Characteristics of Acacia mangium shoot apical meristems in natural and in vitro conditions in relation to heteroblasty

Abstract

Abstract.The influence of heteroblasty on morphological and histocytological characteristics of Acacia mangium shoot apical meristems (SAMs) was assessed comparing materials with mature and juvenile leaf morphology in natural and in vitro conditions. SAM dome height (H), basal diameter (D) and shape (S) varied significantly according to the four origins of plant material investigated. H and D were highly correlated, with bigger values for the mature source from outdoors "Mat" than for the other origins. Mat SAMs scored also the higher values for the size and the number of cells of the two tunica layers (L1 and L2), the central mother cells (CMC), the peripheral zone (PZ) and the combination of these four SAM zones (4CZ). Overall, cells were noticeably more vacuolized in SAMs from Mat and also from the mature ("IVM") and juvenile-like "IVJ" in vitro origins than in those from the outdoor juvenile source "Juv". These latter were characterized by larger cells and nuclei for L1 and L2 tunica layers, whereas Mat SAMs showed smaller nuclei and nucleoplasmic ratios for L1, L2, CMC and PZ zones. Some Mat SAM nuclei looked densely stained by NBB while others exhibited numerous chromocenters disseminated in the nucleoplasm where nucleolei could hardly be distinguished. By contrast Juv as well as IVJ and IVM SAM nuclei appeared more evenly and lightly stained and could show clearly distinguishable darker nucleolei possibly surrounded by less abundant chromocenters.

Acacia (wattle) and Cananga (ylang-ylang): from spiral to whorled and irregular (chaotic) phyllotactic patterns – a pictorial report

“…Thus, the relative size of the SAM as compared to the youngest phyllode primordia is small in A. amblygona whereas it is large in A. rossei. As a result of this relative size difference, young phyllodes in shoot tips of A. amblygona show a (2+3) contact parastichy pattern whereas young phyllodes in A. rossei contact each other according to a (5+8) parastichy pattern, similar to what is known from other acacias [19,20].…”

“…Most Australian acacias are phyllodineous. They show heteroblasty with two leaf types, somewhat correlated with an absolute size increase of the SAM while the plant changes from the juvenile to its adult stage [19,20]. They start with compound (pinnate to bipinnate) leaves along the seedling axis but later they switch to undivided leaves, so-called phyllodes.…”