Salinity is an ever-present threat to crop yields, especially in countries where irrigation is an essential aid to agriculture. Although the tolerance of saline conditions by plants is variable, crop species are generally intolerant of one-third of the concentration of salts found in seawater. Attempts to improve the salt tolerance of crops through conventional breeding programmes have met with very limited success, due to the complexity of the trait: salt tolerance is complex genetically and physiologically. Tolerance often shows the characteristics of a multigenic trait, with quantitative trait loci (QTLs) associated with tolerance identified in barley, citrus, rice, and tomato and with ion transport under saline conditions in barley, citrus and rice. Physiologically salt tolerance is also complex, with halophytes and less tolerant plants showing a wide range of adaptations. Attempts to enhance tolerance have involved conventional breeding programmes, the use of in vitro selection, pooling physiological traits, interspecific hybridization, using halophytes as alternative crops, the use of marker-aided selection, and the use of transgenic plants. It is surprising that, in spite of the complexity of salt tolerance, there are commonly claims in the literature that the transfer of a single or a few genes can increase the tolerance of plants to saline conditions. Evaluation of such claims reveals that, of the 68 papers produced between 1993 and early 2003, only 19 report quantitative estimates of plant growth. Of these, four papers contain quantitative data on the response of transformants and wild-type of six species without and with salinity applied in an appropriate manner. About half of all the papers report data on experiments conducted under conditions where there is little or no transpiration: such experiments may provide insights into components of tolerance, but are not grounds for claims of enhanced tolerance at the whole plant level. Whether enhanced tolerance, where properly established, is due to the chance alteration of a factor that is limiting in a complex chain or an effect on signalling remains to be elucidated. After ten years of research using transgenic plants to alter salt tolerance, the value of this approach has yet to be established in the field.

/pdf/improving-crop-salt-tolerance-aqj3rjbjyc.pdf

Improving crop salt tolerance

Metabolic profiling analyses were performed to determine metabolite temporal dynamics associated with the induction of acquired thermotolerance in response to heat shock and acquired freezing tolerance in response to cold shock. Low-Mr polar metabolite analyses were performed using gas chromatography-mass spectrometry. Eighty-one identified metabolites and 416 unidentified mass spectral tags, characterized by retention time indices and specific mass fragments, were monitored. Cold shock influenced metabolism far more profoundly than heat shock. The steady-state pool sizes of 143 and 311 metabolites or mass spectral tags were altered in response to heat and cold shock, respectively. Comparison of heat- and cold-shock response patterns revealed that the majority of heat-shock responses were shared with cold-shock responses, a previously unknown relationship. Coordinate increases in the pool sizes of amino acids derived from pyruvate and oxaloacetate, polyamine precursors, and compatible solutes were observed during both heat and cold shock. In addition, many of the metabolites that showed increases in response to both heat and cold shock in this study were previously unlinked with temperature stress. This investigation provides new insight into the mechanisms of plant adaptation to thermal stress at the metabolite level, reveals relationships between heat- and cold-shock responses, and highlights the roles of known signaling molecules and protectants.

/pdf/exploring-the-temperature-stress-metabolome-of-arabidopsis-3beojkn5by.pdf

Exploring the temperature-stress metabolome of Arabidopsis.

Legumin and vicilin, storage proteins of legume seeds

Calcium (Ca) oxalate crystals occur in many plant species and in most organs and tissues. They generally form within cells although extracellular crystals have been reported. The crystal cells or idioblasts display ultrastructural modifications which are related to crystal precipitation. Crystal formation is usually associated with membranes, chambers, or inclusions found within the cell vacuole(s). Tubules, modified plastids and enlarged nuclei also have been reported in crystal idioblasts. The Ca oxalate crystals consist of either the monohydrate whewellite form, or the dihydrate weddellite form. A number of techniques exist for the identification of calcium oxalate. X-ray diffraction, Raman microprobe analysis and infrared spectroscopy are the most accurate. Many plant crystals assumed to be Ca oxalate have never been positively identified as such. In some instances, crystals have been classified as whewellite or weddellite solely on the basis of their shape. Certain evidence indicates that crystal shape may be independent of hydration form of Ca oxalate and that the vacuole crystal chamber membranes may act to mold crystal shape; however, the actual mechanism controlling shape is unknown.

Calcium oxalate crystals in plants

SUMMARY
Leaf senescence is a hiphly-controlled sequence of events comprising the final stage of development. Cells remain viable during the process and new gene expression is required. There is some similarity between senescence in plants and programmed cell death in animals. In this review, different classes of senescence-related genes are defined and progress towards isolating such genes is reported. A range of internal and external factors which appear to cause leaf senescence is considered and various models for the mechanism of senescence- initiation are described. The current understanding of senescence at the wrganelle and molecular levels is presented. Finally, same ideas are mooted as to why senescence occurs and why it should be studied further.

Gene expression during leaf senescence

When cowpea (Vigna unguiculata) cells maintained at 26°C are transferred to 42°C, rapid accumulation of γ-aminobutyrate (>10-fold) is induced. Several other amino acids (including β-alanine, alanine, and proline) are also accumulated, but less extensively than γ-aminobutyrate. Total free amino acid levels are increased approximately 1.5-fold after 24 hours at 42°C. Heat shock also leads to release of amino acids into the medium, indicating heat shock damage to the integrity of the plasmalemma. Some of the changes in metabolic rates associated with heat shock were estimated by monitoring the 15N labeling kinetics of free intracellular, extracellular and protein-bound amino acids of cultures supplied with 15NH4+, and analyzing the labeling data by computer simulation. Preliminary computer simulation models of nitrogen flux suggest that heat shock induces an increase in the γ-aminobutyrate synthesis rate from 12.5 nanomoles per hour per gram fresh weight in control cells maintained at 26°C, to as high as 800 nanomoles per hour per gram fresh weight within the first 2 hours of heat shock. This 64-fold increase in the γ-aminobutyrate synthesis rate greatly exceeds the expected (Q10) change of metabolic rate of 2.5- to 3-fold due to a 16°C increase in temperature. We suggest that this metabolic response may in part involve an activation of glutamate decarboxylase in vivo, perhaps mediated by a transient cytoplasmic acidification. Proline appears to be synthesized from glutamate and not from ornithine in cowpea cells. Proline became severalfold more heavily labeled than ornithine, citrulline and arginine in both control and heat-shocked cultures. Proline synthesis rate was increased 2.7-fold by heat shock. Alanine, β-alanine, valine, leucine, and isoleucine synthesis rates were increased 1.6-, 3.5-, 2.0-, 5.0-, and 6.0-fold, respectively, by heat shock. In contrast, the phenylalanine synthesis rate was decreased by 50% in response to heat shock. The differential effects of heat stress on metabolic rates lead to flux and pool size redistributions throughout the entire network of amino acid metabolism.

Effects of heat shock on amino Acid metabolism of cowpea cells.

Nitrate uptake and utilization is modulated by exogenous γ-aminobutyric acid in Arabidopsis thaliana seedlings

Using recently developed techniques for solubilization of RNA polymerase from soybean chromatin and isolation of plasma membrane fractions from plants we can show the presence of a transcriptional factor specifically released from the membranes by auxin, 2,4-dichlorophenoxyacetic acid The nonauxin, 3,5-dichlorophenoxyacetic acid, does not release the factor, but subsequent exposure of the membranes to auxin results in its release Factor activity could not be demonstrated in fractions devoid of plasma membranes The presence of a regulatory factor for RNA polymerase associated with plant plasma membrane and specifically released by auxin provides a mechanism whereby both rapid growth responses and delayed nuclear changes could be derived from a common auxin receptor site associated with plasma membrane

https://www.pnas.org/content/pnas/69/11/3146.full.pdf

Enhancement of RNA Polymerase Activity by a Factor Released by Auxin from Plasma Membrane

BAGLEY, BILL W., JOE H. CHERRY, MARY L. ROLLINS, and AARON M1. ALTSCHUL. (Southern Regional Lab., U.S.D.A., New Orleans, La.) A study of protein bodies during germination of peanut (Arachis hypogaea) seed. Amer. Jour. Bot. 50(6): 523-532. Illus. 1963.-Upon germination of peanut seed (Arachls utypogaea) there is an ordered series of events leading to the degradation of storage protein in cotyledonary cells. In resting seed, the protein is stored in large bodies (protein bodies) about 5-10, in diameter. As the seeds germinate, the protein bodies swell and develop cavities within. Later these swollen bodies break up into many fragments which are digested and disappear. The major changes in proteins as revealed by microscopy and by protein analysis occur between 4 and 9 days of germination. By 15 days, the parenchyma cells are empty of protein bodies or fragments, but they contain many small starch grains. In a given cell population, there is a wide range of protein-body degradation, the degree of degradation being related to the distance from the nearest vascular bundle. In resting seed, there is a honeycomb-like structure between and connected to the subcellular particles. After 2 days of germination this structure is no longer visibly

A study of protein bodies during germination of peanut (arachis hypogaea) seed

Biodegradable polymers offer an environmentally friendly alternative to petroleum-based polymers. Applications of protein based polymers include the use of these compounds in the fields of medicine, molecular-based energy conversions, the manufacture of unique fibers, coatings and biodegradable plastics. We report here expression of a synthetic gene G-(VPGVG) 119-VPGV coding for the EG-120mer (elastomer) in E. coli. Polymer expression is observed in uninduced cells grown in terrific broth in polyacrylamide gels negatively stained with CuCl2. Electron micrographs reveal formation of inclusion bodies in uninduced cells occupying upto 80–90% of the cell volume under optimal growth conditions. To the best of our knowledge this report represents the first demonstration of hyper expression of a synthetic gene (with no natural analog) in E. coli.

Joe H. Cherry

Papers

Effects of heat shock on amino Acid metabolism of cowpea cells.

Nitrate uptake and utilization is modulated by exogenous γ-aminobutyric acid in Arabidopsis thaliana seedlings

Enhancement of RNA Polymerase Activity by a Factor Released by Auxin from Plasma Membrane

A study of protein bodies during germination of peanut (arachis hypogaea) seed

Hyper expression of an environmentally friendly synthetic polymer gene