Some morphological aspects of the synaptonemal complex in higher plants.

The synaptonemal complex is illustrated in electron micrographs from pollen mother cells (p.m.cs) of the following plants: Fritillaria lanceolata, Allium fistulosum, Tulbaghia violacea, Luzula purpurea, Phaedranassa viridiflora and the tulip cultivar Keiserkroon. The possibility that the lateral elements in synaptonemal complexes of plants are tubiform structures is discussed in relation to their fine structure and in the light of a deformity seen in them. An assessment of the evidence suggesting that both lateral and central elements in the complex are ribonucleoprotein structures is made. The effect of brief water treatment on the chromatin and synaptonemal complex at zygotene in p.m.cs of the Phaedranassa is discussed, particularly with reference to two precisely oriented axial strands then seen running between the lateral elements. Examination of stages of premeiotic interphase and early leptotene in p.m.cs of the Fritillaria, revealed that the axial cores laid down at leptotene are formed first in heterochromatic regions, which in this species are locked in chromocentres that persist until pachytene. Further, at leptotene the chromatin in these parts was singularly more decondensed (diffuse) than at any other period, including the premeiotic interphase, subsequent stages of meiosis and mitotic cycle in meristems. It is suggested that the diffuse state of the chromatin in chromocentres at the onset of leptotene, allows the necessary freedom of movement required to promote homologous pairing of the heterochromatic segments. Evidence of such a movement was indicated by a change in position of the nucleoli, which moved from a more central position at early premeiotic interphase to a peripheral one at the onset of leptotene, when they are seen adpressed to the nuclear envelope.     

Ecophysiological aspects of biomass production in higher plants

Photosynthesis as a cosmic process of local entropy decrease is the basic phenomenon for life on Earth. Biomass production is energetically understood as a long-term storage of hydrogen. Endogeneously, the hierarchy of energy storage begins with the electric and proton gradient across the thylakoid membrane. At all higher levels of energy-converting system, efficiency is determined by the interactions between the autotrophic and heterotrophic part of the studied biosystem. Specially, the regulatory function of anabolic and catabolic reduction charge is discussed. From the frame of exogeneous factors, the action of calcium in connection with calmodulin is described as a second messenger.Summarizing, the findings are integrated into the energy-overflow concept in which the loss terms act as system stabilizers especially under injuring conditions.Paper presented at the FESPP meeting in Strasbourg (1984).     

Physiological and molecular aspects of salt stress in plants

The study of salt stress mechanisms in plants has become an important issue for the modern agricultural development, climate change, and global food crisis. The plant response to high salt concentrations is complex and comprehensive; it includes many different processes, which should be correctly coordinated. The effect of excessive salt concentrations on plants results in osmotic stress and creates an ionic inbalance due to the accumulation of toxic ions, such as Cl^? and, especially, Na⁺. Salt stress also has negative impact on mineral homeostasis, in particular Ca²⁺ and K⁺. The progress in transcryptomics, genomics, and molecular biology revealed a new gene families that participate in the formation of salt stress response in plants. This review describes the fundamental principles and mechanisms of plant salt tolerance, maintenance of ion homeostasis. In this paper the detailed analysis of the maine transport membrane systems responsible for the transport of ions and their role in plant salt stress were conducted. The perspectives and directions for the further biotechnological and genetic improvement of salt tolerance in plants are underlied.     

Some aspects of aluminum toxicity in plants

Aluminum toxicity is a major factor in limiting growth in plants in most strongly acid soils. Toxic effects on plant growth have been attributed to several physiological and biochemical pathways, although the precise mechanism is still not fully understood. In general, root elongation is hampered through reduced mitotic activity induced by Al, with subsequent increase in susceptibility to drought. The initial site of uptake is usually the root cap and the mucilaginous secretion covering the epidermal cells. Al ions bind very specifically to the mucilage by exchange adsorption on the polyuronic acid, complexing with the pectic substances and by the formation of polyhydroxy forms, increasing the number of Al atoms per positive charge. Toxicity has been suggested to be initiated at the sites of mucopolysaccharide synthesis. Al is absorbed on all Ca-binding sites on the cell surface. In the intact tissues, most of the Al is bound to the pectic substances of the cell wall and a part to the nucleic acids and cell membrane. Al is also reported to enter the plant by moving into meristematic cells via the cortex, bypassing the endodermal barrier. Being a polyvalent cation, it follows principally the apoplasmic pathway of transport through cortical cells, but may also enter the stele through the plasmalemma. Ultrastructural studies have shown the maximum accumulation to be in the epidermal and cortical cells. The interaction of Al with different systems follows different pathways. The plasma membrane at the outer boundary of the root cell is a potential target and its physical properties can be altered by Al through interaction with membrane-bound ATPase, lipids, carbohydrates and proteins. The Golgi apparatus has been suggested as the primary site of action, followed by damage to the plasmalemma. Aluminum interferes with the uptake, transport and use of several essential elements, including Cu, Zn, Ca, Mg, Mn, K, P and Fe. Excess of Al reduces the uptake of certain elements and increases that of others, the patterns being dependent on the element, the plant part and species involved. A major factor is the pH concentration. At an acid pH, below 5.5, the antagonism between Ca and Al is probably the most important factor affecting Ca uptake by plants. The molecular mechanism of tolerance of Al is as yet not clear. Tolerant plants reduce the absorption by the root or detoxify Al after absorption. Al tolerant plants may be grouped into those with higher Al concentrations in tops and those with less. In the latter, more Al is entrapped in roots. Uptake of Al may be reduced by binding to cell wall or to membrane lipid. Tolerance may be different in different species and seems to be controlled by one or more genes. Absorption of Al in non-metabolic conditions is affected only slightly by temperature. Anaerobic conditions, like the presence of nitrogen and metabolic inhibitors, damage the endodermal membrane barrier, increasing the uptake and enhancing injurious effects. Aluminum also causes morphological damage to plant parts. It affects photosynthesis by lowering chlorophyll content and reducing electron flow. Reduced respiratory activity might be due to reduced metabolic energy requirement. Protein synthesis is decreased probably due to effect on ribosome distribution at endoplasmic reticulum. Aluminum is known to bind to DNA and nuclei. However, its penetrance to DNA of mitotically active centers is slow. On accumulating in roots, it initially inhibits mitotic activity, possibly through affecting the integrated control function of the root meristem. Aluminum toxicity in acid soil is of special importance due to the destruction of components of forest ecosystems under specific conditions. It reduces biomass yield and tree growth and represses litter-degrading microflora. Further information is required on the factors affecting membrane permeability, distribution and accumulation of Al in different plant parts and different species. Al tolerance may be studied with relation to the presence of different ligands, nitrogen metabolism (nitrate reductase and protein accumulation), nitrogen tolerance in relation to pH change and metal ion activities, the role of Ca and P and interference with water relations and litter degradation.     

Some mechanisms of salt tolerance in crop plants

Summary In the first part of this review the main features of salt tolerance in higher plants are discussed. The hypothesis of intracellular compartmentation of solutes is used as a basis for models of tolerance mechanisms operating in roots and in leaves. Consideration is given to the implications of the various mechanisms for the yield potential of salt-tolerant crop plants.Some work on the more salt-tolerant members of the Triticeae is then described. The perennial speciesElytrigia juncea andLeymus sabulosus survive prolonged exposure to 250 mol m^–3 NaCl, whereas the annual Triticum species are severely affected at only 100 mol m^–3 NaCl. In the perennial species the tissue ion levels are controlled within narrow limits. In contrast, the more susceptible wheats accumulate far more sodium and chloride than is needed for osmotic adjustment, and the effects of salt stress increase with time of exposure.Two different types of salt tolerance are exhibited in plants capable of growing at high salinities. In succulent Chenopodiaceae, for example, osmotic adjustment is achieved mainly by accumulation of high levels of sodium and chloride in the shoots, accompanied by synthesis of substantial amounts of the compatible solute glycinebetaine. This combination of mechanisms allows high growth rates, in terms of both fresh and dry weight. At the opposite end of the spectrum of salt tolerance responses are the halophytic grasses, which strictly limit the influx of salts into the shoots, but suffer from very much reduced growth rates under saline conditions. Another variation is shown in those species that possess salt glands. The development and exploitation of crop plants for use on saline soils is discussed in relation to the implications of these various mechanisms.     

Some characteristics of nitrate reductase from higher plants

With respect to cofactor requirements, NADH, and FMNH₂ were equally effective as electron donors for nitrate reductase obtained from leaves of maize, marrow, and spinach, when the cofactors were supplied in optimal concentrations. The concentration of FMNH₂ required to obtain half-maximal activity was from 40- to 100-fold higher than for NADH. For maximal activity with the corn enzyme, 0.8 millimolar FMNH₂ was required. In contrast, NADPH was functional only when supplied with NADP:reductase and exogenous FMN (enzymatic generation of FMNH₂).

All attempts to separate the NADH₂- and FMNH₂-dependent nitrate reductase activities were unsuccessful and regardless of cofactor used equal activities were obtained, if cofactor concentration was optimal. Unity of NADH to FMNH₂ activities were obtained during: A) purification procedures (4 step, 30-fold); B) induction of nitrate reductase in corn seedlings with nitrate; and C) inactivation of nitrate reductase in intact or excised corn seedlings. The NADH- and FMNH₂-dependent activities were not additive.

A half-life for nitrate reductase of approximately 4 hours was estimated from the inactivation studies with excised corn seedlings. Similar half-life values were obtained when seedlings were incubated at 35° in a medium containing nitrate and cycloheximide (to inhibit protein synthesis), or when both nitrate and cycloheximide were omitted.

In those instances where NADH activity but not FMNH₂ activity was lost due to treatment (temperature, removal of sulfhydryl agents, addition of p-chloromercuribenzoate), the loss could be explained by inactivation of the sulfhydryl group (s) required for NADH activity. This was verified by reactivation with exogenous cysteine.

Based on these current findings, and previous work, it is concluded that nitrate reductase is a single moiety with the ability to utilize either NADH or FMNH₂ as cofactor. However the high concentration of FMNH₂ required for optimal activity suggests that in vivo NADH is the electron donor and that nitrate reductase in higher plants should be designated NADH:nitrate reductase (E.C. 1.6.6.1).

     

Some properties of ferric citrate relevant to the iron nutrition of plants

Ferric citrate, the form in which iron is transported in dicotyledonous plants, diffuses slowly through cotton cellulose dialysis membranes, used to serve as a model for plant cell walls. KCl at m M concentrations stimulates diffusion.Photoreduction of ferric citrate results in a rapid and nearly complete reduction of iron when the citrate concentration is low (50 M) as in the xylem sap of plants growing on non-calcareous soils. In 1 m M citrate, as in the xylem sap of plants that activate their Fe-efficiency reactions, fast reoxidation prevents the buildup of high ferrous levels until after citrate has been largely broken down by photodestruction.Photodestruction of citrate, catalyzed by iron, results in increase of pH in the solution and in the formation of a non-dialyzable form of iron, and thus can lead to deposition of inactive iron in leaves.     

Genetics of salt tolerance in higher plants: theoretical and practical considerations

Summary An interdisciplinary approach to breeding for stress tolerance in plants has gained considerable recognition in the past few years. Accordingly, this article presents a synthesis of the genetic, physiological, and ecological aspects of salt tolerance in plants. An understanding of these aspects and the interrelationships between them is essential for an efficient breeding program.A significant part of the presentation concentrates on the basic problems associated with the genetics of tolerance to stresses and of quantitative characters in general, since many of the unsolved problems relevant to the genetics of salt tolerance are still general. Significant progress in the breeding of quantitative as well as qualitative traits in multicellular organisms depends on an understanding of the genetic and epigenetic dimensions of gene action. The discussion therefore includes an overview of (1) the limited existing knowledge on the genetic control of salt tolerance and (2) the physiological mechanisms and molecular targets central to the control of salt resistance as expressed by the amount and stability of yield.An additional subject emphasized here concerns the main strategies of adaptation of wild species to their natural habitats. An understanding of them is essential to (1) enable distinction between traits that can increase agricultural yield and traits that are favorable only for survival under natural conditions (such a distinction is essential, especially when wild species are used as a gene source), and (2) predict the best combinations of characters for efficient agricultural production in stressful environments.     

Some important physiological selection criteria for salt tolerance in plants

Undoubtedly, plant breeders have made a significant achievement in the past few years, improving salinity tolerance in a number of potential crops using artificial selection and conventional breeding approaches, although molecular biology approaches are currently being intensively pursued for achieving this goal. However, most of the selection procedures used so far, were based merely on differences in agronomic characters. Agronomic characters represent the combined genetic and environmental effects on plant growth, and include the integration of the physiological phenomena conferring salinity tolerance. In fact, physiological criteria are able to supply more reliable information than agronomic characters. Although there are large numbers of reports in the literature mainly dealing with water relations, photosynthesis, and accumulation of various inorganic ions and organic metabolites in individual crops, there is little information available on the use of these attributes as selection criteria for improving salt tolerance through selection and breeding programs. In this review, the major adaptive components of salt tolerance such as osmotic adjustment, photosynthesis, water relations and ion relations are reviewed. In view of the complexity of salt tolerance and its great variation at intra-specific and inter-specific levels, it is difficult to identify single criteria, which could be used as effective selection targets. Rather it is most meaningful if physiological and biochemical indicators for individual species are determined rather than generic indicators.     

Effect of salt stress on antioxidant system of plants as related to nitrogen nutrition

In plants of wheat (Triticum aestivum L.) grown in the media with nitrate (NO ₃ ^? plants), ammonium (NH ₄ ⁺ plants), and without nitrogen (N-deficient plants), the response to oxidative stress induced by the addition of 300 mM NaCl to the nutrient solution was investigated. Three-day-long salinization induced chlorophyll degradation and accumulation of malondialdehyde (MDA) in the leaves. These signs of oxidative stress were clearly expressed in NO ₃ ^? and N-deficient plants and weakly manifested in NH ₄ ⁺ plants. In none of the treatments, salinization induced the accumulation of MDA in the roots. Depending on the conditions of N nutrition, salt stress was accompanied by diverse changes in the activity of antioxidant enzymes in the leaves and roots. Resistance of leaves of NH ₄ ⁺ plants to oxidative stress correlated with a considerable increase in the activities of ascorbate peroxidase and glutathione reductase. Thus, wheat plants grown on the NH ₄ ⁺ -containing medium were more resistant to the development of oxidative stress in the leaves than those supplied with nitrate.     

Some variations in the composition of suberin from the cork layers of higher plants

The monomeric composition of the suberins from 16 species of higher plants was determined by chromatographic methods following depolymerization of the isolated extractive-free cork layers with sodium methoxide-methanol. 1-Alkanols (mainly C₁₈C₂₈), alkanoic (mainly C₁₆C₃₀), α,ω-alkanedioic (mainly C₁₆C24), ω-hydroxyalkanoic (mainly C₁₆C₂₁), dihydroxyhexadecanoic (mainly 10,16-dihydroxy- and 16-dihydroxyhexadecanoic), monohydroxyepoxyalkanoic (9,10-epoxy-18-hydroxyoctadecanoic), trihydroxyalkanoic (9,10, 18-trihydroxyoctadecanoic), epoxyalkanedioic (9,10-epoxyoctadecane-1,18-dioic) and dihydroxyalkanedioic (9,10-dihydroxyoctadecane-1 18-dioic) acids were detected in all species. The suberins differed from one another mainly in the relative proportions of these monomer classes and in the homologue content of their 1-alkanol, alkanoic, α,ω-alkanedioic and ω-hydroxyalkanoic acid fractions. C₁₈ epoxy and vic-diol monomers were major components (32–59%) of half of the suberins examined (Quercus robur, Q. ilex, Q. suber, Fagus sylvatica, Castanea sativa, Betula pendula, Acer griseum, Fraxinus excelsior) where as ω-hydroxyalkanoic and α,ω-alkanedioic acids predominated in those that contained smaller quantities of such polar C₁₈ monomers (Acer pseudoplatanus, Ribes nigrum, Euonymus alatus, Populus tremula, Solanum tuberosum, Sambucus nigra, Laburnum anagyroides, Cupressus leylandii). All species, however, contained substantial amounts (14–55 %) of ω-hydroxyalkanoic acids, the most common homologues being 18:1 (9) and 22: 0. The dominant α,ω-alkanedioic acid homologues were 16: 0 and 18: 1 (9) whereas 22: 0, 24: 0 and 26: 0, and 20: 0, 22: 0 and 24: 0 were usually the principal homologues in the 1-alkanol and alkanoic acid fractions, respectively. The most diagnostic feature of the suberins examined was the presence of monomers greater than C₁₈ in chain length; most of the C₁₆ and C₁₈ monomers identified in the suberins also occur in plant cutins emphasizing the close chemical similarity between the two anatomical groups of lipid biopolymer.     

Some effects of varied calcium nutrition on the growth and composition of tomato plants

Summary Tomato plants were grown in nutrient solutions containing 0.05, 0.2, 1.0, 5.0, 15.0 and 30.0 meq Ca/l. Plants grown at the lowest level of calcium suffered from calcium deficiency and produced the least amount of dry matter. Dry matter yield was optimal from plants grown in the solution containing only 0.2 meq Ca/l and decreased at higher levels of substrate calcium. Despite large differences in the concentrations of the individual ions in the dried material, highly significant (P < 0.001) relationships were found between total cations and total anions and between insoluble calcium and oxalate.An explanation for the observed response to calcium is suggested based on the stimulation of the synthesis of oxalate by tissue calcium at the expense of carbohydrates. re]19760812