Effect of Abscisic Acid on Photosynthesis in Lemna minor L

Terrestrial and Floating Aquatic Plants Differ in Acclimation to Light Environment

The ability of plants to respond to environmental fluctuations is supported by acclimatory adjustments in plant form and function that may require several days and development of a new leaf. We review adjustments in photosynthetic, photoprotective, and foliar vascular capacity in response to variation in light and temperature in terrestrial plants. The requirement for extensive acclimation to these environmental conditions in terrestrial plants is contrasted with an apparent lesser need for acclimation to different light environments, including rapid light fluctuations, in floating aquatic plants for the duckweed Lemna minor. Relevant features of L. minor include unusually high growth rates and photosynthetic capacities coupled with the ability to produce high levels of photoprotective xanthophylls across a wide range of growth light environments without compromising photosynthetic efficiency. These features also allow L. minor to maximize productivity and avoid problems during an abrupt experimental transfer of low-light-grown plants to high light. The contrasting responses of land plants and floating aquatic plants to the light environment further emphasize the need of land plants to, e.g., experience light fluctuations in their growth environment before they induce acclimatory adjustments that allow them to take full advantage of natural settings with such fluctuations.

Growing duckweed for biofuel production: a review

Duckweed can be utilised to produce ethanol, butanol and biogas, which are promising alternative energy sources to minimise dependence on limited crude oil and natural gas. The advantages of this aquatic plant include high rate of nutrient (nitrogen and phosphorus) uptake, high biomass yield and great potential as an alternative feedstock for the production of fuel ethanol, butanol and biogas. The objective of this article is to review the published research on growing duckweed for the production of the biofuels, especially starch enrichment in duckweed plants. There are mainly two processes affecting the accumulation of starch in duckweed biomass: photosynthesis for starch generation and metabolism-related starch consumption. The cost of stimulating photosynthesis is relatively high based on current technologies. Considerable research efforts have been made to inhibit starch degradation. Future research need in this area includes duckweed selection, optimisation of duckweed biomass production, enhancement of starch accumulation in duckweeds and use of duckweeds for production of various biofuels.

A comparative analysis of the effects of in-vivo and in-vitro abscisic-acid treatment on the surface electrical properties of barley chloroplast membranes

The effects of in-vivo and in-vitro abscisic acid (ABA) treatments on the surface charge density (σ) of barley (Hordeum vulgare L.) thylakoids were compared using 9-aminoacridine fluorescence. The estimated surface charge density of isolated thylakoid membranes from control (non-treated) barley leaves was-0.065 C · m(-2). The net negative surface charge density decreased after application of various concentrations of ABA (10(-6), 10(-5) M) for 7 d in-vivo, the more pronounced effect being observed at 10(-5) M ABA. When ABA was added to the suspension of isolated thylakoids the opposite effect was observed. The average charge density increased in in-vitro-treated thylakoids at 10(-5) M ABA to -0.081 C · m(-2). The results are discussed in terms of a specific ABA-induced influence of the composition and-or stoicheometry of charged protein complexes within the thylakoid membranes.

Literature review on duckweed toxicity testing

Duckweed commonly refers to a group of floating, flowering plants of the family Lemnaceae. Duckweed plants are fast growing and widely distributed. They are easy to culture and to test. Some reports suggest that duckweed plants are tolerant to environmental toxicity. Other studies, however, indicate that duckweed plants are as sensitive to toxicity as other aquatic species. Duckweed plants are especially suitable for use in complex effluent bioassays, and for testing herbicide pollution in the aquatic environment, lake and river pollution, sediment toxicity, and the like. Duckweed and algae represent different levels of complexity in the plant kingdom. They complement each other as phytotoxicity test organisms, instead of mutually excluding each other. Many duckweed species have been studied, primarily of the Lemna and Spirodela genera. Lemna minor and L. gibba have been recommended as standard test species. Differences in duckweed test methodology occur with regard to test types, test vessels, control tests, nutrient media, end points, and applications.

Effect of abscisic acid on the photosynthetic oxygen evolution in barley chloroplasts

In vivo effect of abscisic acid (ABA) on photosynthetic oxygen evolution was investigated in barley chloroplasts. The most important kinetic parameters of O2-producing reactions were changed. The results show inhibition of the O2-flash yields at ABA concentrations of 10 μmol/l and 100 μmol/l and an increase in the degree of damping of the oscillations. ABA has a marked effect on the distribution of the oxygenevolving centers in S0 and S1 states and on sum of the centers (S0+S1) estimated according to the Kok model. In addition, the amplitude and the shape of the initial oxygen burst under continuous illumination are also significantly altered. At a concentration of 100 μmol/l, ABA strongly inhibits Hill reaction activity measured by DCPIP reduction. The results cannot be explained by the hypothesis of socalled "stomata effect". On the other hand, no effects were observed on the investigated parameters in experiments involving ABA applied in vitro to isolated chloroplasts. It is hypothesized that ABA disrupts the granal chloroplasts structure and raises the degree of participation of the cooperative mechanism of O2-evolution connected with the functioning of PS IIβ centers in the stroma situated thylakoids.

Growth, photosynthesis and photorespiration of Lemna gibba: response to variations in CO2 and O 2 concentrations and photon flux density

Dry weight and Relative Growth Rate of Lemna gibba were significantly increased by CO2 enrichment up to 6000 μl CO2 l(-1). This high CO2 optimum for growth is probably due to the presence of nonfunctional stomata. The response to high CO2 was less or absent following four days growth in 2% O2. The Leaf Area Ratio decreased in response to CO2 enrichment as a result of an increase in dry weight per frond. Photosynthetic rate was increased by CO2 enrichment up to 1500 μl CO2 l(-1) during measurement, showing only small increases with further CO2 enrichment up to 5000 μl CO2 l(-1) at a photon flux density of 210 μmol m(-2) s(-1) and small decreases at 2000 μmol m(-1) s(-1). The actual rate of photosynthesis of those plants cultivated at high CO2 levels, however, was less than the air grown plants. The response of photosynthesis to O2 indicated that the enhancement of growth and photosynthesis by CO2 enrichment was a result of decreased photorespiration. Plants cultivated in low O2 produced abnormal morphological features and after a short time showed a reduction in growth.