Photosynthesis and assimilate partitioning characteristics of the coconut palm as observed by 14C labelling

Abstract

A technique was developed on the use off l4COz rapid labelling of foliage and to ascertain photosynthesis and partitioning characteristics of labelled assimilate into other parts of the coconut palm. An eight-year-old Tall x Tall young coconut palm growing under field conditions at Bandirippuwa Estate and with six developing bunches, was selected for this study. The labelling was carried out on a bright sunny day and soil was at field capacity. Seventh leaf from the youngest open leaf was used for labelling with 5 mCi of NaHJ4C 0 3. The results revealed that within 24 hours, 60% of the labelled assimilate was partitioned into other parts of the palm and at the end of the seventh day about 18% of the labelled assimilate still remained in the labelled leaf. Among the developing bunches fifth and sixth bunches from the youngest developing bunch received more labelled assimilate than young developing bunches above them. It was revealed that partitioning of assimilate into various ’’sinks1' is determined by the developmental stage or activeness of the ’’sink". The proportion off l4C labelled assimilate, partitioned into developing bunches was substantially low compared to the total amount of l4C fixed by the labelled leaf. Further, it was observed that partitioning of assimilated ,4C into the young leaves above, as well as the mature leaves below the labelled leaf. The complex vascular anatomy of the palms could be attributed to this pattern of partitioning of assimilates into upper and lower leaves from the labelled leaf.