Showing papers on "Plant physiology published in 1998"

Effects of increased atmospheric CO2 and N supply on photosynthesis, growth and cell composition of the cyanobacterium Spirulina platensis (Arthrospira)

Abstract: The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2 enrichment determined the lack of response in maximum growth rate.

A Possible Role for Jasmonic Acid in Adaptation of Barley Seedlings to Salinity Stress

Abstract: The changes caused by NaCl salinity and jasmonic acid (JA) treatment (8 days) on growth and photosynthesis of barley plants (Hordeum vulgare L., var. Alfa) have been studied. Gas exchange measurements and analysis of enzyme activities were used to study the reactions of photosynthesis to salinity and JA. Both 100 mm NaCl and 25 μm JA treatment led to a noticeable decrease in both the initial slope of the curves representing net photosynthetic rate vs intercellular CO2 concentration and the maximal rate of photosynthesis. The calculated values of the intercellular CO2 concentration, CO2 compensation point, and maximal carboxylating efficiency of ribulose-1,5-bisphosphate carboxylase support the suggestion that biochemical factors are involved in the response of photosynthesis to JA and salinity stress. The activities of phosphoenolpyruvate carboxylase and carbonic anhydrase increased more than twofold. Pretreatment with JA for 4 days before salinization diminished the inhibitory effect of high salt concentration on the growth and photosynthesis. The results are discussed in terms of a possible role of JA in increasing salinity tolerance of the barley plants.

Evolution of C4 photosynthetic genes and overexpression of maize C4 genes in rice

Abstract: C3 plants including many agronomically important crops exhibit a lower photosynthetic efficiency due to inhibition of photosynthesis by O2 and the associated photorespiration. C4 plants had evolved the C4 pathway to overcome low CO2 and photorespiration. This review first focuses on the generation of a system for high level expression of the C4-specific gene for pyruvate, orthophosphate dikinase (Pdk), one of the key enzyme in C4 photosynthesis. Based on the results with transgenic rice plants, we have demonstrated that the regulatory system controlling thePdk expression in maize is not unique to C4 plants but rice (C3 plant) posses a similar system. Second, we discussed the possibility of the high level expression of maize C4-specific genes in transgenic rice plants. Introduction of the maize intact phosphoenolpyruvate carboxylase gene (Ppc) caused 30–100 fold higher PEPC activities than non-transgenic rice. These results demonstrated that intact C4-type genes are available for high level expression of C4 enzymes in rice plants.

The cryptochrome family of blue/UV-A photoreceptors

Abstract: The structural and functional properties of cryptochrome blue light receptors ofArabidopsis thaliana are described. Cryptochromes from ferns and algae, as well as a cryptochrome-like sequences from mammals, are discussed.

Irradiance-induced alterations of growth and cytokinins in Phaseolus vulgaris seedlings

Abstract: Light is a major environmental factor affecting plant growth and development. The cytokinins have many similar effects on these processes and may be involved in photomorphogenesis. In order to study the correlation between light and endogenous cytokinins, we have examined growth parameters and endogenous cytokinins in stems, leaves and other organs of Phaseolus vulgaris, cultivated for 10 days under a range of irradiances (25, 110, 350 and 500 µmol m−2 s−1). The nucleotides isopentenyladenosine-5′-monophosphate and zeatin riboside-5′-monophosphate were the dominant cytokinins, whereas both free bases and ribosides were below the detection level (0.5 pmol g−1). Plants grown at the highest irradiance had in their stems, leaves, petioles and roots significantly higher levels of cytokinins than had plants grown at the lowest irradiance. As expected, increased light influx increased the dry weight of the root, petiole and leaf, and increased the leaf area, with concomitant increases in the cytokinins in these plant parts. However, the stem showed a different and more complex relationship with irradiance. Stem cytokinin levels increased drastically between 350 and 500 µmol m−2 s−1, but this was not correlated with any change in stem length; the light inhibition of stem elongation was mainly seen when irradiance was increased to 110 µmol m−2 s−1. Taken as a whole, the results are consistent with an effect of irradiance and cytokinins on the processes favouring biomass production.

Effect of plant growth regulators and different nitrogen sources on nadp-isocitrate dehydrogenase activity of radish cotyledons

Abstract: NADP-isocitrate dehydrogenase (NADP-ICDH) activity of radish (Raphanus sativus L.) seedlings pretreated with various plant growth regulators: KiN, GA, and ABA and different nitrogen sources viz. KNO3, NH4Cl and NH4NO3 in light and dark was investigated. ICDH activity was significantly higher in light than in dark; addition of different nitrogen sources reduced it to a greater extent in NO3 supplementation. Among hormonal treatment only KiN showed slight promotion with KNO3 and NH4NO3. On the other hand in light KNO3 and/or NH4NO3 promoted ICDH activity and among hormones, KiN significantly promoted the activity in KNO3 and NH4NO3 supplemented seedlings while ABA was effective in NH4CL. It is suggested that in non-photosynthetic tissues, NADP-ICDH provides both reductant and carbon skeleton for glutamate synthesis.

Regulation of Ferritin Synthesis and Degradation in Plants

Abstract: Iron is essential for plants, and either starvation or excess of this element can be responsible for severe nutritional disorders deeply affecting the physiology of plants. For example, iron is known to play an important role in photosynthesis, which takes place in the chloroplasts in plants. Iron starvation is responsible for the syndrome of chlorosis, which leads to a yellowing of leaves and to a disorganization of the photosynthetic apparatus. Treatment of roots and leaves with iron salts can relieve chlorosis (Gris 1844; Briat et al. 1995a, b). Besides photosynthesis, iron is also important in plant physiology for nitrogen fixation, which involves iron proteins such as leghemoglobin and nitrogenase (Nash and Shulman 1976; Appleby et al. 1969). It is also associated with key enzymes such as lipoxygenases and 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase involved in plant hormone synthesis (Siedow 1991; Bouzayen et al. 1991). Although iron is essential for plants, in excess it can be highly damaging, leading to a variety of morphological symptoms. An excess of iron can occur under anaerobic and low pH conditions. This environment favors stability of ferrous iron ions, which are readily taken up by the roots of plants; this can be a natural environmental problem in acidic flooded soils. Among the morphological symptoms due to iron excess, the one best characterized is leaf bronzing in rice (Ponnamperuma et al. 1955).

Photosynthesis and the Environment. Edited by Neil R. Baker

Abstract: transduction, its role in pathenogenesis and stress, its involvement in plant growth and development, and the biotechnological control of its function and formation. The book contains 42 chapters, written by experts in the field; it provides an informative update on current research into this ubiquitous plant hormone. Each chapter is concise and contains few illustrations, but all are accurate and well references. The contents are grouped into six sections which provide a basic theme as indicated above. Section 1 provides information on ACC synthase and ACC oxidase structure and function, the roles of auxin and jasmonates in ethylene biosynthesis and the involvement of ethylene autocatalysis in fruit ripening. Ethylene perception and signal transduction pathways are described in Section 2. The role of ethylene in developmental processes, such as stem development, flowering, circadian rhythms, seed dormancy and fruit ripening, is covered in the next section. A further section is devoted specifically to ethylene and senescence of plant organs, with some emphasis on abscission-related gene expression. Section 5 contains nine chapters devoted to the involvement of ethylene in stress-related phenomena. The final section provides some insights into molecular biological advances which are being utilised by gene technology to control ethylene, particularly to delay ripening and senescence. This book has been produced quickly so it should be of value to students, researchers and teachers interested in new developments in plant hormone research and plant biotechnology.

Plant Physiology: Manipulating Plant Growth with Solar Radiation

Abstract: Light for the plant is used for producing food through the process of photosynthesis. The characteristics of direction and spectral composition of light in the plant's environment is transferred to the plant through the interception and activation of pigment systems (colored cells of the plant). This information affects the morphological development (size/proportion of root and shoots) of the plant.