Renal Endosomal Phosphate (Pi) Transport in Normal and Diabetic Rats and Response to Chronic Pi Deprivation

Chronic renal adaptation to dietary deprivation of Pi is accompanied by increased Na⁺/Pi co-transport across the brush border membrane of the renal proximal tubule. The increased activity of this co-transport system depends on de novo protein synthesis and insulin. The present study used normal and diabetic rats to determine if the endosomal pool of Na⁺/Pi co-transporters was altered by Pi deprivation and the possible role of insulin. In response to 5 days of dietary Pi deprivation there was a significant increase in endosomal Na⁺/Pi co-transport in control rats but there was no change in diabetic rats. The increase in endosomal Pi uptake was restored in diabetic rats treated with exogenous insulin. Na⁺/Pi-independent Pi uptake and proline uptake remained unchanged in all groups. The changes in endosomal Na⁺/Pi co-transport correlated with the abundance of the specific Na⁺/Pi co-transporter protein, as determined by Western blots. The pattern of endosomal changes paralleled that observed in brush border membranes. One possibility consistent with these findings is that the endosomal fraction contains newly synthesized Na⁺/Pi co-transporters targeted for delivery to the apical brush border membrane. Increased synthesis and delivery is required to maintain the adaptation to chronic Pi deprivation. © 1997 John Wiley & Sons, Ltd.     

Floral structure, development and diversity in Thunbergia (Acanthaceae)

Floral structure and development of 18 species of Thunbergia (Thunbergioideae si , Acanthaceae) were studied comparatively. The flowers of Thunbergia are highly diverse and show a wide range of pollination syndromes. In general they are large and showy. Their pollination apparatus is highly elaborate, floral organs are often synorganized, and floral architecture is complex. In contrast to the high diversity of the anthetic flowers, their bauplan is uniform and their early development shows no major differences, i.e. in all species studied, the calyx arises as a ring primordium, the corolla is 'late sympetalous', and petals and stamens are initiated more or less simultaneously. Some differences are found in further calyx development, where several developmental patterns are present. More significant differences arise only later during development and mainly concern the structures of the calyx, the anthers, the stigma, and corolla aestivation. In the anthetic flowers there are many special characters that are present in all or the majority of the species studied, e.g. the calyx is reduced, the corolla tube is subdivided into two compartments and the anthers lack an endothecium. The present results on development and morphology of the flowers of Thunbergia are compatible with an earlier subdivision of the genus into eight subgenera.