Similarities between the effects of aphid infestation and cytokinin application on dark respiration and plant growth of legumes.
Vigna unguiculata cv. Caloona, Vicia faba cv. Aquadulce and garden peas cv. Victory Freezer seedlings were infested with cowpea aphids (Aphis craccivora) or pea aphids (Acyrthosiphon pisum) for 10 days and then infested host plant tissue was examined for foreign substances injected by the aphids. No foreign compound was detected in any of the aphid-infested plant tissues. Both aphid species were also assayed for growth regulators, utilizing the epinastic response of tomato cv. Roma Teardrop seedlings, and both aphid species contained growth regulators in concn higher than plant physiological concn. V. faba and pea seedlings were also treated with foliar and root applications of benzyladenine to determine if there were any similarities in plant growth or respiratory responses, following aphid infestation or benzyladenine treatment. Root respiration in benzyladenine treated plants decreased while shoot respiration increased in a response analogous to that observed for aphid-infested tissue. However the alternative respiratory pathway was engaged for all benzyladenine treatments, whereas in aphid-infested plant roots and shoots it was not. Both benzyladenine treated and aphid-infested plants displayed a loss of apical dominance. These data suggest that part of the physiological response of the plant to aphid feeding is induced by changes in the cytokinin:auxin ratio.