S. Herman Lips

The activity of antioxidant enzymes in maize and sunflower seedlings as affected by salinity and different nitrogen sources

Abstract The effect of salinity (100 mM NaCl) and different nitrogen sources (NaNO 3 /(NH 4 ) 2 SO 4 ) on the activity and spatial distribution of antioxidative enzymes (glutathione reductase, GR; superoxide dismutase, SOD; guaiacol peroxidase, POD; and catalase, CAT) and glutathione-S-transferase (GST) was investigated in maize and sunflower seedlings. Leaves and roots were collected after 2 weeks of treatment. Roots of maize were cut into segments and the cortex and stele were also separated. Salinity caused a clear reduction in plant biomass. The biomass production of ammonium-fed plants was lower than that of nitrate-fed plants. The antioxidant enzymes exhibited higher activities in salinity-treated plants. Changes in antioxidant enzyme activities caused by different N sources differed in the two species. Ammonium-fed plants showed higher CAT activity in both plant species and higher GR activity in maize and sunflower leaves, with the highest GST activity in maize. POD and SOD activities were lower in both maize and sunflower seedlings and lower GR activity was observed in maize roots. SOD and POD activities were higher in the mature sections of the root than in the tips. GR activity was higher in the younger parts of the nitrate-fed plant roots. The antioxidant enzyme activities were higher in the cortex than in the stele of the nodal roots.

The Mo-hydroxylases xanthine dehydrogenase and aldehyde oxidase in ryegrass as affected by nitrogen and salinity

The influence of salinity and nitrogen source on xanthine dehydrogenase (XDH; EC 1.2.1.37) and aldehyde oxidase (AO; EC 1.2.3.1) was studied in annual ryegrass (Lolium multiflorum cv. Westerwoldicum). The activities of AO and XDH in the roots and shoots of ryegrass plants increased with salinity and NH 4 concentration. The salinity-enhanced activities of XDH and AO were more pronounced in the roots than in the shoots. Roots of NH 4 -grown plants had higher AO and XDH activities than plants grown in NO 3 . Immunoblotting revealed a higher level of AO protein in roots than in shoots. Root AO protein increased with salinity and was the highest in roots of NH 4 -grown plants. The assays of the molybdenum cofactor (MoCo) hydroxylases (XDH and AO) showed a similar response to salinity and nitrogen, and differed in molecular weight and substrate specificity. The concentration of ureides (allantoic acid and allantoin) increased with salinity and NH 4 , especially in the roots. The ureide contents of plants grown on NH 4 were higher than in plants receiving NO 3 . The increase in Mo-hydroxylases with salinity and NH 4 may constitute part of the mechanisms of plant adaptation to stress by (1) enhancing the activity of AO, which catalyzes the final step in biosynthesis of phytohormones such as abscisic acid (ABA), and (2) increased XDH activity and the subsequent production of ureides allowing transport of organic nitrogen compounds with a low C:N ratio.

Control of plant growth resides in the shoot, and not in the root, in reciprocal grafts of flacca and wild-type tomato (Lysopersicon esculentum), in the presence and absence of salinity stress

Grafted plants of flacca, an ABA-deficient mutant of tomato (Lycopersicon esculentum), and the wild-type variety Rheinlands Ruhm were grown with and without salinity stress to test the roles of roots and shoots in the regulation of plant growth. Fourteen days after exposure to 200 mM NaCl, shoot and root fresh weight, endogenous ABA concentrations, nitrate concentration, activities of selected enzymes related to nitrogen assimilation, and cation accumulation were determined. Rootstock genotype had little influence on the growth of the grafted plants, whereas grafted plants having wild-type shoots (Ws) produced more biomass than those having flacca shoots (Fs), irrespective of the salinity level. Growth of flacca shoots grafted onto wild-type rootstock (Fs/Wr) was superior to that of flacca shoots grafted onto flacca rootstock (Fs/Fr). The improved growth correlated with enhanced levels of ABA in the flaccashoots of Fs/Wr. In all the graft combinations, ABA content was higher in wild-type shoots than in flacca shoots, with or without salinity. There were no significant differences in root ABA concentrations among the different grafted types. Enhanced growth correlated with higher nitrate levels and higher nitrate reductase activity in the roots and shoots of plants with wild-type shoots and with higher shoot concentrations of ABA in plants with wild-type shoots. There were no significant differences in glutamine synthetase and phosphoenol pyruvate carboxylase activities in the shoots and roots of all the grafted plants, regardless of the salinity level. While shoot genotype determined the accumulation of K+ and Na+ in grafted plants regardless of salinity, it had no influence on Ca2+ concentrations. Regardless of the salinity, the total concentration of cations was the same in all the plants, while salinity decreased Mg2+ concentration in roots and shoots of all grafts, with the exception of flacca grafted shoots. The scion genotype – and its ABA level – thus played the major role in the growth of grafted plants, regardless of the rootstock genotype and the salinity of the growth medium.

Distribution of the Mo-enzymes aldehyde oxidase, xanthine dehydrogenase and nitrate reductase in maize (Zea mays L.) nodal roots as affected by nitrogen and salinity

The distribution of the Mo-enzymes aldehyde oxidase (AO; EC 1.2.3.1) xanthine dehydrogenase (XDH; EC 1.2.1.37) and nitrate reductase (NAD(P)H NR; EC 1.6.6.1-2) was studied along the longitudinal and transversal axes of maize (Zea mays L. cv. Jubily) nodal roots as affected by nitrogen sources and salinity. Activities of the Mo-enzymes were considerably enhanced under mild saline conditions. The activities of AO and XDH increased following addition of ammonium to the nutrient solution. Immunoblot analysis with antibodies raised against maize AO protein revealed increased levels of AO proteins in root tips of ammonium fed plants. Application of salinity to nitrate fed plants did not affect the enzyme protein level, although it enhanced the activity of the Mo-hydroxylases. The specific activities of the Mo-enzymes were the highest in root tips (0-1 cm segments) while on the transversal axis maximal activity was observed in the stele or vascular cylinder. Activity staining of AO after native PAGE of root extracts revealed four bands of AO proteins (AO1-4) capable of oxidizing a number of aliphatic and aromatic aldehydes. Increased AO activity in maize nodal roots grown with ammonium, and salinity were observed mainly at the AO3 and AO4 bands. Tips and stele contained primarily AO3 and AO4, and only traces of AO1 and AO2. SDS-PAGE of root extracts followed by Western blots revealed, besides the major 150 kD subunit of AO, two polypeptides with molecular masses of 72 and 85 kD located specifically in the cortex. Part of the polymorphism of AO in plant roots may be related to the allocation of distinct isoforms to different regions of the root, although the specific metabolic roles of the different bands have not been established.

Growth and nutrition of carob plants as affected by nitrogen sources

Abstract 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 adequat...

Biomass production, transpiration rate and endogenous abscisic acid levels in grafts of flacca and wild-type tomato (Lycopersicon esculentum)

ABA is a plant signalling-molecule that plays a key role in regulating stomatal response, stress-tolerance responses, and coordinated growth of roots and shoots. Knowledge of the relationship between endogenous ABA level and plant growth is essential for improving plant growth and productivity. The wild-type tomato Rheinlands Ruhm (RR) and its flacca mutant were grafted in order to determine the relationship between endogenous ABA levels and biomass production. The flacca genotype is an ABA-deficient mutant, characterized by high stomatal conductance during the day or the night, high transpiration rate, marked tendency to wilt, and smaller size. Flacca scions grafted on to wild-type rootstock (Fs/Wr) exhibited higher ABA levels, lower transpiration rate, and higher water content than those of a control graft of flacca scion on flacca rootstock (Fs/Fr). Fs/Wr exhibited a lower ABA concentration, xylem exudate rate, ABA xylem-loading rate, and dry weight biomass in wild-type rootstock than in control grafts of wild-type scion on wild-type rootstock (Ws/Wr). Flacca rootstock grafted to wild-type scion (Ws/Fr) showed a higher ABA level, xylem exudation rate, ABA xylem-loading rate, dry weight biomass and length than grafts to flacca scion (Fs/Fr). Ws/Fr did not induce significant changes in wild-type scion as compared with Ws/Wr. In double grafts, flacca shoot fresh weight was significantly increased in flacca scion and wild-type scion grafted on to flacca rootstock (Fs + Ws/Fr) or wild-type rootstock (Fs + Ws/Wr). There was a significant linear relationship between biomass and ABA in scions (r=0.997, P=0.001). These results support the notion that ABA increases growth of tomato seedlings via improved stomatal control.

Effect of root temperature on carob growth: Nitrate versus ammonium nutrition

Abstract The response of carob (Ceratonia siliqua L.) seedlings grown at different root zone temperatures affected by nitrate and ammonium nutrition was studied. When root temperatures ranged from 10 to 35°C, ammonium‐fed plants were significantly larger than nitrate‐fed plants. Ammonium‐fed plants displayed toxicity symptoms and were much smaller at 40°C root temperature in comparison with the nitrate‐fed plants grown at the same root temperature. Root/shoot ratio slightly increase with root temperature in ammonium‐ and nitrate‐fed plants in a similar way, and shoot demand per root unit decreased with root temperature between 15 and 25°C. There was a general increase in net photosynthesis with root temperature, though nitrate‐fed plants were more sensitive to low and ammonium‐fed plants to high temperatures. Increasing the root temperature of ammonium fed plants from 10 to 40°C leads to a 30% increase in the amount of photosynthates sent to the roots. The presence of ammonium resulted in the distribution...

Nitrate assay by multiple wavelength spectroscopy and analysis of kinetic parameters of net nitrate uptake by barley seedlings

Abstract A method for determination of nitrate concentration and estimation of kinetic parameters of nitrate uptake by spectroscopy based on absorbances at multiple wavelengths has been developed to estimate nitrate uptake by barley (Hordeum vulgare L. cv. Steptoe) seedlings. Nitrate concentration in the nutrient solution was determined from the slope of the linear regression line of the absorbances to nitrate absorption coefficients at 12 wavelengths. Interference by root exudates was only due to an absorption component changing with wavelength in correlation with nitrate absorption. The standard error of the determination decreased in reverse proportion to the square root of the number of the wavelengths. A linear form of the net uptake equation, NUR = ImaxC/Km+C‐E, could be expressed as NUR = (Imax ‐ E) ‐ Km NUR/C ‐ KmE I/C where NUR is net uptake rate, Imax is maximum influx, C is concentration, Km is the Michaelis constant, and E is an efflux constant. The method described here was used to determine the time course of nitrate depletion by barley seedlings from their nutrient solution. The isotherm of net nitrate uptake rates derived from the time course was analyzed after modifications based on the linear form of the net uptake equation. The analysis yielded highly significant results (P<0.0001).

A PARTICULATE CYTOPLASMIC FRACTION ENHANCING PHOTOSYNTHESIS OF ISOLATED PEA CHLOROPLASTS. I. KINETIC ASPECTS AND SOME CHARACTERISTICS OF THE PHENOMENON

ABSTRACT A particulate cytoplasmic fraction was found capable of enhancing CO2 fixation, accompanied by CO2-dependent O2 evolution, in isolated chloroplasts obtained from pea seedlings (Pisum sativum L. cv. Dan). Carbon dioxide fixation by chloroplasts obtained from seedlings kept in the dark for 24 h prior to extraction could be enhanced up to 300%, while the photosynthetic rate of chloroplasts from pre-illuminated seedlings was enhanced only by 50%. The enhancement of photosynthetic capacity of the isolated chloroplasts persisted at maximal rates for a longer time than that of isolated chloroplasts without addition of the cytoplasmic fraction. This enhancement was light dependent. The particulate cytoplasmic fraction by itself did not fix CO2 but did consume oxygen. The enhancement was not the result of chloroplast fragments being present in the particulate fraction.