Ontogeny of solasodine-containing mucilage layer inSolanum viarum Dunal, ploidy types

Abstract

Berries of steroid-bearing Solanum viarum Dunal are exploited commercially in India as raw material by steroid industries for solasodine, a glycoalkaloid, present in the mucilaginous exotesta of the seed. Comparative ontogeny of exotesta studied through histochemical studies in diploid, autotetraploid and trisomic plants indicated similarity in the histochemical changes occurring during ontogeny of the outermost seed coat layer which culminated in the transformation of this layer into the mucilage layer. The increased cell size in this layer in the autotetraploid plants probably accounts for the higher steroid content reported. Corroborative evidences for histochemical changes observed in the mucilage layer were obtained from studies of ultrastructure using transmission electron microscopy. autotetraploid (both healthy and aborted seeds) and tertiary trisomic plants were collected separately from plants grown .in t~e field under uniform conditions. The material was collected regularly at an interval of 10 days (d) from the day of anthesis, until 80 d during which the fruits turned greenish yellow (70 d) and subsequently completely yellow (80 d). The seeds resulting from the above eight samplings were directly subjected to histochemical studies.The seeds were fixed in two lots: in formalin-acetic acid-alcohol (1.1: 18 by volume) to localize insoluble polysaccharides and Carnoy's B fixative (ethyl alcohol, chloroform and acetic acid in 6: 3 : 1 by volume) to localize nucleic acids and proteins. The material was dehydrated using ethanol-n-butanol grades and embedded in paraffin wax of 58°C melting point. Microtome sections of :t 8 ~m thickness were stained with periodic acidSchiffs (PAS) reagent for total insoluble polysaccharides, mercuric bromophenol blue for proteins and toluidine blue for nucleic acids before mounting in DPX medium.In addition, at 60 d of development smears of the mucilaginous exotesta were stained with toluidine blue and iodine solution separately after processing in alcohol-nbutanol series following fIXation in Carnoy's B fixative.

The sticky tale of seed coat mucilages: production, genetics, and role in seed germination and dispersal

“…In studies of P. ovata, S. viarum and B. campestris, the authors also note the accumulation of large starch granules which are then lost as mucilage accumulates. Similar results have also been noted at the light microscopy level for flax, suggesting that starch is providing sugar for mucilage synthesis (Hyde, 1970;Boesewinkel, 1980;Van Caeseele et al, 1981;Srinivas et al, 1998). While these species have a reduction in cytoplasm and/or vacuole that accompanies mucilage production, none of them has cellulosic fibres or inclusions similar to the columella of Arabidopsis.…”

“…In addition to the work in Arabidopsis, seed coat mucilage synthesis has been studied at the ultrastructural level using chemical fixation and TEM in Brassica campestris, Plantago ovata, Cydonia oblonga (Rosaceae) , Solanum viarum (Solanaceae) , C. grandiflora and Ruellia spp. (Hyde, 1970; Van Caeseele et al , 1981; Schnepf and Deichgräber, 1983a, b; Abeysekera and Willison, 1988; Srinivas et al , 1998). Similar to Arabidopsis, a prominent feature of mucilage production in each case is the appearance of large numbers of swollen Golgi stacks and associated secretory vesicles that are apparent as mucilage accumulates in the apoplastic space of the seed coat epidermal cells.…”