Foliar nutrient resorption patterns of four functional plants along a precipitation gradient on the Tibetan Changtang Plateau

Nutrient resorption from senesced leaves as a nutrient conservation strategy is important for plants to adapt to nutrient deficiency, particularly in alpine and arid environment. However, the leaf nutrient resorption patterns of different functional plants across environmental gradient remain unclear. In this study, we conducted a transect survey of 12 communities to address foliar nitrogen (N) and phosphorus (P) resorption strategies of four functional groups along an eastward increasing precipitation gradient in northern Tibetan Changtang Plateau. Soil nutrient availability, leaf nutrient concentration, and N:P ratio in green leaves ([N:P]g) were linearly correlated with precipitation. Nitrogen resorption efficiency decreased, whereas phosphorus resorption efficiency except for sedge increased with increasing precipitation, indicating a greater nutrient conservation in nutrient-poor environment. The surveyed alpine plants except for legume had obviously higher N and P resorption efficiencies than the world mean levels. Legumes had higher N concentrations in green and senesced leaves, but lowest resorption efficiency than nonlegumes. Sedge species had much lower P concentration in senesced leaves but highest P resorption efficiency, suggesting highly competitive P conservation. Leaf nutrient resorption efficiencies of N and P were largely controlled by soil and plant nutrient, and indirectly regulated by precipitation. Nutrient resorption efficiencies were more determined by soil nutrient availability, while resorption proficiencies were more controlled by leaf nutrient and N:P of green leaves. Overall, our results suggest strong internal nutrient cycling through foliar nutrient resorption in the alpine nutrient-poor ecosystems on the Plateau. The patterns of soil nutrient availability and resorption also imply a transit from more N limitation in the west to a more P limitation in the east Changtang. Our findings offer insights into understanding nutrient conservation strategy in the precipitation and its derived soil nutrient availability gradient

Grano ed eccesso di rame: può il tocoferolo inibire l'azione della fosfolipasi A?

Piante di grano (Triticum durum cv. Adamello) sono state incubate in una soluzione contenente CuSO4 100 μM per differenti periodi di tempo (da 1 a 960 minuti). Le radici già dopo 1 min di incubazione hanno presentato un aumento del contenuto di rame. In corrispondenza del contenuto massimo degli isomeri del tocoferolo è stato registrato un minimo livello dei lisati dei fosfolipidi, conseguenza di una disattivazione della fosfolipasi A2 (PLA2), enzima in grado di catalizzare l’idrolisi del legame sn-2 acil estere dei glicerofosfolipidi formando lisofosfolipidi ed acidi grassi liberi

Lipid composition of pea (Pisum sativum L.) and maize (Zea mays L.) root plasma membrane and membrane-bound peroxidase and superoxide dismutase

Plasma membrane was isolated from roots of pea and maize plants and used to analyze POD and SOD isoforms, as well as lipid composition. Among lipids, phospholipids were the main lipid class, with phosphatidylcholine being the most abundant individual component in both pea and maize plasma membranes. Significant differences between the two plant species were found in the contents of cerebrosides, free sterols, and steryl glycosides. Most maize POD isoforms were with neutral and anionic pI values, but the opposite was observed in pea. While both anionic and cationic SOD isoforms were isolated from maize, only two anionic SOD isoforms were detected in pea

Effect of soil drying on rate of stress development, leaf gas exchange and proline accumulation in Robusta coffee (Coffea canephora pierre ex froehner) clones

Seasonal drought stresses as a result of changes in global climate and local weather conditions are among the major factors adversely affecting growth and productivity of Robusta coffee (Coffea canephora pierre ex froehner) in many areas producing the crop. It is believed that there exists a wide range of genetic variability among Robusta coffee clones for traits associated with drought tolerance. Therefore, in an attempt to determine differences among Robusta coffee clones for some growth, physiological and biochemical parameters and identify drought-tolerant materials, 12 months old seedlings of six clones (IC-2, IC-3, IC-4, IC-6, IC-8 and R-4) were subjected to two treatments: well-watered control and drought-stressed (soil drying) by withholding irrigation for three weeks in a rain shelter at University Putra Malaysia, Malaysia. The rate of stress development, expressed as extent of wilting and damage to leaves, was considerably higher for clones IC-8, IC-4, R-4 and IC-2 than for IC-3 and IC-6 during the stress period. Leaf water potential (LWP), stomatal conductance (gs ) and rate of net photosynthesis (PN ) progressively decreased but leaf proline (LP) concentration substantially increased with time of exposure of the plants to soil drying. There was a considerable difference between coffee clones for the rate of change in these parameters. All the clones except IC-6 and IC-8 showed a negative carbon balance with the most negative value for R-4 at the end of the stress period. Six days after rewatering, LWP, gs and PN increased rapidly while LP concentration decreased and reached a level equivalent to those of well-watered plants, especially for clones IC-3 and IC-6. Among the drought-stressed plants, IC-6 and IC-3 had still significantly higher shoot growth, total dry matter yield and root to shoot ratio than did IC-2, IC-4, IC-8 and R-4. In general, clones IC-6 and IC-3 exhibited quite a better performance in almost all the parameters considered in this study and seemed to be less sensitive to drought stress. Hence, drought tolerance attributes in these clones could be linked to a more effective osmotic adjustment due to more rapid accumulation of LP and probably some morphological parameters, such as increased root-to-shoot ratio. However, further analyses at molecular level, detail biochemical studies and observations under diverse field conditions are required to come up with more conclusive recommendations

Exogenously induced expression of ethylene biosynthesis, ethylene perception, phospholipase D, and Rboh-oxidase genes in broccoli seedlings

In higher plants, copper ions, hydrogen peroxide, and cycloheximide have been recognized as very effective inducers of the transcriptional activity of genes encoding the enzymes of the ethylene biosynthesis pathway. In this report, the transcriptional patterns of genes encoding the 1-aminocyclopropane-1-carboxylate synthases (ACSs), 1-aminocyclopropane-1-carboxylate oxidases (ACOs), ETR1, ETR2, and ERS1 ethylene receptors, phospholipase D (PLD)-α1, -α2, -γ1, and -δ, and respiratory burst oxidase homologue (Rboh)-NADPH oxidase-D and -F in response to these inducers in Brassica oleracea etiolated seedlings are shown. ACS1, ACO1, ETR2, PLD-γ1, and RbohD represent genes whose expression was considerably affected by all of the inducers used. The investigations were performed on the seedlings with (i) ethylene insensitivity and (ii) a reduced level of the PLD-derived phosphatidic acid (PA). The general conclusion is that the expression of ACS1, -3, -4, -5, -7, and -11, ACO1, ETR1, ERS1, and ETR2, PLD-γ 1, and RbohD and F genes is undoubtedly under the reciprocal cross-talk of the ethylene and PAPLD signalling routes; both signals affect it in concerted or opposite ways depending on the gene or the type of stimuli. The results of these studies on broccoli seedlings are in agreement with the hypothesis that PA may directly affect the ethylene signal transduction pathway via an inhibitory effect on CTR1 (constitutive triple response 1) activity

Implication of phospholipase D in response of Hordeum vulgare root to a short-term potassium deprivation

SUMMARY To verify a possible implication of lipids and some other compounds such as hydrogen peroxide (H2O2) and glyceraldehydes-3-phosphate dehydrogenase (G3PDH) in the response of Hordeum vulgare to an early potassium deprivation, plants were grown in hydroponics for 30 days with a modified Hewitt nutrient solution containing 3 mM K+ and then incubated for increasing time ranging from 2 h up to 36 h in the same medium deprived of K+. In contrast to leaves, root K+ concentration showed its greatest decrease after 6 h of treatment. The main lipids of the control barley roots were phospholipids (PL), representing more than 50% of the total lipids. PL did not change with treatment whereas free sterols (FS) amounts decreased following K+ deprivation, showing an about 17% reduction after 36 h. As regards the individual PL, 30 h K+ deprivation caused a reduction in phosphatidylcholine (PC), phosphatidylserine (PS) and phosphatidylinositol (PI) levels whereas phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and phosphatidic acid (PA) increased. The maximum PA accumulation as well as the highest phospholipase D (PLD) activation, estimated by an accumulation of phosphatidylbutanol (PtBut), were observed after 24 h of K+ starvation. At the root level, after 6 h of incubation in –K solution, H2O2 level showed the maximum value. At the same time G3PDH activity reached the minimum. On the basis of a concomitant stimulation of PLD activity and, consequently, PA accumulation, enhancement of H2O2 production, and inhibition of G3PDH activity we can suggest a possible involvement of these three compounds in an early response to K+ deprivation