Carbon and nitrogen metabolism in peach trees on different Prunus rootstocks in response to flooding.

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]