Abstract
Light is primary source of energy and also plays signaling and regulatory roles in developmental processes and defense responses of plants. The aim of the study was to determine the performance, settling preferences, probing, and feeding behavior of Acyrthosiphon pisum on Pisum sativum grown in complete darkness (NL), with light at minimum level required for photoperiodic reaction (LL) and under full-light (FL) conditions. The effect of A. pisum infestation on metabolic status and defense responses of peas under FL, LL, and NL conditions was also determined. The population growth rate was limited on LL and NL pea plants as compared to FL plants. The reproductive period of aphids on LL and NL plants was eight times shorter than on plants growing in FL. In contrast to aphids on FL plants, the majority of A. pisum rejected LL and NL plants during settling. Aphid probing activities were not impeded on LL and NL plants but the probes were significantly shorter than on FL plants and consisted mainly of non-phloem activities. The analysis of tolerance of P. sativum to A. pisum showed that on FL plants, the number of aphids was nearly five times higher than on plants growing in low light (LL) at the end of the 2-week experiment but the tolerance index of FL plants was higher than that of LL plants. The contents of chlorophyll a, chlorophyll b, carotenoids, saccharides, and phenolics and the activity of β-d-glucosidase were notably lower in LL and NL plants than in FL plants. The increase in light intensity from complete darkness to the minimum level required for photoperiodic reaction did not stimulate evident changes in the measured plant biochemical parameters. These trends occurred in aphid-free (AF) and aphid-infested (AI) plants. However, under FL conditions, β-d-glucosidase activity and the content of saccharides were lower in AI plants than in AF plants. No differences in the measured plant biochemical parameters between AI and AF plants occurred under LL and NL conditions. The low β-d-glucosidase activity and low content of phenolics in the light-deprived plants that have reduced ability to photosynthesize show that under the biotic stress of aphid infestation plants invest in supporting basic metabolism rather than in defense against herbivores.
Highlights
Pea (Pisum sativum L.) (Fabaceae), originally a plant of the Near East and one of the most ancient crops dating back to the end of the last Ice Age in Europe, is currently grown all over the world in temperate regions, at low and high elevations or during cool seasons in warm regions (Ljustina and Mikic 2010; Pavek 2012)
The aim of the study was to determine the performance, settling preferences, probing, and feeding behavior of Acyrthosiphon pisum on Pisum sativum grown in complete darkness (NL), with light at minimum level required for photoperiodic reaction (LL) and under full-light (FL) conditions
The analysis of tolerance of P. sativum to A. pisum showed that on FL plants, the number of aphids was nearly five times higher than on plants growing in low light (LL) at the end of the 2-week experiment but the tolerance index of FL plants was higher than that of LL plants
Summary
Pea (Pisum sativum L.) (Fabaceae), originally a plant of the Near East and one of the most ancient crops dating back to the end of the last Ice Age in Europe, is currently grown all over the world in temperate regions, at low and high elevations or during cool seasons in warm regions (Ljustina and Mikic 2010; Pavek 2012). The intensity of light is one of the crucial environmental factors that determine the life of autotrophic plants, including basic life processes such as the level of photosynthesis and photoperiodic reactions. All plants have evolved diverse mechanisms to counteract the rapid and irregular changes in light intensity during the day to optimize the light energy absorption and use. These mechanisms are long-term or short-term and may involve whole plants as well as cellular and molecular levels, including the leaf area and plant height, leaf orientation, position of chloroplasts in the cell, chlorophyll content, and photosystem modulation (Ruban 2009, 2015). The defensive role of secondary metabolites may involve a deterrent or an antifeedant activity, toxicity, or participation as precursors in physical defense (Bennett and Walsgrove 1994)
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