Mourad Baghour

The plant stress hormone ethylene controls floral transition via DELLA-dependent regulation of floral meristem-identity genes

The length of the Arabidopsis thaliana life cycle depends on the timing of the floral transition. Here, we define the relationship between the plant stress hormone ethylene and the timing of floral initiation. Ethylene signaling is activated by diverse environmental stresses, but it was not previously clear how ethylene regulates flowering. First, we show that ethylene delays flowering in Arabidopsis, and that this delay is partly rescued by loss-of-function mutations in genes encoding the DELLAs, a family of nuclear gibberellin (GA)-regulated growth-repressing proteins. This finding suggests that ethylene may act in part by modulating DELLA activity. We also show that activated ethylene signaling reduces bioactive GA levels, thus enhancing the accumulation of DELLAs. Next, we show that ethylene acts on DELLAs via the CTR1-dependent ethylene response pathway, most likely downstream of the transcriptional regulator EIN3. Ethylene-enhanced DELLA accumulation in turn delays flowering via repression of the floral meristem-identity genes LEAFY (LFY) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1). Our findings establish a link between the CTR1/EIN3-dependent ethylene and GA–DELLA signaling pathways that enables adaptively significant regulation of plant life cycle progression in response to environmental adversity.

Relationship between boron and phenolic metabolism in tobacco leaves

Abstract Tobacco plants ( Nicotiana tabacum var. Sevilla) were treated with boron (B) as H 3 BO 3 in the following concentrations B1: 0.5 μM, B2: 5 μM, B3: 10 μM and B4: 20 μM, and we analysed: total B, total phenols, orthodiphenols, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD) and dry weight. The effect of the B treatments were differentiated by: (1) foliar accumulation of phenols induced by the minimum B treatment (B1) and maximum (B4); and (2) oxidation of the phenols induced by the intermediate treatments (B2 and B3). The two predominant forms in which B is found in leaves (forming complexes with pectins and phenols, or in the free form) appears to determine and explain the effect of this element on the metabolism of the phenols.

Role of CaCl2 in nitrate assimilation in leaves and roots of tobacco plants (Nicotiana tabacum L.)

Abstract The aim of this study was to determine the response of NO 3 − assimilation in roots and leaves to different CaCl 2 application (T1, 1.25 mM CaCl 2 ·2H 2 O; T2, 2.5 mM CaCl 2 ·2H 2 O and T3, 5 mM CaCl 2 ·2H 2 O). Tobacco plants ( Nicotiana tabacum cv Sevilla) were grown under controlled conditions and submitted to regular fertilization with macro- and micronutrients. The content of Ca 2+ , Cl − and NO 3 − , the activity of the enzymes related to the process of NO 3 − reduction (NR: nitrate reductase, EC 1.6.6.1; NiR: nitrite reductase, EC 1.7.7.1; GS: glutamine synthetase, EC 6.3.1.2; GOGAT: glutamate synthase, EC 1.4.1.14; PEPC: phosphoenolpyruvate carboxylase, EC 4.1.1.31), and the end products of this process (amino acids and proteins) were analysed in roots and leaves. Our results indicate that the utilization of NO 3 − in the plant was influenced by the different treatments. NO 3 − was translocated towards the aerial part and subsequently assimilated in the leaves in treatments T1 and T2, the latter significantly intensifying these processes and giving rise to greater production of dry matter both in the leaves and in the roots. With the T3 treatment, NO 3 − assimilation occurred principally in the roots, due possibly to decreased NO 3 − translocation towards the aerial part, thereby increasing its availability in the roots. In addition, the possible negative effect of the maximum foliar concentrations of Ca 2+ and Cl − on the foliar activity of NR in this treatment could also cause NO 3 − assimilation in the roots with the T3 treatment. Finally, it is noteworthy that the application of T3 significantly reduced root growth.

Influence of root temperature on phytoaccumulation of As, Ag, Cr, and Sb in potato plants (Solanum tuberosum L. var. Spunta).

Three consecutive years of field experiments were carried out to investigate the effect of root temperatures induced by the application of mulches for phytoextraction of As, Ag, Cr and Sb using potato plants (roots, tubers, stems and leaflets). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene; and T4: black polyethylene), taking uncovered plants as control (T0). The different treatments had a significant effect on mean root temperatures (T0 = 16°C, T1 = 20°C, T2 = 23°C, T3 = 27°C and T4 = 30°C) and induced a significantly different response in the As, Ag, Cr and Sb phytoaccumulation. The T3 treatment gave rise to the greatest phytoaccumulation of As, Ag, Cr and Sb in the roots, leaflets and tubers. In terms of the relative distribution of the phytoaccumulated metals (with respect to the total of the plant), As accumulated mainly in the roots and leaflets whereas Ag, Cr and Sb accumulated primarily in the tubers, establishing a close relationship between biomass development of each organ and phytoaccumulation capacity of elements in response to temperature in the root zone. With regard to phytoremediation using the potato plant, it is necessary to ascertain the influence and include the control of the thermal regime of the soil to optimize the phytoextraction of pollutants.

Metabolism and efficiency in nitrogen utilization during senescence in pepper plants: Response to nitrogenous fertilization

Abstract The effect that application of nitrogen (N) rates exerts on some parameters of N metabolism in pepper plants (Capsicum annuum L. cv. Lamuyo) during senescence was studied. All plants were grown under controlled conditions in an experimental greenhouse. The treatments consisted of the application of 4 rates of N at the onset of flowering in the form of KNO3 (N1: 6 g m‐2, N2:12 g m‐2, N3:18 g m‐2, N4:24 g m‐2). The results obtained show a optimal effect ofN2 fertilization on uptake, translocation, and assimilation of NO3 ‐ in the leaves. The N2 treatment registered maximums in the concentration of chlorophyll a and b, and in commercial yield. In conclusion, for improved pepper cultivation during senescence, treatment N2 gave the maximum yield, and increased metabolism and efficient utilization of N.

METABOLISM AND EFFICIENCY OF PHOSPHORUS UTILIZATION DURING SENESCENCE IN PEPPER PLANTS: RESPONSE TO NITROGENOUS AND POTASSIUM FERTILIZATION

Application rates of nitrogen and potassium were studied in relation to parameters of phosphorus metabolism in pepper plants (Capsicum annuum L. cv. Lamuyo) during senescence. All plants, grown under controlled conditions in a greenhouse, were administered 4 rates of nitrogen (N) as NH4NO3 (N1: 6 g N m−2, N2: 12 g N m−2, N3: 18 g N m−2, N4: 24 g N m−2) and three rates of potassium (K) as K2SO4 (K1: 4 g K m−2, K2: 8 g K m−2, K3: 12 g K m−2) at the onset of flowering. The plants treated with the N2 treatment had the highest leaf concentrations of phosphorus (P) forms (inorganic P, lipid P, DNA-P, RNA-P, proteic P and total P), whereas the concentrations of organic and soluble P were the lowest. In these plants potassium fertilization exerted a negative effect on the concentrations of the different P forms, although yield significantly rose with K applied, reaching the highest values at K3. Finally, acid phosphatase activity and carbohydrate proved to be good indicators of the nutritional status of P.

Efficiency of the different genotypes of tomato in relation to foliar content of Fe and the response of some bioindicators

Abstract Tomato plants grown under controlled greenhouse conditions were submitted to constant fertilization of macro‐ and micronutrients. The aim of the experiment was to determine both the effect of different genotypes of tomato plants on the foliar content of Fe as well as the behaviour of some of its physiological indicators. For the 12 tomato genotypes used, the following parameters were analysed: total Fe, HCl‐extractable Fe, peroxidase (POD), catalase (CAT), chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenes. The results showed a strong influence of genotype on the foliar content of Fe, both in its total and HCl‐extractable form. With regard to the POD and CAT activities, as physiological indicators of Fe, the POD activity proved predominant. The activities of the chlorophyll and carotene pigments provided good indicators of the Fe level in the different genotypes.

Effect of root zone temperature on accumulation of molybdenum and nitrogen metabolism in potato plants

Abstract Changes in root temperature caused by the application of plastic covers were studied in relation to the uptake and content of molybdenum (Mo) in the different organs of potato (Solanum tuberosum L. var. Spunta) plants (roots, tubers, stems, and leaves) and in relation to nitrogen (N) metabolism. For the semi‐forcing technique of mulching, four different covers were used: T 1 (transparent polyethylene), T 2 (white polyethylene), T 3 (coextruded black and white polyethylene), and T 4 (black polythylene). The control treatment had no mulch. The results revealed a positive and significant effect of plastic covers on root temperatures: T 0 = 16°C, T 1 = 20°C, T 2 = 24°C, T 3 = 27°C, T 4 = 30°C. These thermal differences significantly influenced the Mo concentration, particularly in the T 2 and T 3 treatments in the leaves, roots, and tubers. The same temperatures significantly altered N metabolism in both the aerial and underground parts of the plants, and a strong interrelationship was found between Mo and nitrate reductase (NR) activity. The mulching of this crop proved to be a promising technique in phytoremediation.

INFLUENCE OF THERMAL REGIME OF SOIL ON THE SULFUR (S) AND SELENIUM (Se) CONCENTRATION IN POTATO PLANTS

ABSTRACT Three consecutive years of field experiments were carried out to investigate the effect of different root temperatures, induced by the application of mulches on the concentration of sulfur (S) forms (organic-S, total-S and ) and Se in different organs of potato plants (roots, tubers, stems and leaves). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene, and T4: black polyethylene), using uncovered soil as control (T0). The different treatments had a significant effect on mean root temperatures (T0 = 16°C, T1 = 20°C, T2 = 23°C, T3 = 27°C and T4 = 30°C) and induced a significantly different response in the S forms and Se concentration, showing the T3 treatment (27°C) the greatest concentration of total S and organic S in the stems and leaflets. The Se reached higher levels in the roots and tubers in T3. With regard to possibilities in phytoremediation, it is necessary to control the thermal regime of the soil to optimize the accumulation of elements.

Root zone temperature affects the phytoextraction of Ba, Cl, Sn, Pt, and Rb using potato plants (Solanum tuberosum L. var. Spunta) in the field.

Three consecutive years of field experiments were conducted to investigate how different root-zone temperatures, manipulated by using different mulches, affect the phytoextraction of Ba, Cl, Sn, Pt and Rb in different organs of potato plants (roots, tubers, stems and leaves). Four different plastic covers were used (T1: transparent polyethylene; T2: white polyethylene; T3: white and black coextruded polyethylene, and T4: black polyethylene), using uncovered plants as control (T0). The different treatments had a significant effect on mean root zone temperatures (T0 = 16°C, T1 = 20°C, T2 = 23°C, T3 = 27°C and T4 = 30°C) and induced a significantly different response in Ba, Cl, Sn, Pt and Rb concentration and accumulation. The T3 treatment gave rise to the greatest phytoextraction of Ba, Pt, Cl and Sn in the roots, leaflets and tubers. In terms of the relative distribution of the phytoaccumulated elements (as percentage of the total within the plant), Pt and Ba accumulated mainly in the roots whereas Rb, Sn and Cl accumulated primarily in tubers, establishing a close relationship between the biomass development of each organ and phytoaccumulation capacity of metals in response to temperature in the root zone.