摘要:

The accumulation of the isoflavonoid phytoalexin, glyceollin, occurs in hypocotyls of green soybean seedlings (Glycine maxL. Merr. cv Harosoy 63) in response to the injection of a glucan elicitor isolated from the mycelial walls of the fungus,Phytophthora megaspermaf. sp.glycinea.This accumulation, which levels off after 24 hours, is preceded by a dramatic, transient rise in extractable activities of two early enzymes in the biosynthetic pathway, phenylalanine ammonia-lyase (PAL) andp-coumaryl CoA ligase (pCL). The maximum amount of extractable activity occurs 12 to 16 hours after elicitor treatment and is coincident with the most rapid period of glyceollin accumulation. These results suggest a regulatory role for these early enzymes in the biosynthesis of this secondary metabolite. High performance liquid chromatography analysis of the early intermediates in the pathway further corroborates this hypothesis. The relative pool size and rate of turnover ofp-coumaric acid, an early intermediate in glyceollin production, increase during the period of rapid increases in enzyme activities. Removal of cotyledons from elicitor-treated seedlings reduces glyceollin accumulation approximately 70%. This limitation of phytoalexin accumulation by cotyledon removal is correlated with a similar cotyledon effect on reduction of extractable activities of both PAL and pCL as well as a decrease in the flux of carbon through thep-coumaric acid pool. This research further supports the hypothesis that early enzymic steps in a biosynthetic pathway diverting carbon from primary to secondary metabolites function as regulatory control points.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Red light (R) stimulates an increase in the total concentration of intracellular calcium in the spores ofOnoclea sensibilisL. as determined by atomic absorption spectroscopy. Subsequent exposure to far-red light inhibits the R-induced increase in intracellular calcium. The majority of the increase occurs 5 minutes after the onset of irradiation. The calcium antagonist, La3+, inhibits both germination and the R-induced increase in intracellular calcium. The R-induced increase in calcium is sufficient to account for an increase in the concentration of intracellular calcium ions from 0.1 micromolar to 1 to 10 micromolar. Large detectable changes in other elements tested are not required for germination.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Cytidine 5′-triphosphate (CTP):phosphatidate cytidyltransferase from the endoplasmic reticulum and mitochondria ofRicinus communisL. var Hale was characterized. The endoplasmic reticulum enzyme has a pH optimum of 6.5 and a divalent cation is required, Mn2+being preferred and giving maximum activity at 2.5 millimolar. The estimatedKmfor CTP is 16.7 micromolar, but that for phosphatidate could not be determined accurately. The activity was inhibited by both deoxycholate and Triton X-100 at concentrations as low as 0.01% (w/w).The mitochondrial enzyme has a pH optimum of 6.0 and a divalent cation requirement similar to that of the endoplasmic reticulum. Maximum stimulation of the reaction by substrates occurred with 1.5 millimolar phosphatidate (from egg phosphatidylcholine) and about 400 micromolar CTP. The apparentKmfor phosphatidate could not be estimated accurately since activity was obtained in the absence of added lipid, apparently utilizing endogenous substrate. TheKmestimated for CTP was altered by the presence of the detergent Triton X-100; in its absence the value was 33.3 micromolar, but in its presence the value was 66.7 micromolar. Inclusion of 0.6% (w/w) Triton X-100 in the assay mixture stimulated the activity about 2.5-fol

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

A decline in growth, flowering, and boll (fruit) retention is referred to as cutout in cotton (Gossypium hirsutumL.). Fruit load affects cutout, possibly through hormonal effects. Experiments were conducted to test the hypothesis that fruits are a source of abscisic acid (ABA) that moves into fruiting branches and growing points where it inhibits growth, flowering, and boll retention. Removal of the flower or young boll at the first node of fruiting branches did not decrease the ABA content of fruiting branches or the abscission zone at the second node. Effects on ABA content of the boll at the second node varied. In one field test, ABA content of bolls at the second node decreased with successive harvests as bolls were removed from first node positions of several fruiting branches. Thus, the effect was cumulative and was not limited to individual branches. Removal of the flower or boll at the first node increased boll retention at the second node. Removal of all flowers during the first 3 weeks of flowering delayed the decreases in growth, flowering, and boll retention that occurred as fruit load increased. But, the ABA content of fruiting branches and mainstem apices was not decreased by early defruiting and did not increase with increasing fruit load. The results do not support the hypothesis that fruits are a source of ABA that moves into fruiting branches and growing points where it then inhibits growth, flowering, and boll retention.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

The fluorescent compound trisodium, 3-hydroxy-5,8,10-pyrenetrisulfonate (PTS) was used to quantify the apoplastic flux through red pine (Pinus resinosaAit.) root systems—that portion of the total water flux reaching the xylem without ever crossing a semipermeable membrane. Flow was induced by pressure through detopped root systems, and by transpiration through intact seedlings. Apoplastic flux was determined by multiplying total flux by the ratio of PTS concentration in the xylem exudate to PTS concentration in the bathing medium.Under aeration, apoplastic flux was less than 1% of total flux. Under anaerobic conditions, up to 50% of total flux was apoplastic suggesting that anaerobic conditions change the pathway of water flow into root xylem. The change under anaerobic conditions was reversible. Detopped root systems under pressure and intact seedlings under transpiration gave similar results. In detopped root systems, the magnitude of the pressure gradient may alter the apoplastic contribution to total flu

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Abscisic acid (ABA) accumulated in detached, wilted leaves of spinach (Spinacia oleraceaL. cv Savoy Hybrid 612) and reached a maximum level within 3 to 4 hours. The increase in ABA over that found in detached turgid leaves was approximately 10-fold. The effects of water stress could be mimicked by the use of thin slices of spinach leaves incubated in the presence of 0.6 molar mannitol, a compound which causes plasmolysis (loss of turgor). About equal amounts of ABA were found both in the leaf slices and in detached leaves, whereas 2 to 4 times more ABA accumulated in the medium than in the slices. When spinach leaf slices were incubated with ethylene glycol, a compound which rapidly penetrates the cell membrane causing a decrease in the osmotic potential of the tissue and only transient loss of turgor, no ABA accumulated. Ethylene glycol was not inhibitory with respect to ABA accumulation. Spinach leaf slices incubated in both ethylene glycol and mannitol had ABA levels similar to those found when slices were incubated with mannitol alone. Increases similar to those found with mannitol also occurred when Aquacide III, a highly purified form of polyethylene glycol, was used. Aquacide III causes cytorrhysis, a situation similar to that found in wilted leaves. Thus, it appears that loss of turgor is essential for ABA accumulation.When spinach leaf slices were incubated with solutes which are supposed to disturb membrane integrity (KHSO3, 2-propanol, or KCl) no increase in ABA was observed. These data indicate that, with respect to the accumulation of ABA, mannitol caused a physical stress (loss of turgor) rather than a chemical stress (membrane damage).

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Corn was grown under greenhouse and controlled light quality conditions incluing full spectrum, red (R), and far-red (FR) sources. Young leaf samples were analyzed for pigments, pigment-proteins, membrane polypeptides, and ultrastructure. Chloroplast development in full spectrum white light was similar to that found in R but different from that found in FR plus low R. Compared to greenhouse and R, FR plus low R (670-760) repressed the formation of photosystem I reaction center protein (CP1 + CP1a) and enhanced those of photosystem II (CPa) in both bundle sheath and mesophyll cells. Photosystem II polypeptides were present in both cell types, with the 46 and 34 kilodalton proteins predominant in mesophyll cells. Bundle sheath cells contained relatively more of the 51 kilodalton and less of the 46 kilodalton proteins. However, they also contained measurable amounts of ribulose bisphosphate carboxylase which may interfere with estimates of the 51 kilodalton protein.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Adherence ofAgrobacterium tumefaciensto suspension-cultured tomato cells has been characterized using a quantitative binding assay. Saturable binding of radiolabeledA. tumefaciensto plant cells resulted in 100 to 300 bacteria bound per cell. Specificity ofA. tumefaciensbinding was also inferred from two additional results: (a) an initial incubation of plant cells withA. tumefaciensreduced subsequent binding of radiolabeledA. tumefaciensby 60% to 75%; (b) tomato cells bound less than threeE. coliper cell. Protease treatment of plant cells had no effect on subsequent bacterial binding, but prior treatment of plant cells with pectinolytic enzymes increased binding 2- to 3-fold. Pectin-enriched and neutral polymer-enriched fractions were obtained from tomato cell walls. The soluble pectin-enriched fraction inhibited binding of bacteria to plant cells by 85% to 95%, whereas the neutral polymer fraction only partially inhibited binding. Preliminary characterization of the activity showed it is heat stable, partially inactivated by protease treatment, and substantially inactivated by acid hydrolysis.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

Three varieties ofPhaseolus vulgariswhich differ in their sensitivity to ozone were examined for changes in some physiological and structural plasma membrane characteristics. Plasma membrane vesicles were prepared from control and ozone-treated (0.2 to 0.5 microliters per liter ozone for 5 hours) leaf tissue, and the (K++ Mg2+)-ATPase activity determined and compared. No major changes were observed in the resistant varieties. The sensitive variety showed a severe inhibition of ATPase activity which was largely due to a decrease in the K+-stimulated component. This inhibition was completely reversed by the addition of sulfhydryl compounds.Ozone-induced plasma membrane permeability changes may be effected by damage to membrane proteins, perhaps by oxidation of amino acid sulfhydryl groups to disulfide and sulfenic moieties.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB

摘要:

The substrate and ionic requirements of ATP and inorganic pyrophosphate (PPi) hydrolysis by tonoplast vesicles isolated from storage tissue of red beet (Beta vulgarisL.) were compared with the requirements of ATP-and PPi-dependent proton translocation by the same material. Both ATP hydrolysis and ATP-dependent proton translocation are most stimulated by Cl−and inhibited by NO3−. NaCl and KCl support similar rates of ATP hydrolysis and ATP-dependent proton translocation while K2SO4supports lesser rates for both. PPi hydrolysis and PPi-dependent proton translocation are most stimulated by K+. KCl and K2SO4support similar rates of PPi hydrolysis and PPi-dependent proton translocation but NaCl has only a small stimulatory effect on both. Since PPi does not inhibit ATP hydrolysis and ATP does not interfere with PPi hydrolysis, it is inferred that the two phosphohydrolase and proton translocation activities are mediated by different tonoplast-associated enzymes. The results indicate the presence of an energy-conserving proton-translocating pyrophosphatase in the tonoplast of red b

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1985

数据来源: ASPB