The mobilization of defence mechanisms in the early stages of pea seed germination against Ascochyta pisi

Abstract

Ascochyta pisi is a necrotrophic pathogenic fungus, which mainly survives between seasons through infected seeds. Defence responses of pea embryo axes to A. pisi were investigated in the heterotrophic phase of seed germination and during the transition from the heterotrophic to the autotrophic phase. Germinated pea seeds, both non-inoculated and inoculated with A. pisi, were cultured in perlite for 96 h. Polarographic studies performed on intact embryo axes of germinating pea seeds infected with A. pisi showed a high respiratory intensity in time from 48 to 96 h after inoculation. Forty-eight-hour embryo axes of germinating pea seeds exhibited the highest respiration rate, which in infected axes was maintained at the following time points after inoculation. Moreover, at 72 and 96 h after inoculation, respiratory intensity was by 64% and 73% higher than in the control. Electron paramagnetic resonance analysis revealed a higher concentration of semiquinone free radicals with g values of g|| = 2.0031 ± 0.0004 and g⊥ = 2.0048 ± 0.0004 in infected axes than in the control. Generation of superoxide anion radical was also higher in infected axes than in the control but stronger at 72 and 96 h after inoculation. Starting from 72 h after infection, the level of Mn2+ ions in infected axes decreased in relation to the control. At the same time, the highest activity of superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) was observed in 72-h infected axes. In turn, the activity of peroxidase (EC 1.11.1.7) up to 72 h after infection was lower than in the control. In 48-h infected embryo axes, a very high level of pterocarpan pisatin was observed. Infection of germinating pea seeds with A. pisi restricted mainly the growth of the epicotyl, but did not inhibit the increase in length and fresh weight of root embryo axes versus cultivation time. These results indicate that in pea during the stages of seed germination and early seedling growth, protective mechanisms are induced in embryo axes against A. pisi.

The role of sugar signaling in plant defense responses against fungal pathogens

“…Enhanced ROS production occurs from the moment of recognition of the attack by the plant and in the case of biotrophic pathogens it is concluded with HR programmed death of the attacked cells and cells surrounding the infection site. In in vitro cultured embryo axes of yellow lupine the infection by hemibiotrophic fungus Fusarium oxysporum also caused an increase in respiration and ROS production Morkunas et al , 2013. We have shown that these processes are much more intensive when embryos are nourished with an exogenously supplied sucrose.…”

“…It has been shown that the induction of defense is cost intensive (Swarbrick et al 2006). In infected tissues the intensity of respiration processes is increased (Scharte et al 2005;Morkunas et al , 2013Rampitsch and Bykova 2012). Vargas et al (2012) found an enhanced expression of respiration-related genes at infection sites on maize leaves inoculated with a hemibiotrophic fungus Colletotrichum graminicola.…”

Reactive Oxygen Species Generated by NADPH Oxidases Promote Radicle Protrusion and Root Elongation during Rice Seed Germination

“…Finally, peroxidases catalyze the formation of • OH from O 2 − and H 2 O 2 in the apoplast [ 13 , 44 ]. A portion of ROS participate in the regulation of respiratory metabolism, mobilization of nutrients and other physiological processes through signal transduction [ 45 , 46 ], whereas some ROS can directly cleave cell wall polysaccharides, further loosening the plant cell wall and eventually facilitating the completion of germination [ 47 ].…”

Plant Responses to Sugar Starvation

“…For example, the link between low sugar content and plant sensitivity to fungal diseases known as "low-sugar diseases", was first reported over 50 years ago by Horsfall and Dimond (1957). It must be emphasized that many environmental factors, such as insufficient light, high humidity, excessive nitrogen fertilization, and excessively deep sowing, may cause a decrease in the level of carbohydrates in host plant tissues, contributing to an increase in plant sensitivity to fungal infection (Vidhyasekaran 1974a, 1974b, Morkunas et al 2004, Huber and Thompson 2007, Yoshida et al 2008, Morkunas et al 2010, Morkunas et al 2012. By contrast, low temperature can induce plant resistance to specific pathogens, because it results in accumulation of soluble carbohydrates, affecting the cell water potential and other osmotically-active molecules, as well as accumulation of pathogenesis-related (PR) proteins (Tronsmo 1993, Thomashow 1998, Hiilovaara-Teijo et al 1999, Płażek and αur 2003, Yuanyuan et al 2009).…”