Carmen Lamsfus

Pea responses to saline stress is affected by the source of nitrogen nutrition (ammonium or nitrate)

The effect of the source of nitrogen nutrition (ammonium or nitrate), onthe response of pea plants to a moderate saline stress (30 mMNaCl)was studied. Growth declined under saline stress but nitrate-fed plants wereless sensitive to salinity than ammonium-fed plants. This different sensitivitywas due mainly to a better maintenance of root growth in nitrate-fed plants.Organic nitrogen content decreased significantly in roots of ammonium-fedplants. Water relations changed slightly under saline stress leading to adecrease in stomatal conductance, which was correlated to a decline in carbonassimilation rates regardless of nitrogen source. Salinity affects the uptakeofseveral nutrients in a different way, depending on the nitrogen source. Thus,chloride was accumulated mainly in nitrate-fed plants, displacing nitrate,whereas sodium was accumulated mainly in ammonium-fed plants, especially inroots, displacing other cations such as ammonium and potassium. It is concludedthat the nitrogen source (ammonium or nitrate) is a major factor affecting pearesponses to saline stress, plants being more sensitive when ammonium is thesource used. The different sensitivity is discussed in terms of a competitionfor energy between nitrogen assimilation and sodium exclusion processes.

Nitrogen nutrition and antioxidant metabolism in ammonium‐tolerant and ‐sensitive plants

Ammonium nutrition is of interest as an alternative to that of using nitrate. However, the former has been reported as stressful to many plant species especially to some important crops, as most abiotic stresses may trigger oxidative imbalances in plants. In this work, we investigate the response of oxidative metabolism of two plant species, spinach (Spinacia oleracea L. cv. Gigante de invierno) and pea (Pisum sativum L. cv. Rondo), which have distinct tolerance to ammonium. Plants were grown in the presence of 1.5 and 3.0 mM N as ammonium and compared with equivalent nitrate nutrition. The antioxidant enzymes and metabolites as well as oxidative damage to proteins were determined. Protein and amino acid contents in both types of plants were also analysed. Ammonium nutrition in sensitive spinach or in the tolerant pea plants does not alter the redox status of ascorbate and glutathione or the phenolic contents, while no clear effect is seen in the antioxidant enzymes. The results showed that the stress originated from applying ammonium as the only N source is not an oxidative stress, independent of the ammonium tolerance of the plant species studied. Moreover, ammonium stress diminishes oxidative damage to proteins in the spinach plants. The data of the protein oxidation together with those from N metabolism highlight the relation between the stress induced by ammonium and an increased protein turnover.

The sensitivity to ammonium nutrition is related to nitrogen accumulation

Abstract Ammonium and NO3− can be utilized as nitrogen sources by most plant species although the plant response to continuous ammonium nutrition is species dependent. The effect of the nitrogen source (nitrate and ammonium) on growth, photosynthetic parameters and nitrogen content in spinach (Spinacea oleracea L.), sunflower (Helianthus annuus L.) and pea (Pisum sativum L.) was studied. Results showed spinach to be highly sensitive, sunflower moderately sensitive and pea tolerant to ammonium nutrition. Ammonium accumulation in shoots was closely correlated to growth reduction. Moreover, ammonium accumulation was correlated to an increase of organic nitrogen content. The data suggest that the site of ammonium assimilation is a key factor controlling tolerance to ammonium nutrition in the different plant species, with plants being more tolerant when ammonium is assimilated in roots.

Short-term ammonium supply stimulates glutamate dehydrogenase activity and alternative pathway respiration in roots of pea plants

Summary The changes of C and N metabolism after switching Pisum sativum L. plants from nitrate to ammonium were studied. Pea plants were grown for three weeks in nutrient solution containing 0.5 mmol/L nitrate, and then randomly divided into five sets for five different nitrogen treatments: control (0.5 mmol/L nitrate) and four ammonium concentrations (0.5, 1, 2.5 and 5 mmol/L). After 72 hours, activities of enzymes related to C and N metabolism were measured. Ammonium content in roots increased with ammonium concentration showing saturation from a concentration of 2.5 mmol/L. Increasing external ammonium concentration also increased free amino acid content (mainly glutamine and asparagine), whereas starch content decreased and neither organic acid or soluble carbohydrates changed. Glutamine synthetase (GS; EC 6.3.1.2) activity decreased and root glutamate dehydrogenase (GDH; EC 1.4.1.2) activity increased with ammonium regardless of the concentration used. Root respiration rate increased with ammonium, due mainly to an increase of the alternative pathway. These results could be consistent with the assumption of a possible role for GDH in ammonium detoxification. Our results show a close relationship between GDH activity and respiration rate through alternate pathways in order to ensure the supply of C skeletons for ammonium assimilation, whereas surplus NADH is oxidised directly via the non-phosphorylating route.

Effects of low and high levels of magnesium on the response of sunflower plants grown with ammonium and nitrate

The effect of the nitrogen source (ammonium and nitrate) and its interaction with magnesium on various physiological processes was studied in sunflower plants (Helianthus annuusL.). Plants were grown in hydroponic culture with nitrate (5 mM) or ammonium (5 mM) and four concentrations of magnesium (0.1, 0.8, 5 and 10 mM). After 2 weeks, growth, gas exchange and fluorescence parameters, soluble carbohydrates, free amino acids, soluble protein and mineral elements were determined. Ammonium nutrition resulted in a reduction of dry matter accumulation, as well as in a decrease in the CO2 assimilation. Moreover, ammonium-fed plants showed a greater content of free amino acids, soluble protein, Rubisco and anions, and a lower cation content, mostly Mg2+. The presence of high levels of Mg2+ in the nutrient solution containing NH4+ resulted in a stimulation of growth and CO2 assimilation to the levels observed in nitrate-fed plants. The lower photosynthetic rate of ammonium-fed plants grown with low level of magnesium does not seem to be due to a lower photosynthetic pigment content, or a deficiency in Photosystem II activity, or to lower Rubisco content. Hence, Rubisco activity or other enzymes involved in CO2 fixation could have been affected in ammonium-fed plants.

Comparison of hydroponic culture and culture in a peat/sand mixture and the influence of nutrient solution and plant density on seed potato yields

SummaryTwo culture systems for propagating first generation potatoes were compared; the traditional system used a peat/sand mixture with mineral fertilizer, and hydroponic culture used perlite and nutrient solution. Total production and the number of tubers obtained using the hydroponic system were significantly higher than using the traditional culture system. Tuber yields from in vitro plants and minitubers depended upon time of year. During the autumn/winter cycle yield from minitubers was double that from in vitro plants, whereas the reverse was true during the spring/summer cycle. Four hydroponic test cultures were carried out to study the influence of seed density. The number of tubers obtained increased significantly with seed density but there was no decrease in the number of large-diameter tubers.

Alternative pathway respiration is associated with ammonium ion sensitivity in spinach and pea plants

Spinach and pea plants were grown in hydroponic culture with nitrate orammonium salts as the nitrogen source. Dry matter accumulation andphotosynthetic rate declined in spinach plants fed with ammonium salts, whereasthey did not change in pea plants compared with nitrate-fed plants. Measurementof organic nitrogen and free amino acid content showed that ammonium ions wereassimilated in shoots in spinach plants and in roots in pea plants. Ammoniumionnutrition led to a decline in starch content in both species. Organic acidsincreased in roots of pea plants fed with ammonium ions whereas they declinedinspinach plants. In both species ammonium ions increased root respiration ratebut the contribution of both routes (cytochromic and alternative pathway) tothis increase was different depending on the species. In spinach plants,ammonium ions increased the cytochromic path and decreased the alternativepathway, whereas in pea plants both routes were stimulated mainly through thealternative pathway. The differences in the sensitivity to ammonium ionsbetweenboth species are discussed in terms of differences in the availability of Cskeletons and energy, which could be due in part to differences in the capacityto stimulate the alternative pathway.

Source of nitrogen nutrition affects pea growth involving changes in stomatal conductance and photorespiration

Abstract The effect of the source of nitrogen (N) nutrition [N2 fixation and nitrate (NO3) assimilation] on plant productivity, gas exchange, N assimilation, water relations, and glycollate oxidase activity were studied in pea plants. Nitrogen‐fixing plants showed a higher RGR over the study period. This higher RGR was correlated with higher stomatal conductance and, consequently, a higher transpiration rate. Photosynthetic N‐use efficiency was also higher when plants were nodulated. We found glycollate oxidase activity, a key enzyme of the photorespiratory pathway, much lower in N2 fixing plants, what strongly suggests that energy losses due to photorespiration are lower in these plants, and therefore, photosynthetic efficiency was higher.

The influence of 3,4-dimethylpyrazole phosphate and dicyandiamide on reducing nitrate accumulation in spinach under Mediterranean conditions

The European Union has limited the maximum nitrate (NO 3 - ) content allowed for industrial processed spinach (Spinacia oleracea L.) to 2000 mg/kg fresh weight in order to avoid human pathologies associated with. uptake of high amounts of nitrate. Nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD) allow changing of the molecular form (NH 4 + or NO - 3 ) in which soil mineral N is available for plants. Enhancing ammonium nutrition has successfully reduced the amount of nitrate accumulated in plants in hydroponic culture. Therefore, fertilizers containing NIs have been proposed to reduce nitrate accumulated by vegetables grown in field conditions. Basammon Stabil® (BS) and Entec 26®-(E26) are commercial fertilizers containing DCD and DMPP respectively. In the present paper, the effect of applying ammonium sulphate nitrate (ASN), BS and E26 at three rates (0, 150 and 250 kg N/ha) to spinach crops cultivated under Mediterranean growing conditions for industrial processing is analysed. During 1998 and 1999, eight field split-plot trials with four replicates were carried out in the Ebro Valley, northern Spain, during different seasons and with various soil types. The fertilizer effects were influenced by the season and the type of soil. In spring, fertilizers containing NIs increased the mineral N (Nmin) in the soil and greatly reduced nitrate accumulation in the crop. In autumn, with less solar radiation, the nitrate accumulation was more than 2000 mg/kg fresh weight on many occasions and the effect of NIs was smaller. The present paper concluded that, under Mediterranean growing conditions, DCD can reduce nitrate accumulation in spinach between 18 and 61% and DMPP between 33 and 84% without reducing yield or changing other quality characteristics. NIs are especially useful in the spring, when soil temperature is low and solar radiation interception by the crop is high.

Effect of defoliation on garlic yield.

The results of the four trials to determine the effects of different defoliation treatments on garlic yield, carried out in the Central Ebro Valley (Spain), are presented. Four defoliation levels of 0 (control), 33, 66 and 100% were applied at seven different developmental stages. The results demonstrate a close relationship between yield reduction and the defoliation treatment inflicted. The higher the defoliation level, the higher the yield reduction. Defoliation imposed at the onset of bulb formation resulted in maximum yield reduction.