摘要:

AbstractAnalysis of nodule inputsviathe phloem and outputsviathe xylem leads to the conclusion that water fluxes along those conduits alone would give a xylem sap osmolality in excess of that of sieve tubes and would thus plasmolyse the latterunlessN2fixation involved a very high respiratory consumption of organic C entering in the phloem, or there is significant water influx from soil through the nodule surface. Whether N2fixation by attached nodules not in contact with an external water supply is energetically inefficient (and hence also, at a whole plant level, inefficient in terms of water‐use) is as yet untested. However, the hypothesis which we prefer involves the shortfall in water entryviathe phloem being made up the parenchymatic water flux from the root to the nodul

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01628.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractEvidence is drawn from previous studies to argue that C3—C4intermediate plants are evolutionary intermediates, evolving from fully‐expressed C3plants towards fully‐expressed C4plants. On the basis of this conclusion, C3—C4intermediates are examined to elucidate possible patterns that have been followed during the evolution of C4photosynthesis. An hypothesis is proposed that the initial step in C4‐evolution was the development of bundle‐sheath metabolism that reduced apparent photorespiration by an efficient recycling of CO2using RuBP carboxylase. The CO2‐recycling mechanism appears to involve the differential compartmentation of glycine decarboxylase between mesophyll and bundle‐sheath cells, such that most of the activity is in the bundlesheath cells. Subsequently, elevated phosphoenolpyruvate (PEP) carboxylase activities are proposed to have evolved as a means of enhancing the recycling of photorespired CO2. As the activity of PEP carboxylase increased to higher values, other enzymes in the C4‐pathway are proposed to have increased in activity to facilitate the processing of the products of C4‐assimilation and provide PEP substrate to PEP carboxylase with greater efficiency. Initially, such a ‘C4‐cycle’ would not have been differentially compartmentalized between mesophyll and bundlesheath cells as is typical of fully‐expressed C4plants. Such metabolism would have limited benefit in terms of concentrating CO2at RuBP carboxylase and, therefore, also be of little benefit for improving water‐ and nitrogen‐use efficiencies. However, the development of such a limited C4‐cycle would have represented a preadaptation capable of evolving into the leaf biochemistry typical of fully‐expressed C4plants. Thus, during the initial stages of C4‐evolution it is proposed that improvements in photorespiratory CO2‐loss and their influence on increasing the rate of net CO2assimilation per unit leaf area represented the evolutionary ‘driving‐force’. Improved resourceuse efficiency resulting from an efficient CO2‐concentrating mechanism is propos

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01629.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractIn green as well as in etiolated leaves of rye (Secale cerealeL. ev. ‘Halo’), exposed to strong light at low temperature (0.4°C) catalase was inactivated. Other heme‐containing enzymes (peroxidases) and various enzymes of photosynthetic, photorespiratory or peroxide metabolism were not photoinactivated. After returning plants from a low to a physiological temperature (22°C), catalase activity recovered within 12 h through new synthesis. The leaf contents of H2O2and organic peroxides were not affected by the photoinactivation of catalse. The content of malondialdehyde generally increased after exposure to a higher light intensity. High‐light‐induced increases of ascorbate, and particularly of glutathione, were more marked in catalase‐deficient than in normal leaves. Photoinactivation of catalase was accompanied by severe inhibition of photosynthesis. Photoinhibition of photosynthesis was not related to the lack of catalase because photosynthesis was not impaired when catalase activity was kept low by growing the plants under non‐photorespiratory conditions. Photoinhibition appeared to result from photodamage in primary photochemistry of photosystem II, as indicated by a decrease of the maximal variable fluorescence. Photoinhibition of photosynthesis and of catalase have in common that in both instances proteins are involved that are continuously inactivated in light and, therefore, particularly sensitive to stress conditions that prevent their replacement by r

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01630.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe ureide content of soybean (Glycine max(L.) Merr.) nodules was unaffected by variations in the transpirational rate, while whole plant manipulations designed to decrease phloem supply to nodules resulted in lower rates of nitrogenase activity and anincreasein the ureide content of the nodules. The rate of ureide export from the nodule was estimated from the exponential rate of decrease in the pool size of ureides in nodules, following exposure to an N2‐free atmosphere (Ar:O2). Export was greatly reduced under treatments which reduced phloem supply to the nodule. A water budget for nodules suggested that the delivery of water to the nodule via mass flow in the phloem was comparable to that required for export of ureides from the nodule in the xylem from the nodule. Therefore, we suggest that xylem export from nodules is related to the phloem supply to the nodule rather than to the transpirational flux in the parent root. This suggestion is related to the reported decreases in nodule permeability to gases under conditions of phloem deprivatio

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01631.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractDark‐grown cell suspension cultures ofChenopodium rubrumlacking chlorophyll greened strongly upon transfer to illumination and fresh medium. This greening took place both in the presence of sucrose as a carbon source and in a mineral salt medium under an atmosphere enriched in CO2. The synthesis of chlorophyll was in each case closely accompanied by the development of high levels of enzymes typical of photosynthesis. Greening in sugar‐containing medium resulted in a rapid acquisition of characteristic features of photomixotrophic cultures, which have the ability to survive for a prolonged period in a minimal photoautotrophic environment in the light long after the initially present sucrose has been depleted from the medium. Greening under autotrophic conditions represented a direct transition from starvation conditions resulting from prolonged heterotrophic batch growth to successful photoautotrophy. Thus, light triggered the build‐up of a competent photosynthetic apparatus irrespective of the nutritional necessity for autotrophy. Illumination and greening did not influence catabolic enzyme activities beyond that increase of metabolic activity which is required for the production of photosynthetic mach

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01632.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractA method is described for the measurement of auxin‐induced H+‐efflux from small populations ofAvenacoleoptile segments. The method allows the simultaneous investigation of the kinetics of rapid auxin responses over a wide concentration range. IAA promoted linear rates of H+‐efflux and the change in amplitude of response occurred mainly over a low, narrow concentration range (10–50 μmol m‐3). The sigmoidal curve of best‐fit to each set of dose‐response data was determined using non‐linear regression techniques, allowing the objective determination of characteristic tissue sensitivity parameters (RMIN, RMAX, KDand p). The sensitivity parameters for the auxin‐type herbicide fluroxypyr are also presented as well as IAA parameters determined in the presence of abscisic acid and the ‘antiauxin’ PCIB. The interpretation of the parameter values and the potential use of sensitivity parameter analysis for the evaluation of theories concerning plant hormone action and in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01633.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractRates of oxygen uptake were measured in leaves ofSaxifraga cernuawhich had been exposed to an 18‐h photoperiod. These rates were compared to those in plants which had been exposed to continuous light. Rates of total dark respiration and alternative pathway respiration measured at the end of the photoperiod gradually decreased over the initial 3 d of exposure to an 18‐h photoperiod. Thereafter, respiratory rates were constant. Rates of total dark respiration and alternative pathway respiration decreased during the 6h dark period. Rates of normal and alternative pathway respiration are equally affected during the dark period. The respiratory rates had reached a new minimum level 3 d after the initiation of a dark period. These results suggest that respiration rates in arctic plants are high because of the long photoperiod in the arctic. The kinetics of photoperiod induced changes in respiration are slow enough to suggest the involvement of the biological clock in setting respiration rates. Indeed, total dark respiration and alternative pathway respiration show a definite circadian rhythm. Free‐running experiments show that normal respiration changes much less (has a smaller amplitude of variation) than alternative pathway respiration and that alternative pathway respiration accounts for most of the rhythmicity of respir

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01634.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractCytoplasmic concentrations, fluxes of K+, Na+and Cl and microsomal membrane lipids were investigated in a salt‐sensitive and salt‐resistant variety ofZea mays.The salt resistance of Protador relative to LGH(salt‐sensitive) appears to be related to higher K+fluxes and cytoplasmic concentrations, and lower Na+and Cl fluxes and cytoplasmic concentrations, when grown in NaCl. There were no apparent differences in the simple chemical composition of root microsomal membrane lipids between the two varicties, neither were these affected by

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01635.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

AbstractThe role of chlorophyll in the mature embryos of several tropical plants (Phthirusa pyrifolia[H.B.K.] Eichl. [Loranthaceae].Murraya koenigiaKurz. [Rutaceae],Murraya paniculataJack. [Rutaceae],Syzygium cuminii[L.] Skeels [Myrtaceae]) was investigated. Extracted chloroembryos of all species do photosynthesize when illuminated. Whole mature fruits ofM. koeningii, M. paniculataandSyzygium cuminiiexhibited some photosynthetic activity, but pericarps of none of the fruits photosynthesized when exposed to light. Thus the photosynthetic activity of fruits may be ascribed to CO2uptake by chloroembryos embedded in the fruits. A specific aspect of plant physiology, namely the re‐utilization of respired CO2in the process of photosynthesis is emphasized. It is postulated that within embedded chloroembryos, conditions such as high CO2concentration, high light intensity, and low oxygen concentration are favourable for conducting intensive photosynthesis. Photosynthesis within enclosed organs has an additional advantage in that is does not expose the plant to any risk of water loss usually associated with photosynthesi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1989.tb01636.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY