Cambial activity, annual rhythm of xylem production in relation to phenology and climatic factors and lignification pattern during xylogenesis in drum-stick tree (Moringa oleifera)

The interrelationship among seasonality of cambium, wood formation, cell size variation, lignification, tree phenology and climatic factors has been examined in Moringa oleifera, a tropical evergreen tree. The vascular cambium in Moringa is a storied with a distinct seasonal variation in its structure due to dimensional changes in rays. Though cambium remains active throughout the year it is sensitive to water availability. Peak cambial cell division and rate of xylem differentiation are influenced by average rainfall during the monsoon period. Cambial cell division reaches higher up in the tree trunk when it is supporting a high number of branches and leaves. Statistical analysis of cell size variation and climate factors revealed that xylem cell development is greatly influenced by rainfall and rarely by temperature. Lengths of fusiform initials and vessel elements are positively correlated. The pattern of lignification during xylogenesis shows that the vessels are the first element to develop lignified walls and ray cells are the last elements to become lignified. Fiber cell walls show more syringyl lignin, while the cell walls of other xylem elements are characterized by relatively more guaiacyl lignin units.