Chloroplast Breakdown Research Articles

Altered gene expression in three plant species in response to treatment with Nep1, a fungal protein that causes necrosis.

Nep1 is an extracellular fungal protein that causes necrosis when applied to many dicotyledonous plants, including invasive weed species. Using transmission electron microscopy, it was determined that application of Nep1 (1.0 micro g mL(-)(1), 0.1% [v/v] Silwet-L77) to Arabidopsis and two invasive weed species, spotted knapweed (Centaurea maculosa) and dandelion (Taraxacum officinale), caused a reduction in the thickness of the cuticle and a breakdown of chloroplasts 1 to 4 h after treatment. Membrane breakdown was most severe in cells closest to the surface of application. Differential display was used to isolate cDNA clones from the three species showing differential expression in response to Nep1 treatment. Differential gene expression was observed for a putative serpin (CmSER-1) and a calmodulin-like (CmCAL-1) protein from spotted knapweed, and a putative protein phosphatase 2C (ToPP2C-1) and cytochrome P-450 (ToCYP-1) protein from dandelion. In addition, differential expression was observed for genes coding for a putative protein kinase (AtPK-1), a homolog (AtWI-12) of wound-induced WI12, a homolog (AtLEA-1) of late embryogenesis abundant LEA-5, a WRKY-18 DNA-binding protein (AtWRKY-18), and a phospholipase D (AtPLD-1) from Arabidopsis. Genes showing elevated mRNA levels in Nep1-treated (5 micro g mL(-)(1), 0.1% [v/v] Silwet-L77) leaves 15 min after Nep1 treatment included CmSER-1 and CmCAL-1 for spotted knapweed, ToCYP-1 and CmCAL-1 for dandelion, and AtPK-1, AtWRKY-18, AtWI-12, and AtLEA-1 for Arabidopsis. Levels of mRNA for AtPLD-1 (Arabidopsis) and ToPP2C-1 (dandelion) decreased rapidly in Silwet-L77-treated plants between 15 min and 4 h of treatment, but were maintained or decreased more slowly over time in Nep1-treated (5 micro g mL(-)(1), 0.1% [v/v] Silwet-L77) leaves. In general, increases in mRNA band intensities were in the range of two to five times, with only ToCYP-1 in dandelion exceeding an increase of 10 times. The identified genes have been shown to be involved or are related to gene families that are involved in plant stress responses, including wounding, drought, senescence, and disease resistance.

S nutrition affects the pools of S available to developing grains of wheat

Developing grains of rain-fed wheat must obtain S from reserves that the plant accumulated during vegetative growth. The effect of S nutrition on the sources of S that were transported from vegetative tissues during grain development was examined. Wheat was grown in solution culture with 2 mM N and either 200μM S (high-S) or 50 μM S (low-S). All nutrients were withdrawn either at booting, ear emergence, anthesis, or 8 d post anthesis. Plants were harvested at 13 or 25 d post anthesis. At 13 d post anthesis, high-S plants contained sulphate in roots and leaves, GSH (glutathione) in leaves, and S in leaf proteins. Between harvests, sulphate was lost from roots and GSH was lost from leaves. Sulphate and GSH were not detected in roots or leaves of Iow-S plants at 13 d post anthesis, and between harvests, S in leaf-proteins decreased. During reproductive growth, redistribution of sulphate from roots was likely to be in response to S demand, redistribution of GSH was likely to result from the breakdown of chloroplasts, and in low-S plants, hydrolysis of leaf proteins in response to N demand was the most important source of S for grain development.

Rethinking Apple Scald: New Hypothesis on the Causal Reason for Development of Scald in Apples

Superficial scald is still one of the most important postharvest physiological disorders in apples. Commercial control of this disorder has been accomplished by selecting resistant cultivars, treating fruit with DPA and ethoxyquin, using oil-soaked fruit wraps and storing the fruit under low O2. However, the causal reason for scald development is still a mystery. Research has indicated that the scald-promoting factor or inducing compound may be formed or accumulated in apple cuticle then rediffused back into the hypodermis, thereby causing damage. Hydroperoxides, auto-oxidative product from α-farnesene, have been thought to be the toxic compounds, inducing scald; however, it is not explained how the hydroperoxides move from the cuticle to the hypodermis. The identification and dynamic changes of 6-methyl-5-heptene-2-one as a natural volatile in apple fruit during ripening were made, which accumulated in higher quantitaty in cuticular wax than in headspace. The close relationship between the chloroplast breakdown and amount of α-farnesene changes, the induction of scald-like symptom on the surface of apple fruit by 6-methyl-5-heptene-2-one and the sensitivity of fruit to this ketone damage were investigated. Our results suggest that the accumulation of 6-methyl-5-heptene-2-one in the cuticular wax of apple fruit might be the causal reason for scald development in apples.

Physiological and Structural Changes in Tobacco Leaves Treated with Cryptogein, a Proteinaceous Elicitor fromPhytophthora cryptogea

Cryptogein was applied on the petiole section of excised tobacco leaves. It elicited necroses that can be correlated with histological alterations, such as rapid chloroplast breakdown and a collapse of cells leading to disorganization of the parenchyma tissue. In addition, it induced ethylene production and accumulation of capsidiol. In order to detect an early response, we analyzed the kinetics of chlorophyll fluorescence induction (...)

セントポーリアのリーフスポットの発生と葉組織からの電解質漏出

This study was carried out to clarify the relation between occurrence of leaf injury, so-called “leaf spot”, and amount of electrolytes leaked from leaf tissue of Saintpaulia ionantha Wendl cv. Beth Elen. Leaves were dipped in water at a temperature lower than leaf (rapid fall of leaf temperature) for the development of leaf spot, and the leakage of electrolytes from leaf discs to water at different temperatures was determined.1. Leaves were dipped in water at 40, 45 and 50°C for 60sec, followed by a dipping in water at 25°C for 60sec. The degree of leaf injury increased with the increasing differences between water and leaf temperatures.2. The degree of leaf injury due to rapid fall of leaf temperature was influenced by temperature conditions during plant growth and pre-treatment.3. Electrolyte leakage from leaf discs was minimum by soaking in 20-25°C water and increased above and below these temperatures. In this case, the amount of leakage in darkness was larger than that in exposure to light.4. Exposure of leaf discs to a rapid fall of leaf temperature considerably increased the amounts of K+ and Mg++ leakage.5. Leaf discs were divided transversely into two portions, adaxial and abaxial, and they were exposed to rapid fall of leaf temperature. The adaxial half containing palisade tissue had a greater amount of K+ leakage than the abaxial half.6. Shrinkage of palisade cells was microscopically observed in injured leaf portions one day after rapid fall of leaf temperature, and then breakdown of chloroplasts was observed.7. Electrolyte leakage from old leaves was greater than that from young leaves.8. Exposure of leaves to high light intensity before rapid fall of leaf temperature increased leaf injury and electrolyte leakage.

Preferential digestion of chloroplast nuclei (nucleoids) during senescence of the coleoptile ofOryza sativa

The coleoptile ofOryza sativa develops, grows and ages within 4 days that follow imbibition. It is, thus, a very useful system for experimental analysis of the life cycle of organelles, for example, the development, growth and aging of plastids in higher plants. We examined the behavior and levels of DNA and chlorophyll in the plastid by epifluorescence microscopy after staining with 4′-6-diamidino-2-phenylindole (DAPI), and by fluorimetry with a video-intensified-photon counting system (VIMPCS). The whitish yellow coleoptile appeared soon after imbibition and, between the first 24 and 60 h that followed imbibition, it grew markedly in a longitudinal direction, with concomitant elongation of the cells, and an increase in the volume of plastids and in the amount of DNA in the plastids. The chlorophyll content per plastid began to increase when the coleoptile turned green, 48 h after imbibition, and reached a plateau value when the coleoptile was 3.5 mm in length, 72 h after imbibition. More than 12 h later, the chlorophyll disappeared just before the breakdown of chloroplasts was initiated. Proplastids in young coleoptiles, contained a plastid nucleus which was located in the central area of the plastids and each nucleus consisted of approximately 6 copies of plastid DNA (ptDNA). The number of copies of ptDNA per plastid increased gradually, with a concomitant increase in the volume of the plastids after imbibition, and reached approximately 130 times the value in the young proplastids, 60 h after imbibition, when the plastid developed into a chloroplast. However, each plastid nucleus did not scatter throughout the entire interior region of each chloroplast. The disappearance of each plastid nucleus occurred more than 12 h before the degeneration of the chloroplasts. The number of plastids per cell increased from 10 to 15 in young coleoptiles within 12 h after imbibition. Yet the number remained constant throughout subsequent growth and aging of the coleoptile. Thus the preferential reduction in the amount of chloroplast DNA was not due to the division of the plastid but could, perhaps, be associated directly with the aging of the cells of the coleoptile which precedes senescence of the coleoptiles.

Ultrastructural changes occurring in wheat leaves following triadimefon treatment

AbstractChanges occurred in leaf cells following treatment of glasshouse grown wheat seedlings with triadimefon by foliar application, root drench and vapour action. The effects were limited to cells adjacent to stomata, and included damage to the tonoplast and plasmalemma followed by breakdown of chloroplasts. These effects probably resulted from changes in membrane sterols induced by triadimefon treatment. They were severe local reactions, distinct from modification of gibberellin biosynthesis.

The biochemistry and regulation of senescence in chloroplasts

The biochemical events in chloroplast breakdown are described. Special attention is given to the regulation of RNA, lipid, chlorophyll, and protein degradation. A new hypothesis is presented concerning the relationship between proteolysis and the initial steps in chlorophyll breakdown. It is argued that the dismantling of the chloroplast is a highly organized process and that the concept of loss of chloroplasts by digestion in a lytic vacuole is not tenable.

Vacuolar Localization of Proteases and Degradation of Chloroplasts in Mesophyll Protoplasts from Senescing Primary Wheat Leaves

Mesophyll protoplasts isolated from primary leaves of wheat seedlings were used to follow the localization of proteases and the breakdown of chloroplasts during dark-induced senescence. Protoplasts were readily obtained from leaf tissue, even after 80% of the chlorophyll and protein had been lost. Intact chloroplasts and vacuoles could be isolated from the protoplasts at all stages of senescence. All the proteolytic activity associated with the degradation of ribulose bisphosphate carboxylase in the protoplasts could be accounted for by that localized within the vacuole. Moreover, this localization was retained late into senescence. Protoplasts isolated during leaf senescence first showed a decline in photosynthesis, then a decline in ribulose bisphosphate carboxylase activity, followed by a decline in chloroplast number. There was a close correlation between the decline in chloroplast number and the loss of chlorophyll and soluble protein per protoplast, suggesting a sequential degradation of chloroplasts during senescence. Ultrastructural studies indicated a movement of chloroplasts in toward the center of the protoplasts during senescence. Thus, within senescing protoplasts, chloroplasts appeared either to move into invaginations of the vacuole or to be taken up into the vacuole.

Ultrastructural changes in chloroplasts of lettuce infected with beet western yellows virus

An electron microscope examination of lettuce plants infected with beet western yellows virus (BWYV) showed that the interveinal leaf-yellowing disease symptoms were associated with the degeneration of the chloroplasts. The disappearance of grana stacks, stroma lamellae and the appearance of abnormally large starch grains in chloroplasts was ultimately followed by an abnormal increase in the number and size of osmiophilic granules. In infected lettuce plants treated with carbendazim (methyl benzimidazole-2-yl carbamate), chloroplasts were normal and disease symptoms were largely prevented. Degeneration of chloroplasts of BWYV-infected Claytonia perfoliata leaves followed a similar pattern to that observed in lettuce, and disease symptoms were evident when leaves changed from green to an orange-red discoloration. Chloroplast breakdown and symptoms in infected C. perfoliata plants were not prevented by the application of carbendazim. BWYV-induced chloroplast degeneration is discussed in relation to chloroplast degeneration during the natural senescence of leaves of other plant species in which senescence is probably controlled by endogenous hormones.

Ultrastructural changes in resistant and susceptible varieties of Phaseolus vulgaris following artificial inoculation with Pseudomonas phaseolicola

Infiltration of resistant (Red Mexican) and susceptible (Prince) varieties of Phaseolus vulgaris with a suspension containing 10 10 cells/ml of Pseudomonas phaseolicola (race 1) led to an initial phase of leaf cell death at the time of infiltration, followed by a second phase of cell death that was delayed in the susceptible variety but progressed rapidly in the resistant host. At the inoculation site, within 2 days, all the leaf cells were dead in the susceptible host but many leaf cells remained alive in the resistant cultivar. The induction of death appeared to be by two distinct mechanisms. In one case the pathogen caused a rapid degeneration of cells that was characterized by chloroplast breakdown and the retention of a high frequency of free cytoplasmic ribosomes. These changes were the same for both hosts, indicating a similar mechanism for the killing of cells by the pathogen. In addition, the resistant host also showed degenerative changes in palisade mesophyll cells and some of the spongy mesophyll cells that were similar to natural senescence, and involved a fall in the frequency of free ribosomes without gross initial disruption of chloroplasts. These more gradual changes may have been due to the isolation of living cells by dead cells rather than the direct effect of the pathogen. Measurement of vacuolar sizes indicated that water-soaking and tissue dehydration were caused by the loss of water from cells at the time of their death and not by water loss from living cells.

Compositional changes in developing rape seed (Brassica napus L.)

The growth and composition of siliquas and seeds of oilseed rape was followed over 12 weeks from shortly after anthesis to maturity. Each plant produced 220 siliquas, this number being constant throughout development. Seed numbers per siliqua fell from 19 to 9 by week 5 and declined to 7 at maturity. Hull(1) and seed growth followed a sigmoid pattern, but were not in phase. Seed development could be divided into 3 phases: In Phase 1, seed weight was low and starch and ethanol soluble compounds accounted for 80% DM. Phase 2, seed growth increased and storage oil and proteins were deposited accounting for 40% and 20% DM respectively at the end of this stage. Starch, glucose and fructose were utilized in this process. Phase 3 was largely concerned with the deposition of oil and protein in fixed proportions. Seed weight more than doubled while DM composition remained constant. Sugars were transferred from the hull to the seed to support this growth.The proportion of hull lipids remained constant throughout development until shortly before maturity when MGDG and DGDG fell due to chloroplast breakdown as indicated by chlorophyll disappearance. The FA composition of the hull lipids resembled that of photosynthetic tissue. In the seeds, the neutral lipids increased from 20% of the total lipids in Phase 1 to 93% at maturity. The proportion of structural lipids declined as the storage lipids increased. In Phase 1 the FA composition of the lipid resembled that of photosynthetic tissue (high in C16:0; C18:2; C18:3). In Phase 2, FA typical of storage triglycerides (C20:1; C22:1, appeared, C18:1 transitorily increased, but C18:2 and C18:3 fell dramatically. In Phase 3, the content of C22:1 continued to rise, but the proportions of the other FA remained constant.

The Occurence of δ-Tocopherylquinone in Higher Plants and Its Relation to Senescence

delta-Tocopherylquinone (deltaTQ) content was determined in tobacco and yellow maple leaves, green ivy leaves and cactus tissues. It was found that the concentration of delta-TQ was highest in mature or senescent tissues, such as white tobacco leaves (0.02 mumole/g dry wt) while its detection was uncertain in young, green leaves from the apex of tobacco plants. Fractionation by centrifugation of senescent tobacco leaves showed that the osmiophilic globule fraction was enriched in delta-TQ. Electron microscope studies of young, mature and senescent tobacco tissues showed progressive changes in the size and number of osmiophilic globules. After chloroplast breakdown in senescent tobacco leaves, these globules became the predominant constituents of the organelle. delta-TQ which is associated with osmiophilic globules may play a role in the development of plants, particularly during senescence.

Chlorophyll changes, photosynthesis, and ultrastructure of chloroplasts in Albugo candida induced "green islands" on detached Brassica juncea cotyledons

Brassica juncea cotyledons were detached from the plant 3 days after inoculation with Albugo candida. Changes in chlorophyll content of infected and noninfected tissue were determined over a 4-day period, during which time distinct "green islands" developed. Following incubation with glycine-2-14C in the light, radioactivity was detected in chlorophylls a and b of both infected and noninfected tissue. Both infected and noninfected tissue fixed 14CO2 in the light during the 4 days after detachment. Most of the incorporated activity was in the 70% ethanol-soluble fraction. At 4 days after detachment, "green islands" fixed 5 times more 14CO2 in the light than noninfected tissue while both types of tissue fixed about the same amount in the dark. Photosynthesis per mole of chlorophyll fell at the same rate in "green island" and noninfected tissue. The maintenance of chlorophyll and continued photosynthetic activity in "green islands" paralleled delayed chloroplast breakdown. "Green island" chloroplasts still had intact grana and relatively small osmiophilic globules 96 h after detachment. In noninfected tissue, grana began to break down and osmiophilic globules increased in size 48 h after detachment. At 96 h after detachment, little grana structure remained and chloroplasts contained greatly enlarged osmiophilic globules interspersed with strands of stroma lamellae. Tissue treated with kinetin responded in essentially the same way as "green island" tissue. Chlorophyll content and photosynthetic capacity were maintained and chloroplast breakdown was delayed.

Metabolic Regulation in Diseased Leaves II. Changes in Nicotinamide Nucleotide Coenzymes in Barley Leaves Infected With Powdery Mildew

Nicotinamide nucleotide coenzymes were estimated spectrophotometrically in noninfected barley leaves and leaves infected with Erysiphe graminis var hordei (powdery mildew). Amounts of NADH, NADP(+) and NADPH were not altered by infection. In contrast, the NAD(+) content rose sharply and at 144 hours was 100% greater than in noninfected leaves. The respiratory rate was increased in infected leaves and the pattern of this increase was similar to that of NAD(+).The effect of infection on the intracellular distribution of NADP(+) was examined by fractionating lyophilized leaves in a nonaqueous medium. In noninfected leaves almost all of the NADP(+) was localized in the chloroplasts. In infected leaves where some chloroplast breakdown occurs, about 60% of the NADP(+) was detected in the nonchloroplast part of the cell. This intracellular redistribution of NADP(+) is discussed in relation to the increased pentose-P pathway activity occuring after infection.

Winter-type california tobacco rattle virus in its relation to the infected cell

Particles of California tobacco rattle virus (CTRV) were observed in thin sections of vascular elements of leaves showing oak leaf symptoms. At no time during this study were particles observed in mesophyl cells of these leaves. A peculiar chloroplast breakdown is described.