Structural, Physiological and Biochemical Alterations on the Galled-Stem of Tamarix nilotica

Abstract

Tamarix nilotica (Tamaricaceae) is an important wild medicinal plant. It inhabits semi-arid environment, where it is often one of the most important plants suitable for insects’ infestation. Thrips (Thysanoptera: Insecta) infect T. nilotica causing galls that affect plant growth and development. The present work therefore was undertaken to study the morpho-anatomical, biochemical, and physiological aspects induced by insect infestation. Zeatin (Zn), gibberellins (GA3), salicylic acid (SA), 24-epibrassinolide (BR), and abscisic acid (ABA) were increased in the infected stems relative to the healthy ones. Galled-stem shown increased thickness of periderm and phellem layers whereas large portion of vascular cylinder disappeared leaving a large C shaped cavity where the mature insect nested. Gall sites had declined chlorophyll contents which were associated with a decrease in the emission of chlorophyll a fluorescence. While total soluble sugars, sucrose, total free amino acids, total soluble protein and minerals contents as well as the activities of SOD, CAT, PX, PO, APX, and AO significantly reduced in the infested Tamarix stems , polysaccharides, proline, MDA and H2O2 have been increased compared with the healthy ones. Galled-stems exhibited increased antiradical activity (expressed as IC50) which was concomitant with accumulation of phenolics, tannins, alkaloids, flavonoids and enhanced PAL. Six endophytic fungi inhabited Tamarix galls. Development of thrips galls on T. nilotica stems drastically impacts the host structure and its cellular metabolism as well as induction of an oxidative stress. The roles and impacts of endophytic fungi on insect induced galls still need further exploration.