Osmoregulation and nutritional relationships betweenOrobanche foetidaand faba bean

Abstract

The present study aims at comparing the phloem composition of the tolerant XBJ90.03-16-1-1-1 and the susceptible Bachaar genotypes and the impact of the faba bean genotype on the levels of the major solutes and invertase activities in the parasite Orobanche foetida. In comparison to Bachaar, the XBJ90.03-16-1-1-1 genotype limited the growth of orobanche tubercles under in vitro conditions. The limited growth was due to low soluble invertase activity, low osmotic potential of the infected roots and the organic nitrogen deficiency of the host phloem sap. The faba bean genotype did not affect the osmoregulation process of O. foetida. Among the organic solutes, stachyose, hexoses, starch and free amino acids, mainly asparagine and aspartate were highly accumulated in orobanche. However, asparagine/ aspartate, glutamine/glutamate, alanine, serine, gamma amino butyric acid, stachyose, sucrose were identified as the main organic components in the host phloem exudates. The key role of the enzymes α-galactosidase, asparagine synthetase and aspartate oxaloglutarate aminotransferase in the utilization of the host solutes is proposed in O. foetida parasitizing faba bean.Broomrapes (Orobanche spp.) are obligate parasites that infect roots of many economically important crops, causing serious losses in yields. 1 In Tunisia, Orobanche foetida is an important agricultural parasite of faba bean in the region of Beja with yield losses varying between 66-90%. 2,3 Various strategies were tried to control this plant parasite but without enough success. 4,5 Recently, in field experiments, some faba bean genotypes like XBJ90.03-16-1-1-1 were identified as resistant to O. foetida in Tunisia. 3 Their resistance was characterized by a decrease in Orobanche attachment and reduction in parasite emergence, nevertheless without observing parasite necrosis on the host roots. In comparison to a susceptible genotype, this genotype showed low stimulatory activity for Orobanche seed germination, and showed a delay of parasite formation and a limited growth of Orobanche tubercles under in vitro conditions. 6,7 Knowing that tubercle growth is strongly related to uptake of water and nutrient from host, osmotic relationships between host and parasite were investigated by measuring the difference in osmolarity between faba bean roots and tubercles. Orobanche tubercles were taken from Petri dishes at stage 4, stage during which nutriment transfer from the plant host to parasite should be optimal. 8 In both tolerant and susceptible genotypes, tubercle osmolarity was significantly higher than root osmolarity, then facilitating water and nutrient fluxes from host to parasite. 9,10 The XBJ90.03-16-1-1-1 genotype showed higher root osmolarity values than the susceptible cv. Bachaar, then lowering the magnitude in osmolarity (Fig. 1). This should trigger difference in kinetic of tubercle development as previously indicated on these genotypes. In the same way, the cultivar Giza402 was considered tolerant to O. crenata due to its higher osmotic values compared...

Study of some resistance mechanisms toOrobanchespp. infestation in faba bean (Vicia fabaL.) breeding lines in Tunisia

“…For cv. najeh, the slow in the tubercles growth after their formation is due to low soluble invertase activity, low osmotic potential of the infected roots and the organic nitrogen deficiency of the host phloem sap (Abbes et al, 2009a(Abbes et al, , 2009b. Slow growth tubercles were also observed on faba bean roots following inoculation by some rhizobium strains (Bouraoui et al, 2016).…”

Source-to-sink transport of sugar and regulation by environmental factors

“…Orobanche also accumulates high amounts of polyols like mannitol, and this decreases the osmotic potential below that of the host plant (Harloff and Wegmann, 1993; Abbes et al, 2009b). This mechanism is essential for increasing the parasite’ s sink strength.…”

Metabolic Investigation of Phelipanche aegyptiaca Reveals Significant Changes during Developmental Stages and in Its Different Organs

“…Several studies previously measured the levels of a few amino acids, sugars, or polyols in several parasitic plants (e.g., Aber et al, 1983; Abbes et al, 2009a,b; Delavault, 2015), however, they usually concentrated on one group of metabolites, or even on one metabolite. Metabolic profiling or metabolomics is a rapidly developing technology of the post-genomics era that focuses on global changes in biological samples and enables determining metabolic differences in plants during various developmental stages, growth conditions and stresses (Nakabayashi and Saito, 2015).…”