Free amino acid and amide composition of pea leaf juice, pea aphid haemolymph, and honeydew, following the rearing of aphids on single pea leaves treated with amino compounds

Abstract

Single amino compounds absorbed via the petiole of pea leaves ( Pisum sativum L.) were recovered in higher amounts in the leaf juice. Most absorbed compounds were partially metabolized by the leaves into other free amino compounds. The growth of pea aphids ( Acyrthosiphon pisum (Harr.)) feeding on such treated leaves was slightly accelerated, but the difference in growth rate between treated leaves and checks was significant only when dl-homoserine, or a mixture of l-asparagine and l-glutamine, was used. The latter three compounds, plus leucines and valine, were recovered in increased amounts in pea leaf juice, aphid haemolymph, and honeydew; aspartic, glutamic acid, and serine increased in honeydew and haemolymph; and proline increased in haemolymph. These increases indicated a direct influence of the aphid diet on the qualitative and quantitative amino acid content of haemolymph and honeydew. The possible significance of amides and of homoserine in pea varietal resistance to aphids is discussed.