Nitric oxide modifies photosynthetic electron transport in pea leaves

Previous electron paramagnetic resonance (EPR) and chlorophyll a fluorescence studies on isolated thylakoid membranes showed that nitric oxide (NO), a transmembrane messenger gaseous free radical, slows down the rate of photosynthetic electron transport in vitro. NO could reversibly bind to several sites of photosystem II (PS II) (e.g. non-heme iron complex between QA and QB, QB binding site, water-oxidizing complex) by replacing bicarbonate and causes an inhibitory effect on photophosphorylation. Our results show that in vivo application of NO by several specific NO donor molecules slowed down the rate of QA-reoxidation in pea leaves. NO reduced the optimal quantum efficiency by increasing the dark fluorescence yield (Fo) and decreasing the variable fluorescence (Fv). It also decreased the photochemical quenching (qP) and modified the non-photochemical (NPQ), mainly energy-dependent quenching (qE) in a concentration related manner. Dark relaxation of NPQ also showed, that NO enlarged the photoinhibitory quenching. Since NO acts as a signalling molecule in plant cells during various stresses, our results predict that NO, in a nanomolar concentration range, can assist to avoid the potential stress induced photodamage by inducing heat dissipation of excess light in the PS II antenna. In contrast, higher, cytotoxic concentrations, NO serves as a photosynthetic inhibitor

The effect of exogenous NO on PSI photochemistry in intact pea leaves

We investigated the effect of exogenous NO on PSI photochemistry by measuring P700 absorbance changes at 810-870 nm in intact pea leaves treated with the NO donor GSNO. Our results indicate that NO increases PSI quantum efficiency and the pool size of electrons in the intersystem chain

Investigating the role of potassium channel KAT1 in NO mediated stomatal closure

KAT1, a hyperpolarization-activated, inward-rectifying K+ channel is one of the main transportersparticipating in guard cell volume regulation. The voltage-dependence of KAT1 channel is regulated by several intracellular factors, including pH, ATP and cGMP (Hoshi 1995). NO, a regulator of a branch of ABA signalling pathways in guard cells decreases the Ca2+-dependent inward potassium current by increasing the cytosolic free Ca2+ concentration. Based on the Ca2+-independent feature of KAT1 homotetramer protein, we aimed to examine the direct and indirect effects of NO on this channel

Effect of salinity stress on ion accumulation and on the photosynthetic activity of a new energy plant, phalaris arundinacea cultivars

Reed canarygrass (Phalaris arundinacea) is a good candidate for bioenergy production in Northern and Middle Europe. The crop is well-adapted to cold and drought stress but its resistance to high salinity has not been revealed in details. In this study the effects of 75 and 150 mM NaCl treatments were investigated on the ion accumulation, water potential changes and photosynthetic activity of three Romanian reed canarygrass genotypes, Tardin, Romanesti diverse and Timpuriu. Since cv. Tardin was able to maintain high K+ level and relatively low Na+ concentration in leaf tissues, high stomatal conductance and net CO2 fixation rate under salt stress and as it could maintain the water potential of tissues at control level, this genotype can be defined as salt tolerant. Salt stress induced significant Na+ accumulation, very low K /Na+ ratio, and severe reduction in stomatal conductance and photosynthetic activity in the leaf tissues of Timpuriu cultivar, which proved to be sensitive to high salinity

The effect of xanthan gum as an elicitor on guard cell function and photosynthesis in Vicia faba

Many plant species respond to pathogen attacks by closing stomata in a process called basal resistance. Pathogen-associated molecular patterns (PAMPs) are recognized by pattern recognition receptors (PRRs). This interaction can lead to the activation of different signaling cascades, which can lead to stomatal closure. The immune-active behavior of the bacterial elicitor xanthan gum has been demonstrated in barley where a xanthan treatment lead to the accumulation of the enzyme ß-1,3 glucanase. However, its short-term physiological effects have not been investigated yet. In this study we investigated the effect of xanthan gum on the guard cell function. Xanthan gum applied at dawn can induce stomatal closure, reduce stomatal conductance and the rate of CO2 assimilation, and it can also reduce PSII photochemistry in guard cells

Effect of EDTA-assisted Copper Uptake on Photosynthetic Activity and Biomass Production of Sweet Sorghum

Sweet sorghum (Sorghum bicolor L. Moench cv. Róna) is a widely grown sugar crop that is used for bioenergy production. Since sorghum shows increased sensitivity to nutrient deficiency, the objective of this study was to reach an appropriate Cu level in plant tissues using various concentrations of Cu and ethylenediaminetetraacetic acid (EDTA) in order to enhance the photosynthetic activity and biomass production of plants. Copper accumulation increased in the root and stem of plants irrigated for 12 weeks with 0.1 μM CuCl2 both in the presence and absence of 300 μM EDTA and as a consequence, the plant-available Cu concentration in the soil extracts was lower at harvest. Although the copper content of leaves slightly increased, the transport of Fe and Mn, the microelements participating in light reactions of photosynthesis was negatively affected. In spite of this, 0.1 μM CuCl2 alone and with 200 or 300 μM EDTA enhanced the maximal CO2 assimilation rate (Amax) as a function of photon flux density (PPFD) and increased soluble sugar content in all plant parts. The dry mass of plants especially that of stems increased very significantly after 0.1 μM CuCl2 + 300 μM EDTA treatment. These results show that non-toxic concentration of copper in combination with suitable concentration of EDTA can enhance photosynthesis, biomass production, sugar content and the total copper accumulation in the shoot of sweet sorghum plants