Photosynthetic response and peroxidases in relation to water and nutrient deficiency in gerbera

Abstract

CO 2 assimilation rate ( A), transpiration rate ( E), stomatal conductance ( g s), chlorophyll concentrations ( a, b, a+ b), specific peroxidase activities (PA) and peroxidases (anionic and cationic) isoforms were examined in two gerbera cultivars (cv. Lilabella and cv. Baracuda) grown in perlite hydroponically in three irrigation treatments [nutrient-irrigation (control), water-irrigation (nutrient deficiency) and non-irrigation (water and nutrient deficiency) treatment]. ( A), ( E), and ( g s) values were reduced in different ways between the two cultivars. CO 2 assimilation rate ( A) was unchanged in the nutrient-irrigation treatment in both cultivars and was rapidly reduced (0–100% from day 0 to day 11) in the order: non-irrigation > water-irrigation, more in cv. Baracuda than in cv. Lilabella in which this reduction was delayed by 1–2 days. Transpiration rate ( E) and stomatal conductance ( g s) values on day 11 of irrigation applications were not significantly different between the nutrient-irrigation and the water-irrigation treatment in cv. Baracuda, while a significant decrease was noticed in cv. Lilabella. On the other hand, the above photosynthetic parameters were drastically decreased in both cultivars in the non-irrigation treatment, more pronounced in cv. Baracuda. Chlorophyll concentration was unchanged on the last day of application (day 11) in cv. Lilabella, while a decrease in both water-irrigation and non-irrigation treatment was noticed in the sensitive to irrigation applications cv. Baracuda. In the nutrient-irrigation treatment the PA remained almost unchanged during the course of the experiment in both cultivars, while from day 1 to day 5 a two-fold increase of the PA was noticed in cv. Lilabella in comparison to cv. Baracuda, followed by a sharp increase in cv. Lilabella and a decrease in cv. Baracuda from day 9 to day 11 of application. Electrophoresis revealed two soluble anionic peroxidase (A 1 and A 2) isoforms in all irrigation treatments in both cultivars. In contrast, cationic peroxidase isoforms were only detected in water-irrigation (C 1, C 2 and C 3) and non-irrigation (C 2 and C 3) treatment in cv. Lilabella. It seems that differences in photosynthetic parameters within the irrigation treatments and between cultivars were related to the increase of specific peroxidase activity and the appearance of new cationic peroxidase isoforms. These results suggest that the less sensitive to water and/or nutrient deficiency cv. Lilabella might provide a better protection against reactive oxygen species (ROS) by increasing the activity of peroxidases and the appearance of new cationic peroxidase isoforms.