Water use efficiency as a function of leaf age and position within the cotton canopy

The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention in recent years. However, insufficient information exists on the coordination of transpiration and CO₂ uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration (E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO₂ mmol⁻¹ H₂O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in stomatal conductance (g_s·H₂O) since decreases in g_s·H₂O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these findings are presented in relation to light competition within the plant canopy during development.     

A pump/leak/buffer model for plant nitrate uptake

A simple simulation model is described to account for the rates at which plants take up nitrate and reduce it to protein. It is based on the pump and leak principle, with the pump working at a constant rate per unit sap volume provided that there is an adequate concentration of nitrate at the root surface. The rate of leakage is assumed to be proportional to the concentration difference between the inside and the outside of the plant. Nitrogen is removed from the plant nitrate pool (the buffer) at a constant fraction of the photosynthesis rate. When applied to data for the diurnal variation in nitrate uptake by ryegrass, the model predicts an uptake pattern similar to that actually observed, with a time lag of about 5 hours between photosynthesis and uptake.     

Expression of C4-like photosynthesis in several species of Flaveria

Abstract Photosynthetic metabolism was investigated in leaves of five species of Flaveria (Asteraceac), all previously considered to be C₄ plants. Leaves were exposed to ¹⁴CO₂ for different intervals up to 16s. Extrapolation of ¹⁴C-product curves to zero time indicated that only F. trinervia and F.bidentis assimilated atmospheric CO₂ exclusively through phosphoenolpyruvate carboxylase. The proportion of direct fixation of ¹⁴CO₂ by ribulose-I, 5-bisphosphate carboxylase/oxygenase (Rubisco) ranged from 5 to 10% in leaves of F. australasica. F. palmeri and F. vaginata. Protoplasts of leaf mesophyll and bundle sheath cells were utilized to examine the intercellular compartmentation of principal photosynthetic enzymes. Leaves of F. australasica, F. palmeri and F. vaginata contained 5 to 7% of the leaf's Rubisco activity in the mesophyll cells, while leaves of F. trinervia and F. bidentis contained at most 0.2 to 0.8% of such activity in their mesophyll cells. Thus, F. trinervia and F. bidentis have the complete C₄ syndrome, while F. australasica, F. palmeri and F. vaginata are less advanced, C₄-like species.     

Measurement of the extent of electron transfer to the bacteriopheophytin in the M-subunit in reaction centers of Rhodopseudomonas viridis

We have measured the extent of flash-induced electron transfer from the bacteriochlorophyll dimer, P, to the bacteriopheophytin in the M-subunit, H_M, in reaction centers of Rhodopseudomonas viridis. This has been done by measuring the transient states produced by excitation of reaction centers trapped in the PH_L ^–H_M state at 90 K. Under these conditions the normal forward electron transfer to the bacteriopheophytin in the L-subunit, H_L, is blocked and the yield of transient P⁺H_M ^– can be estimated with respect to the lifetime of P^*. Under these conditions flash induced absorbance decreases of the bacteriochlorophyll dimer 990 nm band suggest that a transient P⁺ state is formed with a quantum yield of 0.09±0.06 compared to that formed during normal photochemistry. These transient measurements provide an upper limited on the yield of a transient P⁺ H_M ^– state. An estimate of 0.09 as the yield of the P⁺ H_M ^– state is consistent with all current observations. This estimate and the lifetime of P^* suggest that the electron transfer rate from P^* to H_M, k_M, is about 5 × 10⁹ sec^–1 (_M = 200ps). These measurements suggest that the a branching ratio k_L/k_M is on the order of 200. The large value of the branching ratio is remarkable in view of the structural symmetry of the reaction center. This measurement should be useful for electron transfer calculations based upon the reaction center structure.     

Expression of a C3 plant Rubisco SSU gene in regenerated C4 Flaveria plants

We report the successful transformation, via Agrobacterium tumefaciens infection, and regeneration of two species of the genus Flaveria: F. brownii and F. palmeri. We document the expression of a C₃ plant gene, an abundantly expressed ribulose 1,5-bisphosphate carboxylase/oxygenase small subunit gene isolated from petunia, in these C₄ plants. The organ-specific expression of this petunia gene in Flaveria brownii is qualitatively identical to its endogenous pattern of expression.     

The biennial life strategy in a random environment

In a previous paper (J. Math. Biol. 26, 199–215 (1988)) we calculated the mean and variance of the long-run geometric growth rate of a discrete-time population model with two age classes in a random environment. The formula which was used in that paper as the starting point for the computation of the variance represents only the contribution of the one-period variances. Here we supplement these results by a calculation of the exact variance. All qualitative conclusions reached before are unaffected.     

Intrinsic and extrinsic variables controlling the productivity of asexual populations of Nais spp, (Naididae,Oligochaeta)

The productivity of Nais spp. from periphyton of fishponds of the Dombes area (Ain) was studied in semi-natural conditions by cultivation of zooids in experimental glass enclosures immersed in situ and filled with pond water receiving injections of fertilizers (P₂O₅) and natural filtered periphyton extracts (particles < 70 µm). The growth rate of the experimental populations was not significantly affected by the concentration of fertilizers added to culture media. On the contrary, the water management of the culture media (as renewal or non-renewal of the water in experimental enclosures), the closing procedure of the enclosures and the load and composition of the nutritive substrate controlled the produced biomass. Temperature and food supply were the principal extrinsic variables controlling the asexual growth rate of the Nais species. The stolonization rate was analyzed as a biological parameter implicated in the instantaneous birth rate of zooids and the growth of naidid populations.     

Fatty acid-binding to erythrocyte ghost membranes and transmembrane movement

Summary Palmitate binding to human erythrocyte ghost membranes has been investigated with ghost preparations suspended in 0.2% albumin solutions. Free unbound palmitate in the extracellular water phase was measured in equilibrium studies using albumin-filled acid loaded ghosts as small semipermeable bags. The apparent dissociation constant of binding to the membrane is 13.5 nM and the binding capacity 19 nmoles per 7.2 × 109 cells.The 0°C exchange efflux kinetics of palmitate from albumin-filled ghosts is described by a model, which provides estimates of the rate constant of membrane transfer, k₃ = 0.024 s^–1, independent of the molar ratio of palmitate to albumin () and of a mean dissociation rate constant of the palmitate-albumin complex, k₁ = 0.0015 s^–1 at 0.2, allowing for a heterogeneity of the palmitate binding to albumin.The values of a third kinetically determined dependent model constant, Q, the ratio of palmitate bound to the membrane inner surface to palmitate on intracellular albumin, are not different from the Q values obtained by equilibrium experiments.The temperature dependences of k₁ and k₃ in the interval 0°C to 15°C give activation energies of 96 and 103 kJ/mole, respectively. The 0°C exchange efflux increases about 2 fold in response to a rise of pH from 6 to 9. The results suggest a carrier mediated palmitate flux at low with a V_max about 2 pmoles min^–1 cm^–2 at 0°C pH 7.3.     

Effect of alcohol on perceived exertion in relation to heart rate and blood lactate

The purpose of the study was to determine whether the perception of exertion is affected by alcohol during physical performance and whether altered self-rating of exertion is the result of an altered perception per se or of an altered physical capacity to perform work. Ten healthy men participated. Each subject was his own control and received an alcohol dose corresponding to 1 g.kg-1 body mass in 40% solution in the experimental session. The exercise test was performed on a cycle ergometer with an initial intensity of 50 W which was increased stepwise by 50 W at 4-min intervals up to near-maximal. The rating of perceived exertion (RPE) did not differ between alcohol and control sessions. Alcohol induced a significant increase in heart rate during exercise at 50 W (delta x = 8 beats.min-1) and at 100 W (delta x = 10 beats.min-1), while the change at higher intensities was insignificant. The systolic blood pressure and the blood lactate concentration were not significantly changed by alcohol. It is concluded that a moderate dose of alcohol does not alter RPE during physical exercise either per se or secondarily to an altered physical capacity to perform work.