The role of electrogenic xylem pumps in K+ absorption from the zylem of Vigna unguiculata: the effects of auxin and fusicoccin

Abstract We tested the hypothesis that electrogenic ion pumps, working at the parenchyma symplast/xylem interface of pea hypocotyls, provide the driving force for K⁺ uptake from the xylem. Solutions of known composition were perfused through a hypocotyl segment. The K⁺ activity of the solution flowing out of the xylem (K⁺_out) increased (i.e. K⁺ uptake decreased) when aerobic respiration was inhibited by lack of O₂, and this was preceded by a decrease in V_px (electrical potential difference between parenchyma symplast and xylem). Perfusion with auxin (1AA) and fusicoccin (FC) stimulated the electrogenic activity of the ‘xylem pumps’ (111 and 205% respectively) and stimulated uptake of K ⁺ from the xylem (with 71% and 29% respectively). The close correlation between xylem pump activity and K⁺ uptake corroborated the aforementioned hypothesis. Interestingly, inhibition of pump activity by anoxia was incomplete in the presence of FC. It is thought that FC increases the affinity of the ATP-requiring xylem pump for ATP, thus ensuring that ATP production during fermentation is sufficient to fuel the pump in the absence of O₂.     

TRANSPORT OF CATIONS FROM COTYLEDON TO SEEDLING OF THE EMBRYONIC PLANTS OF VIGNA SESQUIPEDALIS

Decrease of dry material, water, potassium and divalent cationsin the cotyledon (catabolic organ and accumulation of thesesubstances in the seedling (anabolic organ) were traced duringthe germination stage of Vigna sesquipedalis, cultured at 15°,25° and 30° in the dark on the sand with the supplyof tap water. One half of the divalent cations finally accumulatedin the seedling came from the root, whereas most of the potassiumfrom the cotyledon. Practically all the calcium in the cotyledonremained untransported, while 90% of K stored in the cotyledonwas transported into seedling. As for divalent cations otherthan Ca, 50–60% of the total divalent cations was transportable.The concentration of K, transportable dry material and transportabledivalent cations decreased linearly with the culture age. Fromthe temperature dependency of the rate of this decrease, itwas inferred that the transport of cations from cotyledon toseedling involved at least two component processes having activationenergies of approximately 5 and 16 Kcal, respectively. The rateof transport at 30° was found to be 10–20 times greaterthan that calculated from the simple diffusion model in water.Fractionation of cell inclusions in the cotyledon by the useof a centrifuge (1,500 and 16,000 rpm) suggested that the amountsof ions in the precipitable fractions, being bound to certaincell components, precisely corresponded to the untransportablefraction. ¹Main part of this work was reported at the Annual Meeting ofthe Botanical Society of Japan held at Fukuoka on Oct. 25. 1958. (Received October 16, 1961; )     

A new method in growth-electrophysiology: Pressurized intra-organ perfusion

Abstract A new experimental system was devised for the simultaneous measurement of elongation rate and the activity of the spatially separate electrogenic ion pumps of a hypocotyl segment excised from a seedling of Vigna unguiculata L. Walp. under enforced intra-organ perfusion by artificial solutions. The pathway of the perfusion medium was apoplastic space, including xylem vessels as main routes. The elongation rate of the segment was highly dependent on the perfusion pressure applied. It was possible to increase the growth rate under pressurized perfusion by 10-30 times as much as that without perfusion. Elongation rate was also dependent on respiration under perfusion, being retarded reversibly by anoxia a few minutes after the activities of the electrogenic ion pumps were stopped. Perfusion pressure had a little influence on the membrane potential (V_px) below a breakdown level (c. 130 kPa). Perfusion of mannitol or sorbitol solution of appropriate concentration reduced the elongation rate reversibly.     

Distribution of electric potential and ion transport in the hypocotyl of Vigna sesquipedalis I. Distribution of overall ion concentration and the role of hydrogen ion in generation of potential difference

Overall concentration of free inorganic ions distributes inthe hypocotyl of a bean seedling {Vigna sesquipedalis) at aconstant level (H⁺) or decreases monotonously from the cotyledonarynode towards the base (K⁺, Na⁺, Ca⁺⁺ and Mg⁺⁺, phosphate, NO₃^–).According to our theory, this is inconsistent with the distributionof electric potential having a definite minimum in the elongatingregion. The discrepancy can not be explained by regional variancein radial potential difference or histological differentiationin passive ionic permeability of the cell membrane. Short circuitcurrent observed through a hypocotyl segment corresponded toa net flux in ions of 10–24 pEq/cm².sec. It is questionable,however, whether this is due to active ion transport, whichcan be the source of electric potential difference, or is apassive flow due to histological heterogeneity in ion concentration. In order to investigate the latter possibility, pH of sap exudingfrom stumps made at various intervals along the hypocotyl axiswas measured, since H⁺ is the ion electro-osmotically most effective.pH Values of acropetal exudates distributed along the axis closelycorresponding to the distribution of electric potential. Thissuggests that potential distribution is determined by a passiveflow of H⁺ through a specific channel in the vascular system.The fact that H⁺ production and the uptake of ions and waterare most active at the elongating zone of hypocotyl is discussedfrom a physiological point of view. (Received December 3, 1969; )     

采后光照条件对白凤桃果实品质和挥发性香气物质形成的影响

研究了白凤桃果实贮藏过程中光照条件对果实成熟的影响。在7月12日(未熟期)和7月16日(硬熟期)采收果实,分别贮藏在光条件(白色荧光灯照明,果顶部光强为80μmol m~(-2)s~(-1))和暗条件中,室温均为25℃。硬熟期采收果实贮藏在光条件下,达到完熟期时,乙烯生成量较低。果肉的硬度在各个采收期,各种贮藏条件下均没有差别。光条件贮藏果实中花青苷含量较高。未熟期采收果实贮藏在光条件下时,可溶性固形物含量增加较多。光条件贮藏果实中天冬酰胺的下降比暗贮藏果实中更多。各时期采收的果实中,在光下贮藏时,果肉和果皮γ-癸内酯和γ-十二内酯的含量都明显增加。以上结果表明,白凤桃果实采收后在光下贮藏,可以明显改善果实的品质。     

Ferricyanide-induced absorbance change of carotenoid in chromatophores of Rhodopseudomonas spheroides correlated to the oxidation of bacteriochlorophyll 885

Addition of high concentrations (e.g., 1–100 mM) of ferricyanideto a chromatophorc suspension of Rhodopseudomonas spheroidescaused a change in the absorption spectrum of carotenoid (spheroidene),which was completely reversed by adding reducing reagents suchas ferrocyanide and ascorbate. The spectral change is representedby a shift in the absorption spectrum of carotenoid by 2 to2.5 nm towards the longer wavelength side. The presence of piericidinA, o-phenanthroline or Cl-CCP in the reaction mixture did notaffect the ferricyanide-induced absorbance change. Triton X-100markedly suppressed the magnitude of the change. The additionof ferricyanide also caused simultaneous absorbance changeswith maxima at 590 and 885 nm. These are ascribed to oxidationof the (bulk) bacteriochlorophyll, BChl 885. There was no absorptionchange at other peaks of bacteriochlorophyll in the infraredregion (i.e., 800 and 855 nm). Therefore, the ferricyanide-inducedabsorbance change of carotenoid did not represent an oxidation-reductionreaction of carotenoid but was intimately correlated with oxidationof BChl 885 in the chromatophores, as judged from similaritiesobserved with respect to the time course patterns, midpointpotential (545–555 mv) in the ferriferrocyanide reactionsystem, as well as behavior towards various reagents and inhibitorsadded. A similar change of carotenoid (i.e., 2–2.5 nmshift of absorption spectrum) was caused by addition of MgCl₂to the chromatophores, but this did not induce any change inthe absorption spectrum of bacteriochlorophyll. The nature ofthe spectral change of carotenoid in chromatophores is discussed. (Received April 16, 1970; )     

Light-induced absorption spectrum changes of carotenoid in chromatophores of photosynthetic bacterium, Rhodopseudomonas spheroides II. Rapid and slow absorption changes of carotenoid in chromatophores

Time courses of light-induced absorption changes of carotenoid(spheroidene) in chromatophores of the photosynthetic bacterium,Rhodopseudomonas spheroides, consisting of an 8–10 nm-shiftin the carotenoid absorption spectrum towards the longer wavelength,were investigated. The whole time course of absorption changecan be expressed as the sum of two first order reactions; arapid change accomplished in several msec after the onset ofillumination with actinic light (800–900 nm) and a slowchange extending over the whole period (200 msec). The rapidchange required a high light intensity, whereas the slow changewas saturated at relatively low light intensity (ca. 5xl0³ erg/cm²sec). Electron transport inhibitors (HOQNO, piericidin A and o-phenanthroline)and Cl-CCP, at concentrations uncoupling photophosphorylation(10^–M), inhibited slow change but did not affect rapidchange. The rapid change was inhibited by higher concentrationsof Cl-CCP (10–4 M) and by o-phenanthroline in the concomitantpresence of an uncoupling concentration of Cl-CCP. The rapidand slow changes have midpoint potentials of 440 and 420 mv,respectively; as calculated from absorption changes in the presenceof ferri- and ferrocyanide mixtures. Relationships between absorptionspectrum changes and other reactions in the chromatophores wereanalyzed. Slow absorption change is closely related to the highenergy intermediate, or state, of photophosphorylation. Rapidabsorption change, with a midpoint potential of 440 mv, is relatedto the electron flow mediated by P870; although it does notdirectly reflect the state of P870, itself. ¹ This article is the second of a series published under thesame title in this journal, volume 11 (1970) p. 519–530. ² Present address: Department of Biology, Faculty of Science,Toho University, Narashino City, Chiba 275, Japan. (Received October 30, 1970; )     

Two proteins regulate the cell wall extensibility and the yield threshold in glycerinated hollow cylinders of cowpea hypocotyl

Glycerinated hollow cylinders of hypocotyl segments excised from the elongation region of cowpea seedlings were heated for 15s in 50% glycerol at 70, 80 or 90°C. Their in vitro yield threshold tension (y) and extensibility (φ) were determined by stress-strain experiments under the perfusion of solutions of pH 4·0 or 6·2. The decrement in y and the increment in φ with acidification were extinguished at 80 and 90°C, respectively. Moreover, such changes in φ and y with acidification were prevented by proteinase treatment for 6 and 10 h, respectively. These results suggest that these two cell wall mechanical properties are controlled, respectively, by two functional proteins activated by acid.     

Predation on the pollinating fig wasp of Ficus erecta by larvae of Silba sp. (Diptera: Lonchaeidae)

This study examined the insect assemblage within the syconium of the dioecious fig Ficus erecta Thunb., 1786 (Moraceae) on Kii‐Oshima Island, Wakayama Prefecture, Japan. Species present included pollinating and non‐pollinating fig wasps Blastophaga nipponica Grandi, 1921 and Sycoscapter inubiae Ishii, 1934, respectively, as well as an undetermined species of Silba Macquart, 1851 (Diptera: Lonchaeidae). Larvae of Silba sp. were found only in fig syconia containing B. nipponica. Observations revealed that larvae of Silba sp. fed on female adults of B. nipponica within fig galls by thrusting their heads through the intersegmental membrane. Furthermore, larvae of Silba sp. had a high predation rate (90%). These observations suggest that larvae of Silba sp. are specialized for feeding on B. nipponica and have a negative effect on populations of this species.