摘要:

Abstract.Xanthoxylin is a cytotoxic and fungicidal compound with the characteristics of a typical phytoalexin. At a concentration of 0.3 mol m−3it inhibits K+‐dependent acid extrusion and K+net uptake (or uptake of equivalent alkaline cations such as Rb+and CS+) by up to about 80% and hyperpolarizes by about 20% the membrane electrical potential. Its inhibition of the acid extrusion does not depend on altered ion exchange involving the anions in the media, a reduction of the metabolic energy available, or detectable changes in the permeability of the cell membrane to H+ions. The drop in K+net uptake depends on a decrease in the influx of K+into the cell. In functional terms, xanthoxylin is an inhibitor of the K+permeation mechanism and does not appear to interact with the mechanisms creating the electrochemical energy gradi

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604637

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Carbonylcyanide,m‐chlorophenyl hydra‐zone (CCCP) decreased the ATP content of barley and corn roots by 80% within 5 min. The protonophore inhibited K and Cl absorption by largely unvacuolated root tips, and vacuolated root segments of barley and corn. The protonophore also inhibited Na absorption by root segments and Na extrusion by root tips of barley; it did not affect these Na fluxes in corn root tips and segments, and Na Influx in barley root tips. It was concluded that corn roots lack a metabolic mechanism for Na extrusion from the cytoplasm to the external solution or vacuole, which is functional in barley ro

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604641

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Ricinus communisplants have an unusually high capacity to exude considerable quantities of phloem sap from bark incisions. We have usedRicinusas an experimental system to study different aspects of sap exudation. Dimensional changes in the bark, monitored by a displacement transducer, showed that pressure release in the sieve tubes was accompanied by elastic shrinkage. The rate of exudation was also controlled by the degree of pressurization and elastic properties of the sieve tubes. A displacement transducer was used to measure the elastic modulus (ɛ) of phloem samples by immersing them in a range of different osmotica. The cells had a low elastic modulus (ɛ= 1.62 ± 0.41 MPa at full turgor). ɛ of phloem tissue in massage pretreated bark, from which exudation was enhanced, was not significantly different from that of unmassaged bark in contrast with the suggestion of Lee (1981). However, anatomical studies showed that massage pretreatment has a stimulating influence on the cambial cell division, which increased the phloem tissue cross‐section up to 160%. The newly‐formed sieve tubes were ‘spliced’ into existing ones in the unmassaged zone to re‐establish vascular continuity. Plants with a greater capacity to exude phloem sap from a given stem location had a greater cross‐sectional area of sieve tubes in the vicinity.The significance of observations with respect to other sap exudation phenomenon is discussed. The importance of the present work in understanding the technique of palm tapping, on which the palm sugar industry depends, is

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604644

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.The size and shape of drops on leaf surfaces strongly affect their persistence. The relationship between volume and exposed surface area of drops on wheat leaves and the log‐normal drop size distribution in a wheat canopy after rain are used to derive equations to describe how the total volume and drop number change with evaporation. Firstly, the behaviour of a single drop as it evaporates is considered and then equations describing the change in a population of drops with an initial log‐normal distribution are derived. The time taken for all the drops to reach complete dryness is about thirty times that for the same volume of water spread uniformly over the surface with the same potential evaporation r

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604646

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.The development of water impermeable seed coats of two members each of the leguminoseae family [Crotalaria spectabilisRoth,Sesbania exaltata(Raf) Cory] and the malvaceae family[Anoda cristata(L.) Schlecht,Abutilon theophrastiMedic.] was investigated. Highest peroxidase (POD) activity ofAnodaandAbutilonseed coat extracts was highly correlated with the developmental stages when soluble phenolics were maximally converted into lignin. Although extensive lignification occurred during seed coat development in both legumes, the patterns of POD activity, soluble phenolic levels and time of lignification were different from those of the malvaceous species. POD activity levels in developing coats of the malvaceous seeds increased as phenolics decreased. Both POD activity and phenolic levels decreased during seed coat development of the legumes. POD was immunocytochemically and immunochemically detected in seed coats of all four species; however, results for polyphenol oxidase were negative. The results confirmed POD involvement in lignification of leguminous and malvaecous species and support and extend our earlier view that POD is involved in lignin formation during development of impermeable seed coats.

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604651

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.The starch concentration in mature leaves of the halophyteSuaeda maritimaincreased from 4.7 to 7.3 mg mg−1chlorophyll when sodium chloride (680 mol M−3) was added to the solution in which the plants were grown. This effect of salinity on the starch: chlorophyll ratio was greater in young than in old leaves. Electron micrographs showed the starch to be in the chloroplasts and this was confirmed by measurements on isolated chloroplasts. Total phosphorus concentration (mg mg−1chlorophyll) in leaves of all ages from plants ofS. maritimadecreased on salinization of the growth medium suggesting an inverse relationship between phosphorus and starch concentrations. However, although leaf starch concentration varied with leaf age, phosphorus concentration did not. The cause of starch accumulation in chloroplasts at salinities which are optimal for growth (340 mol m−3) remains

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604655

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Previous mathematical analyses of stomatal mechanics have demonstrated, and experimental measurements have confirmed, that the turgor‐generated force of the epidermal cells dominates that of the guard cells in determining aperture. DcMichele&Sharpe (1973) termed the phenomenon the mechanical advantage of the epidermal cells, while Cookeet al.(1976) expressed it as an antagonism ratio. Both of these formulations, however, have theoretical or practical limitations. This study presents a biophysical analysis demonstrating that the effective forces in the stomatal system may be studied in terms of simple stomatal geometry. From this analysis, the mechanical advantage can be redefined and interpreted based upon simple geometric relationships calculated from measurable anatomical dimension

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604674

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.An improved method is described for micro‐autoradiography of water‐soluble substances alter freeze‐substitution of plant tissue in which water is rigorously excluded. Resin sections are cut and flattened dry, and dry photographic emulsion is mounted on them. When the location of14C in wheat leaves after assimilation of14CO2was studied with this method, it was found that14C entered the intermediate veins before the laterals and entered both types of veins along the flanks of the veins adjacent to the phloem. High concentrations of14C were found in small spaces in the cells of mesophyll and vein parenchyma; these spaces coincide with the nuclei. The concentration of14C in these nucleus‐associated spaces was as high as that reached at later times in the sieve tubes. Water washed the14C out of these spaces of the sections and the label in the washings was predominantly in sucrose. The high14C concentrations of the nucleus‐associated spaces were particularly easily leached. It is concluded that the raising of the sugar concentration to the high levels found in sieve tubes can take place in these leaves in a special space in each mesophyll cell not, or not only, at the boundary of the si

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604677

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Abstract.Drought avoidance due to cuticular control increases with leaf number to a maximum in the intermediate leaves, decreasing to a minimum in the upper leaves. Dehydrated intermediate leaves do not rehydrate detectably when floated on water for several days. Excision of their petioles when submerged, permits full rehydration, presumably via the xylem. Stressing the plant by withholding water for 1–3 weeks fails to increase this already high resistance to water movement through the leaf surface. It does, however, markedly decrease the loss of water from the fully rehydrated (100% RWC) leaves during the first hour of dehydration, presumably due to a more rapid stomatal closure than in the non‐stressed leaves.Dehydration tolerance increases with leaf number, without an intermediate maximum. The intermediate and upper leaves were markedly more tolerant of dehydration after drought‐induced stress than when non‐stressed. Dehydration tolerance in some cases, was inversely proportional to dehydration rate. It was possible, however, to equalize the rates of dehydration of drought‐stressed and non‐drought‐stressed leaves without affecting the greater tolerance of the drought‐stressed leaves.Dehydration avoidance by osmotic adjustment was markedly developed in the slowly dehydrated attached leaves of drought‐stressed plants, but not in the rapidly dehydrated excised leaves. This is evidence of drought acclimation. It must, therefore, be concluded that the slow dehydration of the drought‐stressed plants also leads to the increase in dehydration tolerance by permitting drought‐induced acclimation.The overall drought resistance of cabbage leaves depends on the three components: drought avoidance, dehydration avoidance and dehydration tolerance. The latter two increase during acclimation but the cuticular control of droug

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604680

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11604684

出版商:Blackwell Publishing    

年代:1985

数据来源: WILEY