistances were more than five fold greater than medulla resistances. It is suggested that this arrangement of resistances may simultaneously encourage refixation of respired CO2and maintain a non desiccating environment for the lichen algae. The internal transport resistances calculated in this work approximate experimentally obtained values.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02710.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

A relationship between tracheary element differentiation and the cell cycle was studied in single cells isolated from the mesophyll ofZinnia elegansL. cv. Canary bird. Almost all nuclei of isolated mesophyll cells were at the 2 C level of DNA, indicating that almost all cells were initially in the G1phase and that somatic polyploidy was absent. Cultured cells underwent partially synchronous DNA replication at 42 h and mitosis at 54 h of culture, and the first cell cycle time was approximately 58 h.The occurrence and timing of DNA replication and mitosis during cytodifferentiation to tracheary elements were investigated using microspectrophotometry, microfluorometry, tritiated thymidine autoradiography, and serial observation. More than 55% of the nuclei of the immature tracheary elements were at the 2 C level of DNA and were not labeled by continuous feeding with tritiated thymidine, providing clear evidence that these cells differentiated without interventing DNA replication. Some tracheary elements (approximately 30%) were formed after one round of the cell cycle, and others (less than 5%) were formed after passing through the S phase, but without intervening mitosis. All types of tracheary elements appeared simultaneously after 58 h of culture, and their patterns of increase in number were similar. From the results, we propose a hypothesis concerning the relationship between cytodifferentiation and the cell cycle.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02711.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Passive fluxes of K+(86Rb) into roots of sunflower (Helianthus annuusL. cv. Uniflorus) were determined at low K+concentration (0.1 and 1.0 mM K+) in the ambient solution. Metabolic uptake of K+was inhibited by 10−4M 2,4‐dinitrophenol (DNP). K+(86Rb) fluxes were studied both continuously and by time differentiation of uptake. In high K+roots passive uptake was directly proportional to the K+concentration of the uptake solution, indicating free diffusion. This assumption was supported by the fact that passive Rb+uptake was not affected by high K+concentrations. In low K+roots the passive uptake of K+was higher than in high K+roots. The increase was possibly due to carrier‐mediated K+transport. As K+effluxes were quantitatively similar to influxes, it is suggested that passive K+fluxes represent exchange diffusion without relation to net K+tran

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02712.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Uptake of Rb+from a complete nutrient solution with 2.0 mM Rb+was studied in roots of spring wheat seedlings (Triticum aestivumL. cv. Svenno) with different K+levels. The relationship between Rb+uptake and concentration of K+in the roots indicated a negative feedback mechanism operating through allosteric control. The Rb+uptake process in root cells was divided into two steps: (1) binding of the ion in the free space, and (ii) transmembrane transport into the cytoplasm. Metabolic and non‐metabolic components of uptake were separated by addition of the metabolic inhibitor 2,4‐dinitrophenol (DNP) to the nutrient solution. It is suggested that metabolic Rb+uptake requires energy in two uptake steps (for binding to the carrier entity in the free space and for transmembrane transport) or in one step only (for transmembrane transport), dependent on the K+status of the roots. The change from metabolic to non‐metabolic binding in the free space is accomplished by changing the conformational state of the carrier (slow/fast transitions). There may be a hysteretic effect on metabolic Rb+uptake through a slow transition between carrier states. This is superimposed on the negative cooperativity, strengthening further cooperativity at intermediate K+levels in the roots. Non‐metabolic Rb+uptake probably consists of two components, a carrier‐mediated (facilitated diffusion) and a parallel diffusive

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02713.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

The properties of membrane‐associated ATPase of cucumber (Cucumis sativuscv. Seiriki No. 2) roots cultured in a complete medium (complete enzyme) and in a medium lacking Ca2+(Ca2+‐deficient enzyme) were investigated. The basal activity of membrane‐associated ATPase increased during Ca2+starvation, while Mg2+‐activation of the enzyme decreased and even resulted in inhibition by high Mg2+concentration at the late stage of the Ca2+starvation. The complete enzyme had low basal activity and showed a Mg2+‐activated hyperbolic reaction curve in relation to ATP concentration. Ca2+‐deficient enzyme with high basal activity showed a biphasic reaction curve and Mg2+‐activation was seen only at high ATP concentrations. Activation of membrane‐associated ATPase by various cations was decreased or lost during Ca2+starvation. The basal ATPase activity of Ca2+‐deficient enzyme increased for various substrates including pyrophosphate, p‐nitrophenyl phosphate, glucose‐6 phosphate, β‐glycerophosphate, AMP, ADP and ATP. Mg2+‐activation was found only for ADP and ATP in both the complete and Ca2+‐deficient enzymes, but the activation for ATP was greatly reduced by Ca2+starvation. The heat inactivation curves for basal and Mg2+‐activated ATPase did not differ much between the complete and Ca2+‐deficient enzyme. The delipidation of membrane‐associated enzyme by acetone affected the protein content and the basal activity slightly, but inhibited the Mg2+‐activated ATPase activity clearly with somewhat different behaviour between th

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02714.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

Normally suspension cultures of potato,Solanum tuberosum, can survive only to a freezing temperature of –2°C. The treated cultures were able to survive at much lower freezing temperature after the addition ofl‐proline of 0.43 M or more to the suspension medium and treatment for 1.5 h. Cultures could survive to ‐14°C with 0.87 M proline treatment. Treatments with higher concentration than 0.87 M resulted in no additional freezing survival. Microscopical observations of the treated cultures before freezing showed that proline induced plasmolysis, which was initiated at the 0.43 M level and reached maximum at 0.87 M. The mode of action of proline, appears to be due to the removal of excessive intracellular water by the osmotic gradient. Sucrose at about the same concentration acted in the same way as proline. The cryoprotective role of proline and sucrose is discussed in relation to the action of the permeant dimethylsu

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1981.tb02715.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY