Journal of Experimental Botany

EEUWENS, C., J.;SCHWABE, W., W.

doi: 10.1093/jxb/26.1.1pmid: N/A

Abstract Developing fruits of Pisum sativum, L., cv. ‘Alaska’, contain relatively large amounts of hormones, mainly concentrated in the embryos and liquid endosperm. A close relationship can be demonstrated between changes in extractable amounts of gibberellins (mainly GA20), auxins (methyl 4-chloroindol-3yl acetate and probably 4-chloroindol-3yl acetic acid), and abscisic acid, and changes in growth rates of both the pod wall and seeds. Growth of the pod wall appears to depend largely on hormones supplied by the seeds. Marked changes in the germination capacity of the maturing seeds are closely associated with changes in extractable amounts of methyl-4-chloroindol-3yl acetate and abscisic acid. It is believed that high concentrations of these substances in the embryo, rather than any restriction imposed by the testa, may prevent precocious germination of the seeds This content is only available as a PDF. © Oxford University Press

, de S. WAIDYANATHA, U. P.;KEYS, A., J.;WHITTINGHAM, C., P.

doi: 10.1093/jxb/26.1.15pmid: N/A

Abstract When solutions of [14C]glycollate, glycine, serine, glycerate, or glucose were supplied to segments of wheat leaves through their cut bases in the light, most of the 14C was incorporated into sucrose in air but in CO2-free air less sucrose was made. The synthesis of sucrose was decreased because metabolism of serine was partly blocked. Sucrose synthesis from glucose and glycerate in CO2-free air was decreased but to a smaller extent; relatively more CO2 was evolved and serine accumulated. The effects of DCMU and light of different wavelengths on metabolism by leaves of L-[U-14C]serine confirmed that simultaneous photosynthetic assimilation of carbon was necessary for the conversion of serine to sucrose. Of various products of photosynthesis fed exogenously to the leaves α-keto acids were the most effective in promoting photosynthesis of sucrose and release of 14CO2 from 14C-labelled serine. This suggests that in CO2-free air the metabolism of serine may be limited by a shortage of α-keto acid acceptors for the amino group. In CO2-free air added glucose stimulated production of CO2 and sucrose from D-[U-14C]- glycerate and no competitive effects were evident even though glucose is converted rapidly to sucrose under these conditions. In addition to a supply of keto acid, photosynthesis may also provide substrates that can be degraded and provide energy in the cytoplasm for the conversion of glycerate to sugar and phosphates and sucrose. This content is only available as a PDF. Author notes 1 Present Address: Rubber Research Institute, Dartonfield, Agalawatta, Sri Lanka. © Oxford University Press

, de S. WAIDYANATHA, U. P.;KEYS, A., J.;WHITTINGHAM, C., P.

doi: 10.1093/jxb/26.1.27pmid: N/A

Abstract Segments of wheat leaves were supplied in the light with 14C-labelled serine or glucose in atmospheres containing different concentrations of O2 and zero or 350 parts/106 CO2. Some O2 was necessary for sucrose synthesis from either serine or glucose but sucrose synthesis from glucose depended on reactions with a high affinity for O2 whereas sucrose synthesis from serine depended both on reactions with high and low affinities for O2. In the presence of CO2 sucrose synthesis from serine was decreased when the O2 concentration was increased from 20 to 80% by volume and CO2 was liberated; sucrose synthesis from glucose was almost unaffected by the same change in conditions. Also, in an atmosphere containing 80% O2 and 350 parts/106 CO2, radioactivity from [14C]serine, was incorporated into glycine. This was not true for glucose feeding. Hence glucose provides a substrate for sucrose synthesis but not for photorespiration whereas serine is used for both processes in the presence of CO2; in the absence of CO2 glucose provides substrate for both sucrose synthesis and photorespiration and serine metabolism to sucrose is restricted. This content is only available as a PDF. © Oxford University Press

POSSINGHAM, J., V.;CRAN, D., G.;ROSE, R., J.;LOVEYS, B., R.

doi: 10.1093/jxb/26.1.33pmid: N/A

Abstract The development and photosynthetic capacity of chloroplasts formed in green light in cultured spinach leaf discs has been studied. At intensities of 4 to 6 mW cm−2 green light stimulates chloroplast replication to about the same extent as white, blue, and red light. However, practically no chloroplast replication occurs in discs grown in low intensity green or white light but considerable chloroplast growth takes place. Ultrastructural studies have shown that these chloroplasts, which can be two to five times the area of control plastids (high intensity white light), have an essentially normal thylakoid system. Double isotope labelling experiments have established that the synthesis of chloroplast ribosomal-RNA is similar in controls and in discs grown in low intensity green or white light. On a per unit chlorophyll basis the CO2 fixation rate of spinach discs grown in low intensity green (or white) light saturates with increasing light intensity or increasing CO2 concentration at values well below control discs. In this respect their photosynthetic characteristics bear a similarity to those of shade plants. This content is only available as a PDF. © Oxford University Press

THOMAS, SUSAN, M.;THORNE, GILLIAN, N.

doi: 10.1093/jxb/26.1.43pmid: N/A

Abstract Wheat was grown in the field with different levels of nitrogenous fertilizer, and the rate of photosynthesis and the activity of ribulose 1,5-diphosphate carboxylase in the flag leaves determined. Additional nitrogen increased the dry-weight and leaf area of the plants, but did not increase grain yield; the rate of photosynthesis of the flag leaves was unchanged but the activity of ribulose 1,5-diphosphate carboxylase increased. The significance of these observations to the loss of potential yield of wheat and the relationship between, photosynthesis and carboxylase activity is considered. This content is only available as a PDF. © Oxford University Press

BOUMA,, D.

doi: 10.1093/jxb/26.1.52pmid: N/A

Abstract Rates of photosynthesis (net CO2 uptake in saturating light) of leaves sampled from phosphorusdeficient subterranean clover plants (Trifolium subterraneum L. cv. Mt. Barker) were lower than those of non-deficient leaves. When comparable deficient leaves were placed in solutions containing 0.13 mM Pi1, there were no responses in photosynthesis, even though earlier results had established these solutions as optimal for responses for intact deficient plants. Deficient leaves, placed for the first 12 h after detachment in solutions of increasing Pi1 concentrations (0.15, 0.70, 2.0, and 6.0 mM) and then in distilled water, showed marked increases in photosynthesis in the three higher phosphate treatments on the first day after detachment. During the following 6 d the decline in photosynthesis was less the higher the initial phosphate treatment. By contrast, non-deficient leaves in the same treatments showed a decline in photosynthesis with increasing phosphate levels, due to leaf damage in the two highest treatments (phosphorus toxicity). Rates of photosynthesis of deficient leaves kept for 3 h in 3 or 6 mM FDP1 or G-6-P1 increased within 24 h and remained higher than those for corresponding leaves in 0.13 mM Pi or distilled water. There were no differences between the same treatments for non-deficient leaves, thus enabling a clear distinction between leaves that were deficient and those that were not. There was no leaf damage in these solutions, even after 48 h. AMP1 or ADP1 had no effect. ATP1 and 3-PGA1 caused toxicity symptoms. Fructose itself (6 mM) had no effect on photosynthesis. This content is only available as a PDF. © Oxford University Press

MINCHIN, F., R.;PATE, J., S.

doi: 10.1093/jxb/26.1.60pmid: N/A

Abstract Nitrogen assimilation of pea plants (Pisum sativum cv. Meteor) was studied in growth cabinets tinder a range of water, salt, and aeration regimes in the rooting medium. Treatments were imposed in the period 14–30 d after germination using seedlings already nodulated in an optimum root environment. Highest nitrogen fixation in water culture required a strength of culture solution one fifth of that optimal for fixation in sand culture. Fixation in water culture of optimum strength was significantly improved by continuous bubble aeration or by lowering the level of culture solution below the main zone of nodulation. However, if supra-optimal concentrations of solution were used, fixation was markedly inhibited by lowering the solution level, this being associated with an accumulation of high levels of salts on exposed root and nodule surfaces. In – N (minus nitrogen) sand culture continuous waterlogging reduced nitrogen content to 40 per cent of that of non-stressed plants. In nitrate-fed plants waterlogging effects were less severe. Waterlogging decreased nodule tissue production and decreased the specific activity of nitrogenase, as assayed by acetylene reduction. These effects were most marked three or more cm below the sand surface. Watering on alternate days with free drainage at all times yielded maximum fixation in – N sand culture. Regimes increasing the extent of waterlogging or drying out in comparison with this optimum produced increasingly great decreases in nitrogen fixation. For equivalent reductions in total fixation, percentage N in dry matter was consistently lower in waterlogged than in droughted plants suggesting that excess water had the more specific effect on symbiotic activity. Both forms of stress affected particularly the transport of nitrogen from root to shoot. This content is only available as a PDF. Author notes 1Present address: Plant Environment Laboratory, Department of Agriculture and Horticulture, University of Reading, RG2 9AD, Berkshire, England. 2Present address: Department of Botany, University of Western Australia, Nedlands, Western Australia 6009. © Oxford University Press

ROGAN, P., G.;SMITH, D., L.

doi: 10.1093/jxb/26.1.70pmid: N/A

Abstract Rates of leaf initiation, emergence, and growth have been measured during the period between the production of one and of ten mature leaves on the primary shoot of Agropyron repens. There is a progressive decline in the growth rate of successively formed leaves so that at the time of formation of the next leaf primordium each primordium is smaller than its predecessor at a comparable stage of development. There is also a trend towards a diauxic pattern of growth with a lag phase apparently coinciding with the transition from apical to intercalary growth of the young leaf. Up to the six-leaf stage the rate of leaf formation exceeds the rate of emergence and leaf primordia accumulate on the shoot apex. Thereafter the rate of emergence exceeds the rate of formation. These changes in rates of leaf formation and growth are interpreted in terms of competition for assimilates between expanding leaves and leaf primordia, and between the primary and axillary shoot apices. This content is only available as a PDF. © Oxford University Press

DREW, M., C.;SAKER, L., R.

doi: 10.1093/jxb/26.1.79pmid: N/A

Abstract The development of the seminal root system, its ability to absorb nitrate, and effects on shoot growth were studied in barley plants in nutrient solution. The roots received either a uniform supply of 1.0 mM nitrate (controls), or a supply of the same solution restricted to a 4-cm length of only one of the main seminal roots (axes) on each plant, the remainder of the root system receiving a solution containing a low concentration (0.01 mM). Marked increases took place in both the growth of lateral roots and the absorption and transport of 15N-labelled nitrate (per unit root weight) from the zone locally supplied with 1.0 mM nitrate. These effects appear largely to compensate for the deficient supply of nitrate to the remainder of the root system, since after 14 d the relative growth rate (g g−1d−1) of the total plant equals that of the controls. Rates of 15N-nitrate uptake (per unit root weight) remain relatively uniform throughout the 29-d experiment, during which root axes develop from their initial unbranched form to a complex system of laterals. The results are discussed in relation to possible mechanisms by which coordination is maintained between root growth, ion uptake, and shoot growth. This content is only available as a PDF. © Oxford University Press

THAINE,, ROBERT;, de MARIA, MARGARET E.;SARISALO, H. I., MARJATTA

doi: 10.1093/jxb/26.1.91pmid: N/A

Abstract Transverse cryostat sections of rapidly frozen vascular bundles of Cucurbita pepo were viewed in a microscope with Nomarski optics. Structural bodies were frequently observed in sieve tube lumina and filling the sieve plate pores. The bodies consist of an outer boundary ring and an inner core, often granular in appearance, and may represent transverse sections of bounded tubes filled by substructural material. This evidence is consistent with earlier observations of strand-like structures with parallel substructural elements seen in longitudinal sections. This content is only available as a PDF. © Oxford University Press