CELL-CYCLE EVENTS IN DEVELOPING NEEM (AZADIRACHTA-INDICA) SEEDS - ARETHEY RELATED TO INTERMEDIATE STORAGE BEHAVIOR

Seeds of neem (Azadirachta indica A. Juss.), a multipurpose tropical t ree, have limited desiccation tolerance. Whether their intermediate st orage behaviour might be caused by an elevated percentage of 4C nuclei in the embryo at maturity was investigated. Morphological development of neem seeds was monitored on selected trees in Ouagadougou, Burkina Faso. Developing seeds were tested for germinability, and cell cycle events were determined by using flow cytometry and analysing the level of beta-tubulin. Germination could occur after 8 weeks of seed develo pment, but normal seedlings resulted only after 10 weeks or more. The change in fruit colour from green to yellow began after approximately 12 weeks of seed development. Immature, 4-week-old embryos about 2 mm in length had 15% of cells in the G(2) phase and 60% in the G(1) phase of the cell cycle, as indicated by 4C and 2C nuclear DNA levels, resp ectively. During maturation, the proportion of G(2) cells declined to 3% at full maturity and slightly further after drying, and the proport ion of G(1) cells increased to approximately 90%. A strong beta-tubuli n signal was observed in tips of young embryonic radicles and cotyledo ns, but a weak or nondetectable signal was found in 9-week-old ones an d in those from green-mature and yellow fruits. Because DNA replicatio n and beta-tubulin level were almost negligible at seed maturity, as i n orthodox tomato seeds, it is suggested that these factors are not in volved in the intermediate storage behaviour of neem seeds.