Root Bleeding Research Articles

Effects of NaCl Salinity on Growth, Development, Ion Transport and Ion Storage in White Lupin ( Lupinus albus L. cv. Ultra)

Effectively nodulated plants of white lupin were grown in silica sand culture and exposed to 1, 5, 10, 25 and 40 mol m −3 NaCl. Dry matter gains of shoot and root were almost linearly decreased with increasing external NaCl, relative growth rate of roots being more affected than that of shoots. Concentrations of Na + and Cl - in root bleeding (xylem) sap and shoot tissues increased proportional to applied NaCl, indicating limited control over entry of Na + and Cl - into root and xylem stream. K: Na ratios were higher in leaflets than in adjoining petioles and stem segments, and in younger than older parts of the shoot, suggesting capacities for Na + retention in stems and selectivity in K + mobilization to young tissues. However, phloem sap of stems and leaf petioles from different sites on the shoot showed dramatic increases in Na + and Cl - with increasing salt in the medium, so non-uniformity in distribution of K + and Na + was all but lost at higher salinities (25 and 40 mol m -3 NaCl). Total amino acid levels in xylem sap increased with increasing salinity, those in phloem increasing or decreasing depending on site of collection. Asparagine contributed most to these changes, but serine increased greatly in all phloem sap samples with increasing applied salt. Proline was only a minor constituent of xylem and phloem, even at the highest salinity. The relatively high sensitivity of the species to salt was ascribed to limited capacity of mature tissues to accommodate or eliminate Na + and Cl - through acquisition of succulence, synthesis of counter osmotica, or abscission of leaves, combined with relatively unrestricted access of Na + and Cl - to both xylem and phloem. Results are discussed in relation to published data for other salt sensitive or salt tolerant species.

Ion Circulation via Phloem and Xylem Between Root and Shoot of Nodulated White Lupin

The exchange rates of mineral cations in the xylem and phloem between root and shoot of white lupin (Lupinus albus L., cv. Ultra) were measured using nodulated plants grown in a defined liquid culture medium low in Na and lacking nitrogen. Harvests were taken at 39 and 49 days after sowing and plant parts analysed for C, N, and the mineral cations K(+), Mg(++), Ca(++), and Na(+). Respiration losses of carbon by nodulated roots were assessed using Pettenkofer assemblies, and concentrations of C, N, and cations in xylem and phloem assayed by collecting root bleeding xylem sap and phloem sap of stem base during the day and night at several times throughout the study period. Flow rates of C and N between root and shoot were determined as in earlier modeling studies (Pate et al., 1979 b), using data on consumption of C by roots, increments of C and N in shoot and root dry matter and, C : N ratios in xylem and phloem sap. Using ratios of cation : C in xylem and phloem, net flow of the various ions between shoot and root were computed. The data showed substantial return of K(+) and Mg(++) from shoot to root with phloem translocate. This return flow provided roots with more K(+) or Mg(++) than was required for growth. It was estimated that 76 % or 87 % of the phloem-borne K(+) and Mg(++) respectively reentered the xylem and was thus circulated within the plant. Rates of return flow to roots and circulation within the plant were very small for Ca(++) and for Na(+) under the conditions of the experiment.

Spontaneous Phloem Bleeding from Cryopunctured Fruits of a Ureide-Producing Legume

The vasculature of the dorsal suture of cowpea (Vigna unguiculata [L.] Walp) fruits bled a sugar-rich exudate when punctured with a fine needle previously cooled in liquid N(2). Bleeding continued for many days at rates equivalent to 10% of the estimated current sugar intake of the fruit. A phloem origin for the exudate was suggested from its high levels (0.4-0.8 millimoles per milliliter) of sugar (98% of this as sucrose) and its high K(+) content and high ratio of Mg(2+) to Ca(2+). Fruit cryopuncture sap became labeled with (14)C following feeding of [(14)C]urea to leaves or adjacent walls of the fruit, of (14)CO(2) to the pod gas space, and of [(14)C] asparagine or [(14)C]allantoin to leaflets or cut shoots through the xylem. Rates of translocation of (14)C-assimilates from a fed leaf to the puncture site on a subtended fruit were 21 to 38 centimeters per hour. Analysis of (14)C distribution in phloem sap suggested that [(14)C]allantoin was metabolized to a greater extent in its passage to the fruit than was [(14)C] asparagine. Amino acid:ureide:nitrate ratios (nitrogen weight basis) of NO(3)-fed, non-nodulated plants were 20:2:78 in root bleeding xylem sap versus 90:10:0.1 for fruit phloem sap, suggesting that the shoot utilized NO(3)-nitrogen to synthesize amino acids prior to phloem transfer of nitrogen to the fruit. Feeding of (15)NO(3) to roots substantiated this conclusion. The amino acid:ureide ratio (nitrogen weight basis) of root xylem sap of symbiotic plants was 23:77 versus 89:11 for corresponding fruit phloem sap indicating intense metabolic transfer of ureide-nitrogen to amino acids by vegetative parts of the plant.

Rhizobium strain effects on yield and bleeding sap amino compounds in Pisum sativum

Bleeding sap composition, dry matter production and nitrogen distribution in pea (Pisum sativum L. cv. ‘Bodil’) grown with and without nitrate and nodulated with either Rhizobium leguminosarum strain 128c53 or strain 1044 were compared. Nitrate increased the total dry matter production of both symbioses, but decreased both the proportions of below‐ground dry matter to total dry matter production and nodule dry matter to total below‐ground dry matter production. The total dry matter yield and N‐accumulation was greater in the symbiosis with strain 1044, whereas the accumulation of N in the roots plus nodules relative to the total N‐accumulation was greater with strain 128c53 due to a higher production of nodule tissue. The root bleeding sap of the symbiosis with the greater yield (strain 1044) contained high levels of asparagine and aspartic acid. In the 128c53 symbiosis, glutamine plus bomoserine accounted for a higher percentage of the organic solutes transporting newly assimilated nitrogen from the root system than in the association with 1044. The Rhizobium strain effect on amino compound composition of the bleeding sap may indicate an influence of the bacteroids on either the N‐assimilatory enzyme system in the plant cytosol, or on the pools of the Krebs cycle intermediates or related compounds in the nodules.

Economy of Carbon and Nitrogen in Nodulated and Nonnodulated (NO3-grown) Cowpea [Vigna unguiculata (L.) Walp.

The response of non-nodulated cowpea (Vigna unguiculata (L.) Walp. cv Caloona) to a wide range of NO(3) levels in the rooting medium was studied 40 days after sowing by in vitro assays of plant organs for NO(3) reductase (EC 1.6.6.1) and analyses of root bleeding (xylem) sap for nitrogenous solutes. Plants fed 1, 5, 10, 20, and 40 millimolar NO(3) showed, respectively, 64, 92, 94, and 91% of their total reductase activity in shoots and 34, 30, 66, 62, and 58% of the total N of their xylem sap as NO(3). These data, and the absence in the plants of significant pools of stored NO(3), indicated that shoots were major organs of NO(3) assimilation, especially at levels of NO(3) (10 to 40 millimolar) that maintained plant growth at near maximum rates. Partitioning and utilization of C and N were studied in nodulated, minus NO(3) plants and non-nodulated plants fed 10 or 20 millimolar NO(3), the levels of NO(3) which gave rates of growth and N assimilation closest to those of the symbiotic plants. The conversion of the C of net photosynthate to dry matter was similar in nodulated plants (67%) and NO(3)-grown plants (64%), but greater proportions of photosynthate were translocated to below ground parts of nodulated plants (37%) than of NO(3)-fed plants (23 to 26%). Greater photosynthate consumption by nodulated roots was associated with proportionately greater root growth and respiration and 2-fold greater export of C in xylem than in the NO(3)-fed plants. Theoretical considerations suggest that the elevated CO(2) output of nodulated roots was due not only to CO(2) loss associated with nodule function, but also to a much greater nonassimilatory component of respiration in the supporting root of the nodulated plant compared to roots of the NO(3)-fed plants. Data are compared with previously published information from other legumes.

Assimilation and Transport of Nitrogen in Nonnodulated (NO3-grown) Lupinus albus L

The response of nonnodulated white lupin (Lupinus albus L. cv. Ultra) plants to a range of NO(3) levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO(3) reductase (EC 1.6.6.1) activity, measurements of NO(3)-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO(3) followed by 10 days with 1, 5, 15, or 30 millimolar NO(3). NO(3) reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO(3) reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO(3), respectively. Stem, petioles, and leaflets contained virtually all of the NO(3) reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO(3)-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO(3) in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO(3), respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO(3). NO(3) failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO(3). Shoot organs were ineffective in storing NO(3). Even when NO(3) was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively.

Rhythmic fluctuations in the synthetic activities of the nodulated root of the legume

If a nodulated legume is decapitated immediately after a brief period of photosynthesis in C14O2 a highly reproducible pattern of labelling is detected among the amino compounds of the root bleeding sap. The sequences of this pattern apparently reflect the consequences of the exchange of labelled carbohydrate with various morphological and metabolic compartments of the root. The progress of the exchange is greatly influenced by diurnal variations in root metabolism.