Abstract
Defoliation tolerance (DT) in Amaranthus cruentus is known to reach its apex at the panicle emergence (PE) phase and to decline to minimal levels at flowering (FL). In this study, defoliation-induced changes were recorded in the content of non-structural carbohydrates and raffinose family oligosaccharides (RFOs), and in the expression and/or activity of sugar starvation response-associated genes in plants defoliated at different vegetative and reproductive stages. This strategy identified sugar-starvation-related factors that explained the opposite DT observed at these key developmental stages. Peak DT at PE was associated with increased cytosolic invertase (CI) activity in all organs and with the extensive induction of various class II trehalose-phosphate synthase (TPS) genes. Contrariwise, least DT at FL coincided with a sharp depletion of starch reserves and with sucrose (Suc) accumulation, in leaves and stems, the latter of which was consistent with very low levels of CI and vacuolar invertase activities that were not further modified by defoliation. Increased Suc suggested growth-inhibiting conditions associated with altered cytosolic Suc-to-hexose ratios in plants defoliated at FL. Augmented cell wall invertase activity in leaves and roots, probably acting in a regulatory rather than hydrolytic role, was also associated with minimal DT observed at FL. The widespread contrast in gene expression patterns in panicles also matched the opposite DT observed at PE and FL. These results reinforce the concept that a localized sugar starvation response caused by C partitioning is crucial for DT in grain amaranth.
Highlights
The ability of plants to cope with leaf-tissue loss caused by herbivory or mechanical damage is a plastic trait influenced by environmental conditions (Maschinski and Whitham, 1989)
Changes in the expression levels of Tre biosynthesis and hydrolysis genes, in addition to genes coding for proteins associated with master regulators of metabolism, were analyzed
The opposite defoliation tolerance detected at panicle emergence (PE) and FL was reflected by the differential ways in which the developmentally augmented Suc and starch reserves were subsequently affected by this stress in all organs examined
Summary
The ability of plants to cope with leaf-tissue loss caused by herbivory or mechanical damage is a plastic trait influenced by environmental conditions (Maschinski and Whitham, 1989). Rapid utilization of C reserves was shown to sustain leaf regrowth in Lolium perenne in the first hours after compensation of defoliation and after repeated grazing (Morvan-Bertrand et al, 2001; Lee et al, 2010). Such response was associated with an increment of sucrose (Suc) transport and the de novo synthesis of Suc transporters (Berthier et al, 2009). The above mechanisms can partially explain compensation and the expression of tolerance, there is limited information about the physiological, biochemical, and molecular processes that support them
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
