Reserve mobilisation exhibits a biphasic pattern during seedling establishment in the Caatinga pioneer species Pityrocarpa moniliformis

Abstract Reserve mobilisation and metabolite utilisation were characterised during seed germination and seedling establishment in Pityrocarpa moniliformis, an endospermic legume from Caatinga. Seeds were germinated under controlled conditions for four days and seedlings were transferred to hydroponics and maintained at a greenhouse during four days. Samples were collected at distinct physiological stages and reserves, metabolites, and enzymatic activities were determined in different seedling parts. Galactomannans stored in the endosperm and non-reducing sugars accumulated in the cotyledons were mobilised from seed germination to hypocotyl emergence. During these processes, the accumulation of reducing sugars in the endosperm coincided with an increase in the starch content in the cotyledons and seedling axis, indicating that sugars released from galactomannans may have been utilised in starch biosynthesis. Starch and storage protein mobilisation in the cotyledons occurred later, from hypocotyl elongation to cotyledon expansion. Starch degradation possibly supported the accumulation of starch and soluble sugars in the root, while storage protein hydrolysis was associated with cotyledon greening and first leaf emergence. Accordingly, reserve mobilisation exhibits a biphasic pattern, enabling fast seedling establishment as a physiological strategy to ensure environmental colonisation.