Differential behaviours in two species of Eucalyptus exposed to aluminium

et al. 2021

BMC Plant Biol

Background Eucalyptus is the main plantation wood species, mostly grown in aluminized acid soils. To understand the response of Eucalyptus clones to aluminum (Al) toxicity, the Al-tolerant Eucalyptus grandis × E. urophylla clone GL-9 (designated “G9”) and the Al-sensitive E. urophylla clone GL-4 (designated “W4”) were employed to investigate the production and secretion of citrate and malate by roots. Results Eucalyptus seedlings in hydroponics were exposed to the presence or absence of 4.4 mM Al at pH 4.0 for 24 h. The protein synthesis inhibitor cycloheximide (CHM) and anion channel blocker phenylglyoxal (PG) were applied to explore possible pathways involved in organic acid secretion. The secretion of malate and citrate was earlier and greater in G9 than in W4, corresponding to less Al accumulation in G9. The concentration of Al in G9 roots peaked after 1 h and decreased afterwards, corresponding with a rapid induction of malate secretion. A time-lag of about 6 h in citrate efflux in G9 was followed by robust secretion to support continuous Al-detoxification. Malate secretion alone may alleviate Al toxicity because the peaks of Al accumulation and malate secretion were simultaneous in W4, which did not secrete appreciable citrate. Enhanced activities of citrate synthase (CS) and phosphoenolpyruvate carboxylase (PEPC), and reduced activities of isocitrate dehydrogenase (IDH), aconitase (ACO) and malic enzyme (ME) were closely associated with the greater secretion of citrate in G9. PG effectively inhibited citrate and malate secretion in both Eucalyptus clones. CHM also inhibited malate and citrate secretion in G9, and citrate secretion in W4, but notably did not affect malate secretion in W4. Conclusions G9 immediately secrete malate from roots, which had an initial effect on Al-detoxification, followed by time-delayed citrate secretion. Pre-existing anion channel protein first contributed to malate secretion, while synthesis of carrier protein appeared to be needed for citrate excretion. The changes of organic acid concentrations in response to Al can be achieved by enhanced CS and PEPC activities, but was supported by changes in the activities of other enzymes involved in organic acid metabolism. The above information may help to further explore genes related to Al-tolerance in Eucalyptus.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Metabolic acclimation supports higher aluminium-induced secretion of citrate and malate in an aluminium-tolerant hybrid clone of Eucalyptus

et al. 2021

BMC Plant Biol

“…The bene cial effect of Al on growth of plants adapted to low pH soils was ascribed to increased uptake of nutrients by roots (Osaki et al, 1997). Similarly, Al tolerance in Eucalyptus was explained by the maintenance of nutrients and photosynthesis (Silva et al, 2010(Silva et al, , 2017. Another study found that a new low-molecular-weight Al-binding ligand, oenothein b, from roots contributed to Al tolerance in E. camaldulensis (Tahara et al, 2008(Tahara et al, , 2017, encouraging further exploration to nd other mechanisms that help fast-growing Eucalyptus clones to manage excessive soluble Al in acidic soil.…”

Section: The Transport Pathways Of Citrate and Malate Secretion Are Pmentioning

confidence: 99%

Metabolic acclimation supports higher aluminium-induced secretion of citrate and malate in an aluminium-tolerant hybrid clone of Eucalyptus

et al. 2020

Preprint

Background Eucalyptus is the main timber species, most of which are hybrid clones, and usually grow in aluminized acid soil in China. The exudation of organic acids from roots may contribute to detoxification of Al and lead to the Al-tolerance in Eucalyptus genotypes. To further understand the organic acid response in Al tolerance in Eucalyptus, the Al-tolerant Eucalyptus grandis × E. urophylla clone GL-9 (marked as “G9”) and the Al-sensitive Eucalyptus urophylla clone GL-4 (marked as “W4”) were used to investigate the secretion and metabolism of citrate and malate in roots. Results Eucalyptus seedlings in hydroponics were exposed to the presence or absence of 4.4 mM Al at pH 4.0 for 24 hours. The protein synthesis inhibitor cycloheximide (CHM) and the anion channel blocker phenylglyoxal (PG) were applied to explore possible pathways involved in organic acid secretion. The Al treatments caused higher Al accumulation in roots of both clones. The secretion of malate and citrate was greater in G9 than in W4, corresponding to the relatively higher tolerance in G9 to Al. The peak Al concentration occurred after 1 h in G9 roots and declined afterward, indicating the activation of detoxification to alleviate Al accumulation. After 6 h of Al exposure, the efflux of citrate dramatically increased in G9 after a substantial lag phase, while both peak Al accumulation in roots and peak malate secretion occurred and there was no induction of citrate secretion in W4. Enhanced activity for citrate synthase and phosphoenolpyruvate carboxylase, and reduced activity for NADP-isocitrate dehydrogenase, aconitase and NADP-malic enzyme were closely associated with the greater secretion of citrate in G9. Both PG and CHM were effective inhibitors of citrate and malate secretion in both Eucalyptus clones, except the malate secretion in W4 was not affected by CHM. Conclusions In two different Al-tolerant Eucalyptus clones, both secretion and internal accumulation of citrate and malate in roots were involved in Al detoxification. An anion channel on the plasma membrane could be an important mode of organic acid secretion. Citrate and relevant metabolizing enzymes led more important role in the response to Al in E. grandis × E. urophylla.

“…We speculate that other organic substances might be involved in detoxifying Al in some Eucalyptus genotypes. A consequence of Al tolerance in Eucalyptus was the maintenance of nutrients and photosynthesis [17,43]. A new low-molecular-weight Al-binding ligand from roots, oenothein b, contributed to Al tolerance in E. camaldulensis [12,44].…”

Section: An Al-tolerant Eucalyptus Hybrid Clone Has Enhanced Accumulamentioning

confidence: 99%

Metabolic acclimation supports higher aluminium-induced secretion of citrate and malate in an aluminium-tolerant hybrid clone of Eucalyptus

et al. 2020

Preprint

Background: Eucalyptus is the main plantation wood species, mostly grown in aluminized acid soils. To understand the response of Eucalyptus clones to aluminum (Al) toxicity, the Al-tolerant Eucalyptus grandis × E. urophylla clone GL-9 (designated “G9”) and the Al-sensitive E. urophylla clone GL-4 (designated “W4”) were employed to investigate the production and secretion of citrate and malate by roots.Results: Eucalyptus seedlings in hydroponics were exposed to the presence or absence of 4.4 mM Al at pH 4.0 for 24 hours. The protein synthesis inhibitor cycloheximide (CHM) and anion channel blocker phenylglyoxal (PG) were applied to explore possible pathways involved in organic acid secretion. The secretion of malate and citrate was earlier and greater in G9 than in W4, corresponding to less Al accumulation in G9. The concentration of Al in G9 roots peaked after 1h and decreased afterwards, corresponding with a rapid induction of malate secretion. A time-lag of about 6h in citrate efflux in G9 was followed by robust secretion to support continuous Al-detoxification. Malate secretion alone may alleviate Al toxicity because the peaks of Al accumulation and malate secretion were simultaneous in W4, which did not secrete appreciable citrate. Enhanced activities of citrate synthase (CS) and phosphoenolpyruvate carboxylase (PEPC), and reduced activities of isocitrate dehydrogenase (IDH), aconitase (ACO) and malic enzyme (ME) were closely associated with the greater secretion of citrate in G9. PG effectively inhibited citrate and malate secretion in both Eucalyptus clones. CHM also inhibited malate and citrate secretion in G9, and citrate secretion in W4, but notably did not affect malate secretion in W4.Conclusions: G9 immediately secrete malate from roots, which had an initial effect on Al-detoxification, followed by time-delayed citrate secretion. Pre-existing anion channel protein first contributed to malate secretion, while synthesis of carrier protein appeared to be needed for citrate excretion. The changes of organic acid concentrations in response to Al can be achieved by enhanced CS and PEPC activities, but was supported by changes in the activities of other enzymes involved in organic acid metabolism. The above information may help to further explore genes related to Al-tolerance in Eucalyptus.