Physiological and ecological constraints play key roles in the evolution of plant growth patterns, especially in relation to defenses against herbivores. Phenotypic and life history theories are unified within the growth-differentiation balance (GDB) framework, forming an integrated system of theories explaining and predicting patterns of plant defense and competitive interactions in ecological and evolutionary time. Plant activity at the cellular level can be classified as growth (cell division and enlargement) of differentiation (chemical and morphological changes leading to cell maturation and specialization). The GDB hypothesis of plant defense is premised upon a physiological trade-off between growth and differentiation processes. The trade-off between growth and defense exists because secondary metabolism and structural reinforcement are physiologically constrained in dividing and enlarging cells, and because they divert resources from the production of new leaf area. Hence the dilemma of plants: Th...

https://www.jstor.org/stable/pdfplus/2830650.pdf

The dilemma of plants: To grow or defend.

Inducible defenses are responses activated through a previous encounter with a consumer or competitor that confer some degree of resistance to subsequent attacks. While the importance of inducible resistance has long been known in host-parasite interactions, it is only recently that its importance has emerged in other natural systems. Althought the structural defenses produced by invertebrates to their competitors and predators are by no means the same as an immune response triggered by parasites, these responses all share the properties of (1) specificity, (2) amplification and (3) memory. This review discusses the following ecological consequences and evolutionary causes of inducible defenses: (1) Inducible defenses render historical factors important in biological interactions and can affect the probability of individual survival and growth, as well as affect population dynamics of consumers in some circumstances. (2) Although the benefits of inducible defenses are often balanced by fitness costs, incl...

The ecology and evolution of inducible defenses

Plant defenses against insect herbivores and necrotrophic pathogens are differentially regulated by different branches of the jasmonic acid (JA) signaling pathway. In Arabidopsis, the basic helix-loop-helix leucine zipper transcription factor (TF) MYC2 and the APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) domain TF ORA59 antagonistically control these distinct branches of the JA pathway. Feeding by larvae of the specialist insect herbivore Pieris rapae activated MYC2 transcription and stimulated expression of the MYC2-branch marker gene VSP2, while it suppressed transcription of ORA59 and the ERF-branch marker gene PDF1.2. Mutant jin1 and jar1-1 plants, which are impaired in the MYC2-branch of the JA pathway, displayed a strongly enhanced expression of both ORA59 and PDF1.2 upon herbivory, indicating that in wild-type plants the MYC2-branch is prioritized over the ERF-branch during insect feeding. Weight gain of P. rapae larvae in a no-choice setup was not significantly affected, but in a two-choice setup the larvae consistently preferred jin1 and jar1-1 plants, in which the ERF-branch was activated, over wild-type Col-0 plants, in which the MYC2-branch was induced. In MYC2- and ORA59-impaired jin1-1/RNAi-ORA59 plants this preference was lost, while in ORA59-overexpressing 35S:ORA59 plants it was gained, suggesting that the herbivores were stimulated to feed from plants that expressed the ERF-branch rather than that they were deterred by plants that expressed the MYC2-branch. The feeding preference of the P. rapae larvae could not be linked to changes in glucosinolate levels. Interestingly, application of larval oral secretion into wounded leaf tissue stimulated the ERF-branch of the JA pathway, suggesting that compounds in the oral secretion have the potential to manipulate the plant response toward the caterpillar-preferred ERF-regulated branch of the JA response. Our results suggest that by activating the MYC2-branch of the JA pathway, plants prevent stimulation of the ERF-branch by the herbivore, thereby becoming less attractive to the attacker.

/pdf/rewiring-of-the-jasmonate-signaling-pathway-in-arabidopsis-17vg3rj71x.pdf

Rewiring of the Jasmonate Signaling Pathway in Arabidopsis during Insect Herbivory.

Contents

Summary 213

I. Introduction 213
II. Source–sink model: carbohydrate signaling 214
III. Effect of ozone on above-ground sources and sinks 216
IV. Decreased allocation below ground 218
V. Carbon flux to soils 220
VI. Soil food web 223
VII. Summary, conclusions and future research 223

Acknowledgements 223


References 223



Summary
The role of tropospheric ozone in altering plant growth and development has been the subject of thousands of publications over the last several decades. Still, there is limited understanding regarding the possible effects of ozone on soil processes. In this review, the effects of ozone are discussed using the flow of carbon from the atmosphere, through the plant to soils, and back to the atmosphere as a framework. A conceptual model based on carbohydrate signaling is used to illustrate physiological changes in response to ozone, and to discuss possible feedbacks that may occur. Despite past emphasis on above-ground effects, ozone has the potential to alter below-ground processes and hence ecosystem characteristics in ways that are not currently being considered.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1469-8137.2003.00674.x

Source–sink balance and carbon allocation below ground in plants exposed to ozone

Summary
1. Induced resistance is now widely accepted as a potent and widespread ecological force although several pieces of the story remain very poorly known. Theory predicts that induced defences should be favoured in variable environments especially when plants can use cues to reliably predict future conditions; however, this idea has not been seriously evaluated for plants.

2. Theory also predicts that plastic, induced defences should be favoured over permanent, constitutive defences if defences are costly and not always needed. This hypothesis has received considerable attention and limited support; resource allocation costs have been difficult to detect although ecological costs of defence may be more common. Recently, priming has emerged as a mechanism that may further reduce costs. Primed plants do not immediately produce the gene products associated with induced resistance but later respond more rapidly and strongly to severe or repeated attacks. It remains to be determined how common priming is.

3. Much of what we know about induced resistance is from the herbivore’s point of view. Induced resistance will be beneficial from the plant’s point of view if herbivores avoid induced plants, but the behavioural responses of herbivores to induced plant variation are still poorly studied.

4. Recent progress in understanding the detailed spatial and temporal extent of induced resistance has improved our appreciation of the phenomenon. Although some induced responses are systemic throughout entire plant individuals, many others have been found to be localized to damaged tissues. Plant vascular architecture and transpiration rates greatly constrain the distribution of vascular cues. Some plants rely on volatile cues that are active over relatively short distances and may be subject to eavesdropping by other plants, herbivores, and carnivores. Similarly, the temporal duration of induced responses may have important consequences on effectiveness although limited information is available concerning lag times before induction and relaxation times following induction.

5. Limited spatial and temporal scales of induced responses make plants more variable from the herbivore’s point of view. Recent work suggests that plant heterogeneity may be difficult for herbivores to cope with although this hypothesis awaits further empirical testing.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2010.01789.x

The ecology and evolution of induced resistance against herbivores

Three scales of wound-induced chemical responses in plants are identified: (1) highly localised chemical changes associated with disruption of cell compartmentation; (2) changes induced in cells surrounding the damaged area, forming a kind of halo around the damage, and (3) more widely-dispersed changes which may affect an entire organ, branch or plant. A brief review of the literature reveals that such chemical responses are very widespread in plants, and many of the substances formed are known to affect adversely the growth, development, or reproduction of insects. It is argued that wound-induced changes in plant chemistry represent for insects a powerful selective pressure for the dispersal of grazing. Levels and patterns of invertebrate grazing in a range of herbaceous and deciduous woody plants sampled at the end of the growing seasons were examined. Leaves of many species exhibited a strikingly evident over-dispersion of grazing initiations, and in some cases the arrangement of holes appeared close to regularity. The pattern of damage between leaves was, in most cases, heavily biased towards a large proportion of leaves receiving a low level of grazing. These highly dispersed patterns of grazing damage are consistent with the hypothesis that wound-induced responses play an important role in determining patterns of insect feeding. They have important implications for the expected levels of insect exploitation of host plants and for the advantages to the plant of distributing grazing damage evenly through the canopy.

S. D. Wratten

Papers

Wound induced defences in plants and their consequences for patterns of insect grazing.