Here we highlight how both the root and shoot environment impact on whole plant hormone balance, particularly
under stresses such as soil drying, and relate hormone ratios and relative abundances to processes influencing
plant performance and yield under both mild and more severe stress. We discuss evidence (i) that abscisic acid
(ABA) and ethylene act antagonistically on grain-filling rate amongst other yield-impacting processes; (ii) that ABA’s
effectiveness as an agent of stomatal closure can be modulated by coincident ethylene or cytokinin accumulation;
and (iii) that enhanced cytokinin production can increase growth and yield by improving foliar stay-green indices
under stress, and by improving processes that impact grain-filling and number, and that this can be the result of
altered relative abundances of cytokinin and ABA (and other hormones). We describe evidence and novel processes
whereby these phenomena are/could be amenable to manipulation through genetic and management routes, such
that plant performance and yield can be improved. We explore the possibility that a range of ABA-ethylene and ABAcytokinin
relative abundances could represent targets for breeding/managing for yield resilience under a spectrum
of stress levels between severe and mild, and could circumvent some of the pitfalls so far encountered in the
massive research effort towards breeding for increases in the complex trait of yield.
Here we highlight how both the root and shoot environment impact on whole plant hormone balance, particularlyunder stresses such as soil drying, and relate hormone ratios and relative abundances to processes influencingplant performance and yield under both mild and more severe stress. We discuss evidence (i) that abscisic acid(ABA) and ethylene act antagonistically on grain-filling rate amongst other yield-impacting processes; (ii) that ABA’seffectiveness as an agent of stomatal closure can be modulated by coincident ethylene or cytokinin accumulation;and (iii) that enhanced cytokinin production can increase growth and yield by improving foliar stay-green indicesunder stress, and by improving processes that impact grain-filling and number, and that this can be the result ofaltered relative abundances of cytokinin and ABA (and other hormones). We describe evidence and novel processeswhereby these phenomena are/could be amenable to manipulation through genetic and management routes, suchthat plant performance and yield can be improved. We explore the possibility that a range of ABA-ethylene and ABAcytokininrelative abundances could represent targets for breeding/managing for yield resilience under a spectrumof stress levels between severe and mild, and could circumvent some of the pitfalls so far encountered in themassive research effort towards breeding for increases in the complex trait of yield.
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