Arbuscular Mycorrhiza Improves Photosynthesis and Restores Alteration in Sugar Metabolism in Triticum aestivum L. Grown in Arsenic Contaminated Soil

Contamination of agricultural soil by arsenic (As) is a serious menace to environmental safety and global food security. Symbiotic plant–microbe interaction, such as arbuscular mycorrhiza (AM), is a promising approach to minimize hazards of As contamination in agricultural soil. Even though the potential of AM fungi (AMF) in redeeming As tolerance and improving growth is well recognized, the detailed metabolic and physiological mechanisms behind such beneficial effects are far from being completely unraveled. The present study investigated the ability of an AM fungus, Rhizophagus intraradices, in mitigating As-mediated negative effects on photosynthesis and sugar metabolism in wheat (Triticum aestivum) subjected to three levels of As, viz., 0, 25, and 50 mg As kg–1 of soil, supplied as sodium arsenate. As exposure caused significant decrease in photosynthetic pigments, Hill reaction activity, and gas exchange parameters such as net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. In addition, As exposure also altered the activities of starch-hydrolyzing, sucrose-synthesizing, and sucrose-degrading enzymes in leaves. Colonization by R. intraradices not only promoted plant growth but also restored As-mediated impairments in plant physiology. The symbiosis augmented the concentration of photosynthetic pigments, enhanced Hill reaction activity, and improved leaf gas exchange parameters and water use efficiency of T. aestivum even at high dose of 50 mg As kg–1 of soil. Furthermore, inoculation with R. intraradices also restored As-mediated alteration in sugar metabolism by modulating the activities of starch phosphorylase, α-amylase, β-amylase, acid invertase, sucrose synthase, and sucrose-phosphate synthase in leaves. This ensured improved sugar and starch levels in mycorrhizal plants. Overall, the study advocates the potential of R. intraradices in bio-amelioration of As-induced physiological disturbances in wheat plant.

Effects of some inhibitors of protein synthesis on the chloroplast fine structure, CO2 fixation and the Hill reaction activity

A comparative study concerning the effects of chloramphenicol (100 μg ml^-1, actidione (10 μg ml^-1), 5-bromouracil (190 μg ml^-1), actinomycin D (30 μg ml^-1) and DL-ethionine (800 μg ml^-1) on the chloroplast fine structure, ¹⁴CO₂ incorporation and the Hill reaction activity was the subject of the experiments presented in this paper. The experiments were conducted on bean seedlings under the conditions when chlorophyll accumulation was inhibited only partially. The results obtained indicate that chloromphenicol is responsible for the reduction of the number of grana per section of plastid and for the formation of numerous vesicles in the stroma. In the presence of actidione, actinomycin D or DL-ethionine the lamellae are poorly differentiated into .stroma and granum regions and there occur disturbances in the typical orientation of lamellae within chloroplasts. Only in the presence of 5-bromouracil the development of chloroplast structure resemble that in control plants. A comparison of the results obtained with those published earlier (Więckowski et al., 1974; Ficek and Więckowski, 1974) shows that such processes as assimilatory pigment accumulation, the rate of CO₂ fixation, the Hill reaction activity, and the development of lamellar system are suppressed in a different extent by the inhibitors used.

Effects of Ozone Stress on Leaf-Level Photosynthesis in Soybean (Glycine max)

Glycine max were exposed in nine the open-top chambers to three levels of ozone (O3) concentration (ambient, approximately 45 nL·L-1 and two elevated ozone, 80±10 nL·L-1 and 110±10 nL·L-1) in four different growing stages (branching, flowering, podding and filling). In order to study the effect of different ozone concentration on photosynthesis parameters, the emphasis of this research was on photosynthetic pigment contents, parameters of photosynthetic gas exchange, Hill reaction activity and Ca2+/Mg2+-ATPase activity in soybean leaves. This paper reveals its response process and degree of photosynthesis in soybean leaves under different elevated O3, and it could establish the foundation for the study of plants adaptability mechanism under elevated O3 on the molecular level. The results showed that elevated O3 concentration accelerated peroxidation damage, and plants could not tolerate O3-induced injure, thus reducing photosynthesis by stomatal closure because of O3 exposure in soybean leaves. And O3 stress caused an acceleration of caducity that might be in part responsible for the reduction of photosynthesis.

The effect of low growth temperature on Hill reaction and Photosystem 1 activities in three biotypes of Kochia scoparia (L.) Schrad. with different sensitivity to atrazine and ALS-inhibiting herbicides

A possible influence of low growth temperature on the photochemical activity of isolated mesophyll chloroplasts was studied in three biotypes of kochia [Kochia scoparia (L.) Schrad.] that showed either double resistance to both atrazine and acetolactate synthase (ALS) inhibitors (Bubny biotype), resistance to ALS inhibitors but not to atrazine (Jihlava biotype), or sensitivity to both types of herbicides (Karlín biotype). Plants 5 or 12 weeks old since the date of sowing were examined. The Bubny biotype displayed the lowest values of Hill reaction activity (HRA) among all biotypes examined, and a significantly lower activity of Photosystem (PS) 1 compared to the Karlín biotype; this applied both for the control and low temperature-grown plants and for both plant ages studied. The comparison of HRA and PS1 activity in the Jihlava and Karlín biotypes showed lower values of both parameters for the Jihlava biotype. The HRA of plants grown at low temperature conditions was usually only slightly lower compared to the control plants of all three biotypes examined. The activity of PS1 in the kochia biotypes grown under low-temperature conditions increased markedly and significantly compared to the control plants; this increase was slightly higher in the atrazine-sensitive biotypes Jihlava and Karlín than in the resistant biotype Bubny. The differences between resistant and susceptible biotypes in the HRA diminished under low-temperature conditions whereas the differences in PS1 activity increased.

A COMPARATIVE ANALYSIS OF LEAF CHLOROPHYLL FLUORESCENCE, HILL REACTION ACTIVITY AND 14C-ATRAZINE TRACER STUDIES TO EXPLAIN DIFFERENTIAL ATRAZINE SUSCEPTIBILITY IN WILD TURNIP RAPE (Brassica campestris) BIOTYPES

Leaf chlorophyll fluorescence in susceptible B. campestris L. plants was greatly enhanced and the Hill reaction activity of isolated chloroplasts was inhibited by 10−4 M atrazine. The herbicide did not produce similar responses in resistant plants. 14C-atrazine was used to determine if, in addition, there were differences in uptake, translocation, and metabolism of the herbicide by the susceptible and resistant biotypes. The 14C-atrazine in nutrient solution was readily taken up by the roots of both biotypes and was rapidly translocated to the shoot. The 14C-atrazine was quickly metabolized and after a 24-h period 56 and 63% of the extractable radioactivity in susceptible and resistant plants, respectively, was present as metabolites, the major one being 2-hydroxyatrazine. Following a foliar application, less than 1% of the applied radioactivity moved into other parts of the plant. These results clearly show that triazine resistance in wild turnip rape is based in the chloroplast and that uptake, translocation, and metabolism of the herbicide play no decisive role in selectivity between the susceptible and resistant biotypes.Key words: Atrazine selectivity, Brassica campestris, chlorophyll fluorescence, Hill reaction, atrazine metabolism.

Bentazon Selectivity in Hot Pepper (Capsicum chinense) and Sweet Pepper (Capsicum annuum)

The susceptibility of sweet pepper (Capsicum annuumL. ‘Keystone Resistant Giant’) and tolerance of hot pepper (Capsicum chinenseL. ‘Bohemian Chili’) to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] was demonstrated under greenhouse and field conditions. Sweet pepper growth and fruit production were inhibited by foliar applications of bentazon at rates of 0.6 to 6.7 kg ai/ha. Severity of injury increased with application rate. Injury symptoms in sweet pepper were leaf chlorosis, with necrosis and death of shoot apices. Foliar applications of bentazon to hot pepper resulted in little or no injury. Bentazon inhibited Hill reaction activity of isolated chloroplasts from both species to a similar extent, suggesting that selectivity of this compound in hot pepper is not due to resistance at the chloroplast level.

Effect of Photosystem II Inhibitors on Thylakoid Membranes of Two Common Groundsel (Senecio vulgaris)Biotypes

Thylakoid membranes isolated from chloroplasts of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine]-susceptible (S) and -resistant (R) biotypes of common groundsel (Senecio vulgarisL.) were assayed to determine the effect of diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], bromacil (5-bromo-3-sec-butyl-6-methyluracil) and severals-triazine herbicides on photosystem II (PSII) activity. Each herbicide inhibited photosynthetic electron transport on the reducing side of PSII in thylakoid membranes from the susceptible biotype. Thylakoids isolated from the resistant biotype were 60 to 3200 times more tolerant to the inhibitors than thylakoids from the susceptible biotype. Electrophoretic analysis revealed no differences in molecular weight of membrane polypeptides of either common groundsel biotype. Three-hour dark incubation did not enhance inhibitor activity in the resistant-type thylakoid membranes. Specific structural or configurational changes associated with the reactive site may account for the differences in Hill reaction inhibition between biotypes. A relationship between herbicide structure and Hill reaction activity is discussed.