Metabolic regulation of leaf senescence: interactions of sugar signalling with biotic and abiotic stress responses

Abstract

Sugars are important signals in the regulation of plant metabolism and development. During stress and in senescing leaves, sugars often accumulate. In addition, both sugar accumulation and stress can induce leaf senescence. Infection by bacterial and fungal pathogens and attack by herbivores and gall-forming insects may influence leaf senescence via modulation of the sugar status, either by directly affecting primary carbon metabolism or by regulating steady state levels of plant hormones. Many types of biotic interactions involve the induction of extracellular invertase as the key enzyme of an apoplasmic phloem unloading pathway, resulting in a source-sink transition and an increased hexose/sucrose ratio. Induction of the levels of the phytohormones ethylene and jasmonate in biotic interactions results in accelerated senescence, whereas an increase in plant- or pathogen-derived cytokinins delays senescence and results in the formation of green islands within senescing leaves. Interactions between sugar and hormone signalling also play a role in response to abiotic stress. For example, interactions between sugar and abscisic acid (ABA) signalling may be responsible for the induction of senescence during drought stress. Cold treatment, on the other hand, can result in delayed senescence, despite sugar and ABA accumulation. Moreover, natural variation can be found in senescence regulation by sugars and in response to stress: in response to drought stress, both drought escape and dehydration avoidance strategies have been described in different Arabidopsis accessions. The regulation of senescence by sugars may be key to these different strategies in response to stress.

Transitioning to the Next Phase: The Role of Sugar Signaling throughout the Plant Life Cycle

“…Senescence can be induced by dark treatment, which results in starvation, but global changes in gene expression during dark treatment only show little similarity with developmental senescence . Instead, senescence triggered by a combination of low nitrogen with 2% Glc supply Pourtau et al, 2004Pourtau et al, , 2006 shows high similarity with developmental senescence (Wingler and Roitsch, 2008;Wingler et al, 2009). Sugar accumulation in old leaves signals an excess of carbon relative to nitrogen availability, and sugars can thereby integrate other environmental signals to regulate nitrogen allocation .…”

Metabolic Regulation of Leaf Senescence in Sunflower (Helianthus annuus L.) Plants

“…By virtue of its lying at the crossroads of carbon and nitrogen metabolism, senescence is regulated by carbon and nitrogen signals. Increasing evidence suggests a role for hexose accumulation in ageing leaves as a signal for either senescence initiation or acceleration in annual plants Moore et al, 2003;Díaz et al, 2005;Masclaux-Daubresse et al, 2005;Parrott et al, 2005;Pourtau et al, 2006;Wingler & Roitsch, 2008;Agüera et al, 2010). Recently, the role of sugar accumulation or starvation in leaf senescence was critically evaluated by van Doorn (2008), who pointed out that little is known about sugar concentrations and senescence regulation in different tissues and cells.…”

“…Nitrogen and carbon metabolism plays a crucial role in the senescence process, which is seemingly governed by both external and internal factors. Thus, leaf senescence induction involves the joint action of external (nitrogen availability, light) and internal signals (regulating metabolites, C/N ratio) Wingler & Roitsch, 2008).…”

Discover and Connect Cellular Signaling

“…Emerging findings have brought numerous exciting new molecular links to support the central roles of SnRK1 (Arabidopsis KIN10/11) in sugar and stress signaling (Baena-González and Sheen, 2008; Ramon et al, 2008;Wingler and Roitsch, 2008;Hanson and Smeekens, 2009). For example, SnRK1 is implicated in resistance to geminivirus infection (Shen et al, 2009), hypersensitive response (Szczesny et al, 2010), and sugar reallocation to roots to tolerate herbivory (Schwachtje et al, 2006).…”

“…Further studies will provide more surprising regulatory mechanisms underlying sugar and hormone connections in different organs and cell types at various developmental stages (Gibson, 2005;BaenaGonzález and Sheen, 2008;Ramon et al, 2008;Hanson and Smeekens, 2009). More complex interactions between sugar and hormonal signaling in stress responses and organ-specific senescence will likely emerge in future research (Wingler and Roitsch, 2008). To deconvolute the signaling complexity and reconcile controversial observations, it will be very important to precisely define specific functions of HXK1 and KIN10/11 in different subcellular compartments with distinct partners and downstream signaling components in different physiological context and developmental stages of specific cell types (Gibson, 2005;Cho et al, 2006;Baena-González and Sheen, 2008;Ramon et al, 2008;Hanson and Smeekens, 2009).…”