Flexible resource allocation during plant defense responses

Abstract

Plants are organisms composed of modules connected by xylem and phloem transport streams. Attack by both insects and pathogens elicits sometimes rapid defense responses in the attacked module. We have also known for some time that proteins are often reallocated away from pathogen-infected tissues, while the same infection sites may draw carbohydrates to them. This has been interpreted as a tug of war in which the plant withdraws critical resources to block microbial growth while the microbes attempt to acquire more resources. Sink-source regulated transport among modules of critical resources, particularly carbon and nitrogen, is also altered in response to attack. Insects and jasmonate can increase local sink strength, drawing carbohydrates that support defense production. Shortly after attack, carbohydrates may also be drawn to the root. The rate and direction of movement of photosynthate or signals in phloem in response to attack is subject to constraints that include branching, degree of connection among tissues, distance between sources and sinks, proximity, strength, and number of competing sinks, and phloem loading/unloading regulators. Movement of materials (e.g., amino acids, signals) to or from attack sites in xylem is less well understood but is partly driven by transpiration. The root is an influential sink and may regulate sink-source interactions and transport above and below ground as well as between the plant and the rhizosphere and nearby, connected plants. Research on resource translocation in response to pathogens or herbivores has focused on biochemical mechanisms; whole-plant research is needed to determine which, if any, of these plant behaviors actually influence plant fitness.

Alteration of plant primary metabolism in response to insect herbivory

“…Consistent with the hypothesis that import of systemic resources promotes plant defense, treatment with volatile defense signal methyl jasmonate, mechanical damage, and actual insect feeding all can increase movement of carbohydrates toward treatment sites in many plant species (Sturm and Chrispeels, 1990;Zhang et al, 1996;Ehness et al, 1997;Ohyama and Hirai, 1999;Allison and Schultz, 2005;Schultz et al, 2013). In methyl jasmonate-treated or wounded Arabidopsis, radioactively labeled carbohydrates were imported into sink leaves within hours after treatment, and were incorporated into defense-related compounds such as cinnamic acid and phenolic glycosides (Ferrieri et al, 2012).…”

“…Reallocation of carbohydrates is thought to be primarily driven by differential sink strength of tissues, which is in turn heavily influenced by activities of cell wall-bound invertases (Sturm and Tang, 1999;Schultz et al, 2013). In congruence with this framework, herbivore-induced carbohydrate depletion has coincided with decreased invertase activities in the same tissues (Machado et al, 2013;Robert et al, 2014).…”

A comparison of plants and animals in their responses to risk of consumption

“…For example, rooted plants cannot flee an attacker so their behavioral responses to risk necessarily involve changing defensive morphology or chemistry or translocating valuable molecules to unattacked tissues [32]. These plant responses are often slower than the speed of movement of many herbivores.…”

Factors Affecting to Allocation in Plants

“…Bu nedenle bitki, yaşam kaynaklarını "minimum enerjiden maksimum fayda sağlama" prensibine göre, en ekonomik biçimde kullanmak zorundadır. Ekofizyolojinin önemli bir konusu olan allokasyon, organizmaların büyüme, hayatta kalma, savunma ve üreme faaliyetleri için, sınırlı kaynakları (enerji, biyomas, besin elementleri vs.) taşıması ve bu fonksiyonları yerine getirmek üzere paylaştırması olarak tanımlanmaktadır (Bazzaz et al, 2005;Schultz et al, 2013). Bu nedenle bitkiler hayatta kalabilmek için, gerek ekolojik faktörler ve gerekse bitkiye bağlı içsel faktörlerin (genetik, ontogenik, yaş, yaşam formu, vs.) oldukça değişkenlik göstermesi nedeniyle, optimal bir kaynak taşıma (allokasyon) modeli geliştirerek başarılı olmaya çalışırlar.…”