We previously reported that inhibition of ethylene biosynthesis with aminoethoxyvinylglycine (AVG) eliminated the inhibitory effect of NO 3 -on nodulation of alfalfa (Medicago sativa L. cv. Aragon) plants grown aeroponically. In this work, the effect of Ag + , as an inhibitor of ethylene action, has been studied in plants growing aeroponically or in darkened tubes with vermiculite, and low-nitrate or high-nitrate solution. Vermiculite-grown plants developed up to 3 times as many nodules as did those growing aeroponically. Nodule formation was mirrored by dry-matter accumulation. High (10 mol m -3 ) NO 3 -applied from planting inhibited nodulation to an equal extent (c. 50%) in the two growth conditions. In contrast, Ag + treatment increased nodule formation at all NO 3 -concentrations assayed under the two growth conditions, with the stimulation being higher in plants grown aeroponically. Finally, no effect of Ag + (10 mmol m -3 ) on plant growth was observed in either of the growth conditions. The effectiveness of NO 3 -as a nodulation inhibitor and enhancer of ethylene biosynthesis in roots of alfalfa was also studied. Within 24 h after inoculation, 10 mol m -3 NO 3 -exerted most of its inhibitory effect on nodulation. At the same time, both 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase activity and ethylene evolution rates markedly increased in inoculated and uninoculated alfalfa roots treated with NO 3 -. Support for a role of endogenous ethylene in the control of nodule formation in legumes is discussed.Key-words: Medicago sativa; endogenous ethylene; growth system; nitrate; nodulation control. INTRODUCTIONNodule formation in legumes is tightly controlled by an internal mechanism called autoregulation, but the establishment and function of the symbiosis is also regulated by fixed nitrogen (mainly nitrate) in the soil (Streeter 1988;Carroll & Mathews 1990;Gresshoff 1993). Basically, autoregulation involves early infection events that systemically suppress the development into nodules of subsequent infected cell-division foci (Caetano-Anollés & Gresshoff 1990); the result is restriction of nodulation to the root crown. The shoot is believed to be the source of the autoregulation inhibitor (Delves et al. 1986). Supernodulating mutants, which lack this autoregulatory response and show prolific nodulation, have been generated for several legume species. It is feasible that such a regulatory mechanism operates in other nodulated legumes, although variation in the mode of action may also exist (see Postma, Jacobsen & Fenstra 1988;Gremaud & Harper 1989;Akao & Kouchi 1992;Sagan & Gresshoff 1996). For example, nodule detachment experiments in alfalfa and soybean revealed both additional regulatory mechanisms controlling nodule number and different stages at which autoregulation could be exerted (CaetanoAnollés & Gresshoff 1991).Nitrate inhibition of nodulation is a common phenomenon among legume species; however, considerable variation in the degree of regulation exists even between cultivars or accessions with...

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A thorough knowledge of tiller development is essential in the analysis of grain production in most cultivated cereals, since the final number of ears produced by these plants is dependent on tillering. The object of this study was to investigate, under field conditions, the pattern of tillering, ear production, and survival of the component tillers in six barley cultivars: four six‐rowed (Hordeum vulgare L.) and two two‐rowed (H. distichon L.). The cultivars were grown in Granada, Spain, during 1980 and 1981 on a fine‐loamy, carbonatic, thermic, Calcixerollic Xerocrept soil, and each was subjected to two levels of N fertilizer(25 and 40 kg ha‐1), both at seeding and as a top‐dressing. From the data collected on tiller development during this study, the existence of a critical survival height for tillers is postulated: tillers less than one‐third the height of the main stem at the end of shooting would fail to produce ears. The end of shooting corresponds to stages 8 and 9 of Feekes' scale when the last leaf or the ligule of the last leaf, respectively, is just visible. Nitrogen treatments at seeding, when added at maximum dosage, increased significantly both the number of tillers at the end of shooting (maximum increase = 21%) and the final number of tillers with ears (maximum increase = 31%), while the N treatments at topdressing (midway during shooting) did not affect the number of tillers at the end of shooting or at harvest.

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SummaryThe object of this study was to investigate the vegetative growth in six barley varieties grown in southern Spain (Granada) during 1979, 1980 and 1981. The results showed that crop dry weight (CDW) was dependent on environmental factors (mean temperature, rain, and radiation) which were the determinants of the two CDW components, leaf area index (LAI) and leaf area ratio (LAR). However, the effects of these climatic factors on crop growth rate (CGR) and on its components, mean leaf area index () and net assimilation rate (NAR), were partially obscured by ontogenetic drift. In addition, a highly significant relationship was demonstrated between CDW (when the LAI reaches its maximum value) and grain yield. This suggests that the pre-anthesis period has a great influence in the determination of grain yield variation in hot, dry areas, where photosynthesis is very limited after ear emergence.

Polyamines (PAs) produce HO and nitric oxide (NO) during their normal catabolism and modulate plant growth and development. To explore the biochemical basis of PAs-induced growth inhibition in Triticum aestivum L seedlings, we examined the role of O, HO or NO in shoot and root development. Although all PA treatments resulted in a variable reduction of root and shoot elongation, spermine (Spm) caused the greater inhibition in a similar way to that observed with the NO donor, sodium nitroprusside (SNP). In both cases, O production was completely blocked whereas HO formation was high in the root apex under SNP or Spm treatments. Catalase recovered root and shoot growth in SNP but not in Spm-treated plants, revealing the involvement of HO in SNP-root length reduction. The addition of the NO scavenger, cPTIO, restored root length in SNP- or Spm-treated plants, respectively, and partially recovered O levels, compared to the plants exposed to PAs or SNP without cPTIO. A strong correlation was observed between root growth restoration and O accumulation after treating roots with SNP + aminoguanidine, a diamine oxidase inhibitor, and with SNP + 1,8-diaminoctane, a polyamine oxidase inhibitor, confirming the essential role of O formation for root growth and the importance of the origin and level of HO. The differential modulation of wheat growth by PAs through reactive oxygen species or NO is discussed. Graphical abstract Polyamines, nitric oxide and ROS interaction in plants during plant growth.

SUMMARYSix varieties of winter barley were grown during the years 1979, 1980 and 1981 in Granada (southern Spain). Grain yield variation in the 3 years studied was a function of the pre-anthesis period (especially as a determinant of number of ears/m2). In comparison leaf area duration and grain: leaf ratio from anthesis to ripening had far less influence on grain yield variation. Though these findings contrast with the generally accepted view, they can be explained by environmental conditions prevailing in southern Spain during grain filling.

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