Interactions of abscisic acid and sugar signalling in the regulation of leaf senescence

Abstract

Leaf senescence can be triggered by a high availability of carbon relative to nitrogen or by external application of abscisic acid (ABA). Most Arabidopsis mutants with decreased sugar sensitivity during early plant development are either ABA insensitive (abi mutants) or ABA deficient (aba mutants). To analyse the interactions of carbon, nitrogen and ABA in the regulation of senescence, wild-type Arabidopsis thaliana (L.) Heynh. and aba and abi mutants were grown on medium with varied glucose and nitrogen supply. On medium containing glucose in combination with low, but not in combination with high nitrogen supply, senescence was accelerated and sucrose, glucose and fructose accumulated strongly. In abi mutants that are not affected in sugar responses during early development (abi1-1 and abi2-1), we observed no difference in the sugar-dependent regulation of senescence compared to wild-type plants. Similarly, senescence was not affected in the sugar-insensitive abi4-1 mutant. In contrast, the abi5-1 mutant did exhibit a delay in senescence compared to its wild type. As ABA has been reported to induce senescence and ABA deficiency results in sugar insensitivity during early development, we expected senescence to be delayed in aba mutants. However, the aba1-1 and aba2-1 mutants showed accelerated senescence compared to their wild types on glucose-containing medium. Our results show that, in contrast to sugar signalling in seedlings, ABA is not required for the sugar-dependent induction of leaf senescence. Instead, increased sensitivity to osmotic stress could have triggered early senescence in the aba mutants.

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 .…”

Living to Die and Dying to Live: The Survival Strategy behind Leaf Senescence

“…Exogenous application of ABA to rice flag leaves results in reduced chlorophyll contents and increased remobilization of carbon reserves (Yang et al, 2002). The senescence-promoting effect of ABA has been linked to its role in sugar signaling (Pourtau et al, 2004). Exogenous sugars can induce senescence, and during ageing, sugars accumulate prior to the onset of leaf senescence (Wingler and Roitsch, 2008).…”

“…Exogenous sugars can induce senescence, and during ageing, sugars accumulate prior to the onset of leaf senescence (Wingler and Roitsch, 2008). Moreover, the Glc-insensitive aba insensitive5-1 (abi5-1) and hexokinase1 (hxk1) mutants display delayed onset of senescence (Moore et al, 2003;Pourtau et al, 2004). Again, several ABA-deficient mutants exhibit precocious senescence even though they are Glc insensitive, suggesting that ABA might not be required for sugar-induced leaf senescence (Pourtau et al, 2004).…”

“…Moreover, the Glc-insensitive aba insensitive5-1 (abi5-1) and hexokinase1 (hxk1) mutants display delayed onset of senescence (Moore et al, 2003;Pourtau et al, 2004). Again, several ABA-deficient mutants exhibit precocious senescence even though they are Glc insensitive, suggesting that ABA might not be required for sugar-induced leaf senescence (Pourtau et al, 2004). However, it should be noted that ABA deficiency impairs stomatal closure, resulting in drought hypersensitivity, which makes it difficult to untangle the relationship between Glc and ABA in regulating the onset of senescence.…”

Sugar Sensing and Signaling

“…The same low glucose levels are inhibitory for seed germination but stimulatory for seedling growth and development (Yuan and Wysocka-Diller, 2006). In addition, ABA is not required for sugar-dependent induction of leaf senescence, although leaf senescence can be triggered independently by application of ABA and sugars (Pourtau et al, 2004). The complexity of these data suggests caution when analyzing tissue-and developmental stagespecific crosstalk between sugars and hormones.…”