Cristina Cruz | Universidad de las Américas - Puebla (original) (raw)

Papers by Cristina Cruz

Physiologia Plantarum, 1993

ABSTRACT Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata)... more ABSTRACT Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata) is localised in the roots. The nitrate concentration in the leaves is relatively low compared to that in the roots, suggesting that nitrate influx into the leaf may be a major factor limiting the levels of nitrate reductase in the shoot. Transport of nitrate from root to shoot appears limited by the entrance of nitrate into the xylem. In order to study this problem, we determined the nitrate concentrations and nitrate reductase activities along the roots of nitrate-grown plants, as well as the composition of the xylem sap and the nitrate levels in the leaves. Some of the the bypocotyl, in order to bypass the loading of nitrate into the xylem of the roots. The results show that the loading of nitrate into the xylem is a limiting step.The cation and anion concentrations of nitrate- and ammonium-fed plants were similar, showing almost no production of organic anions. In both nitrate- and ammonium-fed plants, the transport of nitrogen from root to shoot was in the form of organic nitrogen compounds. The nitrate reductase activity in the roots was more than sufficient to explain all the efflux of OH− into the root medium of nitrate-fed plants. In carob plants the K-shuttle may thus be operative to a limited extent only, corresponding to between 11 and 27%; of the nitrate taken up. Potassium seems to be the cation accompanying stored nitrate in the roots of carob seedlings, since they accumulate nearly stoichiometric amounts of K+ and NO−3.

New Phytologist, 1991

The distribution of nitrate reduction in young carob plants (Ceratonia siliqua L. cv. Mulata) was... more The distribution of nitrate reduction in young carob plants (Ceratonia siliqua L. cv. Mulata) was studied. Plants (three months old) were grown in aerated nutrient solutions under greenhouse conditions. Reduction of nitrate was estimated both in the leaves and in the roots by: (a) accumulation of nitrite in vitro, (b) accumulation of nitrite in vivo and (c) disappearance of nitrate in vivo. Disappearance of nitrate in vivo offered the closest estimation of the rate of nitrate reduction.Leaves consistently showed rates of nitrate reduction lower than those in roots, regardless of assay method. Lowering root temperature had no marked effect on the distribution of nitrate reductase activity in the plant; increasing nitrate concentration in the shoot, however, markedly increased leaf nitrate reduction. The relatively low level of nitrate reductase in leaves appears to be caused mainly by a limitation of nitrate transport from root to shoot. Nitrate reduction takes place in both the root and the shoot of young carob plants with the shoot accounting for approximately 20% of total nitrate reduction in the plant.

Mycorrhiza, 2004

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisatio... more The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.

Journal of Plant Nutrition, 1993

Carob seedlings were grown at different proportions of nitrate NO3) and ammonium (NH4) supplied a... more Carob seedlings were grown at different proportions of nitrate NO3) and ammonium (NH4) supplied at a concentration of 3.5 mM nitrogen (N). The effect of five different combinations of NH4‐ and NO3‐N on growth rates, N and carbon (C) content of the plant and dry matter distribution were studied. The presence of NH4 in the nutrient solution enhanced plant growth rate, although net photosynthesis rates per unit area were lower than in NO3‐fed plants. Nitrate‐fed plants exhibited the highest rates of carbon dioxide (CO2) assimilation, water use, and N‐use efficiency. Nevertheless, plants growing only with NO3 were more fragile and susceptible to fungus infections. The role of cotyledons on the regulation of the supply of photosynthates from leaves to roots in the different combinations of NO3 and NH4 is described. Results suggest that the growth rates of carob may be improved using suitable combinations of NO3‐ and NH4‐N. Equal concentrations of these two N sources allows good development and adequate allocation of low C and N to different developing sinks of the carob seedlings.

Physiologia Plantarum, 1993

Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for ... more Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for 5 weeks, with or without nitrogen at different root temperatures (10, 16, 22, 30, 35 or 40deg;C) and with the air temperature kept between 20 and 24°C. The nitrogen was given as either ammonium or nitrate. At all root temperatures studied, nitrogen-depleted plants developed higher net uptake rates for nitrogen than plants grown in the presence of nitrogen. Temperature affected the kinetic parameters of nitrate uptake more than those of ammonium uptake. With increasing root temperature, the Km of ammonium uptake decreased, but to a lesser extent than the Km for nitrate. The increase in Vmax of ammonium uptake with temperature was also less noticeable than that for nitrate uptake. Ammonium and nitrate uptakes were inhibited in a similar way by respiratory or protein synthesis inhibitors. It may be noted that ammonium uptake in the presence of inhibitors at 40°C was higher than uptake at 10°C without inhibitors. Some similarities between the transport mechanisms for nitrate and ammonium are underlined in the present work. Components of both transport systems displayed saturation kinetics and depended on protein synthesis and energy. The following components of nitrate uptake were distinguished: (a) a passive net influx into the apparent free space; (b) a constitutive active uptake and (c) active uptake dependent on protein synthesis. We may similarly define three ammonium uptake systems: (a) a passive influx into the apparent free space; (b) passive diffusion uptake at high temperature and (c) active uptake dependent on protein synthesis. The possible role of the ratio between mechanism (c) and mechanism (b) as determinant of ammonium sensitivity is discussed.

Physiologia Plantarum, 1995

Three-week-old seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under ... more Three-week-old seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO−3 and NH+4 ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH3 species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH+4/NH3 equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent free space.

Planta, 2006

The wide range of plant responses to ammonium nutrition can be used to study the way ammonium int... more The wide range of plant responses to ammonium nutrition can be used to study the way ammonium interferes with plant metabolism and to assess some characteristics related with ammonium tolerance by plants. In this work we investigated the hypothesis of plant tolerance to ammonium being related with the plants’ capacity to maintain high levels of inorganic nitrogen assimilation in the roots. Plants of several species (Spinacia oleracea L., Lycopersicon esculentum L., Lactuca sativa L., Pisum sativum L. and Lupinus albus L.) were grown in the presence of distinct concentrations (0.5, 1.5, 3 and 6 mM) of nitrate and ammonium. The relative contributions of the activity of the key enzymes glutamine synthetase (GS; under light and dark conditions) and glutamate dehydrogenase (GDH) were determined. The main plant organs of nitrogen assimilation (root or shoot) to plant tolerance to ammonium were assessed. The results show that only plants that are able to maintain high levels of GS activity in the dark (either in leaves or in roots) and high root GDH activities accumulate equal amounts of biomass independently of the nitrogen source available to the root medium and thus are ammonium tolerant. Plant species with high GS activities in the dark coincide with those displaying a high capacity for nitrogen metabolism in the roots. Therefore, the main location of nitrogen metabolism (shoots or roots) and the levels of GS activity in the dark are an important strategy for plant ammonium tolerance. The relative contribution of each of these parameters to species tolerance to ammonium is assessed. The efficient sequestration of ammonium in roots, presumably in the vacuoles, is considered as an additional mechanism contributing to plant tolerance to ammonium nutrition.

Oecologia, 1998

Parasites often exert strong selection pressures on their hosts that have evolved anti-parasite d... more Parasites often exert strong selection pressures on their hosts that have evolved anti-parasite defences to counter the negative effects of parasites. We studied the relationship between intensity of parasitism, one aspect of host immune response, and host reproductive success, using the house martin bug Oeciacushirundinis and its house martin Delichonurbica host as a model system. Experimental manipulation of parasite load of nests during laying of the first clutch altered the intensity of parasitism. Parasites reduced the reproductive success of their hosts measured in terms of body condition and survival of nestlings. Host immune response, measured as the concentration of gammaglobulins and total plasma proteins, was positively associated with parasite reproduction, estimated as the number of juvenile parasites, but was only weakly related to the intensity of adult parasites. The concentration of gammaglobulins was negatively related to nestling body mass, implying a trade-off between immune function and body condition. Parasite reproduction thus exerts a cost on hosts by increasing the immune response.

Inflammation Research, 1994

Most of the previous studies dealing with the effect of nonsteroidal anti-inflammatory drugs (NSA... more Most of the previous studies dealing with the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on the synthesis of inflammatory mediators involved in joint damage have been done in cells culturedin vitro or in blood cells from patients treated for short periods of time. In this work we have evaluated the long-term effect of aceclofenac, a new NSAID, and diclofenac on the production of a series of inflammatory mediators by blood cells from 30 patients with severe knee osteoarthritis. Both aceclofenac and diclofenac significantly inhibited prostaglandin E2 (PGE2) synthesis by blood mononuclear and polymorphonuclear cells after 180 days of treatment. However, no clear effect was noted on leukotriene B4 (LTB4) and platelet activating factor (PAF) production. The generation of O 2− by polymorphonuclear cells, stimulated with FMLP, was decreased after 15 days of treatment with both drugs, but reached normal values after 180 days. Interleukin-1β (IL-1β) production decreased significantly at 180 days with both drugs in the group of high producer patients. In a few (n=3) patients with high basal mononuclear cell tumor necrosis factor α (TNFα) production, this also decreased on treatment for 180 days with the NSAIDs. In the remaining low TNFα-producing patients, TNFα production tended to increase. Interleukin-6 (IL-6) synthesis was not affected by aceclofenac while it was diminished by diclofenac. The decrease in IL-6 in all treated patients was significantly correlated with a worsening of the clinical condition. On the whole, these data could afford a pathogenetic basic for the long-term employment of these drugs in patients with inflammatory conditions.

Physiologia Plantarum, 1993

ABSTRACT Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata)... more ABSTRACT Most of the nitrate reductase activity (80%;) in carob (Ceratonia siliqua L. cv. Mulata) is localised in the roots. The nitrate concentration in the leaves is relatively low compared to that in the roots, suggesting that nitrate influx into the leaf may be a major factor limiting the levels of nitrate reductase in the shoot. Transport of nitrate from root to shoot appears limited by the entrance of nitrate into the xylem. In order to study this problem, we determined the nitrate concentrations and nitrate reductase activities along the roots of nitrate-grown plants, as well as the composition of the xylem sap and the nitrate levels in the leaves. Some of the the bypocotyl, in order to bypass the loading of nitrate into the xylem of the roots. The results show that the loading of nitrate into the xylem is a limiting step.The cation and anion concentrations of nitrate- and ammonium-fed plants were similar, showing almost no production of organic anions. In both nitrate- and ammonium-fed plants, the transport of nitrogen from root to shoot was in the form of organic nitrogen compounds. The nitrate reductase activity in the roots was more than sufficient to explain all the efflux of OH− into the root medium of nitrate-fed plants. In carob plants the K-shuttle may thus be operative to a limited extent only, corresponding to between 11 and 27%; of the nitrate taken up. Potassium seems to be the cation accompanying stored nitrate in the roots of carob seedlings, since they accumulate nearly stoichiometric amounts of K+ and NO−3.

New Phytologist, 1991

The distribution of nitrate reduction in young carob plants (Ceratonia siliqua L. cv. Mulata) was... more The distribution of nitrate reduction in young carob plants (Ceratonia siliqua L. cv. Mulata) was studied. Plants (three months old) were grown in aerated nutrient solutions under greenhouse conditions. Reduction of nitrate was estimated both in the leaves and in the roots by: (a) accumulation of nitrite in vitro, (b) accumulation of nitrite in vivo and (c) disappearance of nitrate in vivo. Disappearance of nitrate in vivo offered the closest estimation of the rate of nitrate reduction.Leaves consistently showed rates of nitrate reduction lower than those in roots, regardless of assay method. Lowering root temperature had no marked effect on the distribution of nitrate reductase activity in the plant; increasing nitrate concentration in the shoot, however, markedly increased leaf nitrate reduction. The relatively low level of nitrate reductase in leaves appears to be caused mainly by a limitation of nitrate transport from root to shoot. Nitrate reduction takes place in both the root and the shoot of young carob plants with the shoot accounting for approximately 20% of total nitrate reduction in the plant.

Mycorrhiza, 2004

The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisatio... more The aim of this research was to investigate the effect of arbuscular mycorrhizal (AM) colonisation on root morphology and nitrogen uptake capacity of carob ( Ceratonia siliqua L.) under high and low nutrient conditions. The experimental design was a factorial arrangement of presence/absence of mycorrhizal fungus inoculation ( Glomus intraradices) and high/low nutrient status. Percent AM colonisation, nitrate and ammonium uptake capacity, and nitrogen and phosphorus contents were determined in 3-month-old seedlings. Grayscale and colour images were used to study root morphology and topology, and to assess the relation between root pigmentation and physiological activities. AM colonisation lead to a higher allocation of biomass to white and yellow parts of the root. Inorganic nitrogen uptake capacity per unit root length and nitrogen content were greatest in AM colonised plants grown under low nutrient conditions. A better match was found between plant nitrogen content and biomass accumulation, than between plant phosphorus content and biomass accumulation. It is suggested that the increase in nutrient uptake capacity of AM colonised roots is dependent both on changes in root morphology and physiological uptake potential. This study contributes to an understanding of the role of AM fungi and root morphology in plant nutrient uptake and shows that AM colonisation improves the nitrogen nutrition of plants, mainly when growing at low levels of nutrients.

Journal of Plant Nutrition, 1993

Carob seedlings were grown at different proportions of nitrate NO3) and ammonium (NH4) supplied a... more Carob seedlings were grown at different proportions of nitrate NO3) and ammonium (NH4) supplied at a concentration of 3.5 mM nitrogen (N). The effect of five different combinations of NH4‐ and NO3‐N on growth rates, N and carbon (C) content of the plant and dry matter distribution were studied. The presence of NH4 in the nutrient solution enhanced plant growth rate, although net photosynthesis rates per unit area were lower than in NO3‐fed plants. Nitrate‐fed plants exhibited the highest rates of carbon dioxide (CO2) assimilation, water use, and N‐use efficiency. Nevertheless, plants growing only with NO3 were more fragile and susceptible to fungus infections. The role of cotyledons on the regulation of the supply of photosynthates from leaves to roots in the different combinations of NO3 and NH4 is described. Results suggest that the growth rates of carob may be improved using suitable combinations of NO3‐ and NH4‐N. Equal concentrations of these two N sources allows good development and adequate allocation of low C and N to different developing sinks of the carob seedlings.

Physiologia Plantarum, 1993

Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for ... more Seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for 5 weeks, with or without nitrogen at different root temperatures (10, 16, 22, 30, 35 or 40deg;C) and with the air temperature kept between 20 and 24°C. The nitrogen was given as either ammonium or nitrate. At all root temperatures studied, nitrogen-depleted plants developed higher net uptake rates for nitrogen than plants grown in the presence of nitrogen. Temperature affected the kinetic parameters of nitrate uptake more than those of ammonium uptake. With increasing root temperature, the Km of ammonium uptake decreased, but to a lesser extent than the Km for nitrate. The increase in Vmax of ammonium uptake with temperature was also less noticeable than that for nitrate uptake. Ammonium and nitrate uptakes were inhibited in a similar way by respiratory or protein synthesis inhibitors. It may be noted that ammonium uptake in the presence of inhibitors at 40°C was higher than uptake at 10°C without inhibitors. Some similarities between the transport mechanisms for nitrate and ammonium are underlined in the present work. Components of both transport systems displayed saturation kinetics and depended on protein synthesis and energy. The following components of nitrate uptake were distinguished: (a) a passive net influx into the apparent free space; (b) a constitutive active uptake and (c) active uptake dependent on protein synthesis. We may similarly define three ammonium uptake systems: (a) a passive influx into the apparent free space; (b) passive diffusion uptake at high temperature and (c) active uptake dependent on protein synthesis. The possible role of the ratio between mechanism (c) and mechanism (b) as determinant of ammonium sensitivity is discussed.

Physiologia Plantarum, 1995

Three-week-old seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under ... more Three-week-old seedlings of carob (Ceratonia siliqua L. cv. Mulata) were grown for 9 weeks under different root temperatures (20, 30 and 40°C) at pH values of 5, 7 and 9 with nitrate or ammonium as nitrogen source. Nitrogen uptake rates were determined by depletion from the medium and decreased with distance from the apex. The decline of nitrogen uptake rates along the roots depended on the form of inorganic nitrogen in the medium as well as on pH and temperature, such that the NO−3 and NH+4 ions were taken up essentially by the root tips (0–2 cm) through processes requiring energy. The uncharged NH3 species entered passively, through the mature parts of the root (2–10 cm). Root zone temperature and pH affect the NH+4/NH3 equilibrium in the nutrient solution and, consequently, the uptake areas of the root for these ions. Furthermore. while root tip uptake of nitrogen is energy dependent, uptake through mature root areas is essentially passive and seems to depend on a well developed apparent free space.

Planta, 2006

The wide range of plant responses to ammonium nutrition can be used to study the way ammonium int... more The wide range of plant responses to ammonium nutrition can be used to study the way ammonium interferes with plant metabolism and to assess some characteristics related with ammonium tolerance by plants. In this work we investigated the hypothesis of plant tolerance to ammonium being related with the plants’ capacity to maintain high levels of inorganic nitrogen assimilation in the roots. Plants of several species (Spinacia oleracea L., Lycopersicon esculentum L., Lactuca sativa L., Pisum sativum L. and Lupinus albus L.) were grown in the presence of distinct concentrations (0.5, 1.5, 3 and 6 mM) of nitrate and ammonium. The relative contributions of the activity of the key enzymes glutamine synthetase (GS; under light and dark conditions) and glutamate dehydrogenase (GDH) were determined. The main plant organs of nitrogen assimilation (root or shoot) to plant tolerance to ammonium were assessed. The results show that only plants that are able to maintain high levels of GS activity in the dark (either in leaves or in roots) and high root GDH activities accumulate equal amounts of biomass independently of the nitrogen source available to the root medium and thus are ammonium tolerant. Plant species with high GS activities in the dark coincide with those displaying a high capacity for nitrogen metabolism in the roots. Therefore, the main location of nitrogen metabolism (shoots or roots) and the levels of GS activity in the dark are an important strategy for plant ammonium tolerance. The relative contribution of each of these parameters to species tolerance to ammonium is assessed. The efficient sequestration of ammonium in roots, presumably in the vacuoles, is considered as an additional mechanism contributing to plant tolerance to ammonium nutrition.

Oecologia, 1998

Parasites often exert strong selection pressures on their hosts that have evolved anti-parasite d... more Parasites often exert strong selection pressures on their hosts that have evolved anti-parasite defences to counter the negative effects of parasites. We studied the relationship between intensity of parasitism, one aspect of host immune response, and host reproductive success, using the house martin bug Oeciacushirundinis and its house martin Delichonurbica host as a model system. Experimental manipulation of parasite load of nests during laying of the first clutch altered the intensity of parasitism. Parasites reduced the reproductive success of their hosts measured in terms of body condition and survival of nestlings. Host immune response, measured as the concentration of gammaglobulins and total plasma proteins, was positively associated with parasite reproduction, estimated as the number of juvenile parasites, but was only weakly related to the intensity of adult parasites. The concentration of gammaglobulins was negatively related to nestling body mass, implying a trade-off between immune function and body condition. Parasite reproduction thus exerts a cost on hosts by increasing the immune response.

Inflammation Research, 1994

Most of the previous studies dealing with the effect of nonsteroidal anti-inflammatory drugs (NSA... more Most of the previous studies dealing with the effect of nonsteroidal anti-inflammatory drugs (NSAIDs) on the synthesis of inflammatory mediators involved in joint damage have been done in cells culturedin vitro or in blood cells from patients treated for short periods of time. In this work we have evaluated the long-term effect of aceclofenac, a new NSAID, and diclofenac on the production of a series of inflammatory mediators by blood cells from 30 patients with severe knee osteoarthritis. Both aceclofenac and diclofenac significantly inhibited prostaglandin E2 (PGE2) synthesis by blood mononuclear and polymorphonuclear cells after 180 days of treatment. However, no clear effect was noted on leukotriene B4 (LTB4) and platelet activating factor (PAF) production. The generation of O 2− by polymorphonuclear cells, stimulated with FMLP, was decreased after 15 days of treatment with both drugs, but reached normal values after 180 days. Interleukin-1β (IL-1β) production decreased significantly at 180 days with both drugs in the group of high producer patients. In a few (n=3) patients with high basal mononuclear cell tumor necrosis factor α (TNFα) production, this also decreased on treatment for 180 days with the NSAIDs. In the remaining low TNFα-producing patients, TNFα production tended to increase. Interleukin-6 (IL-6) synthesis was not affected by aceclofenac while it was diminished by diclofenac. The decrease in IL-6 in all treated patients was significantly correlated with a worsening of the clinical condition. On the whole, these data could afford a pathogenetic basic for the long-term employment of these drugs in patients with inflammatory conditions.