Interaction among species, time-of-day, and soil water potential on biochemical and physiological characteristics of cladodes of Opuntia.

The physiology and biochemistry of young Opuntia spp. cladodes relate with their Crassulacean acid metabolism, which extends over the day-night cycle in four phases, is species-dependent and is affected by water availability. This study aimed to assess the interaction among species, time-of-day, and the soil water potential (Ψ) on biochemical and physiological characteristics of cladodes of Opuntia species. Three-week-old cladodes were harvested at 7:00 a.m. and 3:00 p.m. from plants with or without irrigation for 30 d (-0.17 and -5.72 MPa soil Ψ), from O. albicarpa, O. ficus-indica, O. hyptiacantha, O. megacantha, and O. streptacantha. The experimental design was a factorial 5 x 2 x 2 (species, sampling time and soil Ψ). The experimental unit was one cladode per plant, and six repetitions were evaluated. Total acids, glucose, fructose, sucrose, starch, total phenolics, free amino acids, and soluble proteins concentrations were evaluated, as well as acid invertase and neutral invertase activities. The interaction among species x soil Ψ and species x time of the day was significant (P ≤ 0.05) in all variables evaluated. An exception was the species x soil Ψ on starch concentration (P = 0.1827). The biochemical and physiological characteristics of Opuntia cladodes were modified by the time of the day and soil Ψ interaction, but most of the characteristics were positively or inversely affected depending on the species, frequently displaying a descending trend following O. streptacantha, O. hyptiacantha, O. megacantha, O. albicarpa and O. ficus-indica. The total acids, glucose, fructose, starch, soluble proteins, and free amino acids concentrations revealed that domestication significantly modifies C and N metabolism in Opuntia.