Stem metabolism under drought stress – a paradox of increasing respiratory substrates and decreasing respiratory rates

Abstract

Metabolic changes underpinning drought-induced variations in stem respiration (R s ) are unknown. We measured R s rates and metabolite and gene expression profiles in Ulmus minor Mill. and Quercus ilex L. seedlings subjected to increasing levels of drought stress to better understand how carbon, nitrogen and energy metabolism interact during drought. In both species, only plants showing extreme stress symptomsi.e. negligible rates of leaf stomatal conductance and photosynthesis, and high stem dehydration (30-50% of maximum water storage) and contraction (50-150 μm week −1 )exhibited lower R s rates than well-watered plants. Abundance of low-molecular weight sugars (e.g. glucose and fructose) and sugar alcohols (e.g. mannitol) increased with drought, at more moderate stress and to a higher extent in Q. ilex than U. minor. Abundance of amino acids increased at more severe stress, more abruptly, and to a higher extent in U. minor, coinciding with leaf senescence, which did not occur in Q. ilex. Organic acids changed less in response to drought: threonate and glycerate increased, and citrate decreased although slightly in both species. Transcripts of genes coding for enzymes of the Krebs cycle decreased in Q. ilex and increased in U. minor in conditions of extreme drought stress. The maintenance of R s under severe growth and photosynthetic restrictions reveals the importance of stem mitochondrial activity in drought acclimation. The eventual decline in R s diverts carbon substrates from entering the Krebs cycle that may help to cope with osmotic and oxidative stress during severe drought and to recover hydraulic functionality afterwards.

Mechanistic drivers of stem respiration: A modelling exercise across species and seasons

“…Stem respiration did not seasonally increase with NSC availability in any of the surveyed species, nor consistent positive relationships were found when separately regressing maintenance and growth respiration components against [SS] and [starch] across sampled tissues. On the contrary, R S decreased with increasing respiratory substrate in oak trees, as similarly observed in Ulmus minor and Quercus ilex trees (Rodríguez‐Calcerrada et al, 2020). In this study, when stem girth‐increment was successfully captured (for maple and oak trees), R S was positively related to stem growth and decoupled from shoot photosynthesis.…”

“…However, our results provide evidence against this view in woody tissues and support our first hypothesis (Figure 3). (Rodríguez-Calcerrada et al, 2020). In this study, when stem girthincrement was successfully captured (for maple and oak trees), R S was positively related to stem growth and decoupled from shoot photosynthesis.…”

Transcriptomic and Metabolomic Analyses Reveal That Fullerol Improves Drought Tolerance in Brassica napus L

“…The glycerate level was elevated in both Ulmus minor Mill. and Quercus ilex L. seedlings under drought [ 22 ]. These findings were in accordance with Rodríguez-Calcerrada et al [ 23 ], who stated that simple sugars and sugar alcohols presented a significant increase, whereas compound sugars (e.g., sucrose) decreased or did not change under severe drought stress conditions.…”

Unveiling resilience mechanisms of Quercus ilex seedlings to severe water stress: Changes in non-structural carbohydrates, xylem hydraulic functionality and wood anatomy

“…However, since sucrose accumulation was not observed, we suggest a high catabolism of this sugar due to the activity of apoplastic invertases, which, even if not directly examined in our study, are usually upregulated under water stress conditions and low pH (Pagliarani et al, 2019). Considering that wood is an important sink tissue for starch accumulation, we can surmise that the severe stress conditions reached in our experiment limited photosynthesis and induced the depletion of carbohydrate reserves that were used to maintain respiration and provide energy for cellular metabolism (Galiano et al, 2012;Noronha et al, 2018;Rodríguez-Calcerrada et al, 2021).…”