Showing papers on "Plant physiology published in 1999"

Effect of ammonium or nitrate nutrition on net photosynthesis, growth, and activity of the enzymes nitrate reductase and glutamine synthetase in blueberry, raspberry and strawberry

Abstract: Blueberry, raspberry and strawberry may have evolved strategies for survival due to the different soil conditions available in their natural environment. Since this might be reflected in their response to rhizosphere pH and N form supplied, investigations were carried out in order to compare effects of nitrate and ammonium nutrition (the latter at two different pH regimes) on growth, CO2 gas exchange, and on the activity of key enzymes of the nitrogen metabolism of these plant species. Highbush blueberry (Vaccinium corymbosum L. cv. 13–16–A), raspberry (Rubus idaeus L. cv. Zeva II) and strawberry (Fragaria × ananassa Duch. cv. Senga Sengana) were grown in 10 L black polyethylene pots in quartz sand with and without 1% CaCO3 (w: v), respectively. Nutrient solutions supplied contained nitrate (6 mM) or ammonium (6 mM) as the sole nitrogen source. Compared with strawberries fed with nitrate nitrogen, supply of ammonium nitrogen caused a decrease in net photosynthesis and dry matter production when plants were grown in quartz sand without added CaCO3. In contrast, net photosynthesis and dry matter production increased in blueberries fed with ammonium nitrogen, while dry matter production of raspberries was not affected by the N form supplied. In quartz sand with CaCO3, ammonium nutrition caused less deleterious effects on strawberries, and net photosynthesis in raspberries increased as compared to plants grown in quartz sand without CaCO3 addition. Activity of nitrate reductase (NR) was low in blueberries and could only be detected in the roots of plants supplied with nitrate nitrogen. In contrast, NR activity was high in leaves, but low in roots of raspberry and strawberry plants. Ammonium nutrition caused a decrease in NR level in leaves. Activity of glutamine synthetase (GS) was high in leaves but lower in roots of blueberry, raspberry and strawberry plants. The GS level was not significantly affected by the nitrogen source supplied. The effects of nitrate or ammonium nitrogen on net photosynthesis, growth, and activity of enzymes in blueberry, raspberry and strawberry cultivars appear to reflect their different adaptability to soil pH and N form due to the conditions of their natural environment.

Engineering seed dormancy by the modification of zeaxanthin epoxidase gene expression

Abstract: Abscisic acid (ABA) is a plant hormone synthesized during seed development that is involved in the induction of seed dormancy. Delayed germination due to seed dormancy allows long-term seed survival in soil but is generally undesirable in crop species. Freshly harvested seeds of wild-type Nicotiana plumbaginifolia plants exhibit a clear primary dormancy that results in delayed germination, the degree of primary dormancy being influenced by environmental culture conditions of the mother plant. In contrast, seeds, obtained either from ABA-deficient mutant aba2-s1 plants directly or aba2-s1 plants grafted onto wild-type plant stocks, exhibited rapid germination under all conditions irrespective of the mother plant culture conditions. The ABA biosynthesis gene ABA2 of N. plumbaginifolia, encoding zeaxanthin epoxidase, was placed under the control of the constitutive 35S promoter. Transgenic plants overexpressing ABA2 mRNA exhibited delayed germination and increased ABA levels in mature seeds. Expression of an antisense ABA2 mRNA, however, resulted in rapid seed germination and in a reduction of ABA abundance in transgenic seeds. It appears possible, therefore, that seed dormancy can be controlled in this Nicotiana model species by the manipulation of ABA levels.

Cd/Fe Interaction in Higher Plants - Its Consequences for the Photosynthetic Apparatus

Abstract: Cadmium is one of the most dangerous environmental pollutants, affecting, among other things, plant mineral composition. It easily interacts with iron, one of the most important elements for plant growth and metabolism. This interaction, including modifying effects of lowered or excessive Fe supply on Cd-exposed plants and its consequences for the photosynthetic apparatus is reviewed. The influence of modified Fe and Cd supply on the uptake of both metals, their distribution, plant growth, and photosynthesis is also explained. Moderate Fe excess has a beneficial influence on Cd-treated plants, resulting in more intensive growth, photosynthetic pigments accumulation, and more efficient light phase of photosynthesis. Nutrient-medium Fe deficiency increases plant susceptibility to Cd. The main open questions of Cd/Fe interaction are: (1) the strong Fe-dependency of Cd mobility within the plant, and (2) photosynthetic dark phase adaptation to Cd stress.

Cold Acclimation in Plants: Relationship Between the Lipid Composition and the Cryostability of the Plasma Membrane

Abstract: Cold acclimation of plants requires an orchestration of many different, seemingly disparate processes. However, many of these processes that occur during cold acclimation ultimately contribute to the increased stability of cellular membranes during freeze-induced dehydration-the destabilization of which is the primary cause of the freezing injury. Among all cellular membranes, the plasma membrane is of primary importance to maintain its structural integrity because of the central role it plays during a freeze/ thaw cycle. We will describe here that there is a close association between the alterations of the plasma membrane lipid composition and the difference in the incidence of freeze-induced membrane lesions during cold acclimation. The stability of the plasma membrane during freezeinduced dehydration is also affected by factors associated with the endomembranes (the chloroplast envelope lipid composition) and the cytoplasm (the accumulation of sugars and the cold-regulated gene expression). Collectively, these results indicate that the structural integrity of the plasma membrane during freeze-induced dehydration is maintained by a complex but well-coordinated manner.

The effects of O3 fumigation during leaf development on photosynthesis of wheat and pea: An in vivo analysis

Abstract: Previous studies have shown that short exposure of plants to high doses of ozone decreases subsequent photosynthesis; initially by reducing carboxylation capacity. This study tests the hypothesis that this is also the primary cause of loss of photosynthetic capacity in leaves affected by development under a low level of ozone. Triticum aestivum and Pisum sativum plants were exposed from germination to ozone in air (80 nmol mol-1 for 7 hours per day, for 18 days. Leaves that had completed lamina expansion at this time were free of visible injury and light absorptance was unaffected. However, some significant changes in photosynthetic gas exchange were evident. Photosynthetic CO2 uptake at light saturation was decreased significantly by 35% in T. aestivum but was unchanged in P. sativum. The reduction in photosynthesis of T. aestivum was accompanied by a 31% decline in the maximum velocity of carboxylation measured in vivo. Decreased stomatal conductance did not contribute to this reduction of photosynthesis because there was no significant change in the stomatal limitation to CO2. Processes directly dependent upon photochemical reactions; that is, the quantum yield of CO2 uptake and capacity for regeneration of ribulose 1,5-bisphosphate were not affected by O3 fumigation in either species. This suggests that for wheat, the quantitative cause of decreased photosynthetic rate in vivo is a decrease in the quantity of active ribulose-1,5- bisphosphate carboxylase-oxygenase.

Gradient of photosynthetic pigments in the bark and leaves of lilac [Syringa vulgaris L.]

Abstract: The concentration of chlorophyll and a carotenoids in the bark of stems of different age and in the leaves of lilac (Syringa vulgaris L.) was determined.

Relationship between Carbon and Nitrogen Metabolisms in Photosynthesis. The Role of Photooxidation Processes

Abstract: 14CO2 uptake in leaves of wheat plants (Triticum aestivum L.) fertilized by urea or Ca(NO3)2 (25 mol m-3) was investigated. The Warburg effect (inhibition of 14CO2 uptake by oxygen) under 0.03 vol. % CO2 concentration was observed only in non-fertilized plants. Under 0.03 vol. % CO2, the Warburg antieffect (stimulation of 14CO2 uptake by oxygen) was detected only in plants fertilized by Ca(NO3)2. Under saturating CO2 concentration (0.30 vol. %), the Warburg antieffect was observed in all variants. Under limitation of ribulose-1,5-bisphosphate carboxylase/oxygenase activity (0.30 vol. % CO2 + 1 vol. % O2), the rate of synthesis of glycollate metabolism products decreased in control and urea-fertilized plants but was enhanced in nitrate-fed plants. Hence, there was an activation of glycollate formation via transketolase reaction in fertilized plants, and the products of nitrate reduction function were oxidants in nitrate-fertilized plants whereas the superoxide radical played this role in urea-fertilized plants.

The Effect of Low Growth Temperature on Hill Reaction and Photosystem 1 Activities and Pigment Contents in Maize Inbred Lines and Their F1 Hybrids

Abstract: Young plants of maize inbred lines CE777, CE704, and CE810 and their F1 hybrids displaying a positive heterotic effect in various photosynthetic characteristics were exposed to low temperature during their early growth developmental stage. The photochemical activity of isolated mesophyll chloroplasts and the contents of photosynthetic pigments in leaves of stressed and non-stressed plants were compared with the aim to find out the possible changes in the relationship between parents and hybrids, and to determine the genetic basis of heterosis in F1 generation. Strong decrease in the content of chlorophylls was observed for all genotypes examined when plants were subjected to low growth temperature. Similar change was recorded for Hill reaction activity (HRA) of inbred lines but not of their F1 hybrids, and no significant response at all was found for photosystem 1 (PS1) activity or the total carotenoids content. The intraspecific variation due to differences between genotypes was found for most of photosynthetic characteristics examined. This variation was caused by the additive and dominance genetic effects. Positive dominance was the main cause of positive heterosis in HRA and in the contents of photosynthetic pigments and was much more pronounced in the stressed plants compared to the non-stressed ones. The maternal additive effects participated in the inheritance of contents of photosynthetic pigments in plants exposed to low temperature, too.

Photosynthetic apparatus in primary leaves of barley seedlings grown under blue or red light of very low photon flux densities

Abstract: Chlorophyll (Chl) a and Chl b contents, rate of CO2 gas exchange, quenching coefficients of chlorophyll fluorescence, and endogenous phytohormones have been studied in primary leaves of barley seedlings cultivated under blue (BL) or red (RL) light. Photon flux densities (PFD) were between 0.3 and 12 μmol m-2 s-1. Plants grown at PFD of 0.3 μmol m-2 s-1 demonstrated in BL tenfold and in RL threefold decreased Chl content compared to plants grown at 12 μmol m-2 s-1. Chl a/b ratio increased from 2.3–2.5 to 4.4–4.5 in BL, not in RL, following the decrease in PFD at plant cultivation from 12 to 0.3 μmol m-2 s-1. Plants cultivated at weak BL demonstrated severalfold decreased rate of photosynthetic CO2 uptake, whereas decrease in PFD of RL from 12 to 0.3 μmol m-2 s-1 caused only 20% de cline in the rate of photosynthesis. Decrease in PFD during a plant cultivation reduced the maximum quantum yield of photosynthesis in BL, not in RL leaves. Light response curves of non-photochemical and photochemical quenching of chlorophyll fluorescence calculated on the basis of absorbed quanta were not affected by PFD of RL during plant cultivation. On the contrary, both non-photochemical quenching and accumulation of QA-, reduced primary acceptor of Photosystem II, occurred at lower amounts of absorbed quanta in leaves of BL plants grown at 0.3 than at 12 μmol m-2 s-1. Two photoregulatory reactions were suggested to exert the light control of the development of photosynthetic apparatus in the range of low PFDs. The photoregulatory reaction saturating by very low PFDs of RL was supposed to be mediated by phytochrome. Phytochrome was proposed to enhance (as related to other pigment-protein complexes of thylakoids) the accu mulation of chlorophyll- b-binding light-harvesting complex of Photosystem II (LHC II). It acts independently of the pigment mediating the second photoregulatory reaction, as evidenced by the results of experiments with plant growth under mixed blue plus red light. The contents of cytokinins and indole-3-acetic acid in a leaf were not significantly affected by either light quality and PFD thus indicating those phytohormones not to be involved into photoregulatory processes.

A Prefatory Note on Responses of Plants to Low Temperature-Stress

Abstract: Among various environmental stresses, low temperature is one of the most important factors limiting the productivity and distribution of plants. The precise way in which plants adapt to low temperature is obviously of scientific interest, but there are also practical and economic aspects. Many important crop plants of tropical and subtropical origin are, in general, sensitive to low, nonfreezing temperatures below about 10 to 12 C. In northern climates, plants occasionally encounter unusually cold weather in the early growing season, resulting in a marked physiological dysfunction. A number of the physiological and biochemical studies have suggested that chilling injury is associated with changes in membrane properties, such as solute leakage, reduced transport across the plasma membrane, malfunction of the mitochondria1 respiration and inhibition of photosynthetic activity (Lyons 1973, Lyons et a/. 1979), and induction of active oxygen species (Orman 1980, Prasad et a/. 1994). Chilling sensitivity has been shown to be correlated with the extent of fatty acid unsaturation of the glycerolipids of plastid membranes (Murata et a/. 1992, Kodama et a/. 1994) in genetically engineered tobacco plants. Recently, it has been reported that persistent expression of low molecular mass heat-shock proteins, which are known as molecular chaperons that transiently interact with membrane proteins, is responsible for increase in chilling tolerance in tomato (Sabehat et a/. 1996). This evidence imply that destabilization of protein conformation and its prevention are involved in the mechanism of chilling sensitivity in plants. Our recent studies have suggested that inactivation of vacuolar H+ATPase and, consequently, a disturbance in the homeostasis of the cytoplasmic pH is also involved in the mechanism of chilling injury (Yoshida 1995). The phenomena of chilling injury occurring in the field exhibit complicated aspects due to the influences of composite environmental factors including temperature, light, and humidity. All these factors are mutually interrelated with respect to forms of injury and differences in the chilling-sensitivity. To obtain further insight into the mechanism of chilling injury, more comprehensive approaches are required in the future studies. In contrast to plants indigenous to tropical and subtropical regions, plants from temperate regions are not only chilling tolerant, but also able to survive severe winter frost after

Inhibition of Glutamine Synthetase Activity by Phosphinothricin Results in Disappearance of the Peak M2 of the Chlorophyll Fluorescence Induction Curve

Abstract: The treatment of green algae Chlorococcum lobatum with the herbicide BASTA containing phosphinothricin lead to a significant decrease in the level of peak M2 of the chlorophyll fluorescence induction curve. This agrees with the suggestion that glutamine synthetase activity affects this region of the induction curve.