Consequences of CO2 and light interactions for leaf phenology, growth, and senescence in Quercus rubra

We investigated how light and CO₂ levels interact to influence growth, phenology, and the physiological processes involved in leaf senescence in red oak (Quercus rubra) seedlings. We grew plants in high and low light and in elevated and ambient CO₂. At the end of three years of growth, shade plants showed greater biomass enhancement under elevated CO₂ than sun plants. We attribute this difference to an increase in leaf area ratio (LAR) in shade plants relative to sun plants, as well as to an ontogenetic effect: as plants increased in size, the LAR declined concomitant with a decline in biomass enhancement under elevated CO₂ Elevated CO₂ prolonged the carbon gain capacity of shade‐grown plants during autumnal senescence, thus increasing their functional leaf lifespan. The prolongation of carbon assimilation, however, did not account for the increased growth enhancement in shade plants under elevated CO₂. Elevated CO₂ did not significantly alter leaf phenology. Nitrogen concentrations in both green and senesced leaves were lower under elevated CO₂ and declined more rapidly in sun leaves than in shade leaves. Similar to nitrogen concentration, the initial slope of A/C_i curves indicated that Rubisco activity declined more rapidly in sun plants than in shade plants, particularly under elevated CO₂. Absolute levels of chlorophyll were affected by the interaction of CO₂ and light, and chlorophyll content declined to a minimal level in sun plants sooner than in shade plants. These declines in N concentration, in the initial slope of A/C_i curves, and in chlorophyll content were consistent with declining photosynthesis, such that elevated CO₂ accelerated senescence in sun plants and prolonged leaf function in shade plants. These results have implications for the carbon economy of seedlings and the regeneration of red oak under global change conditions.     

Drought-induced senescence is characterized by a loss of antioxidant defences in chloroplasts

The relationship between drought, oxidative stress and leaf senescence was evaluated in field‐grown sage (Salvia officinalis L.), a drought‐susceptible species that shows symptoms of senescence when exposed to stress. Despite the photoprotection conferred by the xanthophyll cycle, drought‐stressed senescing leaves showed enhanced lipid peroxidation, chlorophyll loss, reduced photosynthetic activity and strong reductions of membrane‐bound chloroplastic antioxidant defences (i.e. β‐carotene and α‐tocopherol), which is indicative of oxidative stress in chloroplasts. H₂O₂ accumulated in drought‐stressed senescing leaves. Subcellular localization studies showed that H₂O₂ accumulated first in xylem vessels and the cell wall and later in the plasma membrane of mesophyll cells, but not in chloroplasts, indicating reactive oxygen species other than H₂O₂ as direct responsible for the oxidative stress observed in the chloroplasts of drought‐stressed senescing leaves. The strong degradation of β‐carotene and α‐tocopherol suggests an enhanced formation of singlet oxygen as the putative reactive oxygen species responsible for oxidative stress to senescing chloroplasts. This study demonstrates that oxidative stress in chloroplasts mediates drought‐induced leaf senescence in sage growing in Mediterranean field conditions.     

Veränderungen der Glyko- und Phospholipidgehalte während der Blattvergilbung

Summary The glyco- and phospholipid levels in green, green-yellow and yellow leaves of Impatients balsamina L., Daucus carota L. and Cucurbita pepo L. were determined on a leaf area basis. In Fagus silvatica L. leaves the kinetics of lipid breakdown during autumnal senescence was analysed. It was shown that yellow tissues still contain 40% to 50% of galactolipids and 50% to 60% of phospholipids present in green tissues. In the early stages of senescence of autumnal Fagus leaves we found a more rapid decline in the levels of the galactolipids and of the phospholipids phosphatidylglycerol and phosphatidylcholine, whereas in the later stages the breakdown of these lipids is slower than that of chlorophyll. The last yellow stage still contains 30% of the galactolipids and about 23% of the phospholipids present in fully greened leaves. Phosphatidylinositol shows a different behavior during senescence.

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Abkürzungen MGD Monogalaktosyldiglycerid - DGD Digalaktosyldiglycerid - SL Sulfolipid - GPC Glycerophosphatidylcholin - GPE Glycerophosphatidyläthanolamin - GPG Glycerophosphatidylglycerin - GPI Glycerophosphatidylinosit - GPS Glycerophosphatidylserin - Gal-Lipide (GL) Galaktolipide - P-Lipide (PL) Phospholipide - Chl Chlorophyll     

Senescence-related changes in the antioxidant status of ginkgo and birch leaves during autumn yellowing

The antioxidant status of birch and ginkgo leaves during autumnal senescence was characterized by the activities of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and superoxide dismutase (SOD). The contents of leaf H₂O₂ and ascorbate were used as indicators of oxidative stress. Degradation of chlorophyll (chl) during natural senescence was not accompanied either by an increase of H₂O₂ or by a decrease of reduced ascorbate. A transient decrease of reduced ascorbate in ginkgo and birch leaves in early senescence was accompanied by CAT inactivation. The activity of ionically-bound PODs was stimulated in late senescence in both species, when more than 30% of chl was degraded. Induction of MnSOD in both species and new isoforms of CuZnSOD in birch in late senescence was accompanied by the disappearance of other CuZnSOD isoforms in birch and FeSOD in ginkgo. The role of antioxidative enzymes in keeping ascorbate reduced and endogenous H₂O₂ at low levels in senescent leaves of deciduous trees was discussed.     

Time course of antioxidant responses of Capsicum annuum subjected to a progressive magnesium deficiency

The effect of magnesium (Mg²⁺)‐deficiency on the antioxidant responses of Capsicum annuum was investigated over a 60‐day period under controlled conditions. This Mg²⁺‐deficiency aimed to mimic the physiological conditions that plants may experience in the field. At each harvest time, five different leaf‐levels (L2 to L6) were distinguished. L2 and L6 correspond to the second and sixth youngest leaves, respectively. The following parameters were determined: Mg²⁺, chlorophyll and protein contents, total and redox pools of ascorbate and glutathione, and the activities of superoxide dismutase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase. Under Mg²⁺‐deficiency, leaf Mg²⁺ contents decreased over time in all leaf‐levels except in the second youngest leaves (L2), where they remained constant at about 0.25% (dry weight basis). Mg²⁺‐deficiency led to an increase in the antioxidant enzyme activities concomitant with an increase in the ascorbate and glutathione pools, whereas total chlorophyll and soluble protein contents decreased. The L2 leaves showed an increase in glutathione reductase activity and in the ascorbate redox state whereas no difference was observed for the other parameters. Superoxide dismutase activities increased in L5 leaves from day 15 and, afterwards, in L3 to L5 leaves, irrespective of Mg²⁺ content. At day 30, glutathione reductase activities increased in L2 to L4 leaves and dehydroascorbate reductase activities in L4 leaves. At day 45, we observed an increase in the ascorbate peroxidase activities in L3 to L5 leaves. At the same time, ascorbate and glutathione pools increased in intermediate leaves, whereas chlorophyll content decreased in L3 and L4 leaves, and protein content decreased in L4 leaves. Results suggest that pepper leaves enhance their defence capacities against oxidative stress by increasing ascorbate more than glutathione synthesis. However, cells showed higher regeneration rates for the glutathione redox state than for the ascorbate redox state.     

Dynamic acclimation to sunlight in an alpine plant,Soldanella alpina L.

In the French Alps, Soldanella alpina (S. alpina) grow under shade and sun conditions during the vegetation period. This species was investigated as a model for the dynamic acclimation of shade leaves to the sun under natural alpine conditions, in terms of photosynthesis and leaf anatomy. Photosynthetic activity in sun leaves was only slightly higher than in shade leaves. The leaf thickness, the stomatal density and the epidermal flavonoid content were markedly higher, and the chlorophyll/flavonoid ratio was significantly lower in sun than in shade leaves. Sun leaves also had a more oxidised plastoquinone pool, their PSII efficiency in light was higher and their non-photochemical quenching (NPQ) capacity was higher than that of shade leaves. Shade-sun transferred leaves increased their leaf thickness, stomatal density and epidermal flavonoid content, while their photosynthetic activity and chlorophyll/flavonoid ratio declined compared to shade leaves. Parameters indicating protection against high light and oxidative stress, such as NPQ and ascorbate peroxidase, increased in shade-sun transferred leaves and leaf mortality increased. We conclude that the dynamic acclimation of S. alpina leaves to high light under alpine conditions mainly concerns anatomical features and epidermal flavonoid acclimation, as well as an increase in antioxidative protection. However, this increase is not large enough to prevent damage under stress conditions and to replace damaged leaves.     

The functional morphology of juvenile plants tolerant of strong summer drought in shaded forest understories in southern Spain

It has been hypothesized that plants cannot tolerate combined shade and drought, as a result of morphological trade-offs. However, numerous plant species are reportedly widespread in shaded forest understories that face drought, whether seasonal or occasional. We studied juveniles of six plant species that cope with strong summer drought in the understoreys of mixed Quercus forests in southern Spain: the tall-shrubs Phillyrea latifolia and Viburnum tinus, the perennial herb Rubia peregrina, the small shrub Ruscus aculeatus, and climbers Hedera helix and Smilax aspera. All of these species persist in evergreen shade (c. 3% daylight). Two other species were studied as comparators, Ruscus hypoglossum, less tolerant of drought, and Ceratonia siliqua, less tolerant of shade. Morphological and chemical variables relevant to shade and drought tolerance were measured for juveniles in a range of sizes, and also for the leaves of mature plants. The species converge in features that confer tolerance of shade plus drought by reducing demand for resources. Demand for water is reduced through a moderate to high below-ground mass fraction and low to moderate specific leaf area (respectively 0.22–0.52 and 112–172 cm² g^–1 at 1.00 g total dry mass). Demand for both irradiance and water is reduced through a low to moderate foliar nitrogen concentration and long-lived, physically protected leaves (2 yr). The species also converge in features that confer tolerance of either low irradiance or drought through specialized capture of resource, without precluding the other tolerance. These features include deep roots relative to shoot size, moderately higher specific leaf area in shade (1.2–2.0 × that in sun) and higher chlorophyll:nitrogen ratio in shade. Foliar chlorophyll per unit mass was higher in shade, but chlorophyll was not necessarily synthesized in greater amounts; rather, it was higher apparently due to shade effects on structural features linked with specific leaf area. In contrast, N per unit mass was higher in sun leaves independently of specific leaf area. Despite these convergences, the species diverge considerably in their root mass allocation and architecture, leaf saturated water content, density of stomata and guard cell size. No single narrowly defined functional type is needed for tolerance of shade plus drought.     

Regulation of the ascorbate-glutathione cycle in wild almond during drought stress

In wild species of almond (Prunus spp.), the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), as well as the levels of ascorbate/glutathione pools and H₂O₂ were subjected to water deficit and shade conditions. After 60 days of water shortage, the species were subjected to a rewatering treatment. During water recovery, leaves exposed to sunlight and leaves under shade conditions of about 20–35% of environmental irradiance were sampled. After 70 days without irrigation, mean predawn leaf water potential of all the species fell from −0.32 to −2.30 MPa and marked decreases in CO₂ uptake and transpiration occurred. The activities of APX, MDHAR, DHAR, and GR increased in relation to the severity of drought stress in all the wild species studied. Generally, APX, MDHAR, DHAR, and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in sun-exposed leaves. The levels in total ascorbate, glutathione, and H₂O₂ were directly related to the increase in drought stress and subsequently decreased during rewatering. The antioxidant response of wild almond species to drought stress limits cellular damage caused by reactive oxygen species during periods of water deficit and may be of key importance for the selection of drought-resistant rootstocks for cultivated almond.     

Gas exchange and antioxidative compounds in young beech trees under free-air ozone exposure and comparisons to adult trees

Three-year-old beech (Fagus sylvatica) seedlings growing in containers were placed into the sun and shade crown of a mature beech stand exposed to ambient (1 x O(3)) and double ambient (2 x O(3)) ozone concentrations at a free-air exposure system ("Kranzberg Forst", Germany). Pigments, alpha-tocopherol, glutathione, ascorbate, and gas exchange were measured in leaves during 2003 (a drought year) and 2004 (an average year). Sun-exposed seedlings showed higher contents of antioxidants, xanthophylls, and beta-carotene and lower contents of chlorophyll, alpha-carotene, and neoxanthin than shade-exposed seedlings. In 2003 sun-exposed seedlings showed higher contents of carotenoids and total glutathione and lower net photosynthesis rates (A(max)) compared to 2004. O(3) exposure generally affected the content of chlorophyll, the xanthophyll cycle, and the intercellular CO(2) concentration (c(i)). Seedlings differed from the adjacent adult trees in most biochemical and physiological parameters investigated: Sun exposed seedlings showed higher contents of alpha-tocopherol and xanthophylls and lower contents of ascorbate, chlorophyll, neoxanthin, and alpha-carotene compared to adult trees. Shade exposed seedlings had lower contents of xanthophylls, alpha-carotene, and alpha-tocopherol than shade leaves of old-growth trees. In 2003, seedlings had higher A(max), stomatal conductance (g(s)), and c(i) under 2 x O(3) than adult trees. The results showed that shade acclimated beech seedlings are more sensitive to O(3), possibly due to a lower antioxidative capacity per O(3) uptake. We conclude that beech seedlings are uncertain surrogates for adult beech trees.     

Evaluation of some coccinellid species for the biological control of aphids in protected cropping

Four species of Coccinellidae, Adalia bipunctata (L.), Coccinella septem-punctata L., Coelomegilla maculata de G. and Cycloneda sanguinea L., were compared as predators of aphids on cucumbers and chrysanthemums. In laboratory feeding tests C. maculata and C. sanguinea proved the most voracious but the former could not remain on cucumber foliage long enough to be effective. The fecundity of C. sanguinea was the highest of those studied and a satisfactory laboratory rearing technique has been developed for this species.     

Photosynthesis and Chlorophyll Fluorescence Characteristics in Relationship to Changes in Pigment and Element Composition of Leaves of Platanus occidentalis L. during Autumnal Leaf Senescence

The loss of chlorophyll and total leaf nitrogen during autumnal senescence of leaves from the deciduous tree Platanus occidentalis L. was accompanied by a marked decline in the photosynthetic capacity of O₂ evolution on a leaf area basis. When expressed on a chlorophyll basis, however, the capacity for light-and CO₂-saturated O₂ evolution did not decline, but rather increased as leaf chlorophyll content decreased. The photon yield of O₂ evolution in white light (400-700 nanometers) declined markedly with decreases in leaf chlorophyll content below 150 milligrams of chlorophyll per square meter on both an incident and an absorbed basis, due largely to the absorption of light by nonphotosynthetic pigments which were not degraded as rapidly as the chlorophylls. Photon yields measured in, and corrected for the absorptance of, red light (630-700 nanometers) exhibited little change with the loss of chlorophyll. Furthermore, PSII photochemical efficiency, as determined from chlorophyll fluorescence, remained high, and the chlorophyll a/b ratio exhibited no decline except in leaves with extremely low chlorophyll contents. These data indicate that the efficiency for photochemical energy conversion of the remaining functional components was maintained at a high level during the natural course of autumnal senescence, and are consistent with previous studies which have characterized leaf senescence as being a controlled process. The loss of chlorophyll during senescence was also accompanied by a decline in fluorescence emanating from PSI, whereas there was little change in PSII fluorescence (measured at 77 Kelvin), presumably due to decreased reabsorption of PSII fluorescence by chlorophyll. Nitrogen was the only element examined to exhibit a decline with senescence on a dry weight basis. However, on a leaf area basis, all elements (C, Ca, K, Mg, N, P, S) declined in senescent leaves, although the contents of sulfur and calcium, which are not easily retranslocated, decreased to the smallest extent.     

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.     

Autumn Leaves of Ginkgo biloba L.: Optical Properties,Pigments and Optical Brighteners

Senescent leaves of Gingko biloba accumulate fluorescent compounds which may contribute to the golden luminous appearance of the autumnal foliage. Apart from the putative effect of such optical brighteners, the changes of spectral optical properties associated with senescence are due to the breakdown of chlorophyll in conjunction with a remarkably high retention of carotenoids. Carotenoid esters accumulate concomitant with chlorophyll breakdown. Optical properties in the infrared range of the spectrum illustrate the intactness of leaf tissue to the end of the senescence period.     

Thermoinduction of Chlorophyll Fluorescence and the Age-Related Condition of Higher Plant Leaves

The age-related changes in the temperature dependence curves (TDC) of chlorophyll fluorescence were studied in leaf segments of wheat (Triticum aestivumL.), tomato (Lycopersicum esculentumMill.), and cucumber (Cucumis sativumL.) plants grown under controlled photoculture conditions. Three major TDC patterns of chlorophyll fluorescence were identified within the temperature range of 25–70°C, with each of the patterns corresponding to a certain phase of leaf development. The transition from one type of thermogram to another was a gradual and ordered process. The magnitude of the low-temperature TDC peak increased until leaves completely expanded and declined with leaf senescence. In the course of leaf senescence, the thermograms exhibited an additional shoulder, which further changed into a peak at 55–65°C with increasing magnitude. Our data provide the basis for assessing leaf age from the type of chlorophyll fluorescence thermogram and the changes in the particular indices characteristic of TDC of chlorophyll fluorescence.     

Comparative changes in the antioxidant system in the flag leaf of early and normally senescing near-isogenic lines of wheat (Triticum aestivum L.)

Key message

The antioxidant system was significantly inhibited in the early aging line than the near-isogenic normal aging line during senescence.

Abstract

The antioxidant system plays pivotal roles in removal of reactive oxygen species (ROS) produced during leaf senescence. To explore its roles in leaf senescence of wheat (Triticum aestivum L.), the concentrations of antioxidants, activities, and gene expression of antioxidant enzymes were evaluated in flag leaves of the early aging line (EAL) and the near-isogenic normal aging line (NL) during senescence. The results showed that the total chlorophyll and soluble protein in the EAL declined earlier and faster, while more malondialdehyde and ROS accumulated compared with the NL. The activities of superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, and glutathione reductase were lower in the EAL than in the NL across multiple measuring dates. Additionally, the EAL had less amounts of reduced ascorbate and glutathione as well as lower reduction state with the progression of senescence. Concomitantly, the gene expression of antioxidant enzymes in the EAL was also significantly repressed relative to those in the NL during natural senescence. Taken together, the earlier onset and faster rate of senescence in the EAL could be a result of an imbalance of ROS production and ROS-scavenging antioxidant system, which provided valuable hints toward understanding leaf senescence of wheat.     

Some ecophysiological features in sun and shade leaves of tall beech trees

Some ecophysiological features in sun and shade leaves of tall European beech trees (Fagus sylvatica L.) growing in a natural forest stand were investigated. Quantitative leaf characteristics were followed in the field and under controlled conditions. In the sun leaves significantly higher rates of photosynthesis, photorespiration and dark respiration, and also photosynthetic CO₂ fixation capacity, photosynthetic productivity, and saturating, adaptation and compensating irradiances were found. Specific leaf mass, mean leaf area, stomata density and size as well as the chlorophyll content per unit dry mass were also significantly different in both types of the leaves. Higher photosynthetic efficiency in the shade leaves allows them a better utilization of the lower irradiance for carbon dioxide uptake. The importance of these findings for annual carbon gain of the shade tolerant European beech species is also discussed.     

Tropical Understory Piper Shrubs Maintain High Levels of Genotypic Diversity Despite Frequent Asexual Recruitment

Many plant species have the capacity to regenerate asexually by resprouting from stem and leaf fragments. In the pan‐tropical shrub genus Piper, this tendency is thought to be higher in shade‐tolerant than light‐demanding species, and to represent a trade‐off with annual seed production. Here we use molecular markers to identify clones in five Piper species varying in light requirements. We test predictions that (i) asexual recruitment success is highest in shade‐tolerant species, and (ii) that consequently, shade‐tolerant species are characterized by lower genotypic diversity than light‐demanding Piper. We found that two shade‐tolerant Piper species recruited asexually more frequently (36–42% of sampled shoots were of asexual origin) than, two light‐demanding and one shade‐tolerant species (0–26%). Furthermore, as predicted, genotypic diversity was negatively correlated with the frequency of asexual recruitment in the population. Nonetheless, genotypic diversity of Piper was high compared with other clonal plants. The proportion of unique genotypes found per population ranged from 0.58 to 1.0 and the genotypic Simpson's diversity ranged from 0.93 to 1.0 for all five species. Our results suggest that even though asexual reproduction plays an important role in maintaining local populations of Piper in the understory, it does not seem to reduce genotypic diversity to levels that will threaten these species ability to respond to environmental change. Abstract in Spanish is available in the online version of this article.     

Waterlogging induced oxidative stress and antioxidant activity in pigeonpea genotypes

The objective of this study was to examine the role of antioxidant enzymes in waterlogging tolerance of pigeonpea (Cajanus cajan L. Halls) genotypes ICP 301 (tolerant) and Pusa 207 (susceptible). Waterlogging resulted in visible yellowing and senescence of leaves, decrease in leaf area, dry matter, relative water content and chlorophyll content in leaves, and membrane stability index in roots and leaves. The decline in all parameters was greater in Pusa 207 than ICP 301. Oxidative stress in the form of superoxide radical, hydrogen peroxide and thiobarbituric acid reactive substances (TBARS) contents initially decreased, however at 4 and 6 d of waterlogging it increased over control plants, probably due to activation of DPI-sensitive NADPH-oxidase. Antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione reductase and catalase also increased under waterlogging. The comparatively greater antioxidant enzyme activities resulting in less oxidative stress in ICP 301 could be one of the factor determining its higher tolerance to flooding as compared to Pusa 207. This study is the first to conclusively prove that waterlogging induced increase in ROS is via NADPH oxidase.     

Changes in the chlorophylls and carotenoids of leaves of Nicotiana tabacum during senescence

In addition to chlorophylls a and b, β-carotene, lutein, violaxanthin and neoxanthin, leaves of tobacco (Nicotiana tabacum L. cv. Virginia Gold) contain antheraxanthin in some harvests. In lower leaves, chlorophylls decreased more rapidly than carotenoids during senescence, but both types of pigment decreased at equal rates in upper leaves. The chlorophyll a:b ratio decreased only in post-mature leaves. Total carotenoid decreased with age, with the relative proportion of β-carotene increasing in lower leaves. Seasonal influences rather than age of leaf determines whether antheraxanthin is present. No esterified xanthophylls were found in senescent leaves.     

Ultrastructure of Necrotic Lesions in Nicotiana glutinosa Leaves Locally Infected with a Variant of Cucumber mosaic virus

CMV(Y/GM2)tr is a variant of Cucumber mosaic virus strain Y [CMV(Y)] which infects Nicotiana species, including N. glutinosa, to induce necrotic local lesions (NLLs) in inoculated leaves, although all other CMV strains including CMV(Y) systemically infect Nicotiana species. To investigate the morphological features of this unique host response in N. glutinosa leaves infected with CMV(Y/GM2)tr, the ultrastructure of cells surrounding completely collapsed NLLs in virus‐inoculated N. glutinosa leaves was compared with that of normal cells of mock‐inoculated N. glutinosa leaves. The changes, which have been reported in other several virus–host plant systems showing the hypersensitive response (HR), were frequently observed in cells surrounding the NLLs. Furthermore, clumping of the nuclear matrix within the nuclei, which is a feature of programmed cell death, also occurred in these cells. These results indicated that the HR‐like host response occurred at the fine structural level in the cells of N. glutinosa plants infected with CMV(Y/GM2)tr.