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Aims: The effect of flooding on carbohydrate and nitrogen metabolism in leaves of peach (Prunus persica cv. UFSun) trees grafted onto six different Prunus spp. rootstock cultivars with either peach or plum parentage (peach: 'Flordaguard', 'Guardian', 'Nemaguard', 'P-22'; plum: 'R5064–5', and 'MP-29') were evaluated. Methods: Young peach trees were divided into two treatments: 1) non-flooded (control) and 2) flooded trees. Trees in the flooded treatment were subjected to 8 days of flooding (the root zone was submerged in containers filled with tap water) before leaves were harvested for biochemical analyses. Carbohydrate contents, enzymatic activity related to sucrose metabolism, glycolysis, nitrogen assimilation, and nitrogen metabolism of the scions were sampled from 40 leaves from each replication of each treatment. Results: Enzymatic activities of acid invertase were lower, and neutral invertase, sucrose synthase, and sucrose phosphosynthase were higher in scions of flooded trees compared to those of non-flooded trees. Trees in the flooded treatment had lower activity of enzymes involved in glycolysis. Carbohydrate contents (glucose, sucrose, and fructose) were higher in flooded than control plants for scions on all rootstocks except 'Flordaguard', in which the scion glucose level was not different between treatments. Scions in the flooded treatment had lower activity of enzymes involved in nitrogen assimilation and metabolism, and consequently lower NO3− and NO2− content than scions of trees in the non-flooded treatment. Conclusions: Flooding of P. persica cv. UFSun on six different Prunus spp. rootstocks caused enzymes in leaves of the scion involved in sucrose metabolism to be more active compared to those in the non-flooded control treatment. However, most enzymes involved in glycolysis were less active in flooded than non-flooded trees, except in scions on plum rootstocks, whose hexokinase (HK) and fructokinase (FK) enzymes were more active in the flooded than the non-flooded treatment. This suggests that scions on plum rootstocks could be more efficient at generating hexose sugars during glycolysis. The higher contents of sugars present in scions on flooded compared to non-flooded rootstocks could be indicative of translocation being hindered by flooding. Compared to non-flooded trees, flooding generally resulted in lower enzymatic activity related to nitrogen assimilation and metabolism (scions on plum rootstocks were largely unaffected), which consequently led to lower levels of nitrate and nitrite, while ammonium levels were higher in flooded scions. The lower HK and FK activities in scions on peach rootstocks compared to plum rootstocks may have made photosynthesis hexose limited, which would disrupt the electron transport chain and lead to less energy being available for nitrogen assimilation and metabolism as these processes are connected. [ABSTRACT FROM AUTHOR]

Past studies have already determined that selenium (Se) is very effective in alleviating cell oxidative damage caused by various abiotic stresses in plants. Past studies have also indicated other physiological pathways by which Se may benefit plants. In order to better understand the full array of potential applications for Se in agriculture, this study investigated the influence of Se on carbohydrate and nitrogen (N) metabolism in potato plants (Solanum tuberosum L. cv. Sante) grown under cadmium (Cd) and/or arsenic (As) toxicity. Potato plants were grown in a growth chamber and fertigated with Hoagland nutrient solution with or without Se (9 μM). After 48-d of growth under Cd (40 μM) and/or As (40 μM) stress, carbohydrate and N metabolism in leaves, roots and stolons were measured. For carbohydrate metabolism, various sugars—i.e., sucrose, starch, glucose, fructose, and total soluble sugar contents (TSSC)—and the activities of enzymes associated with sucrose metabolism and glycolysis—i.e., acid invertase (AI), neutral invertase (NI), sucrose-synthetase (SS), sucrose phosphatesynthetase (SPS), fructokinase (FK), hexokinase (HK), phosphofructokinase (PFK), and pyruvatekinase (PK)—were measured. For N metabolism, NO 3 −, NO 2 − and NH 4 + contents along with the enzymatic activities of nitrate reductase (NRA), nitrite reductase (NiRA), glutamine-synthetase (GS), and glutamate-synthetase (GOGAT) were measured. Overall, Cd and/or As treatments had reduced plant growth relative to those plants grown without heavy metal toxicity, due to hindered photosynthesis and alterations in N metabolism and glycolysis. Regarding N metabolism, heavy metal toxicity caused a reduction in NO 3 − and NO 2 − content and NRA and NiRA enzymatic activity and enhanced NH 4 + content and GDH activity in leaves, roots and stolons. Regarding glycolysis, the activity of enzymes of glycolysis—i.e., FK, HK, PFK, and PK—were also reduced. In the C metabolism study, plants combatted Cd and As toxicity naturally by an adaptation mechanism which caused an increase in soluble sugars (fructose, glucose, sucrose) by increasing NI, SS and SSP enzymatic activity. Supplementation with Se in the Cd and/or As treatments in the carbohydrate and N metabolism studies improved plant growth. Selenium supplementation in the Cd and As treatments decreased Cd and/or As content in the plant tissue and alleviating the Cd- and/or As-induced toxicity by enhancing the C-metabolism adaptation mechanism. Applying Se to Cd and As treatments also decreased nitrogen losses by hindering Cd- and As-induced changes in the N-metabolism. Se also limited Cd and As accumulation in the plant tissue by the antagonistic effect between Cd/Se and As/Se in the roots. The results of this study indicate that in the presence of Cd and/or As. soil toxicity, Se may be a powerful tool for promoting plant growth. Image 1 • Cd and/or As enhanced the enzymes of carbohydrate metabolism except AI activity. • Sugars and starch contents were lowered by Cd and/or As stress. • Cd and/or As toxicity limited the NO 3 − and NO 2 − contents but enhanced NH 4 + content. • Se alleviated Cd and/or As toxicity by modulating the glycolysis. • Se reduced oxidative damage by limiting the Cd and As uptake through roots. [ABSTRACT FROM AUTHOR]