Wild Plant Genetic Resources in North America: An Overview

North America, including Canada, Mexico, and the United States, is rich in plant species used by humans in both ancient and modern times. A select number of these have become globally important domesticated crops, including maize, beans, cotton, and sunflower. Many other native and also naturalized species have potential for use, either directly or as genetic resources for breeding agricultural crops. However, despite increasing recognition of their potential value, deficiencies in information, conservation, and access to the diversity in these plants hinder their further use. This chapter provides an overview of the agriculturally relevant wild plant resources of North America, with focus on wild relatives of globally important major crops, as well as the wild cousins of regionally and locally important domesticates. The chapter concludes by providing an overview of strategies for conserving wild plant genetic resources, including the international regulatory frameworks affecting policies to various degrees in Canada, Mexico, and the United States

LIGHT-DEPENDENT RUBIDIUM UPTAKE INTO ISOLATED MESOPHYLL PROTOPLASTS FROM LEAVES OF PISUM-SATIVUM

A method is described for the isolation of large amounts of physiologically active protoplasts from leaves of Pisum sativum L. Rubidium uptake was determined after separation of the intact protoplasts from the loading medium by rapid centrifugation through a phthalate step gradient. In freshly isolated mesophyll protoplasts of Pisum sativum, rubidium uptake was carbonylcyanide‐p‐trifluoromethoxyphenylhydrazone reduced by metabolic inhibitors such as 5 μM, 0.1 mW cyanide, 2 μM DCMU and 5 mM arsenate and by dark incubation. Reduction of rubidium uptake by inhibition of aerobic respiration or the photosynthetic electron transport system demonstrates that both processes play a role in the energy supply for membrane transport in these protoplasts

Efficiency of nitrate uptake in spinach: impact of external nitrate concentration and relative growth rate on nitrate influx and efflux

Regulation of nitrate influx and efflux in spinach (Spinacia oleracea L., cv. Subito), was studied in short-term label experiments with N-13- and N-15-nitrate. Nitrate fluxes were examined in relation to the N demand for growth, defined as relative growth rate (RGR) times plant N concentration. Plants were grown at different nitrate concentrations (0.8 and 4 mM), with mineral composition of growth and uptake solutions identical. Nitrate influx, efflux and net nitrate uptake rate (NNUR) were independent of the external nitrate concentration, despite differences in internal nitrate concentration. At both N regimes, NNUR was adequate to meet the N demand for growth. RGR-related signals predominantly determined the nitrate fluxes. At high RGR (0.25 g g(-1) day(-1)), nitrate influx was 20 to 40% lower and nitrate efflux was 50 to 70% lower than at lower RGR (0.17 g g(-1) day(-1)); efflux:influx ratio (E:I) declined from 0.5 at low RGR to 0.2 at higher RGR. Thus, the efficiency of NNUR substantially increased with increasing RGR. Differences in nitrate translocation between morning and afternoon coincided with differences in nitrate efflux, which is in accordance with the suggested regulation of nitrate efflux by the root cytoplasmic nitrate concentration

Nitrate and ammonium influxes in soybean (Glycine max) roots:Direct comparison of N-13 and N-15 tracing

We compared influxes and internal transport in soybean plants (Glycine max cv. Kingsoy) of labelled N from external solutions where either ammonium or nitrate was labelled with the stable isotope N-15 and the radioactive isotope N-13. The objective was to see whether mass spectrometric determinations of tissue N-15 content were sufficiently sensitive to measure influxes accurately over short time periods. Our findings were as follows. (1) There was a close quantitative correspondence between estimates of N influx of individual plants using N-15 or N-13 measurements with either NO3- or NH4+ at 4 or 2 mol m(-3), respectively in the external solution. (2) Transport to the shoot of N from NO3 absorbed over a 5-15 min period could be monitored when the external NO3- concentration ranged from 0.05 to 4 mol m(-3). NH4+ as the N source labelled shoot tissue more slowly, and estimates of the transport between root and shoot could be made only with N-13. (3) Influx of NO3- into root tissue could be measured by N-15 enrichment after 5-10 min at concentrations approaching the probable KM of the high-affinity transport system. (4) There was some indication of isotope discrimination, especially with respect to the movement of labelled N to the shoot, when NO3- is the N source. For many purposes, N-15 tracing can be used satisfactorily to estimate influxes of both NO3- and NH4+ in soybean roots. Use of the short-lived radionuclide N-13 remains the method of choice for more refined measurements of internal distribution and assimilation