Struggle to survive: aphid\u2014plant relationships under low-light stress. A case of Acyrthosiphon pisum (Harris) and Pisum sativum L.

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.