摘要:

AbstractBalling and Zimmermann [Planta 182 (1990), 325–338] used a pressure probe to measure directly negative pressures in the xylem of transpiring plants. They obtained data that challenge the standard framework that plant physiologists use when thinking about plant water relations, and, most notably, found a substantial discrepancy between their measurements of xylem pressure and of leaf water potential measured with a Scholander pressure bomb. Their data are critically examined and it is shown that most of them can be accommodated within the established principles of plant water relations. In particular, there are several reasons, consistent with the established principles, why leaf water potential and xylem pressure may diffe

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00250.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00251.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractIn a long‐term experiment with maize grown at different humidities, Tanner and Beevers (1990) demonstrated that the amount of water lost by the plants in transpiration (plus guttation) could be reduced by a factor of three without any adverse effect on growth. As a consequence, the authors questioned the importance of the transpiration stream in supplying the shoot with minerals, arguing that there are other causes of mass flow in the xylem (such as Münch counterflow from phloem to xylem, and water consumed by growing sink tissues) that may, in the limit, be capable on their own of providing the shoot with minerals. This hypothesis is discussed here in the light of recent work on xylem water relations. It is shown to involve the incorrect premise that, if transpiration were required for long‐distance ion transport, plants should grow less well at high humidity. Instead, solute flux to the shoot can be demonstrated by experiment to remain constant over a wide range of transpiration rates, since the concentration of solutes in the xylem sap varies inversely with transpiration rate. Independent evidence suggests that the non‐transpirational component of mass flow in the xylem is small and is unlikely to be able to provide the shoot adequately with minerals in the absence of transpiration. A simple corollary of this view is that plant growth should be reduced at very low transpiration rates, a prediction that should be testable at sufficiently high humidities under carefully controlled cond

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00252.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00253.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe relationships between xylem tension, velocity of water ascending and transpiration in tobacco plants were measured by means of the “xylem pressure probe technique” (Balling, A. and Zimmermann, U., Planta 182, 325–338, 1990). The flow velocity was determined by suction or injection of fluorescein (or FITC‐labelled dextrans of various molecular weights) from the microcapillary of the pressure probe into the punctured xylem vessel, followed by serial‐sectioning of the stem after a given propagation time. The distance travelled was defined as the distance from the injection point to the uppermost xylem section in which the dye could be detected. For a transpiration rate of 0.52 ± 0.12 ml . h−1, a linear dependence between the flow velocity and the tension gradients was found as expected from the Hagen‐Poiseuille law. The slope of the straight lines decreased with increasing molecular weight of the fluorescent labelled compound, presumably because of (partial) plugging of the pit membranes. The average value of the flow velocity (2.5 . 10−4± 0.9 . 10−4m . s−1) was one magnitude smaller than the value estimated from the geometric dimensions of the xylem vessels, but agreed well with the literature value of 2.8 . 10−4m . s−1for herbs (determined by the heat pulse technique; Huber, B. Ber. deutsch. bot. Ges. 50, 89–109, 1932). The average pressure gradient was determined to be 0.39 ± 0.23 MPa . m−1, in agreement with the literature (Begg, J. E. and Turner, N. C. Plant Physiol. 46, 343–346, 1970).The first response of xylem pressure (or tension) and of flow velocity to a reduction of the transpiration rate (0.14 ± 0.06 ml . h−1) occurred after about 24 h, when an increase of the xylem pressure towards higher values associated with a decrease in flow velocity was observed. In contrast, re‐establishment of the normal transpiration rate brought the pressure (or tension) and the flow velocity back to normal values within half an hour.Similary, introduction of a transverse cross‐sectional cut into the stem did not lead during the first 10 h to a change in xylem tension (or velocity). However, during the following day the pressure fell to relatively low values (about −0.13 MPa). The velocity increased 10‐fold. In the next two days the xylem pressure increased again to normal values (average +0.03 MPa), whereas the flow velocity assumed higher values than normal.The data are discussed in terms of the water stat

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00254.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractAcidification of external solution by maize root tips can apparently proceed by two mechanisms. The first, significant only above pH 6, does not require the presence of salts in the medium and appears to be due to respiratory CO2release with subsequent hydration and dissociation into H++ HCO−3. The second, much more efficient process, requires permeant ions and proceeds to well below pH 4 under mediation by the plasma membrane H+‐ATPase.While the first process is affected by acetazolamide (an inhibitor of carbonate dehydratase), the second is blocked by vanadate, erythrosin B, diethylstilbestrol and miconazole, and is strikingly stimulated by fusicoccin. Both mechanisms are markedly inhibited by heavy water, the first by up to 80% with an ID50of 18–25% D2O, the second up to 91%, with an ID50of 20–30% D2O. The inhibition of the acidification by ATPase can be relieved by replacing D2O with H2O, indicating that the effect of D2O is kinetic rather than on covalently‐bound hydrogen atoms. Apparently the H+‐ATPase uses H+(or possibly H3O+) as substrate which binds to a rather specific site where it cannot be functionally replaced b

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00255.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractThe role of apoplastic invertase (β‐d‐fructofuranoside — fructohydrolase, EC 3.2.1.26) of the hostPicea abiesfor carbohydrate uptake and growth of two of its natural ectomycorrhiza partners was studied. For that purpose, hyphae ofAmanita muscaria(Pers. ex Fries) Hock. andHebeloma crustuliniforme(Bull. ex Fries) Quell., as well as roots and suspension cultured cells ofPicea abies(L.) Karst. were used. Apoplastic invertase activity was demonstrated on roots and suspension cultured cells of spruce (in the latter case with 21.7 nkat (g fresh weight)−1). Inhibition of the root cell wall invertase activity (pH optimum 4.5) by increasing the apoplastic pH allowed determination of the permanent release of sucrose from the root. However, underin vivoconditions at a lower cell wall pH the hydrolysation products glucose and fructose were predominantly found. In contrast to spruce cells and certain fungi, such asSaccharomyces(Novick et al., 1981) orPhycomyces(Ruiz‐Herrera et al., 1989) invertase activity of the mycorrhizal fungiHebelomaandAmanitawas negligibly low. Furthermore, sucrose could not be consumed byAmanitaandHebeloma. As a consequence, cultures of these mycorrhizal fungi starved when kept on media with sucrose as sole carbohydrate source. But addition of invertase initiated hyphal growth immediately. Studies on carbohydrate uptake of host and fungal cells confirmed that the monosaccharides glucose and fructose were readily incorporated by spruce and fungal cells, with a clear preference for glucose. From these results it is suggested that apoplastic invertase activity of the hostPicea abiesis a precondition for the utilization of sucrose by the studied mycorrhizal fungi during the nutritional interaction of the symbioti

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00256.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractJasmonates, ubiquitous cyclopentanone compounds, are reviewed as new regulators for plant growth and development. They may complement the group of well‐established “classic” phytohormones. Jasmonates influence a multiplicity of plant physiological processes by inhibition, promotion or induction. In many aspects they are similar to abscisic acid, especially in responses to stress. The review contains information on the chemical structures and metabolism of jasmonates, contributes to their biological role and describes possible mode(s) of action at the level of molecular biology and gene expression. In particular, emphasis is placed on the gene expression and accumulation of jasmonate‐induced abundant polypeptides as a stress response of the plant cells. A hypothesis is attempted in which endogenous jasmonates represent an integral part of the signal transduction chain between stress signal(s) and stress resp

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00257.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have investigated the distribution of transcripts for chloroplast proteins involved in photosynthesis and carbon assimilation inArabidopsis thaliana. The probes that were used for assessment of transcripts represent the chloroplast genespsbA(encoding the D1 protein of photosystem II) andrbcL(for the large subunit of RubisCO) as well as the nuclearrbcSgene family for the RubisCO small subunit. With any of these probes we find a tissue‐specific distribution of transcripts in mature plants, with the highest concentration in rosette leaves and almost undetectable amounts in roots. The transcripts detected by each of these probes reveal similar spatial distribution and temporal kinetics during seedling development, with maximal levels around 70 h after sowing. They each show higher levels under light‐grown as compared to dark‐grown conditions, indicating a coarse control that ensures roughly coordinated levels throughout plastid differentiation. Embryonic transcripts are present in much higher concentration within the ground meristem and protoderm than in the procambium, which seems to reflect the different degree of determination towards the subsequent function in photosynthesis. Transcripts were detected in all characteristic stages throughout embryogenesis including the (non‐green) proembryo stage, suggesting that chlorophyll accumulation is not essential for expression of these genes at the RNA level. Both processes, hence, appear to be triggered by earlier molecular events that remain to be charac

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1991.tb00258.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY