Stem Vegetables

The most important horticultural stem vegetable is asparagus. The asparagus spear is growing very rapidly at harvest (as much as 70 mm per day). Thus its senescence is rapid, becoming unmarketable within 4-5 days at 20 C (King and O'Donoghue, 1995). Changes involved include lignification, ammonia production and rapid loss of protein, lipids, sugars, Chl and disease resistance (resulting in tip rot) and changes in flavor, texture and aroma (King and O'Donoghue, 1995). Ethylene is produced at...

The Molecules that Cause Oxidative Stress

Oxidative stress is caused by a group of extremely reactive molecules comprising free radicals of oxygen, singlet oxygen, and hydrogen peroxide these are collectively known as active oxygen species (AOS). Singlet oxygen (*O2) is formed when the two unpaired Copyright 2004, Elsevier, Inc. All rights reserved Figure 13-1. Formation of active oxygen species. electrons of molecular oxygen become paired, thus increasing the reactivity by making O2 amenable to donation of electrons in different spin...

Tubers Bulbs and Root Vegetables

Tubers, bulbs and some root vegetables are essentially functionally self-sufficient asexual reproductive structures. Examples of each category are potatoes (tuber), onions (bulb), carrots, horseradish and turnip (root vegetables). In general, senescence can be viewed in two phases a dormant phase when little degradation occurs and sprouting is inhibited followed by the active promotion of shoot sprouting and degradation of the storage organ, even under optimal storage conditions (Isenberg et...

The Pollination Signal

A number of studies have demonstrated that pollination results in increased sensitivity of floral tissues to exogenous ethylene (Halevy et al., 1984 Porat et al., 1994). Researchers have suggested various causes for the increased ethylene production and or sensitivity of pollinated flowers, including physical stimulation, auxin, ethylene, pollen ACC, short-chain fatty acids, and a range of other molecules (O'Neill, 1997). Gilissen (1976, 1977) noted that mechanical wounding of the stigma and...

Leaf Senescence and Nitrogen Loss

The nitrogen content of a leaf reaches the maximum level at around the completion of leaf expansion. When mesophyll cells cease their enlargement, increase of chloroplast number and size also stops (Pyke and Leech, 1987 Baumgartner et al., 1989 Sodmergen et al., 1991). In mature leaves of C3 plants, chloroplast nitrogen accounts for 70-80 of leaf Copyright 2004, Elsevier, Inc. All rights reserved nitrogen (Morita, 1980 Makino and Osmond, 1991). In the course of leaf senescence, nitrogen...

References

Self-pollination shortens flower lifetime in Portulaca umbraticola H.B.K. (Portulacaceae). International Journal of Plant Sciences 154, 412-415. Ashman, T.-L., and Schoen, D.J. (1994). How long should flowers live Nature 788-791. Ashman, T.-L., and Schoen, D.J. (1996a). Ashman and Schoen reply (to 'Flower life span and disease risk', Shykoff et al., van Doorn). Nature 379, 780. Ashman, T.-L., and Schoen, D.J. (1996b). Floral longevity fitness consequences and resource costs....

Years

Mortality curves for three perennial range grasses Bouteloua hirsuta (circles), B. chondrosiodes (squares), and B. eriopoda (triangles). Data derived from Canfield (1957), ungrazed treatments. clear whether the increase in mortality was due to the increasing age of individuals in the population, or to a deterioration of the extrinsic environment. In order to definitively show that senescence is occurring in natural plant populations, experiments need to be designed with the proper...

Introduction

This chapter will discuss the more general features of chloroplast breakdown, e.g. the degradation of membranes and of nucleic acids, as well as more specific aspects associated with the photosynthetic apparatus including photosynthetic performance and expression of photosynthesis-related genes. Moreover this chapter will address questions concerning the interrelation of photosynthesis and senescence. During the past ten years, classical approaches to studying photosynthesis have been...

Plastid Gene Expression during Senescence

Plastid gene expression has been studied extensively during biogenesis of chloroplasts. These studies showed that gene expression in plastids is controlled at the level of transcriptional activity and at different posttranscriptional levels including RNA stability, translational activity and posttranslational modifications reviewed by Gruissem and Tonkyn (1993) and by Stern et al. (1997) . Very few studies, however, deal with plastid gene expression during senescence. The decrease in plastid...

Significance of Chlorophyll Breakdown

An important lesson about the significance of Chl breakdown is taught by the various stay-green mutants. In all of them a deficiency in the catabolic system causes a marked retention not only of Chl but also of apoproteins of pigment-protein complexes in the thylakoids (Thomas, 1982 Guiamet etal., 1991 Cheung etal., 1993 Guiamet and Giannibelli, 1994 Bachmann etal., 1994). Hence, Chl appears to protect its apoproteins from proteolysis. The apoproteins account for a substantial proportion of the...

The Senescence Syndrome

Although it is possible to define senescence conceptually as a developmental process, i.e., an endogenous degeneration process leading to death, it still is not possible to describe it in precise biochemical terms (Section II). In other words, the central or primary pathway of senescence is not known, and some of the changes that accompany senescence are likely to be peripheral or secondary as opposed to causal. For example, the glyoxylate cycle enzymes and metallothionein that increase during...

Definitions and Theories of Vegetable Senescence

The term vegetable is used to describe a harvested edible plant product that is a member of the following categories tubers, bulbs, roots, leaves, flowers, stem and fruit vegetables. Since senescence in fruits is discussed elsewhere in this book, we will confine discussion to the other categories. There are several distinct patterns of natural plant senescence 1. Overall senescence, 2. Top senescence, 3. Deciduous senescence, 4. Progressive senescence of leaves, and 5. Bottom senescence of...

Ethylene Signal Transduction Pathway

In fruits tomato, avocado and banana ethylene is known to coordinate and complete the ripening process. Tomato and, in recent years, Arabidopsis have been used as plant models to unravel mechanisms surrounding ethylene action in plants. Since ripening and senescence share many common features during cell death (Gillaspy et al., 1993), one favorite approach to unravel regulation has been the use of mutants as well as molecular genetics. In Arabidopsis, the mutations clearly support a role for...

Reproductive Yield

The question of how senescence affects reproductive yield (or even vegetative yield for certain crops) is an important underlying theme in much of whole plant physiology. Senescence is also an important issue in reproductive development. Here again, it is important to recognize physiological differences among monocarpic species but nonetheless to look for general principles. In monocarpic species, there is a tradeoff or shift in allocation of resources from vegetative to reproductive growth,...

Gametophytes

During megagametogenesis four haploid nuclei are produced. Commonly, three of the four cells resulting from meiosis die, specifically those at the micropylar end of the ovule (Barlow, 1982). Megaspore abortion is proposed to be a consequence of selective apoptosis (Bell, 1996). Gametospore degeneration in the fern Marsilea vestita exhibits characteristics of apoptosis (Bell, 1996). Mutations interpreted to cause an over expression of PCD have been identified in arabidopsis four mutants show...

Leafy Vegetables

Many crucifers, including brussel sprouts, cabbage, and crops such as lettuce, spinach, cress, and chives are included in this category. This diversity of crops is reflected in the very large range in refrigerated commercial storage life from less than two weeks (lettuce and spinach), two to eight weeks (brussels sprouts and chinese cabbage), and even up to six months (cabbage, Fig. 22-2). For those vegetables with short storage, senescence to a large degree parallels that for detached...

Porphyrin Macrocycle Cleavage

The green color of Chl is due to the conjugated system of n electrons in the tetrapyrrolic macrocycle and, hence, the loss of green color must be due to its abolition. Non-green catabolites were first observed in senescing leaves of Festuca pratensis by chromatograph-ical comparison of extracts from leaves of a yellowing wild-type and a stay-green mutant, respectively (D ggelin et al., 1988). A group of compounds was exclusively detectable in wild-type leaves and only transiently so during...

Is Photoinhibition of Photosynthesis a Phototoxicity Mechanism

Photoinhibition of PS II, or simply photoinhibition, is a reaction in which visible light induces the loss of the electron transfer activity of PS II (Aro et al., 1993). The photodamage is a simple first-order process both in vitro (Jones and Kok, 1966) and in vivo (Tyystj rvi and Aro, 1996). Continuous repair of the photodamage explains why plants do not suffer from photoinhibitory symptoms under their normal growth light intensities. The role of ROS in photoinhibition is poorly understood....

Evolutionary Approaches A Theories of Senescence

Both physiological and evolutionary senescence show genetic control, yet the details of our understanding of senescence at these two levels is very different (Bleecker, 1998). Physiological studies have demonstrated that within an individual plant, there is a genetic program which results in an orderly degenerative process leading either to the reabsorption of nutrients and the abscission of plant parts, or in the case of semelparous species, to the death of the whole organism (Nooden, 1988)....

The Relationship of Ethylene and Senescence

Chlorophyll Degradation Pathway

As discussed in Chapter 8, the effects of ethylene in fruit-ripening and flower senescence are of particular interest in agriculture. In climacteric fruits such as apple, pear, tomato, banana, papaya, mango, and avocado, an increase in respiration stimulated by ethylene accompanies the start of the ripening process. It is thought that at the molecular level ethylene coordinates the expression of the genes that participate in ripening (Gray et al., Figure 6-2. Ethylene biosynthetic pathway. SAM,...

Physiology and Biochemistry of Ozoneinduced Accelerated Leaf Senescence

Normal senescence is associated with a change in leaf color and foliar abscission. It is widely accepted that O3 accelerates the rate of leaf abscission in a wide range of species including tree species such as Populus, apple (Malus domestica Brokh.), beech (Fagus sylvatica L.), loblolly pine (Pinus taeda L.) (Braun and Fluckiger, 1995 Nyman, 1986 Pell et al., 1995 Stow et al., 1992 Wiltshire et al., 1993) and numerous agronomic species including soybean (Glycine max L.), chickpea (Cicer...

Unique Features of Plants

Growth forms and theoretical expectations A unique feature, distinguishing plants and animals is the indeterminate growth that takes place in the meristems of plants. Meristem organization may be an important factor determining variation in life span and mortality patterns of different species. Variation within the plant kingdom ranges from unitary organisms to clonal species. A plant species with a unitary organization and determinate growth is expected to follow demographic patterns similar...

Delay of Senescence by Cytokinin

Extensive research has identified cytokinins as the most effective senescence-retarding growth regulators. Cytokinins have been known to regulate various aspects of plant growth and development, including cell differentiation, release of lateral buds from apical dominance, and senescence. Much evidence suggests that cytokinins play an important role in senescence (see Chapter 6 for further details). Interestingly, in the transgenic plants expressing the KNOTTED 1 (KN1) gene under the control of...

Ethyleneinduced Senescence

For a number of flowers, especially in the Caryophyllaceae, Leguminaceae, and Orchi-daceae, the onset of natural or pollination-induced senescence is associated with a climacteric rise in respiration triggered by an increase in ethylene production. For many others, ethylene is involved in the abscission of flowers, petals, or florets (Woltering and van Doorn, 1988). The rapidity of the ethylene response has made flowers whose senescence is coordinated by ethylene a favored system for exploring...

Senescence as a Genetically Programmed Process

Interestingly, selective inhibitors of protein and mRNA synthesis give some clues about the genetic control of senescence and about what might be expected from senescence mutations. For example, enucleation and selective inhibitors of RNA synthesis and cytoplasmic protein synthesis generally block senescence (Brady, 1988 Nooden, 1988c), and this indicates that synthesis of new mRNAs and proteins (e.g., gene expression) is required for senescence. Although senescing tissues undergo an overall...

Photoperiod Effects

The early work (1930s) on photoperiod effects was directed mainly toward control of autumnal leaf senescence and shedding in woody plants and the culture of plants in controlled environments. Autumnal senescence occurs at a time of decreasing day length, and therefore, short days (SDs) would be expected to cause leaf senescence shedding in trees and herbaceous plants if they are photoperiodic. In many, but apparently not all species, autumnal senescence is induced by SDs (Matzke, 1936 Jester...

Prereproductive Cell Death A Aleurone and Scutellum

At the beginning of the life cycle of plants propagated by seed, cells die in the process of germination. For example, aleurone cells in cereal grain seeds facilitate germination however, they also die in the process. Their death fits the general definition of PCD, and attention has been turned to the death process. GA specifically accelerated cell death in isolated aleurone cells and protoplasts, and the GA-signaling inhibitor LY83583 prevented DNA degradation and cell death (Kuo et al., 1996...

The Processes Senescence Aging Programmed Cell Death Apoptosis etcEvolving Concepts

These terms reflect concepts, and they need to be articulated as clearly as we can, albeit imperfectly, with our current knowledge in order to foster the development of this field. They refer to processes that may be similar overall, and different terms may even refer to identical processes. Not surprisingly, different professional groups sometimes use the same terms differently. Before getting into these conceptual problems further, it is important to recognize how these ideas developed, i.e.,...

Patterns

In terms of longevity, plants fall mostly into three categories annual, biennial, and perennial. When considering whole plant senescence, however, it seems better to classify them as monocarpic (semelparous) or polycarpic (iteroparous) which emphasizes their senescence pattern and its relationship to reproduction. Monocarpy(ic) refers to a life cycle with one reproductive episode followed by death, and polycarpy(ic) to more than one reproductive episode (Hildebrand, 1882 Molisch, 1938). The...

Genetic Alterations of Light Control of Senescence

The information available on genetic controls of the regulation of senescence by light is very incomplete. Nonetheless, it provides a useful glimpse at what can be achieved through genetic probes of these light controls. Due to the technical ease of screening for mutations to inhibit dark-induced leaf yellowing, several of these have been reported (Chapter 5). All of the stay-green mutations tested delay dark-induced leaf yellowing and sometimes other senescence processes (Thomas, 1987 Canfield...

Flower Vegetables

These types of vegetables include broccoli or calabrese (compact inflorescence of immature flower buds with stem), cauliflower (aborted floral meristem and stem tissue) and artichokes (a mixture of immature and mature tissue with large sepals and stem). As a group, the rate of senescence is generally rapid. The most prominent effect of senescence in broccoli is the readily observable loss of chlorophyll from the sepals of the immature floral buds after 2-3 days at 20 C, whereas there is no Chl...

The LOX Pathway

Enzymatic peroxidation of lipids occurs by stereospecific dioxygenation of PUFAs such as linolenic acid (LeA) or linoleic acid (LA) catalyzed by LOXs. LeA might be released by activity of a phospholipase A2, as shown for a wound response (Narvaez-Vasquez et al., 1999). Recently, JA deficiency in the Arabidopsis mutant dadl (defective in anther dehiscence 1), which is affected in a flower-specific chloroplast-located phospholipase A1, indicates the role of this enzyme in JA biosynthesis...

Shoot Development and Leaf Senescence A Leaf Phenology

Phenological plant research on both herbaceous and woody plants has focused on the description of seasonal events using pheno-diagrams which are useful (Lieth, 1971) however, this method may provide limited inference about the functional and dynamic aspects of plant life affected by environmental and endogenous conditions. More quantitative description is needed to show the dynamics of tree growth. Description of functional events of tree shoots has provided us with an understanding of their...

Damage and Inhibition by UV

The first observation of ultraviolet radiation damage in plants was probably made by Siemens (1880). Arthur and Newell (1929) review the older literature and try to define the active spectral region using short-wavelength cut-off filters. With sufficient exposure, ultraviolet radiation produces damage to organisms of all species. It was mentioned that DNA is one of the main molecular targets, but that also other targets are important. Let us first take a look at DNA as a target for the damaging...

Leaf Structure and Function

Leaf structural differences may directly or indirectly affect photosynthetic capacity (Nobel et al., 1975 Carpenter and Smith, 1981 Koike, 1988 Terashima, 1989). Alder (Alnus hirsuta) leaves that emerge at the beginning of autumn have two layers of epidermis, while leaves emerging earlier have only one layer. The two layers help to reduce the strong PPFD at low temperature in autumn (Koike, unpublished data). By contrast, late-successional species usually flush leaves only once, in the...

Sources of Variation in Endogenous Shoot Senescence Time in Mayapple

Among-Colony Variation in Mean Endogenous Shoot Senescence Time We regularly note variation among colonies in a number of phenological attributes of mayapple seasonal development, including the timing of shoot emergence and anthesis, as well as senescence (Lu, 1996). This variation may reflect microsite differences among colonies or genetically based and hence selectable variation among genotypes, or some combination of the two. We examined the relative roles of genotype and environment in a...

Herbicides and Heavy Metals Mediating Phototoxic Responses

Several herbicides mediate phototoxic responses, acting as secondary phototoxins in plants. Bipyridinium herbicides, like paraquat (methyl viologen) act as electron acceptors of Photosystem I and the subsequent rapid autooxidation of the paraquat anion radical creates O-. The hydroxyl radical formed in the subsequent Fenton chemistry is the primary reactant causing the destruction of the photosynthetic apparatus. The herbicidal effect of carotenoid biosynthesis inhibitors, like norflurazon, is...

Mayapple as a Study Organism

Rhizome Diagrams

Mayapples are perennial clonal herbs of deciduous forests of the northeastern United States they are found growing in discrete patches or colonies containing one or more genotypes (genets) (Policansky, 1983 Whisler and Snow, 1992). Mayapples are morphologically simple and have a limited number of developmental options that can directly influence their demography (their pattern of birth, death and ramet population increase) and their life history expression (whether they are sexually...

Jasmonates and Related Compounds

Lox Pathway

Jasmonates are lipid-derived cyclopentanone compounds which occur in all plants tested so far, as free acid (JA), methyl ester (JAME) or amino acid conjugates such as that of Copyright 2004, Elsevier, Inc. All rights reserved Figure 9-1. The LOX pathway. Seven different branches originate from the LOX products 13-HPOT and 13-HPOD, respectively. The AOS catalyzes the first step of the most-studied branch leading to OPDA and JA. Figure 9-1. The LOX pathway. Seven different branches originate from...

Ethylene Cross Talk with Other Plant Hormones

Several Phytohormones Affect Root Growth

Various hormones have been shown to regulate senescence (see below). Whether similar is true of their role in plant PCD remains to be determined. Plant hormones do interact or cross talk with one another to influence plant processes. New genomics research is beginning to show that different hormones induce factors or transcription factors that are then transported into the nucleus to bind to specific regulatory sequences and control expression of a specific gene, i.e., in the 5' region of a...

The Relationship of Cytokinins and Senescence A Manipulation of Cytokinin Levels

Cytokinins were originally discovered as factors promoting plant cell division (Miller et al., 1956). Since this discovery, cytokinins have been shown to have effects on many different aspects of plant development. For example, cytokinin suppresses apical dominance and promotes the growth of lateral buds (Phillips, 1975) and viviparous leaves (Estruch et al., 1991), chloroplast development (Parthier, 1979), leaf expansion (Miller et al., 1956), and delays tissue senescence (Richmond and Lang,...

Phototoxicity

Chemical and Biochemical Basis of Phototoxicity III. Phototoxic Compounds and their Roles in Nature IV. Herbicides and Heavy Metals Mediating Phototoxic V. Is Photoinhibition of Photosynthesis a Phototoxicity VI. Phototoxicity and Programmed Cell Death I. Introduction A. History of Phototoxicity Phototoxicity can be defined as a phenomenon in which a substance becomes damaging when activated by light. Primary phototoxins are photosensitizers, i.e. light absorption by the toxin makes it...

Mechanisms of Ozoneinduced Accelerated Leaf Senescence

Ethylene And Senescence

During normal senescence, photosynthesis-associated genes (PAGs) decline. Ozone caused a rapid loss in rbcS transcript levels in potato (Solanum tubersosum L.) leaves immediately after acute exposures to the pollutant (Reddy et al., 1993), and this response was also observed in Arabidopsis and tobacco (Bahl and Kahl, 1995 Conklin and Last, 1995). A prematuare decline in rbcS was observed after more prolonged exposures to lower doses of the gas (Glick et al., 1995 Miller et al., 1999). A drop in...

Contributors

Numbers in parentheses indicate the pages on which the authors' contributions begin. Richard M. Amasino (91), Department of Biochemistry, University of Wisconsin, Madison, WI, 53706-1544 Tia-Lynn Ashman (349), Department of Biological Sciences University of Pittsburgh Pittsburgh, PA Douglas G. Bielenberg (295), Department of Horticulture, Poole Agricultural Center, Clemson University, Clemson, SC 29634 Lars Olof Bj rn (285), Lund University Department of Cell and Organism Biology SE-223 62 Lund...

Aerenchyma

Death and autolysis of cells can be induced in roots of many monocot and dicot species in response to a wide range of environmental factors these include hypoxia Justin and Armstrong, 1991 Drew, 1997 , mechanical impedance He et al., 1996a , transient starvation of inorganic nutrients Drew et al., 1989 and desiccation Drew, 1979 Shone and Flood, 1983 . Death occurs in primary roots usually among the cortical cells in the zone where the cells have just completed their expansion, usually a few cm...

Senescencerelated Genes

Richard Amasino University of Wisconsin both differential screening of cDNA libraries made from mRNAs of naturally senescing leaf tissue and subtractive Buchanan-Wollaston and Ainsworth, 1997 Buchanan-Wollaston and Ainsworth, 1997 Buchanan-Wollaston and Ainsworth, 1997 Buchanan-Wollaston and Ainsworth, 1997 a In most cases gene function has been determined by sequence homology to previously characterized genes published in DNA and protein databases. Up-regulation of...

Loss of Vegetative Regenerative Capacity

Often, monocarpic plants cease their vegetative growth fairly abruptly early in their reproductive phase Nooden, 1980 Kelly and Davies, 1988 Reekie, 1999 . Conversely, the perennial polycarpic pattern requires continued vegetative growth Thomas et al, 2000 . This prominent shift diversion in growth-related allocation of resources in monocarpy seems to be part of a reproductive strategy that optimizes reproductive output for these plants Section V below . Not only does this shift divert the...

Effects of Darkness

An old and extensive literature shows that light deprivation, particularly darkness, accelerates leaf senescence in many species Meyer, 1918 Simon, 1967 Goldthwaite andLaetsch, 1967 . Quite reasonably, it was assumed for many years that the primary action of light on leaf senescence was through photosynthesis, i.e., lack of light for photosynthesis caused starvation and thereby senescence and death. Haber et al. 1969 were among the first to challenge this idea, and one of their lines of...

Hormonal Regulation of Plant PCD

A well-studied PCD model in plants is camptothecin-mediated cell death in tomato cell suspensions see De Jong et al., 2002 and references therein . Camptothecin, a topo isomerase-I inhibitor and inducer of PCD in animals Kaufmann, 1998 Simizu et al., 1998 , causes cell death in tomato suspension in a manner reminiscent of animal apoptosis chromatin condensation, DNA and nuclear fragmentation. Inhibitors that inhibit generation of reactive oxygen species ROS Lamb and Dixon, 1997 , superoxide O2-...

Cell Death in Plant Disease Mechanisms and

Role of Cell Death during Plant-Pathogen Interactions 38 III. Structural and Biochemical Changes Accompanying Cell Death during Plant Disease 38 IV. Definition of Steps Involved in the Signaling Process of Cell Death Induction during Plant-Pathogen Interactions 39 V. Molecular Components for Cell Death Control during Plant-Pathogen Interactions 41 VI. Glogal Analyses of Markers for Cell Death Induction by A. Isolation and Characterization of HR Markers 43 B. Comparative Analyses of Cell...

Senescence in Polycarpic Plants and Clones

Although polycarpic plants and clones may decline in their vigor, e.g., growth rates, etc., and they may even have characteristic longevities, they may not experience whole plant senescence in the sense of endogenously programmed degeneration physiologists' sense , and usually, this decline is gradual Nooden, 1988 . It seems necessary to differentiate here between unitary organisms and clones. A unitary organism would be a single individual integrated physiological unit with a single root-shoot...

Genes Involved in Execution of Senescence A Overview

For the senescence program to proceed, there should be genes that execute the degeneration process. Many senescence-associated genes have been identified from a variety of plants on the basis of mRNA increases see Chapter 4 . Many of these are involved in degradation processes, including chlorophyll breakdown, and nitrogen and lipid remobilization. These individual genes are likely to affect only some senescence symptoms. It is possible that these genes may have to be combined in order to exert...

The Scope of PCD in Plants

Although the widespread occurrence of PCD in plants was recognized in earlier literature Barlow, 1982 Nooden, 1988 , the importance has not been recognized broadly in biology. Ameisen 1998 has stated, the existence of PCD in plants has long remained neglected, and he offered that evidence for its existence has not yet revealed much about the extent of its role, the nature of the mechanisms involved, or the nature of its genetic regulation. Thus, there is a real need to emphasize the scope and...

Isolation and Characterization of HR Markers

Induction of cell death during the HR or by treatment with pathogen derived toxins such as victorin has been shown to require de novo protein synthesis He et al., 1994 Navarre and Wolpert, 1999 . These observations suggest that cell death induction during resistance as well as disease requires the expression of new plant proteins. Several studies aimed at isolating and characterizing genes specifically activated in one particular type of pathogen-induced cell death have been carried out by...

Genes Controlling Vegetative Growth Regeneration and Monocarpic Senescence

Monocarpic senescence is the degeneration leading to death of the whole plant at the end of the reproductive phase in monocarpic plants. As a prerequisite to or as a part of monocarpic senescence, vegetative growth ceases, so the plant can no longer regenerate its assimila-tory structures. Eventually, the existing leaves and other parts senesce, and the plant dies Nooden, 1988b . The mutations that make plants live longer do so mainly by extending their regenerative ability Nooden and Penney,...