Senescence Of Pea Research Articles

Gibberellin Is Involved in the Regulation of Cell Death‐mediated Apical Senescence in G2 Pea

Abstract Senescence is the process of programmed degradation. The G2 line of pea exhibits apical senescence‐delaying phenotype under short‐day (SD) conditions, but the mechanism regulating the apical senescence is still largely unknown. Gibberellin (GA) was proved to be able to delay this apical senescence phenotype in G2 pea grown under long‐day (LD) conditions. Here we show that the initiation of cell death signals in the terminal floral meristem was involved in the regulation of apical senescence in pea plants. SD signals prevented the formation of the cell death region in the apical mersitem. Moreover, GA3 treatment could effectively inhibit the occurrence of cell death‐mediated apical senescence in LD‐grown apical buds. Therefore, our data suggest that the prevention of apical senescence in SD‐grown G2 pea through GA3 treatment may be largely responsible for the regulation of occurrence of the DNA fragmentation in apical meristem.

Antioxidative enzymes from chloroplasts, mitochondria, and peroxisomes during leaf senescence of nodulated pea plants.

In this work the influence of the nodulation of pea (Pisum sativum L.) plants on the oxidative metabolism of different leaf organelles from young and senescent plants was studied. Chloroplasts, mitochondria, and peroxisomes were purified from leaves of nitrate-fed and Rhizobium leguminosarum-nodulated pea plants at two developmental stages (young and senescent plants). In these cell organelles, the activity of the ascorbate-glutathione cycle enzymes ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), and the ascorbate and glutathione contents were determined. In addition, the total superoxide dismutase (SOD) activity, the pattern of mitochondrial and peroxisomal NADPH-generating dehydrogenases, some of the peroxisomal photorespiratory enzymes, the glyoxylate cycle and oxidative metabolism enzymes were also analysed in these organelles. Results obtained on the metabolism of cell organelles indicate that nodulation with Rhizobium accelerates senescence in pea leaves. A considerable decrease of the ascorbate content of chloroplasts, mitochondria, and peroxisomes was found, and in these conditions a metabolic conversion of leaf peroxisomes into glyoxysomes, characteristic of leaf senescence, took place.

Leaf Senescence Induced by Mild Water Deficit Follows the Same Sequence of Macroscopic, Biochemical, and Molecular Events as Monocarpic Senescence in Pea

We have compared the time course of leaf senescence in pea (Pisum sativum L. cv Messire) plants subjected to a mild water deficit to that of monocarpic senescence in leaves of three different ages in well-watered plants and to that of plants in which leaf senescence was delayed by flower excision. The mild water deficit (with photosynthesis rate maintained at appreciable levels) sped up senescence by 15 d (200 degrees Cd), whereas flower excision delayed it by 17 d (270 degrees Cd) compared with leaves of the same age in well-watered plants. The range of life spans in leaves of different ages in control plants was 25 d (340 degrees Cd). In all cases, the first detected event was an increase in the mRNA encoding a cysteine-proteinase homologous to Arabidopsis SAG2. This happened while the photosynthesis rate and the chlorophyll and protein contents were still high. The 2-fold variability in life span of the studied leaves was closely linked to the duration from leaf unfolding to the beginning of accumulation of this mRNA. In contrast, the duration of the subsequent phases was essentially conserved in all studied cases, except in plants with excised flowers, where the degradation processes were slower. These results suggest that senescence in water-deficient plants was triggered by an early signal occurring while leaf photosynthesis was still active, followed by a program similar to that of monocarpic senescence. They also suggest that reproductive development plays a crucial role in the triggering of senescence.

Leaf Senescence Induced by Mild Water Deficit Follows the Same Sequence of Macroscopic, Biochemical, and Molecular Events as Monocarpic Senescence in Pea

Leaf Senescence Induced by Mild Water Deficit Follows the Same Sequence of Macroscopic, Biochemical, and Molecular Events as Monocarpic Senescence in Pea

Active oxygen metabolism in the senescence of pea leaves: ascorbate and glutathione contents in different cell compartments.

Active oxygen metabolism in the senescence of pea leaves: ascorbate and glutathione contents in different cell compartments.

N4-Hexanoylspermidine, a New Polyamine-Related Compound That Accumulates during Ovary and Petal Senescence in Pea.

A previously unknown polyamine conjugate that accumulates in senescing ovaries of pea (Pisum sativum L.) was shown by mass spectrometry, nuclear magnetic resonance, and chemical synthesis to be N4-hexanoylspermidine (hexanoyl-spd) This structure was indicated by analysis of the dansylated polyamine using fast atom bombardment mass spectrometry, following purification by high-performance liquid chromatography. Furthermore, acid hydrolysis of the compound yielded spermidine and hexanoic acid. 1H-nuclear magnetic resonance suggested that spermidine was substituted at N4 in the conjugate. Hexanoyl-spd was synthesized, and its didansyl derivative was shown to have an identical mass spectrum and high-performance liquid chromatography retention time as the derivatized natural compound. Further confirmation of its structure was obtained by comparison of the synthetic and natural polyamines as trifluoroacetyl derivatives using gas chromatography-mass spectrometry. This new polyamine conjugate is present in pea ovaries at low levels at anthesis and its concentration remains low in developing seeded fruit or in parthenocarpic fruit that have been induced by application of growth regulators to emasculated flowers or by topping the plant. Conjugate levels are also low in parthenocarpic fruit induced naturally in the slender (la crys) mutant. However, levels of hexanoyl-spd increase progressively in senescing petals and ovaries, beginning at anthesis or 2 d later, respectively.

Effect of Photoperiod on Polyamine Metabolism in Apical Buds of G2 Peas in Relation to the Induction of Apical Senescence

Polyamine content and arginine decarboxylase activity of apical buds were measured to determine whether polyamines are required to prevent apical senescence in pea. Polyamines were assayed as dansyl derivatives which were separated by reverse phase high performance liquid chromatography and detected by fluorescence spectrophotometry. High polyamine concentrations were found in the vigorous apices of plants grown under a short day photoperiod during which senescence is delayed. As the apex senesced in long days, the amounts of polyamines per organ declined in parallel with decreases in the size of the apical bud. However, a decrease in polyamine concentration, due mainly to a change in spermidine, occurred at the time of marked reduction in bud size and growth rate, but not before the onset of the early symptoms of senescence. No correlation was found with arginine decarboxylase. The results suggest polyamines may be required to support bud growth, but the photoperiodic mechanism which governs apical senescence of G2 peas does not exert control through polyamine metabolism.

Changes in leucyl-tRNA species of pea leaves during senescence and after zeatin treatment.

Abstract Four major leucyl-tRNA peaks were observed from pea leaves as compared to six peaks from soybean cotyledons by fractionation on Freon columns (RPC-2). Correlated with yellowing of pea leaves the late-eluting peaks (tRNA 5 & 6 Leu ) decreased while the other 2 peaks (tRNA 1 & 2 Leu ) remained about the same. Foliar applications of 6-(4-hydroxy-3-methyl- rans -2-butenylamino)purine to intact pea plants delayed yellowing of the leaves and maintained the level of tRNA 5 & 6 Leu . Pea cotyledons contain mainly leucyl-tRNA 1 & 2 while pea leaves and soybean cotyledons contain tRNA 1,2,5 & 6 Leu and tRNA 1−6 Leu , respectively. Transfer RNA isolated from chloroplast preparation of peas contained a higher ratio of tRNA 5 Leu to tRNA 1 & 2 Leu than the whole leaf. The loss in specific tRNAs during senescence of pea and soybean leaves may be related to a general loss of tRNA from the chloroplast.

Changes in leucyl-tRNA species of pea leaves during senescence and after zeatin treatment

Four major leucyl-tRNA peaks were observed from pea leaves as compared to six peaks from soybean cotyledons by fractionation on Freon columns (RPC-2). Correlated with yellowing of pea leaves the late-eluting peaks (tRNA 5 & 6 Leu) decreased while the other 2 peaks (tRNA 1 & 2 Leu) remained about the same. Foliar applications of 6-(4-hydroxy-3-methyl- rans-2-butenylamino)purine to intact pea plants delayed yellowing of the leaves and maintained the level of tRNA 5 & 6 Leu. Pea cotyledons contain mainly leucyl-tRNA 1 & 2 while pea leaves and soybean cotyledons contain tRNA 1,2,5 & 6 Leu and tRNA 1−6 Leu, respectively. Transfer RNA isolated from chloroplast preparation of peas contained a higher ratio of tRNA 5 Leu to tRNA 1 & 2 Leu than the whole leaf. The loss in specific tRNAs during senescence of pea and soybean leaves may be related to a general loss of tRNA from the chloroplast.