Mediation of high-temperature injury by roots and shoots during reproductive growth of wheat

Abstract Previous studies suggest that high temperature stress on wheat (Triticum aestivum L.) involves root processes and acceleration of monocarpic senescence. Physiological changes in wheat roots and shoots were investigated to elucidate their relationship to injury from elevated temperatures after anthesis. Plants were grown under uniform conditions until 10 d after anthesis, when shoot/root regimes of 25°C/25°C, 25°C/35°C, 35°C/25°C and 35°C/35°C were imposed. Growth and senescence of shoots and grain were influenced more by root temperatures than by shoot temperatures. High root temperatures increased activities of protease and RNasc enzymes, and loss of chlorophyll, protein and RNA from shoots, whereas low root temperatures had opposite effects. High root temperatures appeared to induce shoot senescence directly. High shoot temperatures probably disrupted root processes, including export of cytokinins, and induced high leaf protease activity, senescence and cessation of grain development. The authors concluded that responses of wheat to high temperatures, whether of roots or shoots, are manifested as acceleration of senescence and may be mediated by roots during grain development.     

Changes in protein and protease activity during the growth and senescence of Paul's Scarlet rose

A study was performed to determine the relationship between the protein content and protease activity in suspension cultures of rose (Rosa cv Paul's Scarlet) grown over a 30 day period. Protein levels and protease activity were calculated on a per culture and per cell basis. Older nongrowing 14 day-old cultures possessed the largest total protease activity, but the highest concentration of protease activity per cell was in young 4 day-old rapidly dividing cells.     

Changes in the metabolism of nucleic acids during the growth and senescence of tobacco callus

Changes in DNA and RNA metabolism, DNA composition and RNA species in callus of tobacco ( Nicotiana rustica L. cv. Gansu Yellow Flower) were investigated during the growth and senescence. DNA and RNA contents remained almost unchanged during the callus growth period, but started to decrease synchronously at the time that callus senescence was initiated. Synthesis of DNA and RNA, as measured by incorporation of [³H]-labelled precursor, increased during the growth period and did not decrease until late in senescence. The activities of DNase and RNase (pH 4.5) increased during the early senescence period in accordance with the decrease in the levels of DNA and RNA, but appeared to decrease during late senescence. These results suggest that the decrease in the levels of DNA and RNA in senescing tobacco callus may stem from the increase in the hydrolytic activities of DNase and RNase (pH 4.5) in the early stage of senescence, and that the slowdown of synthesis in the late senescence period may also be a cause. DNA and RNA electrophoresis showed that a low-molecular-weight satellite DNA band disappeared after the onset of senescence and that the nuclear main band DNA gradually decreased, whereas the high-molecular-weight satellite DNA seemed to undergo no significant changes during the senescence period tested. Of the RNA species, 4–5S RNA was far more susceptible to damage during senescence than 25S and 18S rRNA. This suggests different susceptibilities of different DNA and RNA components to damage during the senescence of tobacco callus or alternatively a highly sequenced degradation of DNA and RNA molecules.     

Role of ethylene in senescence of watercress leaves

Detached watercress leaves showed a rapid senescence rate as compared with other herbs. It was therefore of interest to investigate the role of ethylene in the rapid senescence of watercress leaves, and So estimate the efficacy of various inhibitors of elhylene synthesis (aminoethoxyvinylglycine, AVG) and action (CO₂, Ag⁺) in retarding senescence processes. The progress of senescence in watercress bunches (leaves attached to cut stems) and in detached leaves was estimated by measuring the rate of chlorophyll (Chl) loss, proteolysis and lipid oxidation. Evidence is presented showing that application of 11% CO₂ to watercress bunches in a flow-through system had a long-lasting effect on senescence, exhibited by highly efficient retardation of all the senescence processes tested. On the other hand, application of AVG (O.1 m M ) or Ag-(30 μ M ) to detached leaves affected Chl loss much more than prciteolysis. These results suggest that the senescence-retarding activity of CO₂ cannot be attributed solely to its action as an anli-ethylene agent and that not all senescence-associated processes are regulated by ethylene.     

Changes in ribulose-1,5-bisphosphate carboxylase and its translatable small subunit mRNA levels during senescence of mustard (Sinapis alba) cotyledons

During the senescence of detached first leaves of oat ( Avena sativa L. cv. Victory) seedlings (grown in continuous light) the protein is hydrolyzed and the proteases increase, but the expected simple relation between these two factors is not always realized. The present experiments examine the timing, the influence of light and darkness and the action of the protein synthesis inhibitors cycloheximide (CHI) and cordycepin. Transfer from dark to light delays the breakdown of both chlorophyll (Chl) and protein, but some residual proteolysis is ascribed to the enzyme initially present. Transfer to CHI resembles transfer to light, while the action of cordyceptin is similar but much weaker. Repeated determinations of the acid protease, which is the most active one and the first to appear, show that this enzyme is formed in the light about as rapidly as in the dark, though with different kinetics. In spite of this there is little proteolysis in light in the first 5 days. One possible explanation of that could be that protein is rapidly resynthesized in light, but treatment with [¹⁴C]-leucine shows that such resynthesis is no faster in light than in darkness. It is therefore concluded that the protease initially does not have access to its substrates and, as a corollary, that the senescence process must be controlled by the gradual impairment of the vacuolar membrane, allowing protease to enter the cytosol and attack the proteins there and in the organelles. This concept is supported by many observations on the timing and on the known changes in membrane permeability during senescence.     

Control by phytochrome of the synthesis of protein related to senescence in chloroplasts of barley (Hordeum vulgare)

Protein synthesis has been measured in chloroplast isolated from detached leaves of barley ( Hordeum vulgare L. cv. Hassan). The effects of hormone and light treatments of the leaves on chloroplast protein synthesis have been compared with effects on other senescence symptoms. Interruption of the dark with red light retards senescence and increases chloroplast protein synthesis. The effect of red light was reversed by far-red light. Red light did not act additively with kinetin, and it competed with ethylene and abscisic acid, accelerators of senescence, which decreased protein synthesis. In contrast to the interruption of the dark with red light, continuous light decreased chloroplast protein synthesis. It may be concluded effects on chloroplast protein synthesis. The retardation of senescence by continuous light is not necessarily related to P_u Instead, energy provided by photosynthesis may be an important factor.     

Modification of nitrogen remobilization, grain fill and leaf senescence in maize (Zea mays) by transposon insertional mutagenesis in a protease gene

A maize (Zea mays) senescence-associated legumain gene, See2beta, was characterized at the physiological and molecular levels to determine its role in senescence and resource allocation. A reverse-genetics screen of a maize Mutator (Mu) population identified a Mu insertion in See2beta. Maize plants homozygous for the insertion were produced. These See2 mutant and sibling wild-type plants were grown under high or low quantities of nitrogen (N). The early development of both genotypes was similar; however, tassel tip and collar emergence occurred earlier in the mutant. Senescence of the mutant leaves followed a similar pattern to that of wild-type leaves, but at later sampling points mutant plants contained more chlorophyll than wild-type plants and showed a small extension in photosynthetic activity. Total plant weight was higher in the wild-type than in the mutant, and there was a genotype x N interaction. Mutant plants under low N maintained cob weight, in contrast to wild-type plants under the same treatment. It is concluded, on the basis of transposon mutagenesis, that See2beta has an important role in N-use and resource allocation under N-limited conditions, and a minor but significant function in the later stages of senescence.     

Glutamine, arginine and the amino acid transporter Pt-CAT11 play important roles during senescence in poplar

Background and Aims

Nitrogen (N) availability in the forest soil is extremely low and N economy has a special importance in woody plants that are able to cope with seasonal periods of growth and development over many years. Here we report on the analysis of amino acid pools and expression of key genes in the perennial species Populus trichocarpa during autumn senescence.

Methods

Amino acid pools were measured throughout senescence. Expression analysis of arginine synthesis genes and cationic amino acid transporter (CAT) genes during senescence was performed. Heterologous expression in yeast mutants was performed to study Pt-CAT11 function in detail.

Key Results

Analysis of amino acid pools showed an increase of glutamine in leaves and an accumulation of arginine in stems during senescence. Expression of arginine biosynthesis genes suggests that arginine was preferentially synthesized from glutamine in perennial tissues. Pt-CAT11 expression increased in senescing leaves and functional characterization demonstrated that Pt-CAT11 transports glutamine.

Conclusions

The present study established a relationship between glutamine synthesized in leaves and arginine synthesized in stems during senescence, arginine being accumulated as an N storage compound in perennial tissues such as stems. In this context, Pt-CAT11 may have a key role in N remobilization during senescence in poplar, by facilitating glutamine loading into phloem vessels.     

Marcescence and senescence in a submediterranean oak (Quercus subpyrenaica E.H. del Villar): photosynthetic characteristics and nutrient composition

We have studied some characteristics of marcescent leaves (withered retained leaves) and senescent leaves in Quercus subpyrenaica, a tree species that plays a major role in the climatic transition forests between temperate and mediterranean environments in north-eastern Spain. Leaves were taken from the upper and lower halves of the tree crown, both in the south- and north-exposed parts of the tree. Leaves receiving low photosynthetic photon flux density (PPFD) undergo autumnal senescence, which is associated with decreases in photosynthetic pigments and decreases in the chlorophyll a to chlorophyll b ratio. Leaves receiving higher PPFD underwent senescence at a later date. Leaves situated in the upper, south-exposed part of the tree, which receive the highest PPFD, showed no signs of senescence and remained photosynthetically active for a longer period of time, marcescence occurring suddenly at the end of the season. Marcescence is unlikely to cause an improvement in nutrient recycling, since the removal of nutrients proceeded similarly in marcescent and senescent leaves. Marcescence may increase the time-span of the assimilation capacity for a significant period of time during September and October, when high light intensities and mild temperatures occur. The phenomena triggering marcescence may be related to low temperatures.     

Changes in polar lipids during ripening and senescence of cherry tomato (Lycopersicon esculentum): Relation to climacteric and ethylene increases

The entire senescence period, including ripening, is characterized in cherry tomato ( Lycopersicon esculentum Mill. var. cerasiforme Alef.) by two successive changes in overall polar lipid content. The rise in respiration of the fruit in the climacteric phase is accompanied by a large increase in lipids, notably phospholipids, such as phosphatidylcholine and phosphatidic acid. This suggests the coexistence of anabolic and catabolic processes in this first period. At the degreening stage of the fruit, decreased levels of monogalactosyldiacylglycerol and the disappearance of trigalactosyldiacylglycerol may indicate some degradation of the chloroplast compartment. Following a respiratory upsurge, a sudden breakdown of total lipids occurs concomitantly with maximal ethylene production. This breakdown is essentially caused by a parallel decrease in the amounts of phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid and also phosphatidylglycerol. However, in the cherry tomato, lipid peroxidation, evaluated by alteration of fatty acid distribution, seems insufficient to account for the ethylene peak.     

越冬期大鸨粪便氨基酸组成与消化能力分析

为评估陕西黄河湿地大鸨越冬期营养状况,于2012年1～2月收集大鸨新鲜粪便并对粪便中的蛋白质、灰分和氨基酸含量等做了测定.结果显示,粪便中粗蛋白、粗灰分含量分别为40.25％、19.81％.谷氨酸含量最高,为0.55％,组氨酸含量最低,为0.10％.粪便中豆苗、豆瓣、麦苗、麦粒、玉米、杂物的干物质比重分别为0.47％、4.05％、84.80％、6.75％、2.86％、1.07％.结果表明,麦苗是粪便干物质的主要成分,但相对大鸨越冬食性而言,麦苗粗蛋白含量偏低.粪便中谷氨酸、甘氨酸、天门冬氨酸和丙氨酸含量较大,这对优化大鸨对食物的选择方面起一定作用.     

Effect of water deficit on photosynthetic and other physiological responses in grapevine (Vitis vinifera L. cv. Riesling) plants

The grapevine (Vitis vinifera L. cv. Riesling) plants subjected to water deficit were studied for changes in relative water content (RWC), leaf dry mass, contents of chlorophyll (Chl), total leaf proteins, free amino acids, and proline, and activities of ribulose-1,5-bisphosphate carboxylase (RuBPC), nitrate reductase (NR), and protease. In water-stressed plants RWC, leaf dry matter, Chl content, net photosynthetic rate (P _N), and RuBPC and NR activities were significantly decreased. The total leaf protein content also declined with increase in the accumulation of free amino acids. Concurrently, the protease activity in the tissues was also increased. A significant two-fold increase in proline content was recorded.     

Differences in digestion and absorption of dietary protein in Atlantic salmon (Salmo salar) with genetically different trypsin isozymes

Digestion and absorption of dietary protein were studied through facilitation of amino acid in the plasma and white muscle after a single feeding. The comparison was made between Atlantic salmon with and without trypsin isozyme TRP-2*92. Higher absorption of dietary protein was associated with the presence of the isozyme, as the post-prandial total levels of free amino acids (FAA) in both plasma and white muscle were significantly higher in salmon with the isozyme than those in salmon without it. Higher digestion rate of the dietary protein in salmon carrying the isozyme was indicated by faster elevation of essential FAA in the plasma and of overall FAA in their white muscle. Other indications which suggest differences in nitrogen metabolism between salmon with and without the isozyme were the observations of significant differences in (a) the levels of lysine, hydroxyproline, alanine, aspartic acid, β-alanine, threonine, valine and a nitrogen-containing compound taurine in plasma, and (b) the levels of alanine, glutamic acid, glycine and anserine in white muscle.
Trypsin activity in the pyloric caeca showed less response to feeding than that in the intestine, but it may have consequence for growth as its activity was significantly higher in growing fish than in non-growing fish.     

Accelerated ethylene production as related to changes in lipids and electrolyte leakage during senescence of petals of cut carnations (Dianthus caryophyllus)

Conditions inhibiting the action of (supply of silver thiosulfate) or the synthesis of (supply of α-aminooxyacetic acid) ethylene, prolonged the vase-life of carnation ( Dianthus caryophyllus L. cv. Ember) flowers. On the other hand, conditions which provoked an advance in the time of appearance of the ethylene rise (previous exposure to exogenous ethylene), accelerated senescence. This action on the morphological changes was accompanied by an effect on the efflux of electrolytes, which was advanced or delayed depending on the type of treatment, in comparison with the control.
The various factors acting on ethylene production also affected membrane lipids. Those which suppressed or delayed the ethylene rise, slowed down the degradation of the total and free fatty acids and the increase in the level of saturation of the chains. The opposite was observed when the ethylene peak occurred early. There was no correlation between the time of appearance of the burst of ethylene and the time of onset of lipid breakdown.
A 48 h water stress provoked neither an advance in the time of appearance of the ethylene peak nor an acceleration in lipid breakdown on return to normal conditions.     

Potato cold hardiness development and abscisic acid. II. De novo synthesis of proteins is required for the increase in free abscisic acid during potato (Solanum commersonii) cold acclimation

During cold acclimation of potato plantlets ( Solanum commersonii Dun, PI 458317), there are two transitory increases in free ABA content corresponding to a three-fold increase on the 2nd day and a five-fold increase on the 6th day (Ryu and Li 1993). During this period, plantlets increased in cold hardiness from −5°C (killing temperature, control grown at 22/18°C, day/night) to −10°C by the 7th day of exposure to 4/2°C (day/night). This increase in free ABA was not found when cycloheximide (CHI), an inhibitor of cytoplasmic protein synthesis, was added to the culture medium 6 h before exposure to low temperatures. Plantlets treated with CHI did not acclimate to cold, maintaining a hardiness level (−5°C) similar to that of the 22/18°C-grown plantlets. When the CHI-treated plantlets were exposed to low temperatures for 3 days, transferred to CHI-free culture medium and grown at low temperatures, the plantlets showed a transitory increase in free ABA 2 days later. This increase was followed by the development of cold hardiness (−8°C). Application of CHI to the culture medium after 3 days of cold acclimation, when the first ABA peak and a partial development of cold hardiness (−8°C) had occurred, blocked the second transitory increase in free ABA and resulted in no further development of cold hardiness. These results suggest that de novo synthesis of proteins is required for these transitory increases in free ABA during cold acclimation of potato plantlets.     

Changes in the levels of abscisic acid and its glucose ester conjugate during maturation of hybrid larch (Larix × leptoeuropaea) somatic embryos, in relation to germination and plantlet recovery

Changes in abscisic acid content during maturation of hybrid larch somatic embryos ( Larix × leptoeuropaea ), were followed using an enzyme immunoassay (ELISA). In the presence of 60 μ M cis-trans (±)-ABA in the maturation medium, the cis-trans (±)-ABA level of the somatic embryos in planta increased during the maturation phase to reach a maximum value at week 5. Concomitantly, an extension of the period of maturation from 3 to 4 and 5 weeks resulted in a significant decrease in both germination and plantlet frequencies. As a consequence, we assume that it was the level of ABA in planta that was responsible for the inhibition. ABA acted in both a stimulatory and an inhibitory manner. If ABA promoted the obtention of high quality somatic embryos in large numbers, it also had a deleterious effect on the subsequent development, i.e. germination and plantlet recovery. The results stressed the importance of both the procedure and duration of maturation.