Determination of resource mobilization during seedling growth of palmyra palm, Borassus flabellifer L.

Abstract

Asian palmyra palm (Borassus flabellifer L.) is a multipurpose tree with year round products as food for the dependent society. Besides edible items the tree offers around 801 useful goods which are economically important. Such a plant’s seedling biology has not been fully understood. Hence, the present study was aimed at understanding seedling developmental stages and resource mobilisation in Palmyra palm and further to determine the role of cotyledonary sheath (CS) during entire seedling growth. We investigated the developmental changes throughout growth of seedlings by providing different sets of growth conditions. Artificial seed bed made of coconut coir was compared with that of soil conditions to study germination and establishment of seedlings. Phloem loading dye was used to track the flow of nutrients from embryo to cotyledonary sheath. Seed germination in palmyra palm is hypogeal by forming ligular and tubular structures remotely in soil. Eight new organs differentiate from the seed embryo that includes haustorium, ligule, cotyledonary sheath, cataphyll, eophyll, mesocotyle (junction), primary root and mesocotyl roots during seed germination. Among these the first four are temporary organs and they disintegrate once the seedling is well established. The last four organs are responsible for developing acomplete plantlet at later stages. The seed and seedling organs of Palmyra palm have four major storage reserves to support successful germination and firm establishment of seedling. Palmyra has evolved to control the solubilisation, movement and regulation of food among transient seedling organs and carry out translocation of food to the developing and differentiating organs. Seedlings also have developed physiological functions and strategies to mobilise the stored food without losing them at any point of their growth and developmental stages. Water required for seed germination permeates laterally only viacotyledonary sheath which has spongy tissues and lenticels all over. These tissues are the primary mode of water supply as the seedlings lack major root organs in the early stages of development. Flourescent microscopic and anatomical studies were carried out to observe the transport and storage of food substances required during seedling growth. Histochemical studies of seedling organs have revealed the presence of various type of nutrients such as simple sugars, carbohydrates, proteins, amino acids and lipids.