Micha Guy

Response of the Cultivated Tomato and Its Wild Salt-tolerant Relative Lycopersicon Pennellii to Salt-dependent Oxidative Stress: Increased Activities of Antioxidant Enzymes in Root Plastids

Root plastids of the cultivated tomato Lycopersicon esculentum (Lem) exhibited salt-induced oxidative stress as indicated by the increased H 2 O 2 and lipid peroxidation levels which were accompanied with increased contents of the oxidized forms of ascorbate and glutathione. In contrast, H 2 O 2 level decreased, lipid peroxidation level slightly decreased and the levels of the reduced forms of ascorbate and glutathione increased in plastids of L. pennellii (Lpa) species in response to salinity. This better protection of Lpa root plastids from salt-induced oxidative stress was correlated with increased activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), guaiacol peroxidases (POD), monodehydroascorbate reductase (MDHAR), glutathione peroxidase (GPX), glutathione- S -transferase (GST) and phospholipid hydroperoxide glutathione peroxidase (PHGPX). In the plastids of both species, activities of SOD, APX, and POD could be resolved into several isozymes. In Lem plastids two Cu/ZnSOD isozymes were found whereas in Lpa an additional FeSOD type could also be detected. In response to salinity, activities of selected SOD, APX, and POD isozymes were increased in Lpa, while in Lem plastids the activities of most of SOD and POD isozymes decreased. Taken together, it is suggested that plastids play an important role in the adaptation of Lpa roots to salinity.

The response of the filamentous cyanobacterium Spirulina platensis to salt stress

The responses of the filamentous cyanobacterium Spirulina platensis to increased NaCl concentrations (0.25–1.0 M) in addition to the concentration of sodium in the growth medium were studied. A two stage response to the salt stress was observed. This consisted of a relatively short shock stage, followed by adaptation process. It was shown that upon exposure to high salt concentrations of 0.5 M and above, immediate inhibition of photosynthesis and respiration, and complete cessation of growth occurred. After a time lag, the energy-yielding processes exhibited restored activity. At 0.5 and 1.0M NaCl photosynthesis reached 80% and 50% that of the control, while respiration was enhanced by 140 and 200%, respectively. The time lags were longer when the cells were exposed to higher NaCl concentrations. The resumption of growth and the establishment of new steady state growth rates were found to be correlated to the recovery in respiration. The relationship between the growth rates after adaptation and the increased NaCl concentrations was found to be inversely linear. The cellular sodium content was maintained at a constant low level, regardless of the external NaCl concentration, while potassium content declined linearly vs. the external NaCl concentration. The carbohydrate content of the cells rose exponentially with the increase in NaCl concentration.

Ascorbate peroxidase gene family in tomato: its identification and characterization

The antioxidative response, where ascorbate peroxidase (APX) is a key enzyme, is an integral part of the plant tolerance response to environmental stresses. As a first step towards the study of the physiological role and the regulation of the members of the Apx gene family, the orthologs of the stress-sensitive cultivated tomato Solanum lycopersicum cv. M82 (Slm) and of the wild salt-tolerant species S. pennellii acc. Atico (Spa) were identified by utilizing the tomato EST database, and characterized. A redundant list of 16 virtual Apx transcripts and four singleton ESTs was shown to correspond to seven genuine Apx genes. The complete tomato Apx gene family is comprised of genes encoding three cytosolic, two peroxisomal, and two chloroplastic APXs. These genes attained differential regulatory patterns in various Slm organs. More detailed study of Apx1 and Apx2 genes, that are the products of a recent gene duplication event, shows that they have already attained differential regulation within and between Slm and Spa under control and stress conditions. It is also suggested that due to lineage-specific gene duplication and lose events, intricate phylogenetic relationships exist among the members of the Apx gene families.

Antioxidative Systems and Stress Tolerance: Insight from Wild and Cultivated Tomato Species

The role of antioxidative systems of the salt-sensitive cultivated tomato, L. esculentum (Lem) and its wild salt-tolerant relative L. pennellii (Lpa) in salt tolerance was studied. For this, leaf and root cell organelles (chloroplasts/plastids, mitochondria, and peroxisomes) isolated from control and salt-treated Lem and Lpa plants were characterized and compared. In general, the inherent organellar antioxidative systems of the two tomato species were highly similar. The activities of SOD and the ascorbate–glutathione cycle isozymes, in the various cell organelles, were separated into soluble and membrane-bound fractions. Latency and solubilization assays were used to map the in situ suborganellar localization of the ascorbate–glutathione cycle isozymes. These activities were localized to both faces of the organellar membranes and in the lumens of various suborganellar compartments and were modeled for peroxisomes, chloroplasts, and mitochondria. Differences between the inherent antioxidative systems of Lem and Lpa were found. These included different ratios of the soluble to membrane-bound activities and different SOD-type inventories. In Lem organelles, stress-induced downregulation of antioxidative isozymes, and oxidants, was correlated with increased oxidative damage, in contrast, in Lpa organelles a stress-induced upregulation of the antioxidative isozymes, and oxidants, was correlated with alleviation of oxidative stress. Similarly, cross-tolerance to imposed oxidative stress by SHAM and 3-AT was found only in Lpa plants grown in salinity and was dependent, at least in part, upon the capacity for de novo GSH synthesis. The failure of Lem to upregulate its antioxidative systems is discussed.

Function of Membrane Transport Systems under Salinity: Plasma Membrane

The plasma membrane is the seat of multiple transport systems which transfer a wide range of solutes into or out of plant cells. These systems mediate both passive and active fluxeTs; the immediate energy source for the latter is frequently the protonmotive force generated by the plasma membrane H+-ATPase. This chapter focusses on the systems which transport K+, Na+, Cl− and H2O (a significant number of which have now been identified at the molecular level), and considers the mechanisms which restrict intracellular Na+ and Cl− concentration, and maintain that of K+, in the face of high external salinity. Key components of the transduction pathway between the signalling of saline stress and response at plasma membrane level have recently been recognized.

Cultivation of Lemna gibba under desert conditions. I, Twelve months of continuous cultivation in open ponds

Abstract Duckweed, Lemna gibba , was grown in 12 m 2 shallow ponds in the Negev desert, during 12 months of continuous cultivation, beginning April 1984. Average monthly growth rates varied with the season of the year. The lowest daily yield, 2·6±0·4 g dry weight m −2 day −1 , was obtained during January. Highest daily yields, 7·9±2·6 g dry weight m −2 day −1 and 7·0±1·2 g dry weight m −2 day −1 , were obtained during September and May. A 35% decline of the yield was seen during midsummer (July), 4·8±1·2 g dry weight m −2 day −1 . The average rate for the year was 5·15±1·7 g dry weight m −2 day −1 . The protein content of the plants ranged from 30 to 38% per unit dry weight. Growth performance is discussed in relation to the prevailing climatic conditions.

Cultivation of Lemma gibba under desert conditions. II: The effect of raised winter temperature, CO2 enrichment and shading on productivity

Abstract The aim of this work was to increase the productivity of Lemna gibba ponds under desert conditions. In the winter season, the ponds were covered with transparent plastic tents which raised water temperature. This also allowed CO2 to be added to the air in the tents to either the ambient, ∼ 340 μmol−1, or to higher concentrations. The plastic covers attenuated photosynthetically active light by ∼ 30%. Winter-season yields in the covered ponds, maintained at ambient CO2 concentration, were 39% higher than in the uncovered ponds. This could be ascribed to raised temperatures. Enrichment of the atmosphere with CO2 further increased yields by as much as 28%. The different treatments did not affect protein content expressed as a percentage of dry weight. Laboratory experiments indicated that the shorter the photoperiod the larger is the growth response of Lemna gibba to CO2 enrichment. Shading of the ponds during the June–August summer season reduced pond temperatures at midday by about 5–6°C and resulted in a 30–80% increase of growth. It was concluded that under desert conditions similar to those prevailing in this trial, high yields of Lemna gibba can be achieved throughout a growing season of 12 months per year by covering the ponds and raising ambient [CO2] during the winter, and by shading in summer. Productivity of 7·4±1·0 g m−2 day−1 can be maintained throughout the year. Whether or not it is worthwhile to do so is a question of local economics.